Envolvimento dos neurônios KNDy na dissipação de calor causada pela deficiência de esteroides sexuais em ratos machos e fêmeas

Abstract

Hot flashes consist of a disorder in thermoregulation, characterized by peripheral vasodilation and increased heat dissipation, caused by reduced levels of estradiol (E2) in the postmenopausal period. Previous evidence suggests that neurons in the arcuate nucleus of the hypothalamus (ARC), which co-express kisspeptin, neurokinin B (NKB) and dynorphin (KNDy), facilitate cutaneous vasodilation in the absence of (E2), suggesting an involvement in the genesis of hot flashes on women and animal models. However, the physiological mechanisms involved remain poorly understood, therefore, in this work, we evaluated the heat dissipation in a model of gonadectomized rats and compared the participation of KNDy neurons in the response of males and females. In experiment 1, we used Wistar rats, which were habituated to the container for 4 weeks; subsequently, the animals underwent surgery to implant intraperitoneal dataloggers. Females were divided Intact: intact gonad (Intact), ovariectomized females treated with oil (OVX) and OVX treated with E2 (OVX+ E2). Males were divided Intact: intact gonad (Intact), orchidectomized treated with oil (ORX), ORX treated with testosterone (T; ORX+T) and ORX treated with dihydrotestosterone (DHT; ORX+DHT). Experiment 1 was performed after 15 days of gonadectomy, in which the skin temperature of the tail (TST), abdominal temperature (Tabd) and oxygen consumption (VO2) were measured. The animals were euthanized by perfusion, the brains were processed for immunohistochemistry and NKB immunofluorescence in the ARC and the blood used to measure the LH concentration by ELISA. Experiment 2 had an experimental protocol similar to that carried out in the first, however, the animals were euthanized by decapitation, had their brains removed and ARC was dissected using the punch technique for analysis of NKB mRNA by RT-PCR in real time. We found that ovariectomy increased TST and heat loss index (HLI), and these effects were completely prevented by E2 treatment in females. Concomitantly, ovariectomy increased the number and diameter of NKB-ir neurons in the ARC, and these parameters were positively correlated with increased TST. In males, orchiectomy also increased TST and HLI, and these effects were similarly prevented by treatments with T and DHT. However, orchiectomy did not increase the number of NKB-ir neurons in the ARC of ORX rats relative to Intact, whereas androgen treatment reduced NKB expression in ORX+T and ORX+DHT rats compared to Intact and ORX groups. There was no significant correlation between the number of NKB-ir neurons in the ARC and TST in males. We then used confocal microscopy to assess changes in the size of KNDy neurons, this analysis demonstrated a similar increase in the diameter of NKB-ir neurons after gonadectomy in both females and males, an effect prevented by the respective treatments with sex steroids. Gene expression analysis also showed similar results between females and males. We did not observe any effect of gonadectomy on Nkb expression, while gonadal steroids suppressed the expression of this peptide in the ARC of females and males. Therefore, in females, increased heat loss due to E2 failure is associated with increased number and size of KNDy neurons. In males, in turn, the increase in heat dissipation after castration is solely associated with the larger size of KNDy neurons induced by the absence of androgens. Taken together, our data demonstrate that the neuroendocrine mechanism that triggers the hot flash phenomenon depends on the activation of KNDy neurons in both sexes, with the hypertrophy of these neurons being the most reliable index of their increased function in conditions of sex steroid deficiency.