Central Norepinephrine‐Kisspeptin Pathway as Part of the Vaso‐motor Effects of Estrogen in an Animal Model of Menopausal Hot Flashes

Abstract

Menopausal transition includes the vasomotor disturbance hot flash as a significant symptom. Thus, the lack of estrogen has pronounced effects on thermoregulation, but how estrogen modulates thermoregulation remains poorly understood. Both norepinephrine (NE) and kisspeptin (Kp) have been shown to be involved in the central control of body temperature. In this work, we investigated the role of NE in the activation of hypothalamic Kp neurons and vasomotor effects caused by the lack of 17β‐estradiol (E2) in ovariectomized (OVX) rats. The first experiment was designed to determine the effects of E2 on tail skin temperature (TST) and correlate neuronal activation. Adult female rats were OVX and implanted with subcutaneous Silastic capsules containing oil (OVX) or E2 (6 ug/capsule/rat; OVX+E2). The TST was recorded for 2 hours on days 3, 7 and 14 after surgery. Rats were perfused on the morning of day 14 and the brains were processed for immunohistochemistry. OVX+E2 rats displayed greater uterine weight than OVX rats. The TST was higher in OVX compared to OVX+E2 rats at 7 and 14 days after ovariectomy. On day 14, OVX rats displayed an increased percentage of tyrosine hydroxylase (TH)‐immunoreactive (ir) neurons expressing Fos in the A1, A2 and locus coeruleus (LC), which was positively correlated with TST. The number of Fos‐ir neurons was also higher in the anteroventral periventricular (AVPV), median preoptic (MnPO), medial preoptic (MPO), and paraventricular (PVN) nuclei of OVX rats compared with OVX+E2. In the arcuate nucleus (ARC), the numbers of Kp single‐labeled and Fos/Kp double‐labeled neurons were markedly higher in OVX rats. In a second experiment, we investigated whether NE projections to the hypothalamus would drive the activity of Kp neurons in OVX rats. The α2‐adrenergic agonist clonidine (CLO) was used to reduce central norepinephrine release and TST and Kiss1 gene expression were measured. OVX and OVX+E2 rats received daily intracerebroventricular injections of CLO (10 ug/3 μL/rat; OVX+CLO) or vehicle (OVX+V and OVX+E2+V) on days 12, 13 and 14 after ovariectomy. OVX+V rats displayed higher TST than OVX+E2+V, and this response was completely restored in OVX+CLO rats, whose TST was similar to that of OVX+E2+V rats. The same response was found for Kiss1 mRNA in the ARC, with higher expression in OVX than in OVX+E 2, and levels fully restored in OVX+CLO rats. On the other hand, CLO significantly increased Kiss1 expression in the AVPV of OVX+CLO rats compared to OVX+V and OVX+E2+V rats, and this response was associated with an increased secretion of luteinizing hormone (LH) in OVX + CLO rats. Thus, the increase in TST caused by the absence of E2 in OVX rats is associated with an increased activity of noradrenergic and hypothalamic nuclei and seems to depend on the NE activation of Kp neurons in the ARC. These findings provide evidence of the involvement of a central NE‐Kp pathway as part of the vasomotor effects of estrogen, with possible implication in origin of postmenopausal hot flash.Support or Funding InformationCNPq; FAPEMIGThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.