Area postrema lesions in rats appear to disrupt rapid feedback inhibition of fluid intake

Area postrema lesions (APX) were produced by vacuum aspiration in adult male rats. After systemic administration of hypertonic saline solutions, significantly more water was consumed by rats with APX than by intact control rats. Similarly enhanced water intake by rats with APX also was observed when marked hypovolemia was induced by s.c. administration of a hyperoncotic colloidal solution. In both conditions, the increased water intake occurred within the first 15 min of the drinking tests. Intakes of liquid diet or 10% sucrose solution after food deprivation by rats with APX also were considerably larger than those of control rats. These and other results suggest that rats with APX experience less inhibition of ingestion while drinking. Thus, the AP may be important for the detection of early, inhibitory signals generated by fluid ingestion, and after its ablation increased drinking may occur because the feedback inhibition provided by such signals is diminished.