Angiotensinergic modulation of osmotic activation of neurosecretory neurons

Extracellular recordings were obtained from 34 phasically active neurosecretory cells in the hypothalamic paraventricular nucleus (PVN) of male rats under urethane anesthesia. Intracarotid injections of hypertonic saline (0.2 M NaCl solution, 0.05 ml) caused an increase in neuronal activity of 27 PVN cells. Pretreatment with saralasin (Sar, 10(-10) M), a specific angiotensin II (ANG II) antagonist, into the median preoptic nucleus (MnPO) diminished the excitatory response to the osmotic stimulation in 13 of 17 cells tested. Pretreatment with Sar in the vicinity of the MnPO or the third ventricle did not cause a marked change. These results suggest that the ANGergic system in the MnPO could contribute to the mechanism of osmotic activation of PVN neurosecretory cells.