DIRECT VASOACTIVE INTESTINAL POLYPEPTIDE-CONTAINING PROJECTION FROM THE SUPRACHIASMATIC NUCLEUS TO SPINAL PROJECTING HYPOTHALAMIC PARAVENTRICULAR NEURONS

In mammals, photoperiodic information is conveyed from the retina to t he pineal through a polysynaptic pathway, which includes the suprachia smatic nucleus (SCN), the paraventricular nucleus of the hypothalamus (PVN), the spinal preganglionic neurons and, finally, the superior cer vical ganglion. Precise data on the site in the PVN or which SCN trans mitters are involved in the transmission of information in this pathwa y is lacking. In the present experiment we investigated whether SCN ef ferents containing vasoactive intestinal polypeptide (VIP) innervate P VN neurons that project to the spinal cord. A combination of retrograd e tracing and immunocytochemistry with the aid of a confocal laser sca nning microscope allowed us to assess possible interaction of SCN effe rents and spinal cord projecting neurons in the PVN. Approximately 30% of identified autonomic projecting neurons in the dorsal PVN and 40% in the ventral PVN received VIP innervation mainly on their dendrites. These results provide further evidence for the involvement of SCN-der ived VIP in the transmission of circadian information to the pineal.