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

International audienceGhrelin 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

The impact of C-Tactile Low threshold mechanoreceptors on affective touch and social interactions in mice.

Affective touch is necessary for proper neurodevelopment and sociability. However, it is still unclear how the neurons innervating the skin detect affective and social behaviours. To clarify this matter, we targeted a specific population of somatosensory neurons in mice, named C-low threshold mechanoreceptors (C-LTMRs), that appears particularly well suited physiologically and anatomically to perceive affective and social touch but whose contribution to these processes has not yet been resolved. Our observations revealed that C-LTMRs functional deficiency from birth induced social isolation and reduced tactile interactions in adults. Conversely, transient increase in C-LTMRs excitability in adults using chemogenetics was rewarding, temporally promoted touch seeking behaviours and thus had pro-social effects on group dynamics. This work provides the first empirical evidence that specific peripheral inputs alone can drive complex social behaviour, demonstrating the existence of a specialised neuronal circuit originating from the skin wired to promote interaction with other individuals

A comparative analysis of the time course of cardiac Ca 2 ÷ current response to rapid applications of fl-adrenergic and dihydropyridine agonists

International audienceA fast perfusion system was used to analyze the kinetics of the response of L-type calcium current (Ica) to rapid exposures to fl-adrenergic or dihydropyridine agonists in whole-cell patch-clamped frog ventricular myocytes. The perfusion system was based on the lateral motion of an array of plastic capillary tubes from which solutions flowed at a velocity of-5 cm/s. Movement from one capillary to the adjacent one occurred in 1 nM. The response of Ica to Iso always started after a delay of several seconds. The delay duration decreased as [Iso] increased, and was typically-3 s at 10 ~tM Iso. The rising phase of Ica increase was monophasic and independent of [Iso] > 100 nM. For short applications of Iso (8.8 s), half maximal and maximal stimulation of Ica occurred-20 s and-40 s after the beginning of Iso application, respectively. When Iso was applied during a depolarizing pulse (with Ba as the charge carrier), IBa never increased during that pulse. The kinetics of the ICa response to Iso were not affected by varying the voltage clamp protocols or the ionic composition of intracellular and extracellular solutions. In comparison with the effects of Iso, the stimulatory effect of the dihydropyridine agonist (-)Bay K 8644 on ICa was-15 times faster: delay, half-time to maximal and time to maximal responses were 15 times shorter with (-)Bay K 8644 than with Iso. It is concluded that frog ventricular myocytes respond slowly to a quick application of fl-adrenergic agonists

A comparative study of the effects of three guanylyl cyclase inhibitors on the L-type Ca 2+ and muscarinic K + currents in frog cardiac myocytes

International audienceTo investigate the participation of guanylyl cyclase in the muscarinic regulation of the cardiac L-type calcium current (I Ca), we examined the eects of three guanylyl cyclase inhibitors, 1H-[1,2,4]oxidiazolo[4,3-a]quinoxaline-1-one (ODQ), 6-anilino-5,8-quinolinedione (LY 83583), and methylene blue (MBlue), on the b-adrenoceptor; muscarinic receptor and nitric oxide (NO) regulation of I Ca and on the muscarinic activated potassium current I K,ACh , in frog atrial and ventricular myocytes. 2 ODQ (10 mM) and LY 83583 (30 mM) antagonized the inhibitory eect of an NO-donor (S-nitroso-Nacetylpenicillamine, SNAP, 1 mM) on the isoprenaline (Iso)-stimulated I Ca which was consistent with their inhibitory action on guanylyl cyclase. However, MBlue (30 mM) had no eect under similar conditions. 3 In the absence of SNAP, LY 83583 (30 mM) potentiated the stimulations of I Ca by either Iso (20 nM), forskolin (0.2 mM) or intracellular cyclic AMP (5 ± 10 mM). ODQ (10 mM) had no eect under these conditions, while MBlue (30 mM) inhibited the Iso-stimulated I Ca. 4 LY 83583 and MBlue, but not ODQ, reduced the inhibitory eect of up to 10 mM acetylcholine (ACh) on I Ca. 5 MBlue, but not LY 83583 and ODQ, antagonized the activation of I K,ACh by ACh in the presence of intracellular GTP, and this inhibition was weakened when I K,ACh was activated by intracellular GTPgS. 6 The potentiating eect of LY 83583 on Iso-stimulated I Ca was absent in the presence of either DLdithiothreitol (DTT, 100 mM) or a combination of superoxide dismutase (150 u ml 71) and catalase (100 u ml 71). 7 All together, our data demonstrate that, among the three compounds tested, only ODQ acts in a manner which is consistent with its inhibitory action on the NO-sensitive guanylyl cyclase. The two other compounds produced severe side eects which may involve superoxide anion generation in the case of LY 83583 and alteration of b-adrenoceptor and muscarinic receptor-coupling mechanisms in the case of MBlue

