Double Innervation of Neurosecretory Neurons by Substance P- and Catecholamine-Containing Neurons in the Supraoptic Nucleus of the Rat Hypothalamus

Abstract

Dual Innervation of magnocellular neurosecretory neurons in the supraoptic nucleus (SON) of the rat hypothalamus by substance P (SP) - and catecholamine-containing neurons was studied at the light and electron microscopic levels by preembedding double immunostaining techniques using the antisera of SP and tyrosine hydroxylase (TH), and also by triple immunostaining that combined the preembedding double immunostaining with postembedding immunogold staining using the antiserum of neurophysin II (NPII), the carrier protein of vasopressin. The preembedding duoble immunostaining was accomplished by the double immunostaining technique which combined the silver-gold intensified (SGI) peroxidase-antiperoxidase complex (PAP) -3, 3'-diaminobenzidine (DAB) method (SOT-PAP-DAB method) using the antiserum of SP with the non-intensified traditional PAP-DAB method using the antiserum of TH. In the double-immunostained sections, both TH-like and SP-like immunoreactive axon terminals were occasionally found to make synapses with the same magnocellular neurosecretory neurons. Furthermore, in the triple-immunostained sections, TH-like and SP-like immunoreactive and other unknown immunonegative axon terminals could be found to make synapse-like contact with the same NP II-like immunoreactive neurons in the SON of the rat hypothalamus. These findings suggest that at least catecholamine- and SP-containing neurons may co-operate to regulate the secretion of vasopressin from the same magnocellular neurosecretory neurons.