Ghrelin Stimulation of Growth Hormone-Releasing Hormone Neurons Is Direct in the Arcuate Nucleus

Inserm U-661, Montpellier, France.
PLoS ONE (Impact Factor: 3.53). 02/2010; 5(2):e9159. DOI: 10.1371/journal.pone.0009159
Source: PubMed

ABSTRACT Ghrelin targets the arcuate nucleus, from where growth hormone releasing hormone (GHRH) neurones trigger GH secretion. This hypothalamic nucleus also contains neuropeptide Y (NPY) neurons which play a master role in the effect of ghrelin on feeding. Interestingly, connections between NPY and GHRH neurons have been reported, leading to the hypothesis that the GH axis and the feeding circuits might be co-regulated by ghrelin.
Here, we show that ghrelin stimulates the firing rate of identified GHRH neurons, in transgenic GHRH-GFP mice. This stimulation is prevented by growth hormone secretagogue receptor-1 antagonism as well as by U-73122, a phospholipase C inhibitor and by calcium channels blockers. The effect of ghrelin does not require synaptic transmission, as it is not antagonized by gamma-aminobutyric acid, glutamate and NPY receptor antagonists. In addition, this hypothalamic effect of ghrelin is independent of somatostatin, the inhibitor of the GH axis, since it is also found in somatostatin knockout mice. Indeed, ghrelin does not modify synaptic currents of GHRH neurons. However, ghrelin exerts a strong and direct depolarizing effect on GHRH neurons, which supports their increased firing rate.
Thus, GHRH neurons are a specific target for ghrelin within the brain, and not activated secondary to altered activity in feeding circuits. These results support the view that ghrelin related therapeutic approaches could be directed separately towards GH deficiency or feeding disorders.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Comprehensive transcriptional profiling of glucose-sensing neurons is challenging because of low expression levels of glucokinase (Gck) and other key proteins that transduce a glucose signal. To overcome this, we generated and validated transgenic mice with a neuronal/endocrine-specific Gck promoter driving cre expression and mated them to mice with cre-dependent expression of an EGFP-tagged ribosomal protein construct (EEF1A1-LSL.EGFPL10) that can be used to map and profile cells. We found significant Gck expression in hypothalamic and limbic regions in cells that are activated following administration of glucose or 2-deoxyglucose. Transcriptional profiling from Gck-cre/EEF1A1-LSL.EGFPL10 mice enriched known and previously unknown glucose-sensing populations including neurons expressing growth hormone releasing hormone (GHRH). Electrophysiological recordings show that hypoglycemia activates GHRH neurons, suggesting a mechanistic link between hypoglycemia and growth hormone release. These studies provide a means for mapping glucose-sensitive neurons and for generating transcriptional profiles from other cell types expressing cre in a cell-specific manner.
    Cell metabolism 10/2013; 18(4):596-607. DOI:10.1016/j.cmet.2013.09.002 · 16.75 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Lateral hypothalamic area (LHA) orexin neurons modulate reward-based feeding by activating ventral tegmental area (VTA) dopamine (DA) neurons. We hypothesize that signals of peripheral energy status influence reward-based feeding by modulating the glucose sensitivity of LHA orexin glucose-inhibited (GI) neurons. This hypothesis was tested using electrophysiological recordings of LHA orexin-GI neurons in brain slices from 4 to 6 week old male mice whose orexin neurons express green fluorescent protein (GFP) or putative VTA-DA neurons from C57Bl/6 mice. Low glucose directly activated ~ 60% of LHA orexin-GFP neurons in both whole cell and cell attached recordings. Leptin indirectly reduced and ghrelin directly enhanced the activation of LHA orexin-GI neurons by glucose decreases from 2.5 to 0.1 mM by 53 ± 12% (n = 16, P < 0.001) and 41 ± 24% (n = 8, P < 0.05), respectively. GABA or neurotensin receptor blockade prevented leptin's effect on glucose sensitivity. Fasting increased activation of LHA orexin-GI neurons by decreased glucose, as would be predicted by these hormonal effects. We also evaluated putative VTA-DA neurons in a novel horizontal slice preparation containing the LHA and VTA. Decreased glucose increased the frequency of spontaneous excitatory post-synaptic currents (sEPSCs; 125 ± 40%, n = 9, P < 0.05) and action potentials (n = 9; P < 0.05) in 45% (9/20) of VTA DA neurons. sEPSCs were completely blocked by AMPA and NMDA glutamate receptor antagonists (CNQX 20 μM, n = 4; APV 20 μM, n = 4; respectively), demonstrating that these sEPSCs were mediated by glutamatergic transmission onto VTA DA neurons. Orexin-1 but not 2 receptor antagonism with SB334867 (10 μM; n = 9) and TCS-OX2-29 (2 μM; n = 5), respectively, blocks the effects of decreased glucose on VTA DA neurons. Thus, decreased glucose increases orexin-dependent excitatory glutamate neurotransmission onto VTA DA neurons. These data suggest that the glucose sensitivity of LHA orexin-GI neurons links metabolic state and reward-based feeding.
    Molecular and Cellular Neuroscience 09/2014; DOI:10.1016/j.mcn.2014.08.001 · 3.73 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Reproduction is a tightly regulated function in which many mechanisms contribute to ensure the survival of the species. Among those, due to the elevated energy requirements of reproduction, metabolic factors exert a pivotal role in the control of hypothalamic-pituitary-gonadal axis. Although this control may occur at multiple levels of the axis, the majority of interactions between metabolic and reproductive systems take place in the hypothalamus. In this article, we present an overview of the state-of-the-art knowledge regarding the metabolic regulation of reproduction at the central level. We aim to identify the neuroanatomical location where both functions interconnect by discussing the likelihood of each component of the neuronal hierarchical network controlling gonadotropin-releasing hormone (GnRH) release to be first-order responders to metabolic cues, especially the peripheral metabolic signals leptin, insulin, and ghrelin. Latest evidence suggests that the primary action of leptin, insulin, and ghrelin to regulate reproduction is located upstream of the main central elicitors of gonadotropin release, Kiss1 and GnRH neurons, and neuroanatomically separated from their metabolic action. The study of the neuronal interactions between the mechanisms governing metabolism and reproduction offers the platform to overcome or treat a number of prevailing metabolic and/or reproductive conditions.
    Current opinion in endocrinology, diabetes, and obesity 08/2013; 20(4):335-341. DOI:10.1097/MED.0b013e32836318ce · 3.77 Impact Factor

Full-text (3 Sources)

Available from
May 16, 2014