Regulatory and secondary water intake in rats with lesions of the zona incerta.

Bilateral electrolytic lesions of the zona incerta (ZI) permanently reduced daily water intake of rats by 20-30%. Lesioned rats did not differ from controls in daily food intake, body weight, hematocrit, or serum osmolality, Na+ or K+ levels. The hypodipsia was not caused by changes in water requirements or excretory function or by a nonspecific depression of behavior. Compensatory reductions in water losses maintained fluid balance. Lesioned rats drank as much water as controls in response to intracellular and extracellular dehydration, but unlike controls, appeared to restrict their daily water intake to these regulatory responses. Lesions of the ZI attenuated the ingestion of extra water observed when rats were maintained on a liquid diet adequate to meet fluid requirements, and daily water intake of lesioned but not control rats closely followed changes in water needs. It was concluded that lesions of the ZI reduce daily water intake towards minimal requirements for fluid balance by attenuating secondary drinking (drinking independent of water needs for fluid homeostasis.