Overview

For the most part, neurons in the human brain communicate with one another by releasing chemical messengers called neurotransmitters. All neurotransmitter molecules undergo a similar cycle of use involving (1) synthesis and packaging into vesicles in the presynaptic cell; (2) release from the presynaptic cell and binding to receptors on one or more postsynaptic cells; and (3) rapid removal and/or degradation. The total number of neurotransmitters is not known, but is well over 100. Despite this diversity, these agents can be classified into two broad categories: small-molecule neurotransmitters and neuropeptides. In general, small-molecule neurotransmitters mediate rapid synaptic actions, whereas neuropeptides tend to modulate slower, ongoing synaptic functions. Abnormalities of neurotransmitter function contribute to a wide range of neurological and psychiatric disorders. As a result, altering aspects of neurotransmitter release, binding, and reuptake or removal by pharmacological or other means is central to many therapeutic strategies.