Lack of effect of drinking of stimulation of the ventral amygdala of rat with GABA.
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Biomedical subjects
Publications and source records attributed to R B Montgomery.
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The interactions of chemically induced thirst and hunger with deprivation-induced hunger and thirst, respectively, were studied in the amygdala. The results suggest direct neurohumoral blocking at this locus, rather than mediation through activated circuits.
Cannulas were stereotactically implanted in the lateral hypothalamus and the ipsilateral amygdaloid cortical nucleus of 7 male albino rats, Wistar strain. After functional checking of the accuracy of implants by adrenergic elicitation of increased food intake, the animals were injected with combinations of noradrenaline, phenoxybenzamine or tolazoline, or placebo under 6 treatment conditions, while food-and water satiated. The elicitation of increased food intake in the satiated rat by adrenergic stimulation of the lateral hypothalamus was confirmed, and it was further found that simultaneous adrenergic stimulation of the amygdaloid cortical nucleus augmented this increase. However, simultaneous anti-adrenergic blockade in the amygdaloid cortical nucleus reduced eating to control level. The lack of response of the amygdaloid cortical nucleus to adrenergic stimulation in the satiated rat, under simultaneous stimulation of the lateral hypothalamus with either placebo or an adrenergic blocker, was also demonstrated. It was concluded that the amygdaloid cortical nucleus has a modulatory influence on eating behavior, which is dependent on the level of activity in the lateral hypothalamus, and further that this modulatory influence is necessary to the behavioral output of the hypothalamic system. This is the same relationship between the hypothalamus and amygdala previously demonstrated in regard to drinking behavior and these results are seen as supporting the behavioral generality of the functional relationships reported.
Norepinephrine, carbachol, or placebo was micro-injected into the perifornical region of the rat hypothalamus, via stereotaxically implanted cannulas. Ingestive behavior was observed in the hour after injection in a cafeteria situation in which water, milk, mash, powdered food, and lab chow were all freely available. After adrenergic stimulation, animals ingested significant amounts of mash only; after cholinergic stimulation, animals ingested significant amounts of water and milk, but water was significantly preferred to milk. These findings are seen as providing further support for the behavioral specificity of direct chemical stimulation of the brain, and as casting serious doubts on the interpretation of milk-ingestion as eating behavior.