Immunocytochemical evidence for synaptic regulation of paraventricular vasopressin-containing neurons by substance P.

Employing a combination of pre-embedding peroxidase-antiperoxidase-labeling for substance P (SP) and postembedding immunogold labeling with protein A-colloidal gold-anti-arginine vasopressin (AVP) complex, we demonstrated immunoreactive SP containing nerve fibers, which terminate synaptically on the perikarya, contained gold-labeled secretory granules in the magnocellular paraventricular nucleus of rats. The perikarya were also synapsed with unlabeled nerve fibers. It is concluded that SP plays a role as an axosomatic neurotransmitter in diverse synaptic controls of vasopressinergic neurons.