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Chapter 2

Chapter 2

Course Code
Suzanne Erb

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Drugs and the Brain
Chapter 2 – Basic Principles of Psychopharmacology
What is a drug?
A non-food chemical that alters one or more biological processes excluding substances used for
nutrition purposes such as salt, water, vitamins, etc
known as an exogenous substance
also does not include chemicals originating or produced within an organism that are used to carry
out normal biological functioning – known as endogenous substances
Factors that determine drugs effect
concentration of the drug at its site of action
rate of accumulation
dose: quantity of drug administered at one time
dosage: administration of drug per unit of time
Drugs and Receptors
biochemical and physiological effects of drugs and their mechanisms of action
-very specific sites all throughout the body where the vast majority of drugs act
-site is comprised of very large molecules, usually proteins
- when ligand binds to receptor, receptor becomes activated
-biologically active chemicals of the body induce the effects of proteins at receptor sites
-include hormones, neurotransmitters, neurohormones and neuromodulators
-when it occupies receptor, it is a bound ligand

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-when it leaves receptor, is it said to dissociate
the relative capacity of a compound to maintain contact with or be bound to a receptor
efficacy/intrinsic activity
the degree of relative capability of a compound to activate the receptor after being bound to it
* compounds affinity and efficacy are independent of each other; however, without affinity,
efficacy is unlikely to be exhibited
-compounds that have affinity and efficacy
-if compound is endogenous, its called a ligand
-if compound is exogenous, its a drug
indirect agonist
-drug enhances the amount of endogenous ligands available for receptor
-doesnt directly combine with receptor
drugs that block the action of agonists
partial agonist
-drugs that display intermediate efficacy in receptor activation
-in between efficacy of full agonist and antagonist
-may actually have higher affinity than full agonist but cannot achieve maximal efficacy
-reduces effects of full agonist because of reduced accessibility – such drugs are used to reduce
excessive receptor activity without totally eliminating it (Ex: schizophrenia drugs)
inverse agonist
a drug that acts through the same receptor as an agonist but produces the opposite effects
mixed agonist-antagonist
-drug acts as agonist but blocks the activity of another agonist in the same system
-similar to partial agonist – both exert agonistic effects but reduce effects of full agonists

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2 main models that explain how receptors and ligands interact to alter biological systems:
1.receptor has one element comprising a binding” site and another element comprising an
“effector site:
- easily explains the idea that agonist is compatible with both sites and antagonist is compatible
only with binding site
-cannot explain inverse antagonists and mixed agonist-antagonists
2.receptors exist in an active and inactive configuration, each configuration is capable of combining
with a drug molecule:
- whether drug acts as agonist or antagonist depends on ratio of drugs affinity for the two
different configurations
2 main classes of receptors:
1.ionotropic receptors
-produce very rapid changes in neuronal activity
-have subunits made up of amino acids that form an internal channel through which only specific
ions can go through
-ion flow changes excitability of the neuron
-size and distribution of negative and positive charges lining the channel determine the direction
and type of ion flow
-ligands can bind onto the subunits and increase or decrease ionic flow depending on whether
they are full agonists, partial agonists, etc.
allosteric modulators:
-ligands that dont alter ion flow but modulate the influence of agonists binding to other sites on
the complex
-example of indirect agonists
2.metabotropic receptors
-produce relatively slow developing and long lasting effects on neurons
-comprised of long string of amino acids that loop back and forth through neuronal membrane
-coupled with a G protein, which in turn is linked to an “effector unit
-effector unit can be an ion channel or an enzymetriggers the formation of a variety of
molecules known as secondary messengers
-secondary molecules lead to biochemical alterations in the neuron (Ex: ion pumps, gene
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