To investigate the characteristics of efferent projections from the preoptic area for the control of shivering and nonshivering thermogenesis, we tested the effects of thermal stimulation and injecting excitatory substances into the preoptic area on shivering and nonshivering thermogenesis in anesthetized rats. Preoptic warming and injection of glutamate suppressed shivering at ambient temperatures of 15-21°C. Likewise, preoptic warming and D,L-homocysteic acid injection suppressed nonshivering thermogenesis elicited by electrical stimulation of the ventromedial hypothalamic nucleus. Inhibitory signals from warm-sensitive neurons, thus, contribute a larger efferent signal for heat production than do signals from cold-sensitive neurons.
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