Photoperiodic Co‐Regulation of Kisspeptin, Neurokinin B and Dynorphin in the Hypothalamus of a Seasonal Rodent

Abstract

In many species, sexual activity varies on a seasonal basis. Kisspeptin (Kp), a hypothalamic neuropeptide acting as a strong activator of gonadotrophin-releasing hormone neurones, plays a critical role in this adaptive process. Recent studies report that two other neuropeptides, namely neurokinin B (NKB) and dynorphin (DYN), are co-expressed with Kp (and therefore termed KNDy neurones) in the arcuate nucleus and that these peptides are also considered to influence GnRH secretion. The present study aimed to establish whether hypothalamic NKB and DYN expression is photoperiod-dependent in a seasonal rodent, the Syrian hamster, which exhibits robust seasonal rhythms in reproductive activity. The majority of Kp neurones in the arcuate nucleus co-express NKB and DYN and the expression of all three peptides is decreased under a short (compared to long) photoperiod, leading to a 60% decrease in the number of KNDy neurones under photo-inhibitory conditions. In seasonal rodents, RFamide-related peptide (RFRP) neurones of the dorsomedial hypothalamus are also critical for seasonal reproduction. Interestingly, NKB and DYN are also expressed in the dorsomedial hypothalamus but do not co-localise with RFRP-immunoreactive neurones, and the expression of both NKB and DYN is higher under a short photoperiod, which is opposite to the short-day inhibition of RFRP expression. In conclusion, the present study shows that NKB and DYN display different photoperiodic variations in the Syrian hamster hypothalamus. In the arcuate nucleus, NKB and DYN, together with Kp, are down-regulated under a short photoperiod, whereas, in the dorsomedial hypothalamus, NKB and DYN are up-regulated under a short photoperiod.

Ontogenesis of peptidergic neurons within the genoarchitectonic map of the mouse hypothalamus

“…Some peptides may coexist in the same neurons (Swanson, 1987 ). OXT and GAL, e.g., co-localize in neurons of the adult paraventricular and supraoptic nuclei (Landry et al, 1991 ; see Rossmanith et al, 1996 ; Foradori et al, 2006 ; Furutani et al, 2013 , and Bartzen-Sprauer et al, 2014 for other examples). As regards its molecular profile, this domain co-expresses Otp and interactive Sim1 / Arnt2 genes, within a Pax6 -positive and Dlx/Arx/Shh/Nkx2.1 -negative background (Figure 1C ; Puelles et al, 2012 ).…”

A Kiss to drive rhythms in reproduction

“…Therefore, the higher expression of ARC Kiss1 expression in sexually active Syrian hamster and ewe has to be driven by strong seasonal cues able to counteract the negative sex steroid feedback. ARC Kp neurons are known to coexpress neurokininB and dynorphin, and these two peptides in Syrian hamster (Bartzen‐Sprauer, Klosen, Ciofi, Mikkelsen, & Simonneaux, ) but only neurokininB in sheep (Weems et al., ) also exhibit seasonal changes driven by steroid‐dependant and steroid‐independent mechanisms. Further studies confirmed the occurrence of seasonal/photoperiodic variation in ARC Kp expression in a number of seasonal breeders, notably the Djungarian hamster (Greives et al., ; Rasri‐Klosen, Simonneaux, & Klosen, ), European hamster (Sáenz de Miera et al., ), Libyan jird (Boufermes et al., ), jerboa (Talbi, Klosen, Laran‐Chich, El Ouezzani, & Simonneaux, ), red deer (Barrell et al., ), and dromedary camel (Ainani et al., ) (Figure ).…”

Neuropeptide co-expression in hypothalamic kisspeptin neurons of laboratory animals and the human

“…Unlike the preoptic cell population, KP neurons of the ARC co-synthesize KP, neurokinin B (NKB) and dynorphin (Dyn) in several species (Burke et al, 2006 ; Foradori et al, 2006 ; Goodman et al, 2007 ; Navarro et al, 2011a ; Bartzen-Sprauer et al, 2014 ), forming the basis for the “KNDy neuron” terminology (Lehman et al, 2010b ). It is only becoming recognized lately that KNDy neurons do not consist of a homogenous cell population in that co-expression of the three KNDy peptides is only partial (Cheng et al, 2010 ; Hrabovszky et al, 2010 , 2011 , 2012 ; Overgaard et al, 2014 ).…”