Localization of thirst and antidiuretic osmoreceptors by intracranial injections in rats

Eighty-six intracranial cannula placements in 51 rats were tested with unilateral, 2-mul injections of a 0.60-osmol/kg solution, sucrose dissolved in isotonic sodium chloride. To assess antidiuretic hormone (ADH) release, a water diuresis was induced and spontaneous urinations were collected and analyzed for sodium by flame photometry. On alternate test days the 0.60-osmol/kg solution was injected into sleeping rats, and latencies to drink and volume drunk were recorded. Injections at 42 placements elicited neither drinking nor adtidiuresis on two separate test days each; at 15, both antidiuresis and drinking on at least two of three tests each; at 19, drinking but not antidiuresis; at 10, antidiuresis but not drinking. Positive drinking and ADH placements were not distinctly separated. They clustered in the bed nucleus of the stria terminalis, the preoptic areas, and the anterior portions of the hypothalamus. Placements in the medial forebrain bundle and dorsal to the anterior hypothalamic area elicited thirst but not ADH release for the most part. Placements nearest the supraoptic nucleus were weak or negative for ADH release. Central nervous system osmo-receptors exist and seem not to be the neurosecretorycells. Thirst osmoreceptors and antidiuretic osmoreceptors seem to be contiguous, but distinct.