title: Evidence that hypothalamic RFamide related peptide-3 neurones are not leptin-responsive in mice and rats.
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.
authors.affiliation: Centre for Neuroendocrinology and Department of Anatomy, University of Otago School of Medical Sciences, Dunedin, New Zealand.
authors.forename: M Z
authors.initials: MZ
authors.lastname: Rizwan
authors.forename: A A
authors.initials: AA
authors.lastname: Harbid
authors.forename: M A
authors.initials: MA
authors.lastname: Inglis
authors.forename: J H
authors.initials: JH
authors.lastname: Quennell
authors.forename: G M
authors.initials: GM
authors.lastname: Anderson
mesh_terms: D000818:Animals; D001483:Base Sequence; D017931:DNA Primers; D007028:Hypothalamic Hormones / Q000235:genetics / Q000502:physiology*; D007031:Hypothalamus / Q000166:cytology*; D020738:Leptin / Q000502:physiology*; D051379:Mice; D008815:Mice, Inbred Strains; D009474:Neurons / Q000502:physiology*; D009479:Neuropeptides / Q000502:physiology*; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats
chemical_list: D017931:DNA Primers; D007028:Hypothalamic Hormones; D020738:Leptin; D009479:Neuropeptides; C416987:RFamide peptide; C000588859:RFamide-related peptide-3, rat; D012333:RNA, Messenger
keywords: GnIH; GnRH; RFamide related peptide-3; leptin