Direct adrenergic and cholinergic stimulation of hypothalamic mechanisms

Abstract

Double-walled cannulas, allowing repeated stimulation of the same site in unrestrained animals with crystalline chemicals, were implanted stereotaxically into the hypothalamus of 36 albino rats. Histological verification of the intended placements showed that the tips of the cannulas were located in an area between the fornix and the mammillothalamic tract, lateral and dorsal to the ventromedial nuclei. Placement of minute amounts of adrenergic substances (epinephrine and norepinephrine) into this area induced vigorous and prolonged eating in satiated animals. Placement of comparable quantities of cholinergic substances (acetylcholine and carbachol) into identical loci in the same animals induced vigorous and prolonged drinking in satiated rats. Adrenergic stimulation increased the food intake of normally hungry animals but decreased the water intake of normally thirsty rats. Similarly, cholinergic stimulation increased the water intake of normally thirsty animals but decreased the food intake of normally hungry animals. Control tests indicated that such side effects of norepinephrine and carbachol as nonspecific activation, osmotic stimulation, vasomotor effects, and changes in the local acid-base composition can be ruled out as potential explanations of the observed results.