κ-Opioid Receptor Is Colocalized in GnRH and KNDy Cells in the Female Ovine and Rat Brain

Abstract

Kisspeptin-neurokinin B-dynorphin (KNDy) cells of the hypothalamus are a key component in the neuroendocrine regulation of GnRH secretion. Evidence in sheep and other species suggests that dynorphin released by KNDy cells inhibits pulsatile GnRH secretion by acting upon κ-opioid receptors (KOR). However, the precise anatomical location and neurochemical phenotype of KOR-expressing cells in sheep remain unknown. To this end, we determined the distribution of KOR mRNA and protein in the brains of luteal phase ewes, using an ovine specific KOR mRNA probe for in situ hybridization and an antibody whose specificity we confirmed by Western blot analyses and blocking peptide controls. KOR cells were observed in a number of regions, including the preoptic area (POA); anterior hypothalamic area; supraoptic and paraventricular nuclei; ventromedial, dorsomedial, and lateral hypothalamus; and arcuate nucleus. Next, we determined whether KOR is colocalized in KNDy and/or GnRH cells. Dual-label immunofluorescence and confocal analysis of the KNDy population showed a high degree of colocalization, with greater than 90% of these neurons containing KOR. Surprisingly, GnRH cells also showed high levels of colocalization in sheep, ranging from 74.4% to 95.4% for GnRH cells in the POA and medial basal hypothalamus, respectively. Similarly, 97.4% of GnRH neurons in the POA of ovariectomized, steroid-primed female rats also contained immunoreactive KOR protein. These findings suggest that the inhibitory effects of dynorphin on pulsatile GnRH secretion may occur either indirectly by actions upon KOR within the KNDy population and/or directly via the activation of KOR on GnRH cells.

Expanding the role of tachykinins in the neuroendocrine control of reproduction

“…In this model, NKB would stimulate kisspeptin release and dynorphin would then inhibit this release through autosynaptic loops, thus shaping a kisspeptin/GnRH/ LH pulse (Keen et al 2008). This is supported by the anatomical findings that virtually all KNDy neurons express NK3R (Navarro et al 2009, 2011b, Amstalden et al 2010) and >90% express kappa-opioid receptor (KOR; (Weems et al 2016)). Furthermore, KNDy cells are interconnected with NKB fibers within the ARC forming a tightly regulated network (Rance & Bruce 1994, Krajewski et al 2010.…”

The interaction of fasting, caloric restriction, and diet-induced obesity with 17β-estradiol on the expression of KNDy neuropeptides and their receptors in the female mouse

“…Of those studies that examined KNDy neurons, the effects of these physiological states on KNDy receptors and the steroid receptors, ERα and PR, which mediate negative feedback on the HPG axis (Eghlidi et al, 2010, Lehman et al, 2010), were not examined. NKB (Tac2) acts as a positive autoregulator to kisspeptin production through the NKB receptor ( Tac3r ) (Lehman et al, 2010) and dynorphin (DYN/ Pdyn ) is thought to act as a negative autoregulator, via an unidentified interneuronal network, through the κ-opioid receptor (KOR/ Kor ) (de Croft et al, 2013, Lehman et al, 2010, Ruka et al, 2016, Weems et al, 2016) Therefore, ERα, PR, and the KNDy-associated receptors, Kiss1r, Tac3r, and Kor, are essential players in the pulse generator and are potential targets for negative and positive energy balance.…”

“…Both AVPV and ARC kisspeptin regulate the HPG axis by binding to its receptor, G protein-coupled receptor 54 (GPR54), or Kiss1r, expressed on gonadotropin releasing hormone (GnRH) neurons (Bosch et al, 2013, Oakley et al, 2009). In ARC KNDy neurons, the two neuropeptides neurokinin B and dynorphin act as positive and negative autoregulators of KNDy neuronal excitability, respectively (de Croft et al, 2013, Ruka et al, 2016, Uenoyama et al, 2014, Weems et al, 2016). Together, the three KNDy neuropeptides act as a pulse generator for GnRH release (Goodman et al, 2013).…”

Expression of genes for Kisspeptin ( KISS1 ), Neurokinin B ( TAC3 ), Prodynorphin ( PDYN ), and gonadotropin inhibitory hormone ( RFRP ) across natural puberty in ewes

“…DYN has an inhibitory effect on GnRH neurons as do other opioid peptides (Goodman et al, 2004; Navarro et al, 2009; Yen, Quigley, Reid, Ropert, & Cetel, 1985). This may be due to its action on kisspeptin cells or directly upon GnRH cells, which express the relevant receptor (Weems et al, 2016). In sheep, DYN neurons in the ARC appear to mediate the negative feedback effect of progesterone on GnRH/LH pulse secretion (Goodman et al, 2004, 2011; Goodman, Parfitt, Evans, Dahl, & Karsch, 1995).…”