MEDIAN EMINENCE-AFFERENT VASOACTIVE-INTESTINAL-PEPTIDE (VIP) NEURONS IN THE HYPOTHALAMUS - LOCALIZATION BY SIMULTANEOUS TRACT TRACING AND IMMUNOCYTOCHEMISTRY

Retrograde tract tracing and immunocytochemistry were used to investig ate the CNS source of the VIP that is present in high concentrations i n the hypophysial portal blood and has been shown to have a stimulator y effect on pituitary prolactin secretion. Fluoro-gold (FG), which ent ers the CNS through areas devoid of the blood-brain barrier, such as m edian eminence, was injected peripherally. Brain sections from FG-trea ted animals were immunostained for VIP. A small population of VIP-cont aining cell bodies in the parvocellular and periventricular parts of t he paraventricular nucleus (PVN) was also labeled with FG. Vasoactive intestinal peptide-immunoreactive perikarya not labeled with FG were a lso observed in the PVN, as well as FG-labeled cells that did not cont ain VIP. The results suggest that some VIP-producing neurons in the PV N project to the median eminence and are, therefore, functionally rela ted to pituitary regulation; the function of other VIP neurons in the PVN is unknown.