Estrogen-Regulated Lateral Septal Kisspeptin Neurons Abundantly Project to GnRH Neurons and the Hypothalamic Supramammillary Nucleus

Abstract

While hypothalamic kisspeptin (KP) neurons play well-established roles in the estrogen-dependent regulation of reproduction, little is known about extrahypothalamic KP-producing (KPLS) neurons of the lateral septum. As established previously,Kiss1expression in this region is low and regulated by estrogen receptor- and GABABreceptor-dependent mechanisms. Our present experiments onKiss1-Cre/ZsGreenknock-in mice revealed that transgene expression in the LS begins at Postnatal Day (P)33–36 in females and P40–45 in males and is stimulated by estrogen receptor signaling. Fluorescent cell numbers continue to increase in adulthood and are higher in females. Viral tracing uncovered that the bulk of KPLSfibers joins the medial forebrain bundle and terminates in the hypothalamic supramammillary nucleus. Smaller subsets innervate the medial amygdala or project to other limbic structures. One-quarter of gonadotropin-releasing hormone (GnRH)-immunoreactive perikarya in the preoptic area and their dendrites receive appositions from KPLSaxons. OVX adultKiss1-Cre/ZsGreenmice treated for 4 d with 17β-estradiol or vehicle were used for RNA sequencing studies of laser-microdissected KPLSneurons. The transcriptome included markers of GABAergic and neuropeptidergic (Penk,Cartpt,Vgf) cotransmission and 571 estrogen-regulated transcripts. Estrogen treatment upregulated the acetylcholine receptor transcriptChrm2and, in slice electrophysiology experiments, caused enhanced muscarinic inhibition of KPLSneurons. Finally, we provided immunohistochemical evidence for homologous neurons in the postmortem human brain, suggesting that KPLSneurons may contribute to evolutionarily conserved regulatory mechanisms. Future studies will need to investigate the putative roles of KPLSneurons in the estrogen-dependent control of GnRH neurons and/or various hypothalamic/limbic functions.