Psychopharmacology psychopharmacology – study of drugs and behavior Drugs and behavior – PSY 459...
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Transcript of Psychopharmacology psychopharmacology – study of drugs and behavior Drugs and behavior – PSY 459...
![Page 1: Psychopharmacology psychopharmacology – study of drugs and behavior Drugs and behavior – PSY 459 some general concepts and issues psychoactive drugs –](https://reader036.fdocuments.net/reader036/viewer/2022062305/5697bf791a28abf838c82132/html5/thumbnails/1.jpg)
Psychopharmacology
• psychopharmacology – study of drugs and behavior
• Drugs and behavior – PSY 459
• some general concepts and issues
• psychoactive drugs – change the way you feel
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Why do people take psychoactive (particularly illicit) drugs?
1. To feel good(positive reinforcement – likely cause DA release!)
• psychological dependence
**greatest amount of psychological dependence occurs if the rewarding effects of drugs happen very quickly after behaviors associated with them.
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drug rewards that happen very soon after a
behavior – strong positive reinforcement for
that behavior
ex. prep for heroin injection, crack smoking, etc.
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Why do people take drugs?
2. To avoid feeling bad (reduce withdrawal)
(negative reinforcement)
– chemical dependence
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Important issues related to how and why we take drugs
• pharmacokinetics:
• includes drug absorption, distribution, metabolism and drug excretion– absorption – how we take drugs into the body– distribution - how the drug reaches its primary
site of action– metabolism - how our body breaks drugs
down– excretion - how we eliminate drugs
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pharmacokinetics.......
- how a drug is taken into the body……
- for drugs of abuse - the more rapidly the drug gets to the brain – the greater the abuse liability!
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routes of administration• oral
• injection– subcutaneous – intramuscular– intravenous - reaches brain in ~ 10 secs
• quick response but also most dangerous
• inhalation - reaches brain in ~8 secs
• dermal – absorbed through the skin
• buccal or nasal membranes
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pharmacokinetics.......2. absorption –
all drugs that change how we feel must be able to cross the blood brain barrier
3. pharmacodynamics- how does drug produce its effects on
behavior (ie what neurotransmitter or neurotransmitters are affected)
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ex of pharmacodynamics –
1. cocaine – blocks reuptake of monoamine neurotransmitters (most important DA)
2. nicotine– acts as an agonist at nicotinic cholinergic
receptors
3. alcohol– works on virtually every neurotransmitter
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4. metabolism (detoxification or breakdown)• how a drug is broken down or made into
inactive forms• mostly done by the liver – via enzymes!
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Tolerance, Dependence, Withdrawal, etc……
• tolerance – either decreased effectiveness or potency of a drug
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Mechanisms for Tolerance
• metabolic tolerance –– enzyme induction-
• enzymes – speed up a chemical reaction
– with repeated exposure, enzymes get better at breaking down drug or liver makes more enzymes
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Mechanisms for Tolerance
• metabolic tolerance –
– enzyme induction- enzymes are either better at breaking down drug or liver makes more of them
– implications?
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Mechanisms for Tolerance
• metabolic tolerance –– enzyme induction
• cross tolerance – tolerance to one drug results in tolerance to other drugs (usually that need similar enzymes for breakdown) – Implications:
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Mechanisms for Tolerance
• cross tolerance – tolerance to one drug results in tolerance to other drugs (usually that need similar enzymes for breakdown) – Implications:
– Person shows up unconscious at ER and is an alcoholic – given a barbiturate for surgery;
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What if amount of drug reaching brain/body is unchanged?
• tolerance can still occur when the amount of drug reaching the brain/body is unchanged
• pharmacodynamic or physiological tolerance –
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What if amount of drug reaching brain/body is unchanged?
• pharmacodynamic or physiological tolerance –
“for every action, there is an equal and opposite
reaction (in your brain)”
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Ways that the brain may try and compensate……
• Use alcohol as an example –
• Acutely – alcohol decreases glutamate activity and increases GABA activity
• Chronic alcohol -------- brain’s compensatory response?
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How might the brain try and compensate for this change if it is
chronic?• upregulation of GLU receptors –
– increase the number or sensitivity of glutamate receptors to compensate for decreased activity and try to get activity back to normal levels….
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How might the brain try and compensate for this change if it is
chronic?• upregulation of GLU receptors –
– increase the number or sensitivity of glutamate receptors to compensate for decreased activity and try to get activity back to normal levels….
• what happens during alcohol withdrawal?– now have too many (or too sensitive) glutamate
receptors – overexcitation, seizures, etc.
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How might the brain try and compensate for this change if it is
chronic?• down regulation of GABA receptors –
– to compensate for increased activity and try to get activity back to normal levels…. – reduce n or sensitivity of GABA receptors
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How might the brain try and compensate for this change if it is
chronic?• down regulation of GABA receptors –
– to compensate for increased activity and try to get activity back to normal levels…. – reduce n or sensitivity of GABA receptors
• what happens during alcohol withdrawal?
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Explanation for various withdrawal symptoms
• the exposure of compensatory changes in brain (and body perhaps) likely explain a number of withdrawal symptoms (that are often opposite of the effects that the drug causes)
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chemical see-saw
drug brain response
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heroin constipation
chemical see-saw
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heroin WD diarrhea
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Environmental Tolerance
• Drugs taken in the same environment can also display tolerance associated with the conditioned cues
• ex. heroin
• explanation – compensatory changes in brain in EXPECTATION of drug
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5. excretion (elimination)• how a drug once broken down (or not) is
eliminated from body
• most psychoactive drugs metabolites excreted in urine