CLASSIFICATION OF NEUROSECRETORY VESICLES

Three classes of messenger molecules transmit synaptic signals between neurons (Table 1). Classic neurotransmitters (acetylcholine, glutamate, GABA, glycine) mediate fast point-to-point synaptic transmis-sion by opening ligand-gated ion channels in the post-synaptic membrane. Classic neurotransmitters, in addi-tion, may exert neuromodulatory roles by activation of metabotropic, seven-transmembrane-domain, G-pro-tein-coupled receptors. Biogenic amines function as both true neurotransmitters (e.g., catecholamines in the sympathetic nervous ystem) and neuromodulators, in either case via activation of G-protein-coupled receptors (except for serotonin, which may open a ligand-gated ion channel). Neuropeptides act as neuromodulators by activation of G-protein-couple