Characterisation of Arcuate Nucleus Kisspeptin/Neurokinin B Neuronal Projections and Regulation during Lactation in the Rat

Abstract

Lactation results in negative energy balance in the rat leading to decreased gonadotrophin-releasing hormone (GnRH) release and anoestrus. Inhibited GnRH release may be a result of decreased stimulatory tone from neuropeptides critical for GnRH neuronal activity, such as kisspeptin (Kiss1) and neurokinin B (NKB). The present study aimed to identify neuronal projections from the colocalised population of Kiss1/NKB cells in the arcuate nucleus (ARH) using double-label immunohistochemistry to determine where this population may directly regulate GnRH neuronal activity. Additionally, the present study further examined lactation-induced changes in the Kiss1 system that could play a role in decreased GnRH release. The colocalised ARH Kiss1/NKB fibres projected primarily to the internal zone of the median eminence (ME) where they were in close proximity to GnRH fibres; however, few Kiss1/NKB fibres from the ARH were seen at the level of GnRH neurones in the preoptic area (POA). Arcuate Kiss1/NKB peptide levels were decreased during lactation consistent with previous mRNA data. Surprisingly, anteroventral periventricular (AVPV) Kiss1 peptide levels were increased, whereas Kiss1 mRNA levels were decreased during lactation, suggesting active inhibition of peptide release. These findings indicate ARH Kiss1/NKB and AVPV Kiss1 appear to be inhibited during lactation, which may contribute to decreased GnRH release and subsequent reproductive dysfunction. Furthermore, the absence of a strong ARH Kiss1/NKB projection to the POA suggests regulation of GnRH by this population occurs primarily at the ME level via local projections.

Food restriction during lactation suppresses Kiss1 mRNA expression and kisspeptin-stimulated LH release in rats

“…Food restriction during lactation produces a useful model in which the length of lactational diestrus can reliably be extended. The results of the present study indicate that this prolongation of lactational diestrus is associated with reduced Kiss1 mRNA expression in the AVPV, similar to that observed at an earlier time period postpartum in AL-fed dams (True et al 2011) and an attenuated LH response to exogenous kisspeptin on day 15 of lactation. The reduced AVPV Kiss1 mRNA expression observed in the day 15 food-restricted dams may represent a key factor involved in the delayed restoration of HPG axis function during the postpartum period resulting from the food restriction manipulation.…”

“…By contrast, in the AL-fed lactating rats, Kiss1 mRNA levels in the AVPV remained stable, between day 15 pp and day 20 pp, and were similar to those in the nonlactating controls, even though basal LH concentrations increased over this period. Although not measured in the present study, decreased AVPV Kiss1 mRNA expression has been observed earlier in lactation (day 10/11 pp) in intact dams using in situ hybridization (True et al 2011). This suggests that during early lactation a reduction in AVPV Kiss1 mRNA expression may be involved in the mechanisms suppressing the HPG axis, and as weaning approaches, and the HPG axis is slowly reactivated, AVPV Kiss1 mRNA expression increases back to control levels.…”

“…Estradiol stimulates Kiss1 mRNA expression in the AVPV and suppresses Kiss1 mRNA expression in the arcuate nucleus . Arcuate nucleus Kiss1 mRNA expression has been shown to be suppressed during early and mid lactation (Yamada et al 2007, Xu et al 2009, True et al 2011, while AVPV Kiss1 mRNA is either unchanged (Yamada et al 2007) or decreased (True et al 2011). These data suggest that a decrease in kisspeptin expression might underlie the loss of fertility during lactation.…”

“…This antibody was initially characterized and distributed by Dr Alan Caraty (Franceschini et al 2006). Low levels of crossreaction with RFRP1 have been suggested (True et al 2011); however, similar to others, we did not detect any staining in the dorsomedial nucleus of the hypothalamus, suggesting that any cross-reaction is minimal (True et al 2011). After w48 h of incubation, the sections were washed and then incubated with a biotinylated goat anti-rabbit antibody for 1 h (1:1000 dilution in TBST containing 2% normal goat serum).…”

Role of Adipose Secreted Factors and Kisspeptin in the Metabolic Control of Gonadotropin Secretion and Puberty

“…Expression of KiSS-1 also is suppressed during negative energy balance associated with lactation (True et al, 2011;Yamada et al, 2007). These data demonstrate that kisspeptin neurons in the hypothalamus are an important component to how the reproductive axis senses nutritional state.…”