Peroxynitrite is a positive inotropic agent in atrial and ventricular fibres of the frog heart

International audienceWe report opposite inotropic effects of NO donors in frog cardiac fibres. The negative effect, elicited by either 3morpholinosydnonimine(SIN_1) or SnitrosoNacetylpenicillamine (SNAP), involved cyclic GMP (cGMP) production. However, SIN_1, unlike SNAP, could elicit a positive effect, in a superoxide dismutase (SOD)sensitive manner. SIN_1, unlike SNAP, can release both NO and superoxide anion, the precursors of peroxynitrite (OONO¦). Therole of these messengers was examined. Catalase did not reduce the positive inotropic effect of SIN_1. Thus, a conversion of superoxide anion into hydrogen peroxide was not involved in this effect. In addition, catalase did not modify the negative effects of SIN_1 plus SOD, or SNAP plus SOD. LY 83583, a superoxide anion generator, elicited a positive inotropic effect, like SIN_1. The effect of LY 83583 was additive to the negative effects of SIN_1 or SNAP, and to the positive effect of SIN_1. Thus, superoxide anion generation, per se, did not account for the positive effect of SIN_1. Authentic peroxynitrite (OONO¦), but not mockOONO (negative control plus decomposed OONO¦), exerted a dramatic positive inotropic effect in cardiac fibres. The effect of OONO¦ was larger in atrial fibres, as compared with ventricular fibres. The positive effect of OONO¦ was not additive with that of SIN_1, suggesting a common mechanism of action. In contrast, the effects of either OONO¦ or SIN_1 were additive with the negative inotropic effect of SNAP. Furthermore, the effect of OONO¦, like that of SIN_1, was not antagonized by 1H[1,2,4]xidiazolo[4,3a] quinoxaline1one (ODQ; 10 ìÒ), the guanylyl cyclase inhibitor. The positive inotropic effects of SIN_1 nd OONO¦ were not modified by hydroxyl radical scavengers, such as dimethylthiourea (DMTU; 10 mÒ). The positive inotropic effect of SIN_1 (100 ìÒ) was abolished in sodium free solutions, a treatment that eliminates the activity of the sodium—calcium exchanger. In contrast, the effect of SIN_1 was unchanged by a potassium channel inhibitor (tetraethylammonium, 20 mÒ), or a sodium—potassium pump inhibitor (ouabain 10 ìÒ). We conclude that OONO¦ is a positive inotropic agent in frog cardiac fibres. The generation of OONO¦ accounts for the positive inotropic effect of SIN_1. OONO¦ itself was responsible for the positive inotropic effect, and appeared to modulate the activity of the sodium—calcium exchanger

Post-translational modifications of cardiac tubulin during chronic heart failure in the rat

International audienceCytoskeletal reorganization has been shown to participate in cellular remodeling and in the alterations of mechanical function of isolated cardiomyocytes during pressure overload hypertrophy. Post-translational modifications of tubulin towards stabilization of microtubules have also been described in animal models of compensatory hypertrophy, but the status of the microtubules network in end stage heart failure is not clearly established. Using a rat model of congestive heart failure (CHF) induced by aortic banding, we studied the expression of αand β-tubulin, as well as their post-translational modification and distribution in the soluble and polymerized fraction by immunoblotting. We found an accumulation of αand β-tubulin protein content specifically in the soluble fraction with no change in the polymerized fraction. Amongst the several variants of α-tubulin examined, only detyrosinated Glu-tubulin and deglutamylated ∆ 2-tubulin levels were selectively increased during heart failure. Glu-tubulin accumulated in the polymerized fraction while ∆ 2-tubulin levels were increased in the soluble fraction in CHF hearts. These results show that a profound remodeling of the microtubule network occurs in heart failure. This remodeling suggests an increase in the stability of the microtubule network which is discussed in terms of possible functional consequences

NO-donors potentiate the β-adrenergic stimulation of the L-type Ca 2+ current and the muscarinic activation of the inward rectifying K + current in rat cardiac myocytes

