Met-enkephalin-Arg6-Gly7-Leu8- and substance P-containing projections from the nucleus preopticus medianus to the paraventricular hypothalamic nucleus.

The nucleus preopticus medianus (POMe) is known to be important for the regulation of fluid balance and cardiovascular control. Direct projections from the POMe to the paraventricular hypothalamic nucleus (PVN), where vasopressin-containing neurons exist, were examined in the rat using immunohistochemistry combined with a retrograde tract tracing method. After injection of WGA-HRP-colloidal gold into the PVN, many neurons were retrogradely labeled in the POMe; some of them were immunoreactive to Met-enkephalin-Arg6-Gly7-Leu8 (mE8) or substance P (SP). The results indicate that mE8- and SP-immunoreactive neurons in the POMe send their axons to the PVN.