Impaired GABAB Receptor Signaling Dramatically Up-Regulates Kiss1 Expression Selectively in Nonhypothalamic Brain Regions of Adult but Not Prepubertal Mice

Abstract

Kisspeptin, encoded by Kiss1, stimulates reproduction and is synthesized in the hypothalamic anteroventral periventricular and arcuate nuclei. Kiss1 is also expressed at lower levels in the medial amygdala (MeA) and bed nucleus of the stria terminalis (BNST), but the regulation and function of Kiss1 there is poorly understood. γ-Aminobutyric acid (GABA) also regulates reproduction, and female GABAB1 receptor knockout (KO) mice have compromised fertility. However, the interaction between GABAB receptors and Kiss1 neurons is unknown. Here, using double-label in situ hybridization, we first demonstrated that a majority of hypothalamic Kiss1 neurons coexpress GABAB1 subunit, a finding also confirmed for most MeA Kiss1 neurons. Yet, despite known reproductive impairments in GABAB1KO mice, Kiss1 expression in the anteroventral periventricular and arcuate nuclei, assessed by both in situ hybridization and real-time PCR, was identical between adult wild-type and GABAB1KO mice. Surprisingly, however, Kiss1 levels in the BNST and MeA, as well as the lateral septum (a region normally lacking Kiss1 expression), were dramatically increased in both GABAB1KO males and females. The increased Kiss1 levels in extrahypothalamic regions were not caused by elevated sex steroids (which can increase Kiss1 expression), because circulating estradiol and testosterone were equivalent between genotypes. Interestingly, increased Kiss1 expression was not detected in the MeA or BNST in prepubertal KO mice of either sex, indicating that the enhancements in extrahypothalamic Kiss1 levels initiate during/after puberty. These findings suggest that GABAB signaling may normally directly or indirectly inhibit Kiss1 expression, particularly in the BNST and MeA, and highlight the importance of studying kisspeptin populations outside the hypothalamus.

Effect of long-term treatment with classical neuroleptics on NPQ/spexin, kisspeptin and POMC mRNA expression in the male rat amygdala

“…On the other hand our results contradict findings showing that haloperidol supports the NPY mRNA expression in the rat amygdala (Śmiałowska et al 2001) and increase hypothalamic GnRH and CRF mRNA levels (Park et al 2011; Umathe et al 2009). The changes in Kiss-1 mRNA expression seem to be especially interesting in the context of recent evidence proving an important role of kisspeptin signaling in the physiology of medial amygdala (Di Giorgio et al 2014; Xu et al 2012; Yeo et al 2016). Taking into account that Kiss-1 expression in the amygdala is controlled by circulating sex hormones (Cao and Patisaul 2013; Kim et al 2011), and kisspeptin neurons in MeA are sensitive to the pheromone molecules (Pineda et al 2017), the analogous comparative study on females has to be definitely proven.…”

Daily successive changes in reproductive gene expression and neuronal activation in the brains of pubertal female mice

“…Double label ISH was performed as described previously (Di Giorgio et al, 2014; Kim et al, 2013; Poling et al, 2012; Robertson et al, 2009). Briefly, slide-mounted brain sections were treated similarly to single-label ISH with the following modifications.…”

“…For double-label assays, red fluorescent DIG-containing cells were identified under microscopy and the grain-counting software quantified the number of silver grains overlying each cell. Signal-to-background ratios for individual cells were calculated, and a cell was considered double-labeled if its ratio was >3 (Di Giorgio et al, 2014; Kauffman et al, 2014; Navarro et al, 2011). …”

Emerging Roles of Kisspeptin in Sexual and Emotional Brain Processing

“…Kisspeptin has been identified in the stria terminalis, amygdala, and thalamus using a polyclonal rabbit antibody to identify the terminal amino acid sequence of kisspeptin [10]. Kiss1 mRNA has also been identified in the rodent amygdala where its expression is positively modulated by gonadal sex steroids [21,22]. Other brain regions demonstrating Kiss1r expression include the habenula, thalamus, hippocampus, and the olfactory system [15,23,24].…”

“…Other neuroendocrine systems may also be at work, as kisspeptin has established roles in nitric oxide [61], neurokinin B [62], dynorphin [63], gamma-aminobutyric acid [22], glutamate [38], and cocaine-and amphetamine-regulated transcript [64] signalling. Hence, there is a complex set of pathways that kisspeptin signalling can interact with, to bring about the aforementioned effects on emotions and sexual processing that will no doubt be a subject of future study.…”