Sodium homeostasis in chronic decerebrate rats

Physiological and behavioral concomitants of sodium need were studied in supracollicularly transected and pair-fed intact rats. Chronic decerebrate rats, like intact rats, reduced their urine sodium output when placed on a sodium-deficient diet. Similarly, 24 hr after sodium loading, decerebrate and intact rats excreted comparable levels of the excess sodium. In the 2 hr immediately following the loading, decerebrate rats excreted less sodium. In contrast, behavioral aspects of sodium homeostasis were completely absent in chronic decerebrate rats. In separate experiments, intraoral intake, and taste-reactivity responses, elicited by intraoral infusions of NaCl were measured during sodium-replete and sodium-deficient conditions. In response to oral infusions of NaCl, intact rats consumed significantly more and produced greater numbers of ingestive taste-reactivity responses when they were sodium deficient than when they were sodium replete. The same sodium-depletion treatments in chronic decerebrate rats, however, altered neither the intraoral intake of NaCl nor the frequency of NaCl-elicited ingestive taste-reactivity responses. These results suggest that the behavioral compensatory responses that follow changes in the internal sodium state are dependent upon forebrain mechanisms.