Short-term stimulation-induced decreases in brown fat temperature.

Electrical stimulation of the ventromedial hypothalamus (VMH) has been shown to activate brown adipose tissue (BAT) thermogenesis; we hypothesized that functional links between the VMH and other hypothalamic areas may serve to regulate intrinsic VMH control of brown fat heat production. Moveable electrodes were implanted in regions surrounding the VMH in adult male rats in order to assess any acute effect of activation of these structures alone on brown fat temperature. Stimulation in the area of the ventral lateral thalamic nucleus and the zona incerta (ZI) elicited a 0.2 to 0.8 degrees C drop from brown fat baseline temperature in 48 of 55 rats; the effective sites in the ZI area are restricted to the actual band of the nucleus. Application of the alpha-adrenergic blocker phentolamine prior to restimulation of active sites yielded mixed results; these findings are compatible with a role for the vasoconstrictive action of alpha-adrenergic receptors in the regulation of BAT temperature drops. The mechanisms underlying thermoregulatory responses or diurnal temperature cycling may provide a physiological context for the findings reported here.