Subfornical organ efferents influence the activity of median preoptic neurons projecting to the hypothalamic paraventricular nucleus in the rat.

Twelve neurons in the median preoptic nucleus were antidromically activated by electrical stimulation of the hypothalamic paraventricular nucleus in the rat. Electrical stimulation of the subfornical organ produced excitation (N = 7) or inhibition (N = 4) of the activity of these identified units. The activity of all identified units that were excited by stimulation of the subfornical organ was also excited by microiontophoretically applied angiotensin II whereas the remaining units were not affected. The excitatory responses of the identified units to subfornical organ stimulation or applied angiotension II were blocked by saralasin, an angiotensin II antagonist.