Fundamentals of Neuroscience; 4th Edition, · Neural circuits engaged during fear conditioning....

$: Fundamentals of Neuroscience; 4th Edition, · Neural circuits engaged during fear conditioning. During fear conditioning, the conditioned stimulus \⠀䌀匀尩 and unconditioned$
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Fundamentals of Neuroscience; 4th Edition,

9/6/2019 8-9 am Fundamentals of Neuroscience (Chapters 3&4) - Cellular & Subcellular Components of Nervous Tissue

751 Neuro Conf rm 3717

9/13/2019 8-9 am Fundamentals of Neuroscience (Chapters 5&6) – Membrane Potential, AP, Neurotransmitters


9/20/2019 8-9 am Fundamentals of Neuroscience (Chapters 7&8) -Neurotransmitter Release & Neurotransmitter Receptors


9/27/2019 8-9 am Fundamentals of Neuroscience (Chapters 7&8) – Intracellular Signaling, Postsynaptic Potentials & Synaptic Integration

751 Neuro Confrm 3717

• Ernesto Solis, Jr.

• September 6, 2019

Neurons

Neuroglia (oligodendrocytes, astrocytes, microglia)

Other important cells (epithelial cells, VSMC, etc.)

Since late 1800s, Santiago Ramón y Cajal “founder of contemporary neuroscience” used Golgi stain to observe neuronal architecture.

Since late 1800s, Santiago Ramón y Cajal “founder of contemporary neuroscience” used Golgi stain to observe neuronal architecture.

Golgi’s “reticular view” (continuous cytoplasm/axons fuse).

Challenged with “neuron doctrine” that states that each neuron is an individual entity (the basic unit of neural circuitry).

Reticular Theory Neuron Doctrine

Which one is correct?

Presenter

Presentation Notes

Nevertheless, the reticularist view is not entirely incorrect, because some neurons do act syncytially via specialized intercellular gap junctions, a feature that is more prominent during embryogenesis.

• Neurons – communicating cell (through synapses), form complex circuits with other neurons• Categorized based on size, shape, neurochemical characteristics, location, and connectivity

(important determinants of the functional role of the neuron in the brain)

• Circuits constitute the structural basis for brain function.

• Macrocircuit – involve a population of neurons projecting from one brain region to another region (example: Retina LGN Visual Cortex)

Macrocircuit

Cellullar components: NEURON


MicrocircuitMacrocircuit

• Neurons – communicating cell (through synapses), form complex circuits with other neurons• Categorized based on size, shape, neurochemical characteristics, location, and connectivity

(important determinants of the functional role of the neuron in the brain)

• Circuits constitute the structural basis for brain function.

• Macrocircuit – involve a population of neurons projecting from one brain region to another region (example: Retina LGN Visual Cortex)

• Microcircuit – reflect the local cell-cell interactions within a brain region (example: Cells in Retina)

Introduction to Psychology (Stangor & Walinga)

• Neurons – communicating cell (through synapses), form complex circuits with other neurons

• Studying the circuits can help to understand neuronal function and dysfunction in the diseased brain (example: corticospinal tract stroke, amygdala fear, hippocampus Alzheimer’s)


Presenter

Presentation Notes

Neural circuits engaged during fear conditioning. During fear conditioning, the conditioned stimulus (CS) and unconditioned stimulus (US) are relayed to the lateral nucleus of the amygdala (LA) from thalamic and cortical regions of the auditory and somatosensory systems, respectively. As shown in FIG. 3, the CS inputs enter the dorsal subregion of the LA, where interactions with the US induce plasticity in two functional cell types (so-called ‘trigger’ and ‘storage’ cells). CS information is then transmitted through further stations in the LA to the central nucleus of the amygdala (CE). Interactions between the lateral and central amygdala are more complex than illustrated, and involve local-circuit connections (see main text). The LA also communicates with the CE by way of connections with other amygdala regions (not shown), but the direct pathway seems to be sufficient to mediate fear conditioning. CG, central grey; LH, lateral hypothalamus; PVN, paraventricular hypothalamus.

• Neurons – communicating cell (through synapses), form complex circuits with other neurons

• Studying the circuits can help to understand neuronal function and dysfunction in the diseased brain (example: corticospinal tract stroke, amygdala fear, hippocampus Alzheimer’s)

Cellullar components: NEURONCircuits underlie all behavior, including fear, anxiety, attention, appetite, etc.

Neural circuits engaged during fear conditioning

(Medina et al., Nature Rev Neuro, 2002)

Behavioral Autonomic Endocrine

Central Amyg.

Presenter

Presentation Notes

Neural circuits engaged during fear conditioning. During fear conditioning, the conditioned stimulus (CS) and unconditioned stimulus (US) are relayed to the lateral nucleus of the amygdala (LA) from thalamic and cortical regions of the auditory and somatosensory systems, respectively. As shown in FIG. 3, the CS inputs enter the dorsal subregion of the LA, where interactions with the US induce plasticity in two functional cell types (so-called ‘trigger’ and ‘storage’ cells). CS information is then transmitted through further stations in the LA to the central nucleus of the amygdala (CE). Interactions between the lateral and central amygdala are more complex than illustrated, and involve local-circuit connections (see main text). The LA also communicates with the CE by way of connections with other amygdala regions (not shown), but the direct pathway seems to be sufficient to mediate fear conditioning. CG, central grey; LH, lateral hypothalamus; PVN, paraventricular hypothalamus.


• Cell body and dendrites receive input.

• One apical and 2 basal dendrites.

• Characteristic dendritic arbor shape defines receptive area.

• Neurons are highly polarized.

Presenter

Presentation Notes

Fig. 3.1. Typical morphology of projection neurons. (Left) Purkinje cell of the cerebellar cortex and (right) a pyramidal neuron of the neocortex. These neurons are highly polarized. Each has an extensively branched, spiny apical dendrite, shorter basal dendrites, and a single axon emerging from the basal pole of the cell. The scale bar represents approximately 200 uM.






• Preferential distribution of synaptic contacts on spines.

Presenter

Presentation Notes

Fig. 3.2. Schematic representation of 4 major excitatory inputs to pyramidal neurons. A pyramidal neuron in layer 3 is shown as an example. Note the preferential distribution of synaptic contacts on spines. Spines are labeled in red. Arrow shows a contact directly on a dendritic shaft. *********Preferential distribution of synaptic contacts on spines.**********







• Neocortical pyramidal neurons display varying cell size and dendritic arborization

• Some exhibit axon collaterals depending on neuron laminar localization (I-VI).

• Different types of pyramidal neurons with a precise laminar distribution project to different brain regions.

• Via corticospinal tract, Betz cells (gygantopyramidal neurons) in layer V of primary motor cortex project to spinal cord.

Presenter

Presentation Notes

Fig. 3.6. Morphology and distribution of neocortical pyramidal neurons. Note the variability in cell size and dendritic arborization, as well as the presence of axon collaterals, depending on the laminar localization (I-VI) of the neuron. Also, different types of pyramidal neurons with a precise laminar distribution project to different regions of the brain (less important projection zones are indicated by parenthesis). Adapted from Jones (1984).







• Neocortical pyramidal neurons display varying cell size and dendritic arborization

• Some exhibit axon collaterals depending on neuron laminar localization (I-VI).

• Different types of pyramidal neurons with a precise laminar distribution project to different brain regions.

• Via corticospinal tract, Betz cells (gygantopyramidal neurons) in layer V of primary motor cortex project to spinal cord.

Where do they synapse on the spinal cord?

• Motor Neuron Diseases (UMN vs. LMN)• Amyotrophic lateral sclerosis (ALS)• Primary lateral sclerosis (PLS)• Progressive muscular atrophy• Progressive bulbar palsy• Pseudobulbar palsy• Spinal muscular atrophy (SMA)• Post-polio syndrome (PPS)

In ALS, are UMNs or LMNs affected?

Presenter

Presentation Notes

Fig. 3.1. Typical morphology of projection neurons. (Left) Purkinje cell of the cerebellar cortex and (right) a pyramidal neuron of the neocortex. These neurons are highly polarized. Each has an extensively branched, spiny apical dendrite, shorter basal dendrites, and a single axon emerging from the basal pole of the cell. The scale bar represents approximately 200 uM. Fig. 3.6. Morphology and distribution of neocortical pyramidal neurons. Note the variability in cell size and dendritic arborization, as well as the presence of axon collaterals, depending on the laminar localization (I-VI) of the neuron. Also, different types of pyramidal neurons with a precise laminar distribution project to different regions of the brain (less important projection zones are indicated by parenthesis). Adapted from Jones (1984). Anterior horn..

(a-e) polecat, otter, raccoon, harp seal, fur seal

(f-j) wild dog, mongoose, caracal, leopard, lion

(k-o) tiger, marmoset, tamarin, tamarin, monkey

(p-t) monkey, monkey, baboon, baboon, gibbon

**Note the very large size of these pyramidal neurons in the representatives of the Genus Panthera (i–k)

(Jacobs et al., J Comp Neurol., 2017)


Betz cells (gygantopyramidal neurons) differ across species

*Giraffes, horses = similar size of cell body but much larger volume.*Large felines have much larger cell body size.

Presenter

Presentation Notes

Giraffes, horses = similar size of cell body but much larger volume. Large felines have much larger cell body size…


5 General Categories of Neurons1. Excitatory projection neurons – distant contacts

(e.g. pyramidal neurons in the cerebral cortex)

2. Inhibitory interneurons – local contacts (e.g. GABAergic interneurons in cerebral and cerebellar cortex and hippocampus)

3. Excitatory interneurons – local contacts (e.g. spiny stellate cells of the cerebral cortex)

(Zumla and Basu, Curr Opinion in Neurobiol., 2017)

Cortico-hippocampal circuit projections

Presenter

Presentation Notes

Simplified model: The inhibitory (GABAergic) interneurons (in color red, blue, purple) are regulating the activity of excitatory projection neurons (black) that send fibers out of the hippocampus. In epilepsy you might expect to much excitatory neuron activity. What do you do to treat it?





4. Inhibitory projection neurons – distant contacts (e.g. medium spiny neurons in the basal ganglia or Purkinje cells in of the cerebellar cortex.

5. Neuromodulatory neurons – influence neurotransmission




MSN in striatum

(Taverno et al., J Neuro., 2012)

(Rangel-Barajas and Rebec, J of HD., 2016)

Presenter

Presentation Notes

An example of inhibitory projection neurons are (GABAergic) MSNs, they project to GPe and SN (MSNs from GPe send projections to Thalamus), receive inputs from the SN.








MSN in striatum





What neurological condition is characterized by degeneration of MSNs?

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Presentation Notes









MSN in striatum





What neurological condition is characterized by degeneration of MSNs?Answer: Huntington’s Disease

What neurological condition is characterized by loss of DAergic neurons?

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Presentation Notes









MSN in striatum





What neurological condition is characterized by degeneration of MSNs?Answer: Huntington’s Disease

What neurological condition is characterized by loss of DAergic neurons?

Answer: Parkinson’s Disease

Presenter

Presentation Notes


Small Basket

w/ arciform axon

Chandelier cell

Double Bouquet

Neurogliaform c.

Peptidergicneuron

GABAergic Interneurons of the CortexInterneuron Nomenclature Group categorized GABAergic cortical interneurons based on:

Anatomical classification – projections (3 major types): 1. Cells that target pyramidal cells2. Cells that do not show target specificity3. Cells that specifically target other interneurons

Molecular classification – expression of cellular biomarkers (5 major types):1. Parvalbumin2. Somatostatin3. Neuropeptide Y (NPY) in the absence of somatostatin4. Vasointestinal peptide (VIP)5. Cholecystokinin (CCK) in the absence of somatostatin

and vasointestinal peptide

Physiological classification – electrical activity (6 types): 1. Fast spiking neurons2. Nonadapting/nonfast spiking neurons3. Adapting neurons4. Accelerating cells 5. Irregular spiking neurons6. Intrinsic bursting neurons


Chandelier cell

Large Basket cellSpiny Stellate cell

GABAergic interneurons (blue)Spiny Stellate cell (local exc.)Excitatory neurons (black)

Presenter

Presentation Notes

Cells classified based on anatomical, molecular (transgenic mouse, parvalbumin cells light up) and physiological classifications (when recording from GABAergic cells, can tell based on its activity what cell type it is). Each of these attempts to classify these neurons has its limitations, and the scientific community still lacks a general catalog of accepted neuron types and names. Nevertheless, standardizing the nomenclature based on the properties of GABAergic interneurons proposed by the Petilla Interneuron Nomenclature Group represents a step in the right direction towards a more comprehensive classification of cortical GABAergic interneurons. Each of these attempts to classify these neurons has its limitations, and the scientific community still lacks a general catalog of accepted neuron types and names. Nevertheless, standardizing the nomenclature based on the properties of GABAergic interneurons proposed by the Petilla Interneuron Nomenclature Group represents a step in the right direction towards a more comprehensive classification of cortical GABAergic interneurons. Fig. 3.5. A schematic circuit based upon the known cortical cells upon which thalamic afferent fibers terminate in cats and monkeys. The GABAergic interneurons (blue) are identified by the names that they have received in these species. Arc, neuron with arciform axon; Ch, chandelier cell; DB, double bouquet cell, LB, large basket cell, Ng, neurogliaform cell; Pep, peptidergic neuron; SB, small basket cell. Excitatory neurons (black) include pyramidal cells of layers II-VI and the spiny stellate cells (SS) of layer IV. Dr. EG Jones.

• 1897, Charles Sherrington postulated that neurons establish functional contact with one another and with other cells via a theoretical structure called the synapse (Greek synaptein, to fasten together).

• Electron microscopy helped demonstrate the structural evidence for the synapse ~50 years later.

• Asymmetric excitatory synapses exhibit round synaptic vesicles presynaptically and thick postsynaptic densities.

• Symmetric inhibitory synapses tend to be made on dendritic shaft, presynaptic ‘boutons’ contain ovoid vesicles.

• Spines emanate from dendritic shaft and contain filamentous material.

(Chen et al., Brain Struct. and Funct., 2012)

Normal Sensory Experience Sensory-deprived

Effect of sensory deprivation on pyramidal neurons of the rat barrel cortex

For sensory-deprived, whiskers are trimmed every day since birth for 1 month

*In pyramidal neuron, more than 40% of total surface area is made out of spines (~20,000)

*Spines are dynamic structures that regulate many neurochemical events related to synaptic transmission and modulate synaptic efficacy

Cellullar components: NEURON Golgi staining

Presenter

Presentation Notes

Whiskers are trimmed every day since birth for 1 month. Golgi staining..

Spines undergo pathologic alterations and reduced number in many developmental, neurologic, and psychiatric illnesses

• Dementing illnesses

• Chronic alcoholism

• Schizophrenia

• Trisomy 21 (Down syndrome)

• Trisomy 13 (Patau syndrome)


Trisomy 13-15(newborn)

Trisomy 21(18-month)

Normal gestation

(Kaufmann and Moser, Cerebral Cortex 2000)

5th gest. month 7th gest. month neonatal period 2nd postnatal month

8th postnatal month

• Neuroglia – “nerve glue” coined by Rudolph Virchow in 1859, non-neuronal cells in brain/SC

• Nonexcitable

• Supporting cells

• Previously thought 10x more glia than neurons (closer to 1:1)

• Make up 50% of the volume of the brain and SC

• Highly diverse functions

• CNS) Oligodendrocytes, Astrocytes (Radial Glia), Microglia, Ependymal Cells

• PNS) Schwann Cells, Satellite Glial Cells

1. Oligodendrocytes / Schwann cells• Myelinate axons

2. Astrocytes• Maintenance of neuronal physiology and extracellular environment

• Secrete trophic factors

• In development, guide neurons

• Help form BBB (structure interposed between the circulatory system and brain substance – serves as the molecular gateway to brain tissue)

• Regulate local vascular tone

3. Microglia• Reactive microglia

4. Ependymal Cells• Production/regulation of CSF

Cellullar components: GLIA

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Neuron

Neuron

Presenter

Presentation Notes

With staining methods Cajal and del Rio-Hortega identified, three types of supporting cells in the CNS: oligodendrocytes, astrocytes, and microglia + ependyma lining the ventricles and central canal. In the peripheral nervous system (PNS), the Schwann cell is the major neuroglial component. These cells are much smaller than the neurons—usually glial cells are 4–10 μm across—yet their size depends on their state of maturation and their possible involvement in a pathological process.

Cellullar components: GLIA Oligodendrocyte (CNS)

Invertebrates have large axon (squid giant axon) Thickness allows fast conduction (10-20 m/s)

Presenter

Presentation Notes

Fig. 3.7. An electron micrograph of a transverse section through part of a myelinated axon from the sciatic nerve of a rat. The tightly compacted multilayer myelin sheath (My) surrounds and insulates the axon (Ax). Mit, mitochondria. Scale bar = 200 nm.

No extracellular space or EC matrix

Cellullar components: GLIA Oligodendrocyte (CNS)

Invertebrates have large axon (squid giant axon) Thickness allows fast conduction (10-20 m/s)

Myelin sheath

• Myelin is made up of PM of the oligodendrocyte.

