MEMBRANE-PROPERTIES OF ORGANUM VASCULOSUM LAMINA TERMINALIS NEURONS RECORDED INVITRO

Intracellular recordings of organum vasculosum lamina terminalis (OVLT ) neurons were obtained from superfused explants of rat hypothalamus. Most (32 of 34) OVLT neurons displayed a low threshold spike response during depolarizing pulses applied from holding membrane potentials ne gative to -70 mV. In 17 of 34 cells, electrical stimulation of the sup raoptic nucleus area evoked antidromic responses. In 20 of the 34 cell s, 8 of which were antidromically driven, identical stimuli also revea led either excitatory (n = 12) or inhibitory (n = 5) or mixed (n = 3) postsynaptic potentials. Axonal projections to the ipsilateral supraop tic nucleus were confirmed afterwards using reconstruction of Lucifer yellow-filled cells. A 10-40 mosmol/kgH2O increase in the osmolality o f the superfusion media by addition of NaCl or mannitol prompted a mem brane depolarization of 2-10 mV in each of nine OVLT neurons tested. T hese results indicate that OVLT neurons project to the supraoptic nucl eus and possess intrinsic properties capable of influencing their exci tability. Because neurons in OVLT depolarize consequent to elevations in media osmolality, the OVLT may provide a means by which hyperosmoti c stimuli influence neuroendocrine function.