International audienceThe effects of nitric oxide (NO) donors on the L-type Ca(2+) current (I(Ca,L)) and the muscarinic activated K(+) current (I(K,ACh)) were studied in isolated rat cardiac myocytes. The nitrosothiol S-nitroso-N-acetyl-D,L-penicillamine (SNAP, 1 pM-1 microM) strongly potentiated the stimulation of the I(Ca,L) elicited by subthreshold concentrations of isoprenaline (Iso, 0.1-0.5 nM) in ventricular myocytes. The effect of SNAP was mimicked by 2-(N,N-diethylamino)-diazenolate-2-oxide (DEANO, 1 pM-1 nM), a NONOate that spontaneously releases NO in a pH-controlled manner, and was blunted by 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (100 microM), a NO trap. 1H-[1,2,4]Oxadiazolo[4,3-a]quinoxaline-1-one (10 microM), a guanylyl cyclase inhibitor, did not alter the effect of SNAP. SNAP (1 pM-1 microM) did not modify the effect of L858051 (0.1-0.3 microM), a forskolin analogue that activates adenylyl cyclase, on I(Ca,L) and did not enhance the basal I(Ca,L) in the presence of rolipram (1 microM), a phosphodiesterase type 4 inhibitor. Superfusion with Rp-CPT-cAMPS (500 microM), or internal dialysis with cAMP-dependent protein kinase (cA-PK) inhibitory peptide (PKI; 20 microM), inhibitors of the cA-PK, blunted the effect of SNAP (1 nM and 1 microM) on the Iso-stimulated (1-100 pM) I(Ca,L). SNAP (1 nM and 1 microM) potentiated the threshold stimulation of I(Ca,L) elicited by internal GTP-gammaS (10 microM), a non-hydrolysable analogue of GTP. SNAP (1 pM-1 microM) and DEANO (1 microM) potentiated the stimulation of I(K,ACh) elicited by low concentrations of ACh (1-2 nM) in rat atrial myocytes. The threshold stimulation of I(K,ACh) elicited by internal 5'-guanylylimidodiphosphate (10 microM) was also potentiated by NO donors. SNAP (1 microM) did not modify I(K,ACh) reconstituted in human embryonic kidney 293 cells, in the absence or in the presence of ACh (1 or 10 nM). Taken together, these data suggest that NO is a cGMP-independent modulator of G-protein-coupled muscarinic and beta-adrenergic receptor actions on cardiac ion channels. Although this action of NO seemed to occur at the level of G proteins, it appeared to require a component distinct from receptors, G proteins or their effectors

Regulation of myocardial calcium channels by cyclic AMP metabolism

International audienceHormonal regulation of cardiac inotropism is often correlated with modification of the L-type Ca-channel current. Among several regulatory pathways that control Ca-channel activity, the best described one is the cAMP cascade. Cyclic AMP-dependent phosphorylation of the Ca-channel results in an increase of the mean open probability of the individual Ca-channels and, thus, of the macroscopic Ca current. Modulation of cAMP concentration can take place at the level of adenylyl cyclases or cAMP phosphodiesterases. Of major interest is the fact that the activity of two different forms of phosphodiesterases is controlled by the level of intracellular cGMP. Thus, cAMP metabolism is intimately associated with cGMP metabolism, and both determine the degree of cAMP-dependent phosphorylation of cardiac Ca-channels. This brief discussion will focus on these two levels of control and their relative importance in the cAMP-dependent regulation of myocardial Ca-channels

The impact of C-tactile low-threshold mechanoreceptors on affective touch and social interactions in mice

International audienceAffective touch is necessary for proper neurodevelopment and sociability. However, it remains unclear how the neurons innervating the skin detect affective and social behaviors. The C low-threshold mechanoreceptors (C-LTMRs), a specific population of somatosensory neurons in mice, appear particularly well suited, physiologically and anatomically, to perceive affective and social touch. However, their contribution to sociability has not been resolved yet. Our observations revealed that C-LTMR functional deficiency induced social isolation and reduced tactile interactions in adulthood. Conversely, transient increase in C-LTMR excitability in adults, using chemogenetics, was rewarding, promoted touch-seeking behaviors, and had prosocial influences on group dynamics. This work provides the first empirical evidence that specific peripheral inputs alone can drive complex social behaviors. It demonstrates the existence of a specialized neuronal circuit, originating in the skin, wired to promote interactions with other individuals.Le toucher affectif est nécessaire au bon développement neurologique et à la sociabilité. Cependant, la manière dont les neurones innervant la peau détectent les comportements affectifs et sociaux n'est toujours pas claire. Les mécanorécepteurs à bas seuil C (C-LTMRs), une population spécifique de neurones somatosensoriels chez la souris, semblent particulièrement bien adaptés, physiologiquement et anatomiquement, pour percevoir le toucher affectif et social. Cependant, leur contribution à la sociabilité n'a pas encore été résolue. Nos observations ont révélé que la déficience fonctionnelle des C-LTMR induit un isolement social et une réduction des interactions tactiles à l'âge adulte. À l'inverse, une augmentation transitoire de l'excitabilité du C-LTMR chez les adultes, en utilisant la chimiogénétique, était gratifiante, