HOW WE STUDY BRAIN & BEHAVIOR (CONT.)

AMHERST COLLEGE INTRODUCTION TO NEUROSCIENCE

WEDNESDAY, JANUARY 30, 2008

Reading: Chapter 1 & 2

Friday: Chapter 7: 168-180; 193-199; 205-235

Chapter 15 (490-497)

Chen, Sandi S.

Coombs, Angela A.

Guha, Pallabi

Gutierrez, Christina

Hopkins, Christina C.

Howard, Clare E.

Kativhu, Chido L.

Kim, Daniel W.

LaMontagne, Laurel

Mattison, Jamie E.

Montgomery, Tracy

Navarro, Yasmin

Rivera, Ashley M.

Salgado, Sanjay M.

Thein, Thuzar

Tsareva, Alina

Zhang, Wen

Zhu, Victor

Tue

sday

lab

Anderson, Nicolle

Cai, Sophia L

Cameron, Rachel

Dalton, Elizabeth D.

Dier, Kirsten N.

Gladstone, Alexandra

Glick, Michelle S.

Hartley, Iris R.

Holaday, Eric J.

Jeppson, Pamela

Jiang, Debbie C.

Kundu, Surya

Lim, Tiffany M.

Ludwig, Susannah W.

Moin, Emily E.

O'Loughlin, Kerry

Romanowicz, Jennifer

Waskom, Michael L

Wed

nesd

ay la

b

Neuroscience definition & history – Chapter 1• Neuroscience: The study of behavior and the

mind through the study of the nervous system.

• Mind and brain:– “Today, some people still believe that there is a

‘mind-brain problem,’ that somehow the human mind is distinct from the brain. However, as we shall see…, modern neuroscience research supports another conclusion: The mind has a physical basis, which is the brain.”

– Combustion of gasoline is the physical basis of a car’s movement, but the car’s movement is distinct from the combustion of gasoline.

Chapter 1 questions

• Before it was understood that nerves signal using electricity, what mode of signalling was attributed to nerves?

• What is the earliest experiment (as distinct from observation) cited in Chapter 1?

• What are the arguments that experiments on animals such as rats can be relevant to understanding human behavior, human mental life, and human brain diseases?

What is the brain made of?• Cells: individual or syncytium?• Cell types• Extracellular space in brain tissue• Ventricles

How we study…

A. Nerve cell structure

B. Neurons in isolation

C. Connections between different parts of the nervous system

D. Electrical activity

E. Chemical signalling between neurons

F. Relation between brain activity and behavior

A. Nerve cell structure: 1. Nissl and other traditional stains

100 m

2. Golgi method

Silver or mercury salts, precipitate within neurons -Camilo Golgi, 1870s -used by Santiago Ramon y Cajal, 1880s-1920s

The “Neuron Doctrine”

Dendrites

Soma

(cell body)

Axon

3. Fluorescence labelling

Neurons vs. glia(University of Florida)

Fused neurons (Institute of Biophysics, Beijing)

…with computer processing

4. Electron microscopy

Shorter wavelength = higher resolution

1 m

Cell membrane

Neurons: a composite picture

The neuron: your typical cell, and more!

Text Fig. 2.7

B. Studying living nerve cells in isolation from their normal surroundings

• Gray vs. white matter – are axons a separate type of cell?

• Cell and tissue culture– Invented by Ross Harrison in 1909 to study this

question

C. Tracing connections between different parts of the nervous system

Pathway tracing:• Dye transport along axons, e.g. Fast Blue • Lesion + degeneration-specific staining• Radioactive tracers (3H-proline)

• Other chemical tracing: horseradish peroxidase (anterograde or retrograde)

Inject into one eye, observe in visual cortex

Text, Fig. 22.18

Horseradish peroxidase

HRP is a plant enzyme. It is transported down nerve axons, and it creates colored product when tissue exposed to hydrogen peroxide (H2O2)

(H2O2 H2O + O, O + chromogen color)

Inject HRP into left eye

From: Kay Fite, UMass

D. Studying the electrical activity of neurons“Electrophysiology:”• Surface recording – evoked potentials, EEG

– Populations of neurons– Can be done in humans

• Single neuron recording • Patch clamp recording

Single neuron recording: intracellular

Fig. 3.11

Glass micropipette:- Tip diameter 0.5 um- Filled with salt solution- Records electrical

difference across the cell membrane

Single neuron recording: extracellular

Sharpened metal probe, tip diameter 1 – 5 um

Records electrical currents flowing outside neurons

Voltage

Time

E. Studying chemical signalling: Pharmacology

• How can chemicals have effects in the body at very low concentrations?

• Concepts:– Receptors– Specific binding– Multiple subtypes for a single neurotransmitter– Agonists, antagonists

Measuring chemicals and chemical signals

(1) Immunological methods

– Antibody to specific protein, e.g. receptor

– Single brain section: Immunohistochemistry

– Piece of brain tissue: Western blotting – ‘gel’

(2) Receptor autoradiography - Radioactively labelled neurotransmitter (or chemical analog of the transmitter molecule) binds to receptor

(3) In situ hybridization – radioactively labelled nucleic acid “probe” detects specific messenger RNAs

C-fos immunohistochemistry

F. Studying the relationship between behavior and brain activity

• Observe brain correlates of behavior (electrical activity, fMRI, 2-deoxyglucose)

• Change brain activity and see effect on behavior– Decrease activity: lesions, chemical block– Increase activity: electrical or chemical stimulation

• Need for animal experiments:– Electroencephalogram vs. single neuron recording– Accidental vs. experimental lesions

Brain imaging• CAT (CT) scan – computed tomography• Magnetic Resonance imaging

– Spin of atomic nuclei perturbed by a pulse of strong magnetic field; when the nuclei return to normal spin they send a signal

– Regular MRI: Regions of different water composition give a different signal

– Functional MRI: detects metabolic differences (hemoglobin when oxygenated vs. unoxygenated)

From: Scott Rauch ’80 (MGH)

Example 1: 2-deoxyglucose

• Radioactively labelled 2DG is taken up by cells as glucose is, but isn’t metabolized.– Highly active cells take up lots of 2DG– After desired stimulation or behavioral

observation, look for labelled regions

Example 2: lesions

• Cut, freeze, heat (via high electrical frequency), toxic chemical (as in our lab later this semester)

• Problems: • Not always precisely specific to desired region• Fibers of passage

Example 3: Brain injections of neurochemicals

• Neuropeptide-Y (NPY) and Melanin Concentrating Hormone (MCH) both increase food intake.

• NPY neurons project to MCH neurons.– Hypothesis: MCH neurons mediate the downstream effects

or “commands” of NPY on feeding.