ABSTRACT
Neurotransmitter receptors are not confined to the postsynaptic membrane but also exist in the presynaptic membrane, where they are termed presynaptic receptors, and over the cell body and dendrites. Autoreceptors have several functions that are normally homeostatic. In addition, in catecholamine- and serotonin-using neurons presynaptic autoreceptors regulate the synthesis of the transmitter, while somatodendritic autoreceptors regulate the firing rate of the neuron. The synthesis of catecholamines and serotonin in their respective neurons is decreased by activation of the corresponding autoreceptor. Autoreceptors are invariably metabotropic receptors. Presynaptic autoreceptors, when activated, usually decrease the release of neurotransmitter. Presynaptic autoreceptors, when activated, usually decrease the release of neurotransmitter. Occasionally activation of presynaptic autoreceptors results in an increase in transmitter release. Some presynaptic receptors are receptors for transmitters not secreted by the neuron in which they are situated. These are called heteroceptors. Such receptors regulate transmitter release.
