Activation of Brainstem and Hypothalamic Areas Related to Increased Tail Skin Temperature in Ovariectomized Rats

Abstract

Hot flushes are usually treated with estrogen replacement in postmenopausal women but the neural pathways involved are poorly understood. We investigated the activation of brain areas associated with the increase in tail skin temperature in an animal model of menopause. Female Wistar rats were ovariectomized (OVX) and implanted with subcutaneous capsules containing 17ß‐estradiol (E2) (OVX+E2) or corn oil (OVX). Tail skin temperature (TST) was recorded during two hours at ambient temperature at 3, 7 and 14 days after surgery. On day 15th, rats were perfused and the brains were processed for immunohistochemistry. Neuronal activity was evaluated by counting the number of Fos‐immunoreactive (ir) cells. On day 14 after ovariectomy, the TST in OVX rats was higher than in OVX+E2 rats. All the brain areas examined exhibited significantly more Fos‐ir cells in OVX than OVX E2 rats. In the brainstem, OVX rats displayed more Fos/tyrosine hydroxylase doubled‐labeled neurons in the A1, A2 and locus coeruleus compared with OVX+E2 rats. OVX rats exhibited more Fos‐ir neurons than OVX+E2 rats in the rostral preoptic area (POA), anteroventral periventricular nucleus (AVPV), and median preoptic nucleus (MnPO) in the preoptic area and in the paraventricular nucleus (PVN) and arcuate nucleus (ARC) of the hypothalamus. Moreover, there was a high correlation between the TST and Fos expression in the A1, A2, AVPV and POA. Thus, ovariectomy gradually increases TST and induces neuronal activation in the brainstem, preoptic area and hypothalamus. Fos expression in neurons of the A1, A2, AVPV, and POA is directly correlated with TST, suggesting these brain areas are associated with the thermoregulatory effects of estrogen. 
 Financial support: CNPQ, FAPEMIG, CAPES