Activity of the locus coeruleus noradrenergic neurons and the release of GnRH in acyclic female rats

Abstract

The process of reproductive senescence in many female mammals, including humans, is characterized by gradual transition from regular reproductive cycles to irregular cycles (i.e., acyclicity), and ultimately to loss of fertility. The period of transition to acyclicity neuroendocrine has not been fully characterized and represents a complex interplay of actions at all levels of the hypothalamic-pituitary-ovarian axis. The gonadotropin-releasing hormone (GnRH) neurons provide the main driving force on the reproductive axis. In addition, the production of the estrogen hormone plays a key role in the neurobiology of aging, because endocrine and neural senescence overlap in time and are mechanistically intertwined in feedback loops. Thus, functional and morphological changes in the GnRH system may result in the transition to acyclicity. The stimuli of the noradrenergic nucleus locus coeruleus (LC) to the medial preoptic area and median eminence are essential for the release of gonadotropins and their neurons express estrogen and progesterone receptors, suggesting a possible control of ovarian steroids. This study will assess the activity of neurons located in nuclei and areas involved in controlling the action of GnRH neurons of female Wistar rats during the transition period of the estrous cycle. We will (1) assess the activity of neurons in the LC and preoptic area of senile rats with acyclicity, as determined by immunoreactivity for Fos-related antigens (FRA); (2) analyze the content of GnRH in the medial basal hypothalamus and (3) analyze the concentration of plasma estradiol, progesterone, LH and FSH of experimental animals. (AU)