The Role Hypothalamic Kisspeptin Neurons Play in Estradiol Negative and Positive Feedback Regulation of Reproduction

Abstract

The brain regulates fertility through gonadotropin-releasing hormone (GnRH) neurons. Estradiol induces negative feedback on pulsatile GnRH/luteinizing hormone (LH) release and positive feedback generating GnRH/LH surges. Negative and positive feedback are postulated to be mediated by kisspeptin neurons in arcuate and anteroventral periventricular (AVPV) kisspeptin neurons, respectively. The work in this dissertation first demonstrated AVPV kisspeptin neurons were more excitable during positive feedback by performing electrophysiological recordings on cells from cycling and hormonal manipulated adult female mice. To test if the estradiol mediated excitability is due to estradiol action on estrogen receptor alpha (ERα) in kisspeptin neurons, kisspeptin specific ERα knockout mice (KERKO) and Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/Cas9 based AAV vectors that target Esr1 gene injected mice were used. The estradiol-induced increase in excitability of AVPV kisspeptin neurons was lost in cells from KERKO or AAV ERα knockdown mice. The comparable intrinsic excitability between two models suggests activational effects of estradiol can regulate firing activity. Besides intrinsic excitability, glutamatergic transmission to AVPV and arcuate kisspeptin neurons was characterized in cycling and hormonal manipulated adult female mice, as well as KERKO mice. This revealed that glutamatergic transmission to AVPV kisspeptin neurons is decreased during estradiol negative feedback whereas transmission to arcuate kisspeptin neurons is increased during negative feedback; frequency of glutamatergic transmission during positive feedback has the opposite pattern, being increased to AVPV and decreased to arcuate cells. Deletion of ERα in kisspeptin cells decreases glutamate transmission to AVPV neurons and markedly increases it to arcuate kisspeptin neurons, which also exhibits increased spontaneous firing rate. KERKO mice exhibit increased LH pulse frequency, indicating loss of negative feedback. The CRISPR/Cas9 based AAV approach enables spatial- and temporal-specific gene editing in mice. This allows us to test the role of estradiol and ERα in AVPV and arcuate kisspeptin neurons plays to sense estradiol and orchestrate pulsatile and surge release of GnRH/LH and thus reproductive output.