Autoreceptors

The Receptors are not confined to the postsynaptic membrane however also exist in the presynaptic membrane, where they are known as presynaptic receptors, and over the cell body and dendrites. When these are receptors for the transmitter released by the neuron in which they are situated, they are autoreceptors. The Autoreceptors, that are invariably metabotropic receptors, have numerous functions which are normally homeostatic. Those on the presynaptic membrane are included in regulating neurotransmitter release. Most presynaptic autoreceptors reduce the release of neurotransmitter by decreasing calcium influx into the presynaptic terminal. This is a negative response mechanism either to avoid extreme excitation, or to curtail postsynaptic receptor desensitization, that would decrease the sensitivity of the synapse.

The Autoreceptors can also reduce the synthesis of transmitter (example, of catecholamines and serotonin by their particular neurons) and few dopaminergic neurons have dopamine receptors on their dendrites and cell body that regulate neuron firing rate.The Heteroceptors are presynaptic receptors for transmitters not secreted by the neuron in which they are located. These also regulate transmitter release. For illustration, GABAB receptors exist presynaptically at glutamatergic synapses where they decrease glutamate release. They are activated by GABA which has diffused from neighboring synapses.