Changes in salt intake after lesions of the area postrema and the nucleus of the solitary tract in rats

Abstract

Several reports have linked the area postrema (AP), a circumventricular organ in the dorsal medulla, to the control of sodium regulation. To clarify its role further we examined the effects of AP ablations in rats on sodium intake as well as on sodium output. Eighteen experimental rats received lesions to the AP while 6 control rats received sham lesions. After the lesions we gave the animals a two-bottle preference test between water and various molar concentrations of NaCl (0.03, 0.1, 0.3, 0.5), glucose (0.1, 0.3) or KCl (0.1, 0.3) solutions. Rats with AP lesions consumed supranormal amounts of NaCl solutions, but their intakes of glucose and KCl solutions were not significantly different from those of control rats. These changes in intake were apparently not secondary to changes in sodium output. Urinary sodium and potassium levels were the same for both groups of rats while on a normal, sodium-replete diet or on a sodium-free diet. Anatomical analyses revealed a significant correlation between the size of the lesion and the animals' salt intake (NaCl, KCl). Only when the lesions destroyed the AP without appreciable damage to the adjacent nucleus of the solitary tract (NST), a sensory relay for gustatory and visceral afferents, was there a significant tendency for rats to consume more salt solution. These changes in intake cannot be accounted for by lesioned produced deficits in gustatory function. The data were discussed with regard to possible hemodynamic effects of the lesions.