Chlorpromazine induces population increase of synaptic vesicles in the rat hypothalamic ventromedial nucleus

The population of synaptic vesicles per synaptic area in the hypothalamic ventromedial nucleus of rats treated with chlorpromazine (CP) for 3 days was compared with that of controls. In type I synapse, which contained 400-800 A small spherical vesicles (s-vesicles), together with 800-1200 A large spherical dense-cored vesicles (lc-vesicles), the population of s-vesicles increased 57.8% in the CP rats, In type II synapse, which contained only s-vesicles, the rate of increase among CP animals was 15.4%. Findings suggested that CP blocks the release of the vesicles from the presynaptic site or inhibits the transport function for biogenic amines through the presynaptic membrane, and type I synapse may be aminergic.