Hypothalamus, sympathetic nerve and brown adipose tissue in the regulation of energy balance.

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Brown adipose tissue (BAT) is known as a major site for chemical thermogenesis during cold acclimation and spontaneous hyperphagia. It has been proposed that the impairment of BAT thermogenesis is a factor contributing to the development of obesity. In this project, we studied regulatory roles of the hypothalamus and sympathetic nervous system for BAT thermogenesis-linked metabolism in rats.1. Electrical stimulation of the ventromedial nucleus of the hypothalamus (VMH) elicited an increase in norepinephrine turnover in the interscapular BAT, an index of sympathetic nerve activity in this tissue, in parallel with a specific increase in BAT temperature and glucose utilization. The thermogenic response to VMH stimulation was completely abolished after surgical sympathetic denervation. These results indicate that the VMH controls BAT themogenesis through the action of sympathetic nervous system.2. Rats with lesions in the VMH became hyperphagia and obese. In these animals, metabolic and thermogenic activities of BAT were remarkably decreased, supporting an idea that impaired BAT thermogenesis contributes to the development of hypothalamic obesity.3. Rats fed intragastrically, compared with those fed orally, showed lower BAT thermogenic activity and got more obese, although they were given the same amount of food. The results suggest a stimulatory role of oropharyngeal sensations for BAT thermogenesis.