chapter four psychopharmacology
DESCRIPTION
Neurotransmitters, Neuromodulators, and Neurohormones Participate in directed synapses by acting on neurons in their own immediate vicinity Neuromodulators and neurohormones Participate in nondirected synapses by acting on more distant neurons Neuromodulators communicate with target diffuse away from the point of release Neurohormones travel in the blood supply to reach their final targetsTRANSCRIPT
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Psychopharmacology
Chapter Four
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• Neurotransmitters – Participate in directed synapses by acting on
neurons in their own immediate vicinity
• Neuromodulators and neurohormones– Participate in nondirected synapses by acting
on more distant neurons– Neuromodulators communicate with target
diffuse away from the point of release– Neurohormones travel in the blood supply to
reach their final targets
Neurotransmitters, Neuromodulators, and Neurohormones
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Neuromodulators and Neurohormones
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• Substances released by one cell that produce a reaction in a target cell
• The substance: – Must be present within a presynaptic cell.– Is released in response to presynaptic
depolarization– Interacts with specific receptors on a
postsynaptic cell
Identifying Neurochemicals
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Types of Neurochemicals
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Features of Small-Molecules and Neuropeptides
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• Produced in cholinergic neurons • Two receptor types:
– Nicotinic receptors– Muscarinic receptors
Small-Molecule Neurochemicals: Acetylcholine
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The Distribution of Cholinergic Systems in the Brain
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• Catecholamines– Dopamine, norepinephrine, epinephrine– Synthesized from tyrosine
• Indoleamines– Serotonin, melatonin– Serotonin is synthesized from tryptophan
Small-Molecule Neurochemicals: Monoamines
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Catecholamines Share a CommonSynthesis Pathway
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• Dopaminergic neurons in the midbrain form connections with other neurons
• Dopamine activity is associated with motivated behavior and reward processing
Dopaminergic Systems in the Brain
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Dopaminergic Systems in the Brain (cont’d.)
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• Norepinephrine– Noradrenergic neurons– Increases arousal and vigilance– Primary neurotransmitter in the sympathetic
nervous system
• Epinephrine– Adrenergic neurons– Regulation of eating, blood pressure
Noradrenergic Systems in the Brain
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Noradrenergic Systems in the Brain (cont’d.)
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• Synthesized from tryptophan• Regulates mood, sleep, and appetite
Indoleamines: Serotonin
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Serotonergic Pathways in the Brain
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• Synthesized from histidine• Associated with wakefulness
Histamine
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• Major excitatory neurotransmitter in the CNS
• Subtypes of glutamate receptors: NMDA, AMPA, and kainate
Amino Acid Messengers: Glutamate
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• Major inhibitory neurochemical in the CNS• Synthesized from glutamate• GABAA and GABAB receptors
– GABAA receptors interact with psychoactive drugs
Amino Acid Messengers: GABA
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The GABAA Receptor Interacts with Several Drugs
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• Major inhibitory neurochemical in spinal cord interneurons
• Excitatory function with glutamate at NMDA receptors
• Synthesized from serine
Amino Acid Messengers: Glycine
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• Act in the CNS and in connections between autonomic neurons and the vas deferens, bladder, heart, and gut– ATP is associated with pain perception and
sleep-waking cycles– Adenosine inhibits the release of many
neurochemicals
ATP and Adenosine
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• Substance P (pain perception)• Endorphins act on same receptors as
opioids and heroin• Insulin and cholecystokinin function in
digestion and as neuromodulators and neurohormones
• Oxytocin and vasopressin act as neuromodulators and neurohormones
Neuropeptides
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Distribution of Endorphin Receptors in the Human Brain
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• Diffuse through membranes and interact with intracellular receptors
• Transmits information from the postsynaptic to the presynaptic neurons
• Nitric oxide (NO)– Neural communication, maintenance of blood
pressure, erection (target of Viagra)
Gasotransmitters
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• Agonists enhance the activity of a neurotransmitter
• Antagonists reduce the activity of a neurotransmitter
Drug Actions at the Synapse
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• Neurochemical production– Manipulating the synthesis of a
neurotransmitter may affect the amount available for release
• Neurochemical storage– Interfering with the storage of a
neurotransmitters in vesicles within a neuron
• Neurochemical release– Can be modified in response to the arrival of
an action potential by drugs
Mechanisms of Drug Actions at the Synapse
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• Mimic the action of a neurotransmitter at the site
• Block the synaptic activity by occupying a binding site
• Influence the activity of the receptor
Mechanisms of Drug Actions at the Synapse: Receptor Effects
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Drug Interactions at the Cholinergic Synapse
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Drug Interactions at the Dopaminergic Synapse
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Drug Interactions at the Serotonergic Synapse
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• Reuptake effects– Cocaine, amphetamine, and Ritalin inhibit
dopamine reuptake– SSRIs (e.g., Prozac) inhibit serotonin
reuptake
• Enzymatic degradation– Organophosphates interfere with AChE
• Deactivation of neurotransmitters
Reuptake Effects and Enzymatic Degradation
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• 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
Basic Principles of Drug Effects
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Concentration of a Drug in the Blood Supply Depends on the Method of Administration
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• 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
despite harm to the user
Tolerance, Withdrawal, and Addiction
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Vaccinations Against Drugs of Abuse
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• Increase alertness and mobility– Caffeine – adenosine antagonist– Nicotine – nicotinic cholinergic receptor
agonist – Cocaine – dopamine reuptake inhibitor– Amphetamine – stimulates release and
inhibits reuptake of dopamine/norepinephrine– Ecstasy (MDMA) – stimulates release of
serotonin and oxytocin; toxic to serotonergic neurons
Effects of Psychoactive Drugs: Stimulants
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Caffeine Content of Common Products
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Caffeine Content of Common Products (cont’d.)
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Health Consequences of Methamphetamine Abuse
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Historical Use of Cocaine
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Ecstasy Damages Serotonergic Neurons
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• Interact with endorphin receptors– Pain relief, relaxation, sense of euphoria
• Opiates– Derived from sap of opium poppy– Morphine, codeine – Heroin
• Synthetic opiate• Derived from morphine
Opioids
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• Active ingredient THC is an endogenous cannabinoid receptor agonist
• Cannabinoid receptors are in the hippocampus and prefrontal cortex
• Effects: mild euphoria, perceptual distortion, hallucination, and depression
Marijuana (Cannabis)
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Cannabis and the Risk of Psychosis
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• Serotonergic agonist• No known medicinal value• Hallucinogens• Use results in tolerance, but not addiction
or withdrawal• Flashbacks with extended use
LSD
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• GABAA receptor agonist • Stimulates dopaminergic reward pathways• Rapid tolerance• Damaging effects on health
Alcohol
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Alcohol and Mortality