Convergence of signals in the zona incerta for angiotensin-mediated and osmotic thirst.

Extracellular single-unit activity was recorded from 109 neurons in the diencephalon of urethane-anesthetized rats. Injections of angiotensin II (ANG II) into the subfornical organ (SFO) increased the activity of 15 zona incerta (ZI) neurons and decreased the activity of 9. Injections of ANG II into the SFO increased the activity of 8 lateral hypothalamic neurons and decreased the activity of 7. Of the units which responded to the injection of ANG II into the SFO, 9 neurons in the ZI and 5 in the lateral hypothalamus (LH) also responded to injections of hyperosmotic saline into the medial preoptic area. The SFO and preoptic area are possible sites of receptors for ANG II-mediated and osmotic thirst, respectively, and the present results suggest that signals important for the initiation of these thirst mechanisms converge on neurons in the ZI and LH. These findings are discussed in relation to other neural structures that have been implicated in the regulation of water intake.