Systemic estradiol administration to ovariectomized rats facilitates thermoregulatory behavior in a cold environment.

Rats place their tails underneath their bodies in the cold (tail-hiding behavior), which is a behavioral indicator of thermoregulation. The aim of the present study was to elucidate the effect of estradiol (E2) on tail-hiding behavior and neural activity assessed by immunohistochemistry. Ovariectomized rats were implanted with a silastic tube with or without E2 underneath the dorsal skin (E2(-) and E2(+) groups), and exposed to 27°C, 16°C, and 10°C for 2h with continuous body temperature (Tb), tail skin temperature (Ttail), and behavioral measurements. cFos immunoreactive (cFos-IR) cells in the insula, secondary somatosensory cortex, medial preoptic nucleus, parastrial nucleus, amygdala, and lateral parabrachial nucleus were counted. Tb and Ttail were not different between the E2(-) and E2(+) groups. At 16°C, the duration and the onset of tail-hiding behavior in the E2(+) group were greater than that in the E2(-) group. The number of cFos-IR cells in the insula of the E2(-) group was greater than that of the E2(+) group in rats kept at 16°C. E2 might modulate tail-hiding behavior of female rats at 16°C, and the insula may be involved in the response.