Kisspeptin Activation of Gonadotropin Releasing Hormone Neurons and Regulation of KiSS-1 mRNA in the Male Rat

TLDR

The KiSS‑1 gene encodes kisspeptins that bind the GPR54 receptor. The study aimed to determine whether central injection of kisspeptin‑52 increases luteinizing hormone secretion in male rats. The authors used a GnRH antagonist, Fos immunocytochemistry, double‑label in situ hybridization, and KiSS‑1 mRNA measurement to investigate kisspeptin action on GnRH neurons. Kisspeptin‑52 stimulates luteinizing hormone via GnRH neurons, which express GPR54 and Fos, and KiSS‑1 mRNA is up‑regulated by gonadal hormone removal, indicating a feedback role.

Abstract

The KiSS-1 gene codes for a family of neuropeptides called kisspeptins which bind to the G-protein-coupled receptor GPR54. To assess the possible effects of kisspeptins on gonadotropin secretion, we injected kisspeptin-52 into the lateral cerebral ventricles of adult male rats and found that kisspeptin-52 increased the serum levels of luteinizing hormone (p < 0.05). To determine whether the kisspeptin-52-induced stimulation of luteinizing hormone secretion was mediated by gonadotropin-releasing hormone (GnRH), we pretreated adult male rats with a GnRH antagonist (acyline), then challenged the animals with intracerebroventricularly administered kisspeptin-52. The GnRH antagonist blocked the kisspeptin-52-induced increase in luteinizing hormone. To examine whether kisspeptins stimulate transcriptional activity in GnRH neurons, we administered kisspeptin-52 intracerebroventricularly and found by immunocytochemistry that 86% of the GnRH neurons coexpressed Fos 2 h after the kisspeptin-52 challenge, whereas fewer than 1% of the GnRH neurons expressed Fos following injection of the vehicle alone (p < 0.001). To assess whether kisspeptins can directly act on GnRH neurons, we used double-label in situ hybridization and found that 77% of the GnRH neurons coexpress GPR54 mRNA. Finally, to determine whether KiSS-1 gene expression is regulated by gonadal hormones, we measured KiSS-1 mRNA levels by single-label in situ hybridization in intact and castrated males and found significantly higher levels in the arcuate nucleus of castrates. These results demonstrate that GnRH neurons are direct targets for regulation by kisspeptins and that KiSS-1 mRNA is regulated by gonadal hormones, suggesting that KiSS-1 neurons play an important role in the feedback regulation of gonadotropin secretion.