Monoaminergic activity in the hypothalamus of lean and obese zucker rats in response to acute and chronic dietary stimuli. Specter, S. E., J. S. Stern, and B. A. Horwitz. Department of Nutrition; Department of Internal Medicine, School of Medicine; and Section of Neurobiology, Physiology, & Behavior - Division of Biological Sciences, University of California Davis, CA 95616
APStracts 2:0238E, 1995.
Monoamine neuromodulators link diet-related signals with autonomic responses in the regulation of energy balance. In view of evidence that sympathetically-mediated expenditure is blunted in genetically obese (fa/fa) Zucker rats, a central defect in neurochemical activity has been proposed. This study tested the hypothesis that genotypic differences in monoaminergic activity in the hypothalamus underlie a blunted sensitivity of fa/fa rats to acute and chronic dietary stimuli, leading to less effective modulation of energy metabolism. Homozygous lean and obese Zucker rats were fed a protein-restricted (PR, protein = 8% of total dietary energy) or control (CF, 21% protein) diet from age five wks. At age 10 wks, post-prandial oxygen consumption (thermic effect of food, TEF) and levels of brown adipose tissue (BAT) uncoupling protein were significantly elevated (p &LT 0.0005) in PR vs. CF lean rats. Serotonin turnover was significantly (p &LT 0.0014) greater in the ventromedial hypothalamus of meal -fed lean PR (vs. CF) rats, consistent with the suggestion that VMH serotonin release stimulates sympathetic outflow and may signal a heightened drive for protein intake. Serotonergic activity, BAT uncoupling protein, and TEF were not elevated in PR obese rats in response to a test meal, supporting the view that activation of sympathetic outflow in response to diet-related stimuli in fa/fa rats is impaired. 

Received 31 August 1995; accepted in final form 15 November 1995.
APS Manuscript Number E424-5.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 8 December 95