• At the end of each myelin segment, there’s a bare portion of the axon (called node of Ranvier).

• Myelin segments are called internodes.

• The main function of myelin is to insulate the axon to be able to have fast conduction.

• Cytoplasm is removed between each turn of myelin to optimize space.

Presenter

Presentation Notes

Fig. 3.7. An electron micrograph of a transverse section through part of a myelinated axon from the sciatic nerve of a rat. The tightly compacted multilayer myelin sheath (My) surrounds and insulates the axon (Ax). Mit, mitochondria. Scale bar = 200 nm. Myelin is made up of plasma membrane of the oligodendrocyte. At the end of each myelin segment, there’s a bare portion of the axon (called node of Ranvier). Myelin segments are called internodes. The main function of myelin is to insulate the axon to be able to have fast conduction. Cytoplasm is removed between each turn of myelin to optimize space (Due to protein composition, CNS lamellae are ~30% thinner than in PNS myelin). Fig. 3.8. An oligodendrocyte (OL) in the CNS is depicted myelinating several axon segments. A cutaway view of the myelin sheath is shown (M). Note that internode of myelin terminates in paranodal loops that flank the node of Ranvier (N). (Inset) An enlargement of compact myelin with alternating dark and light-electron-dense lines that represent intracellular (major dense lines) and extracellular (intraperiod line) plasma membrane appositions, respectively.


• Nonexcitable
















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Neuron

Neuron

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Presentation Notes


Membrane (cytoplasm)Intermediate filaments

“stellate”

Neuron

Cellullar components: GLIA Astrocytes (CNS)

Astrocytes – described as “star-shaped”

• Constitute 20-50% of volume of most brain areas.

• Appear stellate when labeling intermediate filaments.

• Extensive, complex morphology when entire cytoplasm is visualized.

• Envelop neuropil elements (neurons and synapses).

Presenter

Presentation Notes

Fig. 3.10. Astrocytes appear stellate when their intermediate filaments are stained (red, GFAP), but membrane labeling (green, membrane-associated EGFP) highlights the profusion of fine cellular processes that intercalate among other neuropil elements such as synapses and neurons (N). Scale bar = 10 um. Courtesy of MC Smith.


Protoplasmic astrocytes (gray matter)

Fibrous astrocytes (white matter)

Bergmann glial cells

Protoplasmic astrocytes (gray matter)• Processes pass between neuron cell bodies.• Processes are shorter, thicker, more branched.• Store glycogen, phagocytic function, conduit for

metabolites, produce trophic substances.

Fibrous astrocytes (white matter)• Processes pass between nerve fibers.• Each process is long, slender and smooth.• Provide supporting framework, are electrical

insulators, limit spread of NT, take up K+.

Astrocytes in human cerebellar cortex

• The two main forms, protoplasmic and fibrous astrocytes, predominate in gray and white matter, respectively. Most express glial fibrillary acidic protein (GFAP).

Presenter

Presentation Notes

Fig. 3.11. The arrangement of astrocytes in human cerebellar cortex. Bergmann glial cells are in red, protoplasmic astrocytes are in green, and fibrous astrocytes are in blue.


Bergmann glial cells

Protoplasmic astrocytes (gray matter)

Fibrous astrocytes (white matter)

• The two main forms, protoplasmic and fibrous astrocytes, predominate in gray and white matter, respectively. Most express glial fibrillary acidic protein (GFAP).

• Embryonically, astrocytes develop from radial glial cells, which transversely compartmentalize the neural tube.

• Radial glial cells serve as scaffolding for the migration of neurons and play a critical role in defining the cytoarchitecture of the CNS.

• As the CNS matures, radial glia retract their processes and serve as progenitors of astrocytes.

• Some specialized astrocytes of a radial nature are still found in the adult cerebellum (Bergmann glial cells) and the retina (Müller cells).

Astrocytes in human cerebellar cortex

Protoplasmic astrocytes (gray matter)• Processes pass between neuron cell bodies.• Processes are shorter, thicker, more branched.• Store glycogen, phagocytic function, conduit for

metabolites, produce trophic substances.

Fibrous astrocytes (white matter)• Processes pass between nerve fibers.• Each process is long, slender and smooth.• Provide supporting framework, are electrical

insulators, limit spread of NT, take up K+.

Presenter

Presentation Notes

Embryonically, astrocytes develop from radial glial cells, which transversely compartmentalize the neural tube. Radial glial cells serve as scaffolding for the migration of neurons and play a critical role in defining the cytoarchitecture of the CNS (Fig. 3.12). As the CNS matures, radial glia retract their processes and serve as progenitors of astrocytes. However, some specialized astrocytes of a radial nature are still found in the adult cerebellum and the retina and are known as Bergmann glial cells and Müller cells, respectively. Fig. 3.12. Radial glia perform support and guidance functions for migrating neurons. In early development, radial glia span the thickness of the expanding brain parenchyma. (Inset) Defined layers of the neural tube from the ventricular to the outer surface: VS, ventricular zone; IZ, intermediate zone; CP, cortical plate; MZ, marginal zone. The radial process of the glial cell is indicated in blue and a single attached migrating neuron is depicted at the right.

More Common Cephalic Disorders:• Anencephaly• Colpocephaly• Holoprosencephaly• Ethmocephaly• Hydranencephaly• Iniencephaly• Lissencephaly• Megalencephaly• Microcephaly• Porencephaly• Schizencephaly

Can you rule out 3 or 4 of these disorders from the MRI scan?

Presenter

Presentation Notes

Lissencephaly is a set of rare brain disorders where the whole or parts of the surface of the brain appear smooth. The word lissencephaly is derived from the Greek λισσός lissos meaning "smooth" and encephalos meaning "brain." It is caused by defective neuronal migration during the 12th to 24th weeks of gestation resulting in a lack of development of brain folds (gyri) and grooves (sulci).[2] It is a form of cephalic disorder. Terms such as agyria (no gyri) and pachygyria (broad gyri) are used to describe the appearance of the surface of the brain. Children with lissencephaly generally have significant developmental delays, but these vary greatly from child to child depending on the degree of brain malformation and seizure control. Life expectancy can be shortened, generally due to respiratory problems

Lissencephaly – from Greek lissos (“smooth”), affects 4 in 10 million

• Significant developmental delays, but these vary greatly from child to child depending on the degree of brain malformation and seizure control.

• Caused by defective neuronal migration during 12th-24th weeks of gestation (disrupted radial and tangential migration, neurons fail to reach cortical zone).

• Reduced development of gyri and sulci.

• Agyria (no gyri) and pachygyria (broad gyri) used to describe the brain.

• Treatment tailored towards individual symptoms, control seizures.

More Common Cephalic Disorders:• Anencephaly• Colpocephaly• Holoprosencephaly• Ethmocephaly• Hydranencephaly• Iniencephaly• Lissencephaly• Megalencephaly• Microcephaly• Porencephaly• Schizencephaly

Lissencephalic brain of human, lacking gyrification

Can you rule out 3 or 4 of these disorders from the MRI scan?

Presenter

Presentation Notes

Lissencephaly is a set of rare brain disorders where the whole or parts of the surface of the brain appear smooth. The word lissencephaly is derived from the Greek λισσός lissos meaning "smooth" and encephalos meaning "brain." It is caused by defective neuronal migration during the 12th to 24th weeks of gestation resulting in a lack of development of brain folds (gyri) and grooves (sulci).[2] It is a form of cephalic disorder. Terms such as agyria (no gyri) and pachygyria (broad gyri) are used to describe the appearance of the surface of the brain. Children with lissencephaly generally have significant developmental delays, but these vary greatly from child to child depending on the degree of brain malformation and seizure control. Life expectancy can be shortened, generally due to respiratory problems

Presenter

Presentation Notes

Walking for a lissencephaly person was thought to not be possible.


Neuron

Processes spread from outer to inner surfaces of CNS, forming the outer and inner glial limiting membranes (beneath pia mater and ependyma, respectively).

• Astrocytes have in common unique cytological and immunological properties that make them easy to identify, including their star shape, the glial end feet on capillaries, and a unique population of large bundles of intermediate filaments that are composed of an astroglial-specific protein commonly referred to as glial fibrillary acidic protein (GFAP). S-100, a Ca2+-binding protein, and glutamine synthetase are also astrocyte markers.

• Astrocytes are connected to each other, and to oligodendrocytes, by gap junctions, forming a syncytium that allows ions and small molecules to diffuse across the brain parenchyma.

Astrocytes are involved in the neurovascular system.

• For a long time, astrocytes were thought to physically form the BBB, which prevents the entry of cells and diffusion of molecules into the CNS. In fact, astrocytes are indeed the BBB in lower species.

