Effects of adrenergic and cholinergic blocking agents on hypothalamic mechanisms

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Abstract
Double-walled cannulas, allowing repeated stimulation of the same site in unrestrained animals with crystalline chemicals, were implanted stereotaxically into the hypothalami of 14 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. As in previous findings, it was found that the placement of minute amounts of norepinephrine into this area induced vigorous and prolonged eating in food-satiated animals, while the placement of comparable quantities of acetylcholine or carbachol into the identical loci in the same animals induced vigorous drinking in water-satiated rats. Evidence for the neurohumoral nature of these stimulation effects was obtained in experiments demonstrating: a) complete and selective blockade of the adrenergic and cholinergic stimulation effects by central adrenergic or cholinergic blockade, respectively; and b) the effectiveness of precursors of norepinephrine and acetylcholine to mimic the adrenergic and cholinergic stimulation effects. These results suggest that this portion of the hypothalamus contains two populations of neural elements which participate in the regulation of food and water intake and are preferentially sensitive to adrenergic and cholinergic stimulation, respectively. That such neurochemical "coding" may be a functional property of these hypothalamic neurons in the intact animal is suggested by the demonstrated effectiveness of adrenergic and cholinergic blocking agents to selectively reduce normal hunger and thirst, respectively.

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