Evidence that hypothalamic RFamide related peptide-3 neurones are not leptin-responsive in mice and rats

J Neuroendocrinol. 2014 Apr;26(4):247-57. doi: 10.1111/jne.12140.

Abstract

Leptin, a permissive hormonal regulator of fertility, provides information about the body's energy reserves to the hypothalamic gonadotrophin-releasing hormone (GnRH) neuronal system that drives reproduction. Leptin does not directly act on GnRH neurones, and the neuronal pathways that it uses remain unclear. RFamide-related peptide-3 (RFRP-3) neurones project to GnRH neurones and primarily inhibit their activity. We tested whether leptin could act via RFRP-3 neurones to potentially modulate GnRH activity. First, the effects of leptin deficiency or high-fat diet-induced obesity on RFRP-3 cell numbers and gene expression were assessed in male and female mice. There was no significant difference in Rfrp mRNA levels or RFRP-3-immunoreactive cell counts in wild-type versus leptin-deficient ob/ob animals, or in low-fat versus high-fat diet fed wild-type mice. Second, the presence of leptin-induced signalling in RFRP-3 neurones was examined in male and female wild-type mice and rats. Dual label immunohistochemistry revealed leptin-induced phosphorylated signal transducer and activator of transcription-3 in close proximity to RFRP-3 neurones, although there was very little (2-13%) colocalisation and no significant differences between vehicle and leptin-treated animals. Furthermore, we were unable to detect leptin receptor mRNA in a semi-purified RFRP-3 cell preparation. Because GABA neurones form critical leptin-responsive GnRH inputs, we also determined whether RFRP-3 and GABA cells were colocalised. No such colocalisation was detected. These results support the concept that leptin has little or no effects on RFRP-3 neurones, and that these neurones are unlikely to be an important neuronal pathway for the metabolic regulation of fertility by leptin.

Keywords: GnIH; GnRH; RFamide related peptide-3; leptin.

MeSH terms

  • Animals
  • Base Sequence
  • DNA Primers
  • Hypothalamic Hormones / genetics
  • Hypothalamic Hormones / physiology*
  • Hypothalamus / cytology*
  • Leptin / physiology*
  • Mice
  • Mice, Inbred Strains
  • Neurons / physiology*
  • Neuropeptides / physiology*
  • Polymerase Chain Reaction
  • RNA, Messenger / genetics
  • Rats

Substances

  • DNA Primers
  • Hypothalamic Hormones
  • Leptin
  • Neuropeptides
  • RFamide peptide
  • RFamide-related peptide-3, rat
  • RNA, Messenger