• However, in higher species, astrocytes are responsible for inducing and maintaining the tight junctions in endothelial cells that effectively form the barrier.

• Astrocytes also take part in angiogenesis, which may be important in the development and repair of the CNS. Their role in this important process is still poorly understood.

• Astrocyte astrocytic endfeet on blood vessels regulate vascular tone locally (increasing/decreasing CBF).

Astrocytes release EM proteins, adhesion molecules, growth factors and cytokines.

• Astrocytes are a major source of EM proteins and adhesion molecules in the CNS that participate in the migration of neurons, and in the formation of neuronal aggregates (nuclei), as well as networks.

• Astrocytes produce, in vivo and in vitro, a very large number of growth factors. These factors act singly or in combination to selectively regulate the morphology, proliferation, differentiation, and/or survival of distinct neuronal subpopulations.

• Most of the growth factors also act in a specific manner on the development and functions of astrocytes and oligodendrocytes. The production of growth factors and cytokines by astrocytes and their responsiveness to these factors is a major mechanism underlying the developmental function and regenerative capacity of the CNS.

Astrocytes Have a Wide Range of Functions

Presenter

Presentation Notes

Fig. 3.13. Astrocytes (in orange) are depicted in situ in schematic relationship with other cell types with which they are known to interact. Astrocytes send processes that surround neurons and synapses, blood vessels, and the region of the node of Ranvier and extend to the ependymal, as well as to the pia mater, where they form the glial limitans. **Astrocytes “fence in” neurons and oligodendrocytes. Astrocytes achieve this isolation of the brain parenchyma by extending long processes projecting to the pia mater and the ependyma to form the glia limitans by covering the surface of capillaries and by making a cuff around the nodes of Ranvier. They also ensheath synapses and dendrites and project processes to cell somas. Astrocytes Have a Wide Range of Functions role in the neuronal migration and guidance in early development. **Ultrastructurally (with EM), gap junctions (connexins), desmosomes, glycogen granules, and membrane orthogonal arrays are distinct features used by morphologists to identify astrocytic cellular processes in the complex cytoarchitecture of the nervous system. Astrocytes are a major source of EM proteins and adhesion molecules in the CNS; examples are nerve cell–nerve cell adhesion molecule (N-CAM), laminin, fibronectin, cytotactin, and the J-1 family members janusin and tenascin. These molecules participate not only in the migration of neurons, but also in the formation of neuronal aggregates (nuclei), as well as networks.


Prevent excitotoxicity and clean up environment around neurons

• During neurotransmission, NTs and ions released at high concentrations in the synaptic cleft. The rapid removal of these substances is important so that they do not interfere with synaptic activity. The presence of astrocyte processes around synapses positions them well to regulate NT uptake and inactivation. GLU reuptake is performed mostly by astrocytes, which convert GLU into GLN and then release it into the extracellular space. GLN is taken up by neurons, which use it to generate GLU and GABA.

• Astrocytes contain ion channels for K+, Na+, Cl-, HCO3-, and Ca2+, as well as displaying a wide range of NT receptors.

• Astrocytic spatial buffering: K+ ions released from neurons during neurotransmission are soaked up by astrocytes and moved away from the area through astrocyte gap junctions.

• Astrocytes play a major role in detoxification of the CNS by sequestering metals and a variety of neuroactive substances of endogenous and xenobiotic origin.

Astrocytes: From passive glue to excitable cells

• Astrocytic Ca2+ are controversial. In response to stimuli, intracellular Ca2+ waves are generated in astrocytes. Propagation of the Ca2+ wave can be visually observed as it moves across the cell soma and from astrocyte to astrocyte. The generation of Ca2+ waves from cell to cell is thought to be mediated by second messengers, diffusing through gap junctions.

• In the adult brain, gap junctions are present in all astrocytes. Some gap junctions also have been detected between astrocytes and neurons. Thus, they may participate, along with astroglial NT receptors, in the coupling of astrocyte and neuron physiology.

Astrocytes are implicated in CNS conditions

• In neurotoxicity, viral infections, neurodegenerative disorders, HIV, AIDS, dementia, MS, inflammation, and trauma, astrocytes react by becoming hypertrophic and, in a few cases, hyperplastic.

• A rapid and huge upregulation of GFAP expression and filament formation is associated with astrogliosis. The formation of reactive astrocytes can spread very far from the site of origin. For instance, a localized trauma can recruit astrocytes from as far as the contralateral side, suggesting the existence of soluble factors in the mediation process. Tumor necrosis factor (TNF) and ciliary neurotrophic factors (CNTF) have been identified as key factors in astrogliosis.

Astrocytes Have a Wide Range of Functions (continued)

Presenter

Presentation Notes

Fig. 3.14. The glutamate-glutamine cycle is an example of a complex mechanism that involves an active coupling of neurotransmitter metabolism between neurons and astrocytes. The systems of exchange of glutamine, glutamate, GABA, and ammonia between neurons and astrocytes are highly integrated. The postulated detoxification of ammonia and the inactivation of glutamate and GABA by astrocytes are consistent with the exclusive localization of glutamine synthetase in the astroglial compartment.


• Nonexcitable
















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Neuron

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Presentation Notes


Normal brainResting microglia

Diseased CortexActivated/Reactive microglia

Frank PathologyPhagocytic macrophages

Cellullar components: GLIA Microglia

Microglia – specialized macrophages, respond to inflammation, phagocytize necrotic tissue, and foreign substances that invade the CNS. • Microglia Become Activated in Pathological States. “Reactive” microglia can be distinguished from resting microglia by two criteria: (1) change in

morphology and (2) upregulation of monocyte–macrophage molecules. Although the two phenomena generally occur together, reactive responses of microglia can be diverse and restricted to subpopulations of cells within a microenvironment.

• Microglia not only respond to pathological conditions involving immune activation, but also become activated in neurodegenerative conditions that are not considered immunity-mediated. This latter response is indicative of the phagocytic role of microglia. Microglia change their morphology and antigen expression in response to almost any form of CNS injury.

Microglia Have Diverse Functions in Developing and Mature Nervous Tissue • Most ramified microglial cells are derived from bone marrow–derived monocytes, which enter the brain parenchyma during early stages of brain

development. These cells help break down degenerating cells that undergo programmed cell death as part of normal development. They retain the ability to divide and have the immunophenotypic properties of monocytes and macrophages.

• In addition to their role in remodeling the CNS during early development, microglia secrete cytokines and growth factors that are important in fiber tract development, gliogenesis, and angiogenesis.

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Presentation Notes

Fig. 3.15. Activation of microglial cells in a tissue section from human brain. Resting microglia in normal brain (A). Activated microglia in diseased cerebral cortex (B) have thicker processes and larger cell bodies. In regions of frank pathology () microglia transform into phagocytic macrophages, which can also develop from circulating monocytes that enter the brain. Arrow in B indicates rod cell. Sections stained with antibody to ferritin. Scale bar = 40 uM.


• Nonexcitable
















1

2

3

4

Neuron

Neuron

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Presentation Notes


Ependymal cells (ependymocytes) are the thin neuroephithelial lining of ventricular system of the brain and the central canal of the spinal cord.

Specialized forms of ependymal cells make up the choroid plexus that produces and secretes CSF.

Cilia of ependymal cells help move CSF through the cavities of the brain.

These are nervous tissue cells with a ciliated simple columnar shape much like that of some mucosal epithelial cells. The basal membranes of these cells are characterized by tentacle-like extensions that attach to astrocytes.

Cellullar components: GLIA Ependymal Cells

Section of central canal of the spinal cord

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Presentation Notes

Ependymal cells line the CSF-filled ventricles in the brain and the central canal of the spinal cord. Function Lining the CSF-filled ventricles, the ependymal cells play an important role in the production and regulation of CSF. Their apical surfaces are covered in a layer of cilia, which circulate CSF around the CNS. Their apical surfaces are also covered with microvilli, which absorb CSF. Within the ventricles of the brain, a population of modified ependymal cells and capillaries together known as the tela choroidea form a structure called the choroid plexus, which produces the CSF. Modified tight junctions between epithelial cells control fluid release. This release allows free exchange between CSF and nervous tissue of brain and spinal cord, which is why sampling of CSF (e.g. through a "spinal tap") provides a window to the CNS.

Cellullar components: GLIA Schwann Cell (PNS)

How are Schwann cells different than Oligodendrocytes?

Schwann cells

• Produce a basal lamina “sleeve” that runs the entire length of the axon.

• Schwann cell and fibroblast-derived collagens prevent normal wear-and-tear compression damage.

• Respond vigorously to injury (like astrocytes, unlike OG).

