The involvement of the hypothalamic preoptic area on the regulation of thirst in the rat

Acute reversible lesion in the medial preoptic area (MPOA) by unilateral injection of the local anesthetic lidocaine chlorhydrate (1 microliter, 20 ng/microliters) causes a transient increase in water intake induced by water deprivation in rats. Since lidocaine suppresses the nervous activity, leaving intact fibers of passage and blood vessels, the results suggest an intrinsic inhibitory action of the MPOA on the regulation of water intake. Drinking elicited a return to volumes similar to those of control rats, 3-4 h after lidocaine administration. Lidocaine released into the lateral preoptic area (LPO) slightly decreased or did not change water intake, as compared with controls. The urinary excretion in the MPO group was higher than that of the controls and the LPO, while this last group excreted significantly less urine. The ablation of the POA with lidocaine suggests that the medial aspect of the POA has an intrinsic inhibitory factor influencing drinking, while the lateral aspect did not show a relevant effect.