Chapter 15 - Drug addiction & the brain's reward circuits

Chapter 15 - Drug addiction & the brain's reward circuits

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Basic principles of drug action Commonly abused drugs Bio-psychological Theories of Addiction 15.1 Basic principles of drug action Psychoactive drugs – drugs that influence subjective experience & behaviour by acting on the nervous system Drug administration – route of administration influences the rate at which & the degree to which the drug reaches its site of action Oral ingestion – oral route o o Absorption via digestive tract is unpredictable Injection – bypasses digestive tract o Subcutaneously (SC) – under the skin o Intramuscularly (IM) – into large muscles o Intravenously (IV) – into veins, drug delivered directly to brain o Absorbed through capillaries in lungs Absorption through mucous membranes o Mechanisms of drug action Psychoactive drug must pass through blood-brain-barrier to be effective Liver enzymes terminate actions of drug – drug metabolism Drug Tolerance Decreased sensitivity to a drug as a consequence to exposure to it o Shift in the dose-response curve to the right Cross tolerance – exposure to one drug can produce tolerance to similar drugs o More than one form of tolerance Metabolic – less drug is getting to the site of action Functional – decreased responsiveness at the site of action; fewer receptors; decreased efficiency of binding at receptors, receptors less responsive 1
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Withdrawal Seen when drug use is terminated Symptoms are the opposite of the drug’s effects Body has made changes to compensate for drug’s presence – functions normally with the drugs present Addiction “Addicts” are those who continue to use a drug despite its adverse consequences While they may re-occur, each can exist independently 15.2 Role of learning in drug tolerance Contingent drug tolerance o Tolerance only develops to drug effects that are experienced Conditioned drug tolerance
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Chapter 15 - Drug addiction & the brain's reward circuits

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