The subfornical organ (SFO), organum vasculosum of the lamina terminalis (OVLT), and median preoptic nucleus (MnPO) were ablated either individually or in various combinations, and the effects on drinking induced by either intravenous infusion of hypertonic 4 M NaCl (1.3 ml/min for 30 min) or water deprivation for 48 h were studied. Ablation of either the OVLT or SFO alone did not affect drinking in response to intravenous 4 M NaCl, although combined ablation of these two circumventricular

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... s substantially reduced but did not abolish such drinking. Ablation of the MnPO or MnPO and SFO together also substantially reduced, but did not abolish, drinking in response to intravenous hypertonic NaCl. Only near-total destruction of the lamina terminalis (OVLT, MnPO, and part or all of the SFO) abolished acute osmotically induced drinking. The large lesions also reduced drinking after water deprivation, whereas none of the other lesions significantly affected such drinking. None of these lesions altered feeding. The results show that all parts of the lamina terminalis play a role in the drinking induced by acute increases in plasma tonicity. The lamina terminalis appears to play a less crucial role in the drinking response after water deprivation than for the drinking response to acute intravenous infusion of hypertonic saline.