Responses of lateral preoptic neurons and behavioral reactions to angiotensin II and hypertonic NaCl and sucrose administered into the rat cerebral ventricle.

In 18 acutely prepared rats and in 3 chronically implanted rats, multiple-unit responses of lateral preoptic area (LPOA) neurons to angiotensin II (A II) and hypertonic NaCl and sucrose injected into the lateral ventricle were recorded. In addition, behavioral reactions were observed in the chronically prepared rats. Results showed that i.vt. injections of hypertonic solutions or A II affect neural activity in the LPOA, indicating that the LPOA has connections with periventricular structures that are sensitive to these substances. Experiments with chronically implanted animals demonstrated the relevance of i.vt. injections for drinking. Some of the same solutions that produced changes in LPOA MUA in the acute series (or in anesthetized chronically implanted rats) also elicited drinking. A II was a more effective dipsogen than hypertonic NaCl, and in the strongest concentration used, NaCl produced stereotyped running, reduced head movement during quiescence, and caused a progressive fall in baseline MUA. Drinking was elicited by intermediate concentrations of i.vt. NaCl. Implications for the neuropsychology of thirst are discussed.