Leptin Responsive and GABAergic Projections to the Rostral Preoptic Area in Mice

Abstract

The adipocyte-derived hormone leptin plays a critical role in the control of reproduction via signalling in hypothalamic neurones. The drivers of the hypothalamic-pituitary-gonadal axis, the gonadotrophin-releasing hormone (GnRH) neurones, do not have the receptors for leptin. Therefore, intermediate leptin responsive neurones must provide leptin-to-GnRH signalling. We investigated the populations of leptin responsive neurones that provide input to the rostral preoptic area (rPOA) where GnRH cell bodies reside. Fluorescent retrograde tracer beads (RetroBeads; Lumafluor Inc., Naples, FL, USA) were injected into the rPOA of transgenic leptin receptor enhanced green fluorescent protein (Lepr-eGFP) reporter mice. Uptake of the RetroBeads by Lepr-eGFP neurones was assessed throughout the hypothalamus. RetroBead uptake was most evident in the medial arcuate nucleus (ARC), the dorsomedial nucleus (DMN) and the ventral premammillary nucleus (PMV) of the hypothalamus. The uptake of RetroBeads specifically by Lepr-eGFP neurones was highest in the medial ARC (18% of tracer-labelled neurones Lepr-eGFP-positive). Because neurones that are both leptin responsive and GABAergic play a critical role in the regulation of fertility by leptin, we next focussed on the location of these populations. To address whether GABAergic neurones in leptin-responsive hypothalamic regions project to the rPOA, the experiment was repeated in GABA neurone reporter mice (Vgat-tdTomato). Between 10% and 45% of RetroBead-labelled neurones in the ARC were GABAergic, whereas uptake of tracer by GABAergic neurones in the DMN and PMV was very low (< 5%). These results show that both leptin responsive and GABAergic neurones from the ARC project to the region of the GnRH cell bodies. Our findings suggest that LEPR-expressing GABA neurones from the ARC may be mediators of leptin-to-GnRH signalling.

Deletion of Suppressor of Cytokine Signaling 3 from Forebrain Neurons Delays Infertility and Onset of Hypothalamic Leptin Resistance in Response to a High Caloric Diet

“…For example, the AVPV is a region known to be critical for generation of the preovulatory GnRH/LH surge in mice surge (Le et al, 2001). Leptin acts in this nucleus and in the surrounding medial preoptic area (Quennell et al, 2009;Scott et al, 2009) and, given the effects of HCD and SOCS3 knock-out on surge generation described above, might be expected to show altered leptin signaling in response to these treatments. Indeed, at 110 d of HCD feeding during the previously identified window of time when neuron-specific SOCS3 knock-out mice are protected from HCD-induced infertility, significantly reduced leptin-induced pSTAT3 (indicative of leptin resistance) was observed in the mPOA and AVPV of female HCD-fed control mice compared with LCD-fed mice, whereas leptin responsiveness was maintained at normal levels in neuronspecific SOCS3 knock-out mice in these regions ( Fig.…”

“…Central resistance to leptin, a hormone essential for fertility, is known to accompany this condition and is likely to be a major contributing factor. Upregulation of SOCS3 when fed an HCD is one mechanism proposed to cause central resistance to leptin (Bjørbaek et al, 1998;Münzberg et al, 2004) and insulin (Howard and Flier, 2006), of which the former is most important for reproductive activity (Quennell et al, 2009;Evans et al, 2015). Central deletion of SOCS3 protects against the development of obesity (Mori et al, 2004), but until now it has not been determined whether this is also the case in regards to fertility.…”

“…The activity of GnRH neurons is regulated by metabolic factors, in particular the adipocyte-derived hormone leptin, which is permissive for fertility (Barash et al, 1996;Chehab et al, 1996;Chua et al, 1996;Donato et al, 2011a). Although leptin acts centrally to modulate pulsatile GnRH release (Lebrethon et al, 2000;Nagatani et al, 2000), this occurs indirectly via neurons afferent to GnRH cells because they do not contain leptin receptors (Quennell et al, 2009). Potential upstream sites of action for leptin's effects include the ventral premammillary nucleus (PMV), where leptin receptors have been shown to be sufficient for fertility in female mice (Donato et al, 2011b), the arcuate nucleus (ARC), where many of the leptin-responsive GABAergic neurons that have been shown to be required for normal fertility in mice…”

Defining Subpopulations of Arcuate Nucleus GABA Neurons in Male, Female, and Prenatally Androgenized Female Mice

“…One particular ARN population of neurons that is frequently associated with the regulation of these homeostatic mechanisms is the γ-aminobutyric acid (GABA) neurons. GABA neurons residing specifically within the ARN are strongly linked with the regulation of lactation [1,2] , feeding behavior [3,4] , and in the direct regulation of fertility [5][6][7] .…”

Neuroendocrine integration of nutritional signals on reproduction

“…other nutritional signals and/or neuronal mediators) and often undermines the true physiological importance of the targeted pathway. However, widespread deletion of central leptin signaling consistently causes reproductive impairments , Quennell et al 2009, Zuure et al 2016, highlighting leptin is absolutely required for normal reproductive control. Furthermore, although the deletion of LepR signaling from discrete neuronal populations consistently failed to markedly impair HPG axis function, restoring LepR signaling exclusively in the PMV (Donato et al 2011) or in AgRP neurons (O Egan and GM Anderson, unpublished observations) in LepR-null mice was sufficient to reinstate puberty and reproductive competency, respectively.…”