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Photoperiodic Co‐Regulation of Kisspeptin, Neurokinin B and Dynorphin in the Hypothalamus of a Seasonal Rodent
Author(s) -
BartzenSprauer J.,
Klosen P.,
Ciofi P.,
Mikkelsen J. D.,
Simonneaux V.
Publication year - 2014
Publication title -
journal of neuroendocrinology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.062
H-Index - 116
eISSN - 1365-2826
pISSN - 0953-8194
DOI - 10.1111/jne.12171
Subject(s) - kisspeptin , dynorphin , neurokinin b , endocrinology , medicine , hypothalamus , rodent , neuropeptide , biology , receptor , opioid peptide , opioid , substance p , ecology
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 KND y neurones) in the arcuate nucleus and that these peptides are also considered to influence Gn RH 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 KND y 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.