Drinking by rats after lateral hypothalamic lesions: a new look at the lateral hypothalamic syndrome.

Rats that have recovered from aphagia and adipsia following lateral hypothalamic lesions are believed to be incapable of experiencing thirst and to drink water simply to facilitate the consumption of dry food. However, the present results indicate that these animals will drink in response to dehydration of the intracellular or intravascular fluid compartments and to hyperangiotensinemia, if testing continues beyond a few hours. Comparable effects also were obtained in rats with mesencephalic brain damage, which appeared to destroy portions of the substantia nigra and the ascending nigrostriatal dopaminergic projections. These findings, when placed in the context of a recent neurochemical model for recovery of function, provide the basis for a new interpretation of the lateral hypothalamic syndrome.