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Transcript of Chapter Four
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Chapter Four
PsychopharmacologyVersion Dated 21 Sep 2009
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CHAPTER 4PSYCHOPHARMACOLOGY
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Neurotransmitters, Neuromodulators, and Neurohormones
• Identifying Neurotransmitters– Must be synthesized within the neuron– In response to an action potential, the substance is
released in sufficient quantities to produce an effect in the postsynaptic cell
– We should be able to duplicate the action of a suspected neurotransmitter experimentally on a postsynaptic cell
– Some mechanism exists that ends the interaction between the neurotransmitter and the postsynaptic cell
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Figure 4.2 Major Categories of Neurotransmitters, Neuromodulators, and
Neurohormones
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Neurotransmitters
• Types of Neurotransmitters– Small molecule transmitters – meet all or most of
criteria and play a vital role in neurotransmission– Neuropeptides – at least 40 act as
neurotransmitters, neuromodulators, and neurohormones
– Gaseous neurotransmitters – some gases transfer information from one cell to another
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Table 4.1 Features of Small-Molecule Transmitters and Neuropeptides
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Figure 4.3 The Distribution of Cholinergic Systems in the Brain
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Figure 4.4 Catecholamines Share a Common Synthesis Pathway
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Figure 4.5 Dopaminergic Systems in the Brain
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Figure 4.6 Noradrenergic Systems in the Brain
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Figure 4.8 The Distribution of Serotonergic Pathways in the Brain
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Figure 4.9 The NMDA Glutamate Receptor
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Figure 4.10 The GABAA Receptor Interacts with Several Drugs
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Figure 4.11 Distribution of Opiate Receptors in the Human Brain
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Drug Actions at the Synapse
• Agonists enhance the activity of a neurotransmitter• Antagonists reduce the activity of a neurotransmitter
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Drug Actions at the Synapse
• Neurotransmitter Production– Manipulating the synthesis of a neurotransmitter will
affect the amount available for release
• Neurotransmitter Storage– Interfering with the storage of a neurotransmitters in
vesicles within a neuron
• Neurotransmitter Release– Drugs can modify the release of a neurotransmitter in
response to the arrival of an action potential
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Drug Actions at the Synapse
• Receptor Effects– Can mimic the action of a neurotransmitter at the site– Can block the synaptic activity by occupying a binding site– Can influence the activity of the receptor
• Reuptake Effects and Enzymatic Degradation– Deactivation of neurotransmitters
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Figure 4.12 Drug Interactions at the Cholinergic Synapse
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Figure 4.14 Drug Interactions at the Dopaminergic Synapse
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Figure 4.15 Drug Interactions at the Serotonergic Synapse
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Basic Principles of Drug Effects
• Administration of Drugs– Method of administration leads to different effects on
nervous system– Blood-brain barrier
• Individual Differences– Drug effects influenced by body weight, gender, and
genetics
• Placebo Effects– User expectations influence drug effects– Double-blind experiment
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Figure 4.16 Concentration of a Drug in the Blood Supply Depends on the Method of
Administration
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Basic Principles of Drug Effects
• Tolerance and Withdrawal– Tolerance = lessened effects as a result of repeated
administration– Withdrawal = occurs when substance use is discontinued;
opposite of the effects caused by the discontinued drug
• Addiction– Compulsive need to use the drug repeatedly– Causes of addiction– Treatment of addiction
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Figure 4.17 Tolerance and Withdrawal Can Result from Compensation
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Figure 4.18 The Nucleus Accumbens Participates in Reward and Addiction
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Effects of Psychoactive Drugs
• Stimulants – increase alertness and mobility– Caffeine – antagonist for adenosine– Nicotine – agonist at the nicotinic cholinergic receptor– Cocaine and Amphetamine
• Cocaine – dopamine reuptake inhibitor• Amphetamine – stimulates dopamine and norepinephrine release
and inhibits their reuptake
– Club Drugs: Ecstasy and GHB• MDMA – stimulates release of serotonin and oxytocin; toxic to
serotonergic neurons • GHB – mimics inhibitory effects of GABA
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MDMA Ecstasy Destroys Serotonergic Neurons
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Figure 4.20 Caffeine Content of Common Products
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Effects of Psychoactive Drugs
• Opiates– Synthesized from sap of opium poppy– Morphine, codeine, heroin– Endorphin receptors
• Marijuana– THC – agonist at receptors for endogenous cannabinoids– Cannabinoid receptors in the hippocampus and prefrontal
cortex
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Effects of Psychoactive Drugs
• Other hallucinogens – have the ability to produce false perceptions – Mushrooms – agonist for GABA and glutamate– Mescaline – acts on serotonergic neurons– Phencyclidine (PCP) – antagonist at the NMDA glutamate
receptor– LSD – serotonergic agonist
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Effects of Psychoactive Drugs
• Alcohol– Agonist at the GABAA receptor
– Stimulates dopaminergic reward pathways– Damaging effects on health
• St. John’s Wort– Effective for mild depression– Interactions with other drugs