• Exceptional regenerative capacity of PNS (due to growth factor secretion, debris removal after injury, basal lamina axonal guidance).

• Myelination provides trophic support that is essential for axon survival.

• Studies of primary demyelinating diseases, such as multiple sclerosis, and genetic dysmyelinating diseases (e.g., Charcot-Marie-Tooth diseases) indicate that axonal degeneration is the major cause of permanent disability.

“Unrolled” Schwann cell in the PNS in relation to the single axon segment that it myelinates

Compact myelin

Cytoplasmic channels

• Myelin in the PNS is generated by Schwann cells – principal glia of the PNS.

• Cytoplasmic channels remain open even after compact myelin has formed allowing exchange of materials among the myelin sheath, Schwann cell cytoplasm, and axon.

**Peripheral nerves pass between moving muscles and around major joints and are routinely exposed to physical trauma. A hard tackle, slipping on an icy sidewalk, or even just occupying the same uncomfortable seating posture for too long can painfully compress peripheral nerves and potentially damage them. Thus, evolutionary pressures shaping the PNS favor robustness and regeneration rather than conservation of space.

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Presentation Notes

Fig. 3.9. An “unrolled” Schwann cell in the PNS is illustrated in relation to the single axon segment that it myelinates. The broad stippled region is compact myelin surrounded by cytoplasmic channels that remain open even after compact myelin has formed, allowing an exchange of materials among the myelin sheath, the Schwann cell cytoplasm, and perhaps the axon as well. ***Peripheral nerves pass between moving muscles and around major joints and are routinely exposed to physical trauma. A hard tackle, slipping on an icy sidewalk, or even just occupying the same uncomfortable seating posture for too long can painfully compress peripheral nerves and potentially damage them. Thus, evolutionary pressures shaping the PNS favor robustness and regeneration rather than conservation of space. Myelin in the PNS is generated by Schwann cells (Fig. 3.9), which are different to oligodendrocytes in several ways. Individual myelinating Schwann cells form a single internode. Unlike oligodendrocytes, Schwann cells secrete copious extracellular matrix components and produce a basal lamina “sleeve” that runs the entire length of myelinated axons. Schwann cell and fibroblast-derived collagens prevent normal wear-and-tear compression damage. Schwann cells also respond vigorously to injury, in common with astrocytes but unlike oligodendrocytes. Schwann cell growth factor secretion, debris removal by Schwann cells after injury, and the axonal guidance function of the basal lamina are responsible for the exceptional regenerative capacity of the PNS compared with the CNS. **Myelination provides trophic support that is essential for axon survival. Studies of primary demyelinating diseases, such as multiple sclerosis, and genetic dysmyelinating diseases (e.g., Charcot-Marie-Tooth diseases) indicate that axonal degeneration is the major cause of permanent disability.

Cellullar components: GLIA Satellite Glial Cells (PNS)

Satellite glial cells (SGCs) are homologous to astrocytes in the CNS

• SGCs are glial cells that cover the surface of nerve cell bodies in sensory, sympathetic, and parasympathetic ganglia (like Schwann cells are derived from the neural crest of the embryo during development).

• SGCs have a significant role in controlling the microenvironment of sympathetic ganglia (based on the observation that SGCs almost completely envelop the neuron and can regulate the diffusion of molecules across the PM).

• Homologous role to astrocytes in the CNS; they share anatomical and physiological/electrical properties, presence of NT transporters (for GABA and GLU), and glutamine synthetase (GS), which catalyzes the conversion of GLU into GLN.

• Although SGCs express GFAP and different S-100 proteins, the most useful marker for SGC identification is GS. The levels of GS are relatively low at rest, but they greatly increase if the neuron undergoes axonal damage. Furthermore, SGCs also possess mechanisms to release cytokines, ATP, and other chemical messengers.

• Additionally, SGCs contain the glutamate related enzymes glutamate dehydrogenase and pyruvate carboxylase, and thus can supply the neurons with GLN, malate, and lactate.

• Gap junctions exist between SGCs in the sheaths of adjacent neurons as well as between SGCs in the same sheath (reflexive gap junctions). The degree to which SGCs are coupled to SGCs of another sheath or to SGCs of the same sheath is dependent on the pH of the cellular environment.

• SGCs 1) supply nutrients to the surrounding neurons, 2) have some structural function, 3) act as protective, cushioning cells, 4) express a variety of receptors (e.g. mAChR, ErythropoietinR) that allow for a range of interactions with neuroactive chemicals (i.e. Ach, GABA, GLU, ATP, NA, substance P, capsaicin), 5) speculation that in autonomic ganglia have a similar role to the BBB as a functional barrier to large molecules.

• Many of SGC receptors and ion channels have recently been implicated in health issues including chronic pain and herpes simplex.

• There is much more to be learned about these cells, and research surrounding additional properties and roles of the SGCs is ongoing.

Presenter

Presentation Notes

Take-home. Similar to astrocytes, envelop ganglia.. Provide support and nutrients. SGCs most often surround individual sensory and parasympathetic neurons with a complete, unbroken sheath while most sympathetic ganglia neurons lack a completely continuous SGC sheath, allowing for limited direct exchange of materials between the extracellular space of the neuron and the space within the connective tissue where the SGCs are situated. Research is currently ongoing in determining the physiological role of satellite glial cells. Current theories suggest that SGCs have a significant role in controlling the microenvironment of the sympathetic ganglia. This is based on the observation that SGCs almost completely envelop the neuron and can regulate the diffusion of molecules across the cell membrane.[2] It has been previously shown that when fluorescent protein tracers are injected into the cervical ganglion in order to bypass the circulatory system, they are not found on the neuron surface. This suggests that the SGCs can regulate the extracellular space of individual neurons.[22] Some speculate that SGCs in the autonomic ganglia have a similar role to the blood–brain barrier as a functional barrier to large molecules.[23] SGCs role as a regulator of neuronal microenvironment is further characterized by its electrical properties which are very similar to those of astrocytes.[24] Astrocytes have a well studied and defined role in controlling the microenvironment within the brain, therefore researchers are investigating any homologous role of SGCs within the sympathetic ganglia. An established mode of controlling the microenvironment in sensory ganglia is the uptake of substances by specialized transporters which carry neurotransmitters into cells when coupled with Na+ and Cl−.[25] Transporters for glutamate and gamma-Aminobutyric acid (GABA)[26] have been found in SGCs. They appear to be actively engaged in the control of the composition of the extracellular space of the ganglia. The enzyme glutamine synthetase, which catalyzes the conversion of glutamate into glutamine, is found in large amounts in SGCs.[27] Additionally, SGCs contain the glutamate related enzymes glutamate dehydrogenase and pyruvate carboxylase, and thus can supply the neurons not only with glutamine, but also with malate and lactate.[27]

Wikipedia

Normal Brain Alzheimer’s DiseaseThe amyloid (Aβ ) cascade hypothesis

(Barage and Sonawane, Peptides, 2015)

Early role of vascular dysregulation on late-onset AD based on multifactorial data-driven analysis (Y. Iturria-Medina et al. & The Alzheimer’s Neuroimaging Initiative, Montreal, CA)

In cohort of 1,171 subjects (over 7,700 brain images) from the ADNI database, evaluated: 1. Aβ misfolded proteins (Florbetapir PET)

2. Glucose metabolism (Fluorodeoxyglucose)

3. Cerebral blood flow (Arterial Spin Labeling)

4. Functional activity (Resting MRI)

5. Structural tissue brain patterns (Structural MRI)

*(mapped in vivo using corresponding neuroimaging techniques)

Diagnosed as:

• healthy control (HC)

• early mild cognitive impairment (EMCI)

• late mild cognitive impairment (LMCI)

• probable Alzheimer’s disease patient (LOAD)

(Iturria-Medina et al., Nat Comm., 2016)

Presenter

Presentation Notes

Evaluated Aβ misfolded proteins, glucose metabolism, cerebral blood flow, functional activity and/or structural tissue brain patterns in a cohort of 1,171 subjects (over 7,700 brain images) from the ADNI database (Methods section, Study participants; Supplementary Table 1). These five biological factors were mapped in vivo using corresponding neuroimaging techniques (Fig. 1a; Methods section, Data Description and Processing): Florbetapir positron emission tomography (PET; for Aβ deposition), Fluorodeoxyglucose PET (for glucose metabolism), Arterial Spin Labeling (ASL, for cerebral blood flow), resting functional magnetic resonance imaging (MRI; for neuronal activity at rest) and structural MRI (for structural tissular properties). Each participant was previously diagnosed at each visit as healthy control (HC), early mild cognitive impairment (EMCI), late mild cognitive impairment (LMCI) or probable Alzheimer’s disease patient (LOAD). In addition, participants were cognitively and genetically characterized (for example, according to the Mini Mental State Examination (MMSE) or to the number of apoeε4 allele copies, respectively).

