5. When the presynaptic neuron is stimulated, the synaptic cleft should contain the
6. Drugs interfering with the synthesis or reaction at the postsynaptic membrane
should block the effects of the presnaptic neuronal stimulation and
7. Drugs blocking the action of the inactivating enzyme should prolong the
-Though most of the chemicals satisfy one or more of these criteria only Ach and
NE in the peripheral nervous system satisfy all of them
-Virtually every drug that alters psychological function does so by interacting with
one or more neurotransmitter systems in the brain.
-Drugs have been shown to alter the synthesis, storage, release, enzymatic
inactivation, and reuptake of the neurotransmitter.
-Many drugs either mimic (agonists) or block (antagonists) specific
neurotransmitters at their receptors, both presynaptic and postsynaptic.
-If the drug mimics the neurotransmitter at its postsynaptic receptor, it will
enhance the neurotransmitter’s ability to alter activity of the postsynaptic cell.
-If the drug mimics the action of the neurotransmitter at its auto-receptors and
inhibits the release of the neurotransmitter, it will reduce the neurotransmitter’s
ability to alter the activity of the postsynaptic cell.
-If a drug mimics a neurotransmitter at both its auto-receptor and its postsynaptic
receptors, but has a greater affinity for its auto-receptor—a situation that is nor
uncommon. The drug may reduce the neurotransmitter’s action at postsynaptic
receptor when administered in low doses (because activation of the auto-receptors
decrease the amount of endogenous neurotransmitter available for activating the
postsynaptic receptor), but it may activate the transmitter’s postsynaptic receptor
when administered in higher doses. In such cases, even though there is less
endogenous transmitter available for the receptor, the drug takes its place so that
there is more postsynaptic receptor activation that might occur normally with the
-One of the primary problems we currently have with respect to drugs is their
relative lack of speficity, which can result in dependence and side effects that
may, in the long run, be worse for patients than the condition they took the drug to
A psychoactive drug can alter any number of the processes involved in the
communication system. It can:
1. Increase or decrease the rate of synthesizing one of more neurotransmitters
2. Increase or decrease the amount of neurotransmitter released
3. Enhance or prevent the storage of neurotransmitter
4. Increase or decrease a neurotransmitter’s rate of metabolic breakdown.
5. Bind to the presynaptic or postsynaptic receptors for the neurotransmitter and,
depending on whether or not the drug activates the receptor, it can accentuate or blunt
the neurotransmitter’s effect
6. Reduce or enhance the neurotransmitter’s reuptake.