Psychopharmacology and Neurochemistry
Pharmacodynamics and Receptor Kinetics
Agonism and Antagonism
Pharmacodynamics studies what a drug does to the body. Molecules bind to receptors with a specific affinity (measured by the dissociation constant, ) and exert an effect based on their intrinsic efficacy. Full agonists produce maximal biological responses, whereas antagonists bind to the receptor but produce zero intrinsic efficacy, effectively blocking endogenous ligands.
Phases of Pharmacokinetics (ADME)
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1
Absorption: The movement of a drug from its site of administration into the bloodstream.
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2
Distribution: The dispersion of the drug throughout the fluids and tissues of the body.
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3
Metabolism: The biotransformation of the drug, primarily by cytochrome P450 enzymes in the liver.
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4
Excretion: The removal of the drug and its metabolites from the body, typically via the kidneys.
What does the therapeutic index of a drug indicate?
The therapeutic index is a measure of drug safety, calculated as the ratio of the toxic dose (TD50) to the therapeutic dose (ED50). A wider index means a safer drug.
Correct answer: The ratio of the toxic dose to the effective dose
What type of antagonist binds to a different site on the receptor than the endogenous ligand, causing a conformational change that reduces the receptor's activation?
Non-competitive (or allosteric) antagonists bind to an allosteric site, altering the receptor's shape and preventing the endogenous ligand from activating it, regardless of the ligand's concentration.
Correct answer: Non-competitive antagonist
Major Neurotransmitter Pathways
Neurobiology of Addiction
Drugs of abuse hijack the brain's natural reward circuitry by causing a supraphysiological release of dopamine in the nucleus accumbens. Chronic exposure leads to neuroadaptation, including the downregulation of D2 receptors, resulting in tolerance and the characteristic anhedonia experienced during withdrawal.