occurs in occurs in regulation of neurotransmitter levels neurotransmitter transport neurotransmitter secretion GO:0007269 neurotransmitter secretory pathway A neurotransmitter is any of a group of substances that are released on excitation from the axon terminal of a presynaptic neuron of the central or peripheral nervous system and travel across the synaptic cleft to either excite or inhibit the target cell. Among the many substances that have the properties of a neurotransmitter are acetylcholine, noradrenaline, adrenaline, dopamine, glycine, gamma-aminobutyrate, glutamic acid, substance P, enkephalins, endorphins and serotonin. GO:0010554 biological_process neurotransmitter release The regulated release of neurotransmitter from the presynapse into the synaptic cleft via calcium-regulated exocytosis during synaptic transmission. establishment of localization in cell presynapse signal release from synapse