EFFECTS OF LARGE AND SMALL TRANSECTIONS OF THE PREOPTIC-HYPOTHALAMIC REGION ON HYDROMINERAL REGULATION IN RATS

To further elucidate the role of the preoptic-hypothalamic region in f luid and electrolyte balance we studied the effect of surgical preopti c-hypothalamic disconnection using either a large (preoptic-hypothalam ic disconnection) or a small (medial preoptic-hypothalamic disconnecti on) microknife. Both the large and small cuts seemed to transect the p osterior projection originating in the periventricular tissue surround ing the anteroventral third ventricle (AV3V) and extending to supraopt ic nucleus, but the supraoptic-neurohypophysial pathway was severed on ly by the large cut. Seven-day metabolic studies showed a disruption i n hydromineral balance only in large cut rats; they had increased wate r intake and urine volume on day 1, a near-recovery of function on day s 2 and 3, and polydipsia and polyuria on days 4 to 7. There was no di fference between small cut rats and sham-operated rats in metabolic me asurements. The large cut rats also had sustained hypernatremia and hy perosmolality, which was enhanced after water restriction for 48 h but was not accompanied by an increase in plasma arginine vasopressin. Ou r data therefore suggest that the efferent fibers running caudally fro m the AV3V are not involved in mediation of the hydromineral regulatio n of the AV3V.