Glutamatergic Input From Arcuate Nucleus Kiss1 Neurons to Preoptic Kiss1 Neurons Is Required for LH Surge in Female Mice.

Hypothalamic kisspeptin (Kiss1) neurons are vital for maintaining fertility in the mammal. In the female rodent, Kiss1 neurons populate the anteroventral periventricular/periventricular nuclei (Kiss1AVPV/PeN) and the arcuate nucleus (Kiss1ARH). Kiss1ARH neurons (also known as KNDy neurons since they coexpress neurokinin B and dynorphin) are considered the "pulse-generator" neurons that presynaptically excite gonadotropin-releasing hormone (GnRH) axons in the median eminence, whereas the Kiss1AVPV/PeN neurons are the "surge-generator" neurons that depolarize preoptic GnRH neurons directly to drive ovulation. Traditionally, it is believed that Kiss1ARH neurons are relatively quiet during the late follicular, preovulatory stage of the reproductive cycle due to the 17β-estradiol (E2)-mediated downregulation of the expression of the KNDy peptides. However, based on our single-cell, quantitative polymerase chain reaction and whole-cell electrophysiological recordings, we found that the messenger RNA (mRNA) expression of vesicular glutamate transporter 2 (Vglut2) mRNA and excitatory cation channels in Kiss1ARH neurons were significantly upregulated by E2, which increased the excitability and glutamate release from these "pulse-generator" neurons. Presently, we demonstrate that optogenetic stimulation of Kiss1ARH neurons releases glutamate to excite Kiss1AVPV/PeN neurons via activation of both ionotropic and metabotropic glutamate receptors. CRISPR mutagenesis of Vglut2 in Kiss1ARH neurons abolished glutamatergic neurotransmission, which significantly reduced the overall glutamatergic input to Kiss1AVPV/PeN neurons. The mutagenesis of Vglut2 in Kiss1ARH neurons abrogated the E2-induced luteinizing hormone surge and reduced the formation of corpus lutea, indicative of a reduced ovulatory drive in these Vglut2-mutated Kiss1ARH mice. Therefore, Kiss1ARH neurons appear to play a critical role in augmenting the GnRH surge through glutamatergic neurotransmission to Kiss1AVPV/PeN neurons.