Ambient temperature and 17β-estradiol modify Fos immunoreactivity in the median preoptic nucleus, a putative regulator of skin vasomotion

Estrogen has pronounced effects on thermoregulation, but the anatomic sites of integration between the reproductive and thermoregulatory axes are unknown. In this study, we tested whether estradiol-17β (E₂) treatment would alter the activity of thermoregulatory brain regions responding to mild changes in ambient temperature (T_AMBIENT). Core and tail skin temperatures were recorded at the ambient temperatures of 20, 24, or 31 C in ovariectomized (OVX) rats with and without E₂. Neuronal activity was evaluated by counting the number of Fos-immunoreactive cells in the brains of rats killed 90 min after exposure to one of the three ambient temperatures. Of 14 brain areas examined, the median preoptic nucleus (MnPO) was the only site that exhibited increased Fos immunoreactivity at the high T_AMBIENT of 31 C. At 24 C, OVX rats exhibited increased numbers of MnPO Fos-immunoreactive cells, compared with OVX + E₂ rats. Interestingly, tail skin vasomotion and MnPO Fos expression were affected in a similar manner by T _AMBIENT and E₂ treatment. In the arcuate nucleus and anteroventral periventricular nucleus (AVPV), Fos immunoreactivity was highest at the low T_AMBIENT of 20 C, with inhibitory (arcuate nucleus) and stimulatory (AVPV) effects of E₂. No other areas responded to both T_AMBIENT and E₂ treatment. These results implicate the MnPO, the arcuate nucleus, and the AVPV as sites of integration between the reproductive and thermoregulatory axes. Combined with studies showing the importance of MnPO neurons in heat-defense pathways, the MnPO emerges as a likely site for E2 modulation of thermoregulatory vasomotion.