NEUROTENSIN PROJECTIONS TO SUBFORNICAL ORGAN FROM ARCUATE NUCLEUS

Two series of experiments were done in the rat to investigate whether neurons in arcuate nucleus of the hypothalamus (Are) containing neurot ensin (NT)-like immunoreactivity projected to subfornical organ (SFO). In the first series, the anterograde tract-tracer Phaseolus vulgaris leucoagglutinin (PHA-L) was microiontophoresed into the region of Are that contains NT neurons. After a 9-12 day survival period the animals were sacrificed and forebrain sections that contained SFO were proces sed for combined PHA-L and NT immunoreactivity. In the second series o f experiments, unilateral or bilateral electrolytic lesions of Are wer e made and after a 10-17 day survival period SFO was examined to deter mine the relative contribution of NT Are neurons to NT immunoreactivit y within SFO. PHA-L labelled fibers with terminal-like boutons were fo und in SFO primarily on the side ipsilateral to the site of injection. A small number of the PHA-L labelled fibers in the lateral aspect of SFO was also immunoreactive to NT. Unilateral lesions reduced, whereas bilateral lesions of Are eliminated most of the NT-like: immunoreacti vity within SFO. These data demonstrate the existence of a direct path way from Are to SFO that contains the putative neurotransmitter NT. Th ese results suggest that this pathway may function in the modulation o f neural and/or humoral events related to cardiovascular regulation an d body fluid homeostasis by influencing the activity of SFO neurons.