Dose response to carbachol and norepinephrine in rat hypothalamus

Abstract

One microliter of various concentrations of carbachol or norepinephrine was injected via a chronic cannula into the "feeding-drinking" area of the hypothalamus of satiated rats. Doses of 2.7 through 24 x 10^–10 m of carbachol elicited drinking of increasing amounts of water, but progressively higher doses elicited less drinking, some lethargy, and then convulsions. Similar, but probably less, responsiveness occurred to injections of the ventromedial nucleus. Control and weak solutions did not elicit drinking; no dose of carbachol elicited appreciable eating of solid, or drinking of a liquid food, namely, a Metrecal solution made slightly salty so that normally thirsty rats preferred water to it. Doses of from 24 through 216 x 10^–10 m norepinephrine elicited drinking of salty Metrecal (P < .10), while 648 x 10^–10 m elicited reliable consumption of this food. Still higher doses elicited less "eating," some lethargy, and eventually a few convulsions. Control and weak injections did not elicit eating. No drinking of water was elicited at any level of norepinephrine. Histologically determined placement of cannulas correlated with amount of response for both substances.