Central Injection of Substance P Antagonizes the RF Amide-Related Peptide-3 Impacts on Hypothalamic KISS-1 and GnRH Gene Expressions in Male Wistar Rats

Parastoo Rahdar,Homayoun Khazali

doi:10.15171/ijbsm.2018.23

Abstract

Background: Gonadotropin-inhibitory hormone and its mammalian orthologues (RFRP: RF amid related peptide) are known to inhibit the secretion of gonadotropins. In addition, substance P (SP) a member of tachykinin’s family is demonstrated that can increase the firing rate of kisspeptin/neurokinin B/dynorphin (KNDy) neurons and provokes the of secretion gonadotropins. In this experimental study we investigated the effects of co-administration of RFRP-3 and SP on the expression of KISS-1 and GnRH genes in male rats. Methods: forty-two mature Wistar rats were randomly allocated in 7 groups (n=6 in each group). Animals in each group intracerebroventricularly received either saline+DMSO, 1nmol SP, 5 nmol RFRP-3, 1nmol SP plus 5 nmol RFRP-3, 1 nmol SP plus10 nmol RF9 (RFRP-3 receptor antagonist), 1 nmol SP plus 1 nmol P234 (kisspeptin receptor antagonist) plus 5 nmol RFRP-3 or 1 nmol SP plus 5 nmol CP-96,345 (SP receptor antagonist) plus 5 nmol RFRP-3 in final volume of 3 µl. After two hours following injections hypothalamic samples were collected for evaluating the expression of target genes by real-time PCR technique. Results: Injections in SP and SP plus RF9 groups increase the expression of the both GnRH and KISS-1 genes (P<0.05). Injections in RFRP-3 group and SP plus RFRP-3 plus SP antagonist group significantly decrease the expression of both GnRH and KISS-1 genes (P<0.05). Injections of SP plus RFRP-3 group and SP plus RFRP-3 plus P234 group did not significantly change the expression of GnRH and KISS-1 genes. Conclusion: The results indicate that SP antagonizes the effects of RFRP-3 on the expression of Hypothalamic KISS-1 and GnRH genes.

Highlights

Gonadotropin-inhibitory hormone (GnIH) and its mammalian orthologue RF amide-related peptide (RFRP) are known to inhibit the secretion of gonadotropins
The expression of Gonadotropin releasing hormone (GnRH) mRNA in preoptic area (POA) following the injection of substance P (SP) + CP-96,345 (SP receptor antagonist, 5 nmol) + RFRP-3 was suppressed significantly compared to that in the control group (P < 0.05, Figure 3)
Our results showed that injection of SP (1 nmol) resulted in the elevation of both KISS-1 and GnRH mRNA expression; these data are in accordance with the previous findings that suggested SP, by acting through NK1R receptor, increases the activity of kisspeptin/ neurokinin B/dynorphin (KNDy) neurons in arcuate nucleus (ARC) nucleus which contains kisspeptin neurons and acts as critical upstream pulse generator of GnRH system.[26]

Summary

Introduction

Gonadotropin-inhibitory hormone (GnIH) and its mammalian orthologue RF amide-related peptide (RFRP) are known to inhibit the secretion of gonadotropins. Substance P (SP), a member of tachykinin’s family, can increase the firing rate of kisspeptin/ neurokinin B/dynorphin (KNDy) neurons and provoke the secretion of gonadotropins. In this experimental study, we investigated the effects of co-administration of RFRP-3 and SP on the expression of KISS-1 and GnRH genes, as gonadotropin regulator genes, in male rats. The function of GnIH, which is a member of RF amide family, is mediated by 2 G-protein-coupled receptors; GPR 147 and GPR 74.4 One GnIH molecule and 2 GnIH-related peptides are encoded by the precursor mRNA of GnIH These molecules possess LPXRF amide (X = leucine or glutamine) at their C terminus which is flanked by glycine and a single basic amino acid, arginine or lysine. The cDNAs identified from the brains of humans and cows encoded three GnIH orthologues, while 2 GnIH orthologues including RF amide-related peptide-3 and -2 (RFPR-3 and RFRP-2) were detected in rats.[6,7,8] Dorsomedial hypothalamic (DMH) region contains GnIH neural cell bodies and the fibers of these neurons are extended to different locations including paraventricular nucleus (PVN), preoptic area (POA), arcuate nucleus (ARC), Rahdar and Khazali median eminence (ME), ventral paleostriatum, optic tectum, septal area, and dorsal motor of vagus nucleus.[9]

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Conclusion