(Iturria-Medina et al., Nat Comm., 2016)

In cohort of 1,171 subjects (over 7,700 brain images) from the ADNI database, evaluated: 1. Aβ misfolded proteins (Florbetapir PET)

2. Glucose metabolism (Fluorodeoxyglucose)

3. Cerebral blood flow (Arterial Spin Labeling)

4. Functional activity (Resting MRI)

5. Structural tissue brain patterns (Structural MRI)

*(mapped in vivo using corresponding neuroimaging techniques)

Diagnosed as:

• healthy control (HC)

• early mild cognitive impairment (EMCI)

• late mild cognitive impairment (LMCI)

• probable Alzheimer’s disease patient (LOAD)

Early role of vascular dysregulation on late-onset AD based on multifactorial data-driven analysis (Y. Iturria-Medina et al. & The Alzheimer’s Neuroimaging Initiative, Montreal, CA)

Presenter

Presentation Notes

Evaluated Aβ misfolded proteins, glucose metabolism, cerebral blood flow, functional activity and/or structural tissue brain patterns in a cohort of 1,171 subjects (over 7,700 brain images) from the ADNI database (Methods section, Study participants; Supplementary Table 1). These five biological factors were mapped in vivo using corresponding neuroimaging techniques (Fig. 1a; Methods section, Data Description and Processing): Florbetapir positron emission tomography (PET; for Aβ deposition), Fluorodeoxyglucose PET (for glucose metabolism), Arterial Spin Labeling (ASL, for cerebral blood flow), resting functional magnetic resonance imaging (MRI; for neuronal activity at rest) and structural MRI (for structural tissular properties). Each participant was previously diagnosed at each visit as healthy control (HC), early mild cognitive impairment (EMCI), late mild cognitive impairment (LMCI) or probable Alzheimer’s disease patient (LOAD). In addition, participants were cognitively and genetically characterized (for example, according to the Mini Mental State Examination (MMSE) or to the number of apoeε4 allele copies, respectively).

Cellullar components: Vascular Cells

Cortical layers (I-VI)

Corpus Callosum

Microvasculature of adult mouse somatosensory barrel field cortex

Arrow points to area of increased vascular density in layer IV, where contralateral somatosensory inputs from the thalamus terminate.

• The cerebral vasculature delivers O2, glucose, and nutrients into the brain and removes CO2 and other metabolic wastes.

• Endothelial cells interact with neurons, astrocytes, microglia, and other perivascular cells, including smooth muscle cells and pericytes to form a neurovascular unit (NVU).

• Glucose is the main metabolic substrate of neurons, but it cannot cross the BBB. Glucose transporters on endothelial cells and glia supply glucose to brain.

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Presentation Notes

Fig. 3.16. Microvasculature of the adult mouse somatosensory barrel field (S1BF) cortex. Microvessels were stained with antibodies against collagen type IV, a protein component of the extracellular matrix, and lightly counter-stained with cresyl violet (Nissl). Cortical layers (I-VI) and the corpus callosum (CC) are indicated. An area of increased vascular density in layer IV, where contralateral somatosensory inputs from the thalamus terminate, is indicated by an arrow. Scale bar = 50 um.

Cellullar components: Vascular Cells

Different cell types of the neurovascular unit regulate cerebral blood flow (CBF) at different levels of the vascular tree

Penetrating artery – 2-3 layers of vascular smooth muscle cells (VSMCs) and astrocytes are innervated by neurons.

Arterioles – only 1 layer of VSMC. Contain transitional pericytes (a cell type between pericytes and VSMCs).

Capillaries – endothelial cells share common basement membrane with pericytes, both covered by astrocytic endfeet. Astrocytes and pericytesinnervated by local neurons.

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Presentation Notes

Figure 1 | A schematic representation of the neurovascular unit showing cellular elements regulating cerebral blood flow along the vascular tree. Different cell types of the neurovascular unit (NVU), including neurons, astrocytes, mural cells — vascular smooth muscle cells (VSMCs) and pericytes — and endothelial cells, regulate cerebral blood flow at different levels of the vascular tree (part a). The cellular composition of the NVU differs along the vascular tree, but the principal cellular components all remain represented, as illustrated here. b | At the level of penetrating arteries, the NVU is composed of endothelial cells making up the inner layer of the vessel wall, covered by a thin extracellular basement membrane and ringed by one to three layers of VSMCs, and ensheathed by pia. The Virchow–Robin space containing the cerebrospinal fluid is between pia and the glia limitans formed by astrocytic endfeet. Both VSMCs and astrocytes are innervated by local neurons. c | Arterioles differ in that there is only one layer of VSMCs, and astrocyte coverage and innervation of the vessel wall and the endothelial inner layer display continuity with penetrating arteries, and brain capillaries, above and below the arteriole level, respectively. In addition to VSMCs, pre-capillary arterioles may also contain transitional pericytes, a cell type between pericytes and VSMCs. d | At the capillary level, the NVU is composed of endothelial cells that share a common basement membrane with pericytes. Pericytes stretch their processes along and around capillaries and make direct interdigitated or ‘peg-socket’-like contacts with endothelial cells. Pericytes and endothelial cells are covered by astrocyte endfeet. Both astrocytes and pericytes are innervated by local neurons, as shown for astrocytes and VSMCs in the upper segments of the vascular tree.

Cellullar components: Vascular CellsUltrastructural analysis of PFC microvasculature of a

10-month-old wild-type mouse.

Morphological identification of pericytes

• Pericyte on a rat capillary• Label basement membrane with fluorescently-tagged isolectin B4• Soma exhibit classical “bump-on-a-log” appearance

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Presentation Notes

Ultrastructural analysis of the cerebral microvasculature of a 10-month-old wild-type mouse. A transversely sectioned capillary is shown from the prefrontal cortex. An endothelial cell (E) surrounding the lumen, a pericyte (P), and an astrocytic end-foot processes (A) are indicated. Scale bar = 1 um. Fig. S1. Morphological identification of pericytes. (A) Bright field image showing a morphologically-identified candidate pericyte on a rat capillary, with the soma exhibiting the classical bump-on-a-log appearance. Pericytes were identified by the experimenter using images like this, without inspecting the IB4 fluorescence. (B) Same field with IB4-Alexa-568 fluorescence excited, showing that the soma is surrounded by IB4-labeled basement membrane, and thus is confirmed to be a pericyte. In 26 out of 27 trials (96.3%), IB4 fluorescence confirmed the morphologically selected cells to be pericytes.

Cellullar components: Vascular Cells Oligomeric Aβ acts on pericytes to constrict capillaries in human brain slices

Ultrastructural analysis of PFC microvasculature of a 10-month-old wild-type mouse.

Morphological identification of pericytes

• Pericyte on a rat capillary• Label basement membrane with fluorescently-tagged isolectin B4• Soma exhibit classical “bump-on-a-log” appearance

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Presentation Notes

Fig. 1. Oligomeric Ab acts on pericytes to constrict capillaries in human brain slices. IB4-labeled capillary in a human cortical slice, with two pericyte somata (white arrowheads) outlined by their basement membrane. Nuclei are stained with DAPI (blue). Pericyte labeled with antibody to PDGFRb. (C and D) Arteriole (C) and pericyte (D) labeled with IB4 and antibody to a smooth muscle actin (a-SMA, localized in processes originating from the pericyte soma). (E) Images of a capillary (red lines between yellow arrowheads indicate diameter) and pericyte soma (white arrowheads) in a live human brain slice before drug application, in the presence of 2 mM superfused noradrenaline (+NA), with 2 mM NA and 500 mM glutamate superfused (+NA +Glu), and after stopping drug superfusion (washout). Graph shows time course of capillary diameter at red line throughout the experiment. (F) Mean (± SEM) glutamate-evoked dilation and noradrenaline-evoked constriction in experiments as in (E) (numbers of pericytes on bars; change in diameter was quantified relative to that before application of each drug; relative to the pre-noradrenaline diameter, the glutamate-evoked dilation was 26.8 ± 7.7%). (G) Silver staining of an SDS-PAGE gel for Ab solutions prepared as in materials and methods. (H) Images of a human capillary before and after superfusion of 72 nM Ab1–42, showing a region (red line) being constricted by a pericyte (arrowheads). Graph shows mean (±SEM) diameter change at four pericyte locations from four slices treated with Ab and three pericyte locations from three slices superfused with aCSF lacking Ab (significantly reduced at 40 min in Ab, P = 0.01).

