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 negative to -70 mV. In 17 of 34 cells, electrical stimulation of the supraoptic nucleus area evoked antidromic responses. In 20 of the 34 cells, 8 of which were antidromically driven, identical stimuli also revealed either excitatory (n = 12) or inhibitory (n = 5) or mixed (n = 3) postsynaptic potentials. Axonal projections to the ipsilateral supraoptic nucleus were confirmed afterwards using reconstruction of Lucifer yellow-filled cells. A 10-40 mosmol/kgH2O increase in the osmolality of the superfusion media by addition of NaCl or mannitol prompted a membrane depolarization of 2-10 mV in each of nine OVLT neurons tested. These results indicate that OVLT neurons project to the supraoptic nucleus and possess intrinsic properties capable of influencing their excitability. Because neurons in OVLT depolarize consequent to elevations in media osmolality, the OVLT may provide a means by which hyperosmotic stimuli influence neuroendocrine function.