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Ghrelin stimulation of growth hormone-releasing hormone neurons is direct in the arcuate nucleus.

Osterstock G, Escobar P, Mitutsova V, Gouty-Colomer LA, Fontanaud P, Molino F, Fehrentz JA, Carmignac D, Martinez J, Guerineau NC, Robinson IC, Mollard P, Méry PF - PLoS ONE (2010)

Bottom Line: 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.These results support the view that ghrelin related therapeutic approaches could be directed separately towards GH deficiency or feeding disorders.

View Article: PubMed Central - PubMed

Affiliation: Inserm U-661, Montpellier, France.

ABSTRACT

Background: 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.

Principal findings: 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.

Conclusion: 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.

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Related in: MedlinePlus

Ghrelin changed the excitability of GHRH neurons.A, recordings from a GHRH neuron in the absence and presence of 10 nM ghrelin, in the perforated patch-clamp configuration. B, time course of the effect of ghrelin 10 nM on the firing rate (upper graph) and on the resting potential (lower graph) of the GHRH neuron shown in A. C, summary of the effects of ghrelin 10 nM on the mean action potential intervals in GHRH neurons recorded in the perforated patch-clamp configuration. D, mean amplitude of the resting potential in GHRH neurons in the absence and presence of 10 nM ghrelin (same experiments as in C). Bars and lines are the means and the sem of the numbers of experiments indicated. Statistical difference (p<0.05, paired student-t test) with the control level is indicated.
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pone-0009159-g009: Ghrelin changed the excitability of GHRH neurons.A, recordings from a GHRH neuron in the absence and presence of 10 nM ghrelin, in the perforated patch-clamp configuration. B, time course of the effect of ghrelin 10 nM on the firing rate (upper graph) and on the resting potential (lower graph) of the GHRH neuron shown in A. C, summary of the effects of ghrelin 10 nM on the mean action potential intervals in GHRH neurons recorded in the perforated patch-clamp configuration. D, mean amplitude of the resting potential in GHRH neurons in the absence and presence of 10 nM ghrelin (same experiments as in C). Bars and lines are the means and the sem of the numbers of experiments indicated. Statistical difference (p<0.05, paired student-t test) with the control level is indicated.

Mentions: The signature of the neuromodulatory effect of ghrelin on GHRH neurons was further investigated with the perforated patch-clamp technique [49], where amplitudes and kinetics of action potentials can be quantified (as shown by the individual traces of Fig. 9A). In the recording of Fig. 9A–B, the spontaneous action potentials of a GHRH neuron were collected under control conditions in the current-clamp mode (0 pA). Superfusion of the slice with ghrelin 10 nM increased the firing rate of the neuron (Fig. 9B, top panel) and this stimulation was mirrored by a decrease in the resting membrane potential (Fig. 9B, bottom panel). In similar experiments, ghrelin consistently decreased the mean action potentials intervals (from 4.31±2.0 s to 1.40±0.77 s, n = 8, p<0.05, paired student t-test: Fig. 9C), without changing the skewness of the interval distribution (data not shown), consistent with the results from extracellular recordings. Ghrelin consistently depolarized GHRH neurons (from −61.88±2.81 mV to −55.31±2.15 mV, n = 8, p<0.005, paired student t-test: Fig. 9D) and did not alter the parameters of the action potentials (Table 1). Similar results were found when ghrelin was applied in the presence of the AMPA/kainate antagonist DNQX (6,7-dinitroquinoxaline-2,3-dione, 15 µM) plus the GABAA antagonist GABAzine 3 µM, which eliminated spontaneous synaptic depolarisations and hyperpolarizations (data not shown). These experiments showed that ghrelin modified an intrinsic ionic current of GHRH neurons. This was not studied further, however, because of space-clamp limitations [12].


Ghrelin stimulation of growth hormone-releasing hormone neurons is direct in the arcuate nucleus.

Osterstock G, Escobar P, Mitutsova V, Gouty-Colomer LA, Fontanaud P, Molino F, Fehrentz JA, Carmignac D, Martinez J, Guerineau NC, Robinson IC, Mollard P, Méry PF - PLoS ONE (2010)

Ghrelin changed the excitability of GHRH neurons.A, recordings from a GHRH neuron in the absence and presence of 10 nM ghrelin, in the perforated patch-clamp configuration. B, time course of the effect of ghrelin 10 nM on the firing rate (upper graph) and on the resting potential (lower graph) of the GHRH neuron shown in A. C, summary of the effects of ghrelin 10 nM on the mean action potential intervals in GHRH neurons recorded in the perforated patch-clamp configuration. D, mean amplitude of the resting potential in GHRH neurons in the absence and presence of 10 nM ghrelin (same experiments as in C). Bars and lines are the means and the sem of the numbers of experiments indicated. Statistical difference (p<0.05, paired student-t test) with the control level is indicated.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2820089&req=5

pone-0009159-g009: Ghrelin changed the excitability of GHRH neurons.A, recordings from a GHRH neuron in the absence and presence of 10 nM ghrelin, in the perforated patch-clamp configuration. B, time course of the effect of ghrelin 10 nM on the firing rate (upper graph) and on the resting potential (lower graph) of the GHRH neuron shown in A. C, summary of the effects of ghrelin 10 nM on the mean action potential intervals in GHRH neurons recorded in the perforated patch-clamp configuration. D, mean amplitude of the resting potential in GHRH neurons in the absence and presence of 10 nM ghrelin (same experiments as in C). Bars and lines are the means and the sem of the numbers of experiments indicated. Statistical difference (p<0.05, paired student-t test) with the control level is indicated.
Mentions: The signature of the neuromodulatory effect of ghrelin on GHRH neurons was further investigated with the perforated patch-clamp technique [49], where amplitudes and kinetics of action potentials can be quantified (as shown by the individual traces of Fig. 9A). In the recording of Fig. 9A–B, the spontaneous action potentials of a GHRH neuron were collected under control conditions in the current-clamp mode (0 pA). Superfusion of the slice with ghrelin 10 nM increased the firing rate of the neuron (Fig. 9B, top panel) and this stimulation was mirrored by a decrease in the resting membrane potential (Fig. 9B, bottom panel). In similar experiments, ghrelin consistently decreased the mean action potentials intervals (from 4.31±2.0 s to 1.40±0.77 s, n = 8, p<0.05, paired student t-test: Fig. 9C), without changing the skewness of the interval distribution (data not shown), consistent with the results from extracellular recordings. Ghrelin consistently depolarized GHRH neurons (from −61.88±2.81 mV to −55.31±2.15 mV, n = 8, p<0.005, paired student t-test: Fig. 9D) and did not alter the parameters of the action potentials (Table 1). Similar results were found when ghrelin was applied in the presence of the AMPA/kainate antagonist DNQX (6,7-dinitroquinoxaline-2,3-dione, 15 µM) plus the GABAA antagonist GABAzine 3 µM, which eliminated spontaneous synaptic depolarisations and hyperpolarizations (data not shown). These experiments showed that ghrelin modified an intrinsic ionic current of GHRH neurons. This was not studied further, however, because of space-clamp limitations [12].

Bottom Line: 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.These results support the view that ghrelin related therapeutic approaches could be directed separately towards GH deficiency or feeding disorders.

View Article: PubMed Central - PubMed

Affiliation: Inserm U-661, Montpellier, France.

ABSTRACT

Background: 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.

Principal findings: 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.

Conclusion: 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.

Show MeSH
Related in: MedlinePlus