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Suzanne Erb

PSYC62 Lecture 2: Principles of Pharmacology Drug-Receptor Interactions  Pharmacology may also apply to outside of the nervous system  Slide 3: synapse with terminal of one neuron adjacent to membrane of receiving neuron (post- synaptic neuron) projecting to another region  Receptor molecules on post-synaptic membrane  Will bind certain drugs or proteins based on receptor’s configuration selectively  Ligands are chemicals themselves are selectively fit to bind the receptors o Dopamine (ligand) will find itself to ligand receptor o Drugs can be ligands as well (anything that attaches to a receptor) o Endogenous ligands will act at receptor to have its’ exertion effect then dissociate from receptor, but in some cases drugs don’t remove themselves from receptor  Affinity – does ligand fit receptor? o Endorphins fit opiate receptor o Analogy of key and lock o Some keys fit some locks easily (greater affinity for lock), but other times, not so easily (less affinity for drug)  Both keys (drugs) still fit  Intrinsic activity: not only does drug fit, but also activates receptor o Drug can have affinity for receptor, but don’t cause a biological change in receptor o Opposite cannot occur when you have intrinsic activity, but drug doesn’t fit receptor o No direct relationship between affinity and intrinsic activity  drug can have high affinity, but low intrinsic activity and vice versa etc. Drugs act at receptors as ether agonists or antagonists  agonists produce biological activity at receptor  fits lock and opens door  antagonists bind to receptor and produce no biological change  key fits lock, cannot activate lock, but can’t open door Indirect agonist effect  increasing concentration of naturally occurring ligand  cocaine (endogenous agonist)  dopamine synapse – transporter molecules take up dopamine into presynaptic cells  cocaine binds to transporter molecules and dopamine accumulates in synapse o drug increases availability of dopamine Partial agonists  some intrinsic activity at a receptor  will reduce effect of full agonist on system because both are competing with each other  antagonistic effect someway, but still producing intrinsic activity so agonist Inverse agonist  any receptor has base line activity with it even if not being acted on  inverse agonist produces opposite effect of full agonist  competition in system  producing biological change at receptor, but producing an opposite effect relative to agonist Slide 10:  basal activity at receptor – neutral antagonist Competitive Antagonist  antagonist o high affinity for receptor, but do not produce a biological change when bound to receptor o binding causes blocking of what agonist would cause  agonist and competitive antagonist bind to receptors o antagonist will dissociate, so agonist can find it’s way to those receptors and compete for them o agonist can eventually overcome effects of antagonist Non-competitive antagonist  compound not able to dissociate from receptor  addition of more full agonist cannot compete with antagonist  most effective at blocking effects of agonist because it can’t compete and cannot overcome effects of antagonist by adding more agonist Mixed agonist-antagonist  compounds with agonist and antagonist properties  any receptor has many subtype receptors o dopamine receptors have subtypes D1,D2 etc.  drugs developed for treatment purposes that act as antagonists at some subtypes of receptors and agonists at other subtypes of the receptor  cocaine and opiate receptors o prepanorphin?  Drugs bind to mu oipiod receptors to block effects of morphine and heroin  Morphine binds to some receptors and prepanorphin acts on other receptors to reduce effects of oipate  Act as partial agonist, so still serve to reduce effects of full agonist like morphine o Lower level of intrinsic activity Dose-response functions  How the amount or concentration of a drug affects a physiological response to that drug  Does low dose of drug cause a change not seen with high dose of drug  Graphical representations Fig 2-1  Dose always on x-axis  Response of interest on y – axis  Rats administered with diff doses of amphetamine  % time that rats exhibited types of behavior o Locomotor o Responses on contingency to drug reinforcement Fig 2-2  % of individuals who show the response to the drug  What percentage of those who got the dose display the physiological response? Humans – control substance is a placebo Always need a control and 2 treatments Active placebo – known effects of drug treatment  To avoid confound of secondary physiological responses of drug  Vehicle is control in animal study – solution drug is mixed in like saline Slide 24  Concentration of drug and rate of accumulation at site is most important factor o In turn affected by other factors like dose  Dose: quantity of drug per unit body weight (g/kg) at one time  Greater the body weight, other factors held constant, more drug needed for effect to occur  Response – no drug that is defined to one particular shape of curve o All depends on what response  Depends on what response you’re looking at  Diff groups of animals given diff doses of amphetamines and you’re getting diff response shapes of curves  Shape of curve depends on what time of response you’re looking at  Dose response curves are never perfectly linear o Certain minimal threshold dose of the drug required to achieve the effect*** o At some point receptors will become saturated and won’t get any further response regardless of how much more drug you give o Can kill the animal, but curve plateaus at this point Slide 25  Mice are more sensitive to amphetamine than rats, so curve is diff  One specie may have a breakdown enzyme another specie may not  Children and elderly are more sensitive to drug o Effects ar
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