Independent activation of subfornical organ and hypothalamo-neurohypophysial system during administration of angiotensin II

The autoradiographic deoxyglucose method was employed to investigate: 1) whether the increased glucose utilization in the subfornical organ (SFO) during administration of angiotensin II (AII) depends on the neural inputs to the SFO; and 2) to investigate whether the activation of the hypothalamo-neurohypophysial system during administration of AII depends on inputs from the SFO. The ventral stalk of the SFO, which contains the majority of efferent and afferent projections of this circumventricular structure, was interrupted with knife cuts three days before the deoxyglucose experiments. Intravenous infusion of AII (2.5 micrograms/min) for 45 min increased glucose utilization in the SFO and neural lobe in the lesioned animals to the same extent as in the sham-operated animals. Drinking, however, was significantly reduced in lesioned animals. These experiments disclose independent parallel mechanisms responsible for activation of the SFO and the hypothalamo-neurohypophysial system by AII.