KEY CONCEPTS IN
PSYCHOPHARMACOLOGY
KEYWORDS
Pharmacology is the study of how drugs interact with biological processes.
Psychopharmacology is the study of the effects of drugs on brain processes such as
cognition, mood and other psychological phenomena.
- Psychiatric practice revolves around the appropriate use of drugs or medication
understanding they key elements of psychopharmacology can help optimize treatment
- Drugs are generally small synthetic molecules that act in a number of different ways
(Table 1)
Agonists Act to mimic the action of an endogenous neurotransmitter
Their net action is not necessarily to promote synaptic transmission
because of the effect that presynaptic auto receptors may have
Antagonists They block the effects of endogenous neurotransmitters
They oppose normal synaptic transmission
In some cases: they may increase neuronal firing and so increase
neurotransmitter release if they act predominantly on presynaptic
neurons
Partial They act somewhat like agonists because they directly act on receptors
agonists If used in the presence of an agonist they compete for the receptor
They have partial blocking properties, so they are sometimes called
agonist-antagonist
For example: The maximal effect of the partial agonist aripirazole is
between that of the full agonist dopamine and an antagonist
- Once aripirazole has been taken, it will occupy brain receptors
- In brain regions where dopamine is high, it will partially block the effects of dopamine
So, it has a antipsychotic effect
- In brain regions where dopamine levels are lower, aripirazole will act as an agonist
So, it’ll increase dopamine transmission in these regions
- These dual effects means that they are sometimes called agonists-antagonists
- The weak agonist activity of aripirazole means that it never blocks dopamine function
as much as an antagonist
Explanation why it produces fewer extrapyramidal side effects (EPS)
, - There’s always enough dopamine function from aripirazole to allow normal basal
ganglia function
Table 1
RECEPTORS
Receptors are proteins expressed on the surface of neurons and other brain cells. They have
specialized peptide conformations which allow the binding of neurotransmitters or hormones.
- Pharmacore = the specialized binding pockets, they convey the exquisite selectivity of
receptors for substances such as neurotransmitters and drugs
- Affinity = the stickiness or avidity with which a neurotransmitter of drug binds to a
receptor
This is measured in nanomolar concentrations (nM)
Ex: Ki (inhibitory constant) = gives an indication of the concentration of
neurotransmitter or drug needed to displace half of the binding of a tracer from a
receptor in binding studies
- Receptors can be classified in a number of different ways
o Site of localization
o The way in which they transmit information across the cell membrane (Table 2
and Figure 2)
PSYCHOPHARMACOLOGY
KEYWORDS
Pharmacology is the study of how drugs interact with biological processes.
Psychopharmacology is the study of the effects of drugs on brain processes such as
cognition, mood and other psychological phenomena.
- Psychiatric practice revolves around the appropriate use of drugs or medication
understanding they key elements of psychopharmacology can help optimize treatment
- Drugs are generally small synthetic molecules that act in a number of different ways
(Table 1)
Agonists Act to mimic the action of an endogenous neurotransmitter
Their net action is not necessarily to promote synaptic transmission
because of the effect that presynaptic auto receptors may have
Antagonists They block the effects of endogenous neurotransmitters
They oppose normal synaptic transmission
In some cases: they may increase neuronal firing and so increase
neurotransmitter release if they act predominantly on presynaptic
neurons
Partial They act somewhat like agonists because they directly act on receptors
agonists If used in the presence of an agonist they compete for the receptor
They have partial blocking properties, so they are sometimes called
agonist-antagonist
For example: The maximal effect of the partial agonist aripirazole is
between that of the full agonist dopamine and an antagonist
- Once aripirazole has been taken, it will occupy brain receptors
- In brain regions where dopamine is high, it will partially block the effects of dopamine
So, it has a antipsychotic effect
- In brain regions where dopamine levels are lower, aripirazole will act as an agonist
So, it’ll increase dopamine transmission in these regions
- These dual effects means that they are sometimes called agonists-antagonists
- The weak agonist activity of aripirazole means that it never blocks dopamine function
as much as an antagonist
Explanation why it produces fewer extrapyramidal side effects (EPS)
, - There’s always enough dopamine function from aripirazole to allow normal basal
ganglia function
Table 1
RECEPTORS
Receptors are proteins expressed on the surface of neurons and other brain cells. They have
specialized peptide conformations which allow the binding of neurotransmitters or hormones.
- Pharmacore = the specialized binding pockets, they convey the exquisite selectivity of
receptors for substances such as neurotransmitters and drugs
- Affinity = the stickiness or avidity with which a neurotransmitter of drug binds to a
receptor
This is measured in nanomolar concentrations (nM)
Ex: Ki (inhibitory constant) = gives an indication of the concentration of
neurotransmitter or drug needed to displace half of the binding of a tracer from a
receptor in binding studies
- Receptors can be classified in a number of different ways
o Site of localization
o The way in which they transmit information across the cell membrane (Table 2
and Figure 2)
