Area postrema lesions increase drinking to angiotensin and extracellular dehydration

The area postrema (AP) is a circumventricular organ of the caudal medulla oblongata. This structure lacks a blood brain barrier and contains high concentrations of angiotensin II (AII) receptors. Because AII is a participant in the arousal of thirst, we have examined the effect of AP lesions upon drinking in response to exogenous AII and in response to various thirst challenges. We have found that rats with AP lesions (APL) drink more water than control rats in response to isoproterenol and polyethylene glycol. Rats with AP lesions also drank two times as much water as controls in response to subcutaneous injection of exogenous AII. Ad lib water intakes of APL and control rats were not different. Furthermore, drinking in response to 21 hr water deprivation or cell dehydration did not differ for APL and control rats. Our results suggest that AP lesions selectively enhance extracellular thirst, especially the component of that thirst mediated by AII.