Estrogen in the medial preoptic nucleus of the hypothalamus modulates cold responses in female rats

The present study examined the effect of the central administration of estrogen on responses to the cold. Estrogen or cholesterol was applied locally to the medial preoptic nucleus (MPO) or dorsomedial hypothalamic nucleus (DMH) of the hypothalamus in free-moving ovariectomized rats. Forty-eight hours after the application, rats had 2-h exposure at 10 or 25 °C. Body temperature (Tb) and the tail surface temperature (Ttail) were continuously measured by telemetry and thermography, respectively. The change of Tb at 10 °C from the 25 °C baseline was higher in the estrogen application in the MPO than that in the cholesterol application; however, such difference was not observed in the DMH application. The uncoupling 1 protein mRNA level in the interscapular brown adipose tissue involved in non-shivering thermogenesis was not different between the estrogen and cholesterol applications in the MPO and DMH. Ttail decreased in the cold, which was greater after the estrogen application in the MPO than after the cholesterol application. These results show that estrogen affects the MPO in female rats, changing Tb in the cold. Moreover, suppression of heat loss from the tail may be involved in the mechanism.