Slow axonal transport represents the delivery of cytoskeletal and cytoplasmic constituents to the periphery.

• Cytoplasmic proteins are synthesized on free polysomes and organized for transport as cytoskeletal elements or macromolecular complexes (1).

• Microtubules are formed by nucleation at the microtubule-organizing center near the centriolarcomplex (2) and then released for migration into the axon or dendrites.

• The molecular mechanisms are not as well understood as those for fast axonal transport, but slow transport appears to be unidirectional with no retrograde component.

• Studies suggest that motors like cytoplasmic dynein may interact with the axonal membrane cytoskeleton to move the microtubules with their plus ends leading (3).

• Neurofilaments may not be able to move on their own but may hitchhike on microtubules (4).

• Other cytoplasmic proteins may do the same or may be moved by other motors. Once cytoplasmic structures reach their destinations, they are degraded by local proteases (5) at a rate that allows either growth (in the case of growth cones) or maintenance of steady-state levels.

• The different composition and organization of the cytoplasmic elements in dendrites suggest that different pathways may be involved in the delivery of cytoskeletal and cytoplasmic materials to the dendrite (6). In addition, some mRNAs are transported into the dendrites, but not into axons.

Cytoskeleton – Cytoskeletal Proteins – give the cells their shape and provide mechanical resistance to deformation

Presenter

Presentation Notes

Fig. 4.7 Slow axonal transport represents the delivery of cytoskeletal and cytoplasmic constituents to the periphery. Cytoplasmic proteins are synthesized on free polysomes and organized for transport as cytoskeletal elements or macromolecular complexes (1). Microtubules are formed by nucleation at the microtubule-organizing center near the centriolar complex (2) and then released for migration into the axon or dendrites. The molecular mechanisms are not as well understood as those for fast axonal transport, but slow transport appears to be unidirectional with no retrograde component. Studies suggest that motors like cytoplasmic dynein may interact with the axonal membrane cytoskeleton to move the microtubules with their plus ends leading (3). Neurofilaments may not be able to move on their own but may hitchhike on microtubules (4). Other cytoplasmic proteins may do the same or may be moved by other motors. Once cytoplasmic structures reach their destinations, they are degraded by local proteases (5) at a rate that allows either growth (in the case of growth cones) or maintenance of steady-state levels. The different composition and organization of the cytoplasmic elements in dendrites suggest that different pathways may be involved in the delivery of cytoskeletal and cytoplasmic materials to the dendrite (6). In addition, some mRNAs are transported into the dendrites, but not into axons.

Neuronal cytoskeletal changes are an early consequence of repetitive head injuryCase 1A professional boxer aged 23 at death who had started boxing at 11 years of age, and turned professional at the age of 19. He had approximately 80 fights at amateur level, and 20 fights (totaling 105 rounds) in his 4 years as a professional. He had no history of a severe head injury during his career, until his final fight, as a result of which he developed an acute subdural haematoma. He died 48 h after the contest, despite neurosurgical intervention.

Case 2A former boxer had a history of psychotic illness, and was 28 years old at death. He had been an amateur boxer since leaving school at 16, and had fought regularly at local club level, at the rate of one fight every 3 months for 4–5 years. He stopped boxing at the age of 21 as he had suffered from haematuria after contests. At the age of 20 he was admitted to a psychiatric hospital with a diagnosis of paranoid schizophrenia which responded to major tranquillisers. He was readmitted with an acute psychotic illness at the age of 25, this type more depressive in nature, and then again 2 years later. He died unexpectedly the following year during a grand mal seizure. He had no history of a serious head injury during his boxing career.

C A cortical vessel in the temporal lobe of case 1. D A vessel at the base of a sulcus in the insula in case 2.

**It appears that repetitive head injury in young adults is initially associated with neocortical NFT formation in the absence of Aβ deposition.**

**immunostaining included β-amyloid precursor protein, amyloid β-protein (Aβ), tau and apolipoprotein E (apoE). Pathological findings in all cases were of neocortical neurofibrillary tangles (NFTs) and neuropil threads, with groups of tangles consistently situated around blood vessels in the worst affected regions. No Aβ immunoreactivity was detected.

(Geddes et al., Acta Neuropathol., 1999)

Pugilistica dementia

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Presentation Notes

While neuropathological studies have established the pathology of dementia pugilistica to be similar to that of Alzheimer’s disease, there is little information about the early histological changes caused by the repetitive trauma that eventually produces dementia pugilistica. **immunostaining included b-amyloid precursor protein, amyloid b-protein (Ab), tau and apolipoprotein E (apoE). Pathological findings in all five cases were of neocortical neurofibrillary tangles (NFTs) and neuropil threads, with groups of tangles consistently situated around blood vessels in the worst affected regions. No Ab immunoreactivity was detected. The amount of neuronal apoE expression varied widely between the cases with no clear relation to the NFTs. The apoE genotype was determined in only two cases (both e3/e3). It appears that repetitive head injury in young adults is initially associated with neocortical NFT formation in the absence of Ab deposition. The distribution of the tau pathology suggests that the pathogenesis of cytoskeletal abnormalities may involve damage to blood vessels or perivascular elements. Introduction Detailed post mortem studies of elderly retired boxers suffering from dementia pugilistica have shown a neuropathological picture very like that of Alzheimer’s disease (AD), with widespread neocortical neurofibrillary tangles, neuropil threads and diffuse amyloid plaques, although lacking the neuritic plaques typical of AD. Evidence of chronic encephalopathy has also been reported in clinical studies of participants in sports other than boxing in which repeated mild head injury occurs and in anecdotal evidence supplied by neurologists. An autopsy study of a demented woman who had been repeatedly assaulted by her husband showed pathology identical to that seen in boxers. Because of the morphological similarity between the neuropathology of such cases and that of AD, some authors have suggested that the pathogenetic mechanisms operating must be similar. However, while the temporal progression and topographical spread of the lesions of AD are well recognised and clearly documented, there is little information about the early changes caused by repetitive head injury. A single case report of the findings in a 24-year-old autistic woman who was a persistent head-banger has recently been supplemented by our study of the findings in the brain of a 23-year-old professional boxer. Both cases showed neurofibrillary tangles with a morphology and staining pattern identical to, but in arrangement and distribution very unlike, the early pathology of AD. We have now had the opportunity to examine the brain of a second boxer, as well as the brains of an amateur footballer, a young mentally subnormal man who habitually banged his head, and a lobectomy specimen from a patient who had suffered many minor head injuries as a result of intractable epileptic seizures. We have in addition performed further studies on the brain of the young boxer previously reported. Similar neuropathological findings are present in all the cases: we believe that they are early changes caused by chronic head trauma, and as such represent a prelude to the full-blown pathology of dementia pugilistica.

Questions?

Cytoskeleton – Cytoskeletal Proteins – give the cells their shape and provide mechanical resistance to deformation

Basic elements of neuronal subcellular organization. The neuron consists of a soma, or cell body, in which the nucleus, multiple cytoplasm-filled processes termed dendrites, and the (usually single) axon are placed. The neuron is highly extended in space; a neuron with a cell body of the size shown here could easily maintain an axon several miles in length! The unique shape of each neuron is the result of a cooperative interplay between plasma membrane components (the lipid matrix and associated proteins) and cytoskeletal elements. Most large neurons in vertebrates are myelinated by oligodendrocytes in the CNS and by Schwann cells in the in the PNS. The compact wraps of myelin encasing the axon distal to the initial segment permit the rapid conduction of the AP by a process termed “saltatory conduction”.

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Presentation Notes

Fig. 4.1 Basic elements of neuronal subcellular organization. The neuron consists of a soma, or cell body, in which the nucleus, multiple cytoplasm-filled processes termed dendrites, and the (usually single) axon are placed. The neuron is highly extended in space; a neuron with a cell body of the size shown here could easily maintain an axon several miles in length! The unique shape of each neuron is the result of a cooperative interplay between plasma membrane components (the lipid matrix and associated proteins) and cytoskeletal elements. Most large neurons in vertebrates are myelinated by oligodendrocytes in the CNS and by Schwann cells in the in the PNS. The compact wraps of myelin encasing the axon distal to the initial segment permit the rapid conduction of the AP by a process termed “saltatory conduction”.

From Wikipedia

CNS) AstrocytesOligodendrocytes Microglia

PNS) Schwann cells

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Presentation Notes

An astrocyte cell grown in tissue culture stained with antibodies to GFAP and vimentin. The GFAP is coupled to a red fluorescent dye and the vimentin is coupled to a green fluorescent dye. Both proteins are present in large amounts in the intermediate filaments of this cell, so the cell appears yellow, the result of combining strong red and green signals. The blue signal is DNA revealed with DAPI, and shows the nucleus of the astrocyte and of other cells in this image. Image was captured on a confocal microscope in the EnCor Biotechnology laboratory.

