In vitro sensitivity of median preoptic neurons to angiotensin II, osmotic pressure, and temperature.

In vivo experiments suggest an interaction of the mechanisms involved in the regulation of body fluid balance and body temperature. Increases in plasma osmolality initiate drinking and increase the thermal set point for sweating. The median preoptic nucleus (MnPO) has anatomical connections with brain areas important in fluid balance and cardiovascular regulation and, with the preoptic-anterior hypothalamus, a thermoregulatory region. The present experiments employed in vitro single-unit recordings to determine the sensitivity of MnPO neurons to angiotensin II (ANG II), changes in osmotic pressure, and changes in temperature. One-fifth (11 of 55) of the MnPO neurons responded with changes in firing rate during the ANG II treatment, one-fourth (19 of 75) responded to changes in perfusate osmolality, and there was a significant effect of osmolality and ANG II on the thermosensitivity of 25% of the neurons tested.