Sites where drugs may act to alter neurotransmission. The steps are depicted for a typical neurotransmitter (T). Some neurotransmitters do not follow this scheme. Site 1 is an action potential; site 2, synthesis of T from T'; site 3, storage of T in vesicles; site 4, release of T in response to the action potential; site 5, binding of T to receptor; site 6, intracellular response to action of T at site 5; site 7, reuptake of T across neuronal membrane; site 8, metabolism of T to an inactive metabolite, TM.
other CNS transmitter systems, particularly some of the amino acid transmitters, in some of the above-mentioned ways to produce their effects.
In the mammalian CNS powerful inhibitory systems function continually to slow the number of action potentials generated. The effects of stimulating an excitatory pathway can appear to be exaggerated if normal inhibitory influences to that region are diminished. Correspondingly, an inhibitory pathway will appear exaggerated if part of the excitatory influence to that system has been removed.
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