Fast axonal transport represents the transport of membrane-associated materials, having both anterograde and retrograde components.• For anterograde transport, most polypeptides are synthesized on membrane-bound polysomes, also

known as rough endoplasmic reticulum (1), and then transferred to the Golgi apparatus for processing and packaging into specific classes of membrane-bound organelles (2). Proteins following this pathway include both integral membrane proteins and secretory polypeptides in the lumen of vesicles. Cytoplasmic peripheral membrane proteins such as kinesins are synthesized on the cytoplasmic or free polysomes.

• Once vesicles have been assembled and the appropriate motors associate with them, they are moved down the axon at a rate of 100–400 mm per day (3).

• Different membrane structures are delivered to different compartments and may be regulated independently. For example, dense core vesicles and synaptic vesicles are both targeted for the presynaptic terminal (4), but the release of vesicle contents involves distinct pathways.

• After vesicles merge with the plasma membrane, their protein constituents are taken up by coated pits and vesicles via the receptor-mediated endocytic pathway and delivered to a sorting compartment (5).

• After proper sorting into appropriate compartments, membrane proteins are either committed to retrograde axonal transport or recycled (6).

• Retrograde moving organelles are morphologically and biochemically distinct from anterograde vesicles. These larger vesicles have an average velocity about half that of anterograde transport. The retrograde pathway is an important mechanism for the delivery of neurotrophic factors to the cell body. Material delivered by retrograde transport typically fuses with cell body compartments to form mature lysosomes (7), where most constituents are recycled. However, neurotrophic factors and neurotrophic viruses can act at the level of the cell body.

• Although evidence shows that vesicle transport also occurs into dendrites (8), less is known about this process. Dendritic vesicle transport is complicated by the fact that dendritic microtubules may have mixed polarity.

Presenter

Presentation Notes

Fig. 4.8 Fast axonal transport represents the transport of membrane-associated materials, having both anterograde and retrograde components. For anterograde transport, most polypeptides are synthesized on membrane-bound polysomes, also known as rough endoplasmic reticulum (1), and then transferred to the Golgi apparatus for processing and packaging into specific classes of membrane-bound organelles (2). Proteins following this pathway include both integral membrane proteins and secretory polypeptides in the lumen of vesicles. Cytoplasmic peripheral membrane proteins such as kinesins are synthesized on the cytoplasmic or free polysomes. Once vesicles have been assembled and the appropriate motors associate with them, they are moved down the axon at a rate of 100–400 mm per day (3). Different membrane structures are delivered to different compartments and may be regulated independently. For example, dense core vesicles and synaptic vesicles are both targeted for the presynaptic terminal (4), but the release of vesicle contents involves distinct pathways. After vesicles merge with the plasma membrane, their protein constituents are taken up by coated pits and vesicles via the receptor-mediated endocytic pathway and delivered to a sorting compartment (5). After proper sorting into appropriate compartments, membrane proteins are either committed to retrograde axonal transport or recycled (6). Retrograde moving organelles are morphologically and biochemically distinct from anterograde vesicles. These larger vesicles have an average velocity about half that of anterograde transport. The retrograde pathway is an important mechanism for the delivery of neurotrophic factors to the cell body. Material delivered by retrograde transport typically fuses with cell body compartments to form mature lysosomes (7), where most constituents are recycled. However, neurotrophic factors and neurotrophic viruses can act at the level of the cell body. Although evidence shows that vesicle transport also occurs into dendrites (8), less is known about this process. Dendritic vesicle transport is complicated by the fact that dendritic microtubules may have mixed polarity.

Axonal dynamics in a myelinated axon from the peripheral nervous system (PNS). Axons are in a constant flux with many concurrent dynamic processes. This diagram illustrates a few of the many dynamic events occurring at a node of Ranvier in a myelinated axon from the PNS. Axonal transport moves cytoskeletal structures, cytoplasmic proteins, and membrane-bound organelles from the cell body toward the periphery (from right to left). At the same time, other vesicles return to the cell body by retrograde transport (retrograde vesicle). Membrane-bound organelles are moved along microtubules by motor proteins such as the kinesins and cytoplasmic dyneins. Each class of organelles must be directed to the correct functional domain of the neuron. Synaptic vesicles must be delivered to a presynaptic terminal to maintain synaptic transmission. In contrast, organelles containing sodium channels must be targeted specifically to nodes of Ranvier for saltatory conduction to occur. Cytoskeletal transport is illustrated by microtubules (rods in the upper half of the axon) and neurofilaments (bundle of rope-like rods in the lower half of the axon) representing the cytoskeleton. They move in the anterograde direction as discrete elements and are degraded in the distal regions. Microtubules and neurofilaments interact with each other transiently during transport, but their distribution in axonal cross sections suggests that they are not stably cross-linked. In axonal segments without compact myelin, such as the node of Ranvier or following focal demyelination, a net dephosphorylation of neurofilament side arms allows the neurofilaments to pack more densely. Myelination is thought to alter the balance between kinase (K indicates an active kinase; k is an inactive kinase) and phosphatase (P indicates an active phophatase; p is an inactive phosphatase) activity in the axon. Most kinases and phosphatases have multiple substrates, suggesting a mechanism for targeting vesicle proteins to specific axonal domains. Local changes in the phosphoryation of axonal proteins may alter the binding properties of proteins. The action of synapsin I in squid axoplasm suggests that dephosphorylated synapsin cross-links synaptic vesicles to microfilaments. When a synaptic vesicle encounters the dephosphorylated synapsin and actin-rich matrix of a presynaptic terminal, the vesicle is trapped at the terminal by inhibition of further axonal transport, effectively targeting the synaptic vesicle to a presynaptic terminal. Similarly, a sodium channel-binding protein may be present at nodes of Ranvier in a high-affinity state (i.e., dephosphorylated). Transport vesicles for nodal sodium channels (Na channel vesicle) would be captured upon encountering this domain, effectively targeting sodium channels to the nodal membrane. Interactions between cells could in this manner establish the functional architecture of the neuron.

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Presentation Notes

FIGURE 4.9 Axonal dynamics in a myelinated axon from the peripheral nervous system (PNS). Axons are in a constant flux with many concurrent dynamic processes. This diagram illustrates a few of the many dynamic events occurring at a node of Ranvier in a myelinated axon from the PNS. Axonal transport moves cytoskeletal structures, cytoplasmic proteins, and membrane-bound organelles from the cell body toward the periphery (from right to left). At the same time, other vesicles return to the cell body by retrograde transport (retrograde vesicle). Membrane-bound organelles are moved along microtubules by motor proteins such as the kinesins and cytoplasmic dyneins. Each class of organelles must be directed to the correct functional domain of the neuron. Synaptic vesicles must be delivered to a presynaptic terminal to maintain synaptic transmission. In contrast, organelles containing sodium channels must be targeted specifically to nodes of Ranvier for saltatory conduction to occur. Cytoskeletal transport is illustrated by microtubules (rods in the upper half of the axon) and neurofilaments (bundle of rope-like rods in the lower half of the axon) representing the cytoskeleton. They move in the anterograde direction as discrete elements and are degraded in the distal regions. Microtubules and neurofilaments interact with each other transiently during transport, but their distribution in axonal cross sections suggests that they are not stably cross-linked. In axonal segments without compact myelin, such as the node of Ranvier or following focal demyelination, a net dephosphorylation of neurofilament side arms allows the neurofilaments to pack more densely. Myelination is thought to alter the balance between kinase (K indicates an active kinase; k is an inactive kinase) and phosphatase (P indicates an active phophatase; p is an inactive phosphatase) activity in the axon. Most kinases and phosphatases have multiple substrates, suggesting a mechanism for targeting vesicle proteins to specific axonal domains. Local changes in the phosphoryation of axonal proteins may alter the binding properties of proteins. The action of synapsin I in squid axoplasm suggests that dephosphorylated synapsin cross-links synaptic vesicles to microfilaments. When a synaptic vesicle encounters the dephosphorylated synapsin and actin-rich matrix of a presynaptic terminal, the vesicle is trapped at the terminal by inhibition of further axonal transport, effectively targeting the synaptic vesicle to a presynaptic terminal. Similarly, a sodium channel-binding protein may be present at nodes of Ranvier in a high-affinity state (i.e., dephosphorylated). Transport vesicles for nodal sodium channels (Na channel vesicle) would be captured upon encountering this domain, effectively targeting sodium channels to the nodal membrane. Interactions between cells could in this manner establish the functional architecture of the neuron.

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