The role of the anteroventral 3rd ventricle area in the osmotic control of paraventricular neurosecretory cells.

To obtain electrophysiological evidence of an involvement of the anteroventral 3rd ventricle (AV3V) area in the osmotic control of neurohypophysial hormone release, extracellular action potentials of paraventricular (PVN) oxytocinergic and vasopressinergic cells during osmotic stimulation induced by i.p. injection of 1.5 M-NaCl solution were obtained from urethane anesthetized AV3V-lesioned, intact and sham-lesioned lactating rats. In intact and sham-lesioned rats the electrical activities of both oxytocinergic and vasopressinergic cells increased in response to the i.p. injection of hypertonic saline. After electrolytic lesion of the AV3V, the responsiveness of both types of cells to osmotic stimuli was severely impaired, whereas oxytocinergic cells were still capable of responding to suckling stimuli by displaying high frequency discharges of action potentials preceding milk-ejection. These results provide electrophysiological evidence that destruction of the AV3V area selectively impairs osmoregulatory input to PVN neurones and that the area has osmosensitive elements which activate the PVN neurosecretory cells when plasma osmotic pressure rises.