Functional capacity of the deafferented hypothalamus: water balance and responses to osmotic stimuli in the decerebrate cat and rat.

Abstract

The capacity to regulate water metabolism was tested in 34 cats and 8 rats 28-346 days after complete deafferentation of the hypothalamus. Deafferenta-tion was achieved by removal of all extra-hypothalamic parts of the forebrain and transection of the brain-stem by aspiration of a wedge of tissue at the hypothalamo-mesencephalic junction thereby creating an "island" of tissue composed of hypothalamus and pituitary connected to the rest of the body by only a vascular link. In some animals parts of the hypothalamus were included in the removal in an effort to determine the location of osmoreceptor units. Animals of both species were able to regulate water balance under basal conditions and under conditions of water loading and total water deprivation. No gross changes in excitability of the isolated hypothalamus were observed in the acute or chronic phases of survival suggesting that the basic excitability of the supraoptic system is not dependent upon afferent bombardment. Anatomical studies of the cerebral remnants in the cats showed that the capacity to maintain water balance and to respond to osmotic stimuli is retained when only the most rostro-ventral one-fourth to one-third of the hypothalamus remains attached to the pituitary gland. The possible sites of osmoreception were found to occupy a considerably smaller area than that proposed by Jewell and Verney. The most likely sites are: supraoptic nuclei (anterior and tuberal), suprachiasmatic nuclei and dorsal chiasmatic nucleus.