Analysis of hypothalamic network for thermoregulation.

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The body temperature is controlled by the central nervous system including the hypothalamus. There is almost no knowledge of thermoregulatory "network" , which makes it difficult to link electrophysiological and pharmachological data directly with thermoregulatory responses observed in whole animals. Present study was pland to answer this question. First, to examine how the control of shivering is shared between the brain's right and left sides, ketamine anesthetized rats had been implanted thermodes on both sides of the preoptic area and received unilateral transection of the hypothalamus just caudal to the anterior hypothalamus, which severed fibers running rosto-caudal diretion. Unilateral preoptic warming on the intact side produced bilateral suppression of cold-induced shivering without predominance of either side of the body but warming on the transected side had no effect on shivering. Therefore, no information seems to be exchanged between the left and right preoptic aera for control of shivering. When a partial transection covered the lateral part of the hypothalamus (the medial forebrain bundle), the transection had the same effect as did unilateral transections of the whole hyporhalamus. Efferent signals for shivering, thus, descend through the medial forebrain bundle. In the second experiment, skin vasodilation occurs bilaterally during unilateral thermal or electrical stimulation of the preoptic area (Kanosue et al., 1991). In rats which had received similar unilateral transection of the hypothalamus as in the shivering experiment, unilateral preoptic warming not only on the intact side but also on the transected side produced bilateral vasodilation on the hind paw. Therefore, information coutrolling thermoregulatory vasomotion--unlike that controlling shivering--crosses the midline within the preoptic area. Efferent fibers for vasomotor control seem to decend through the medial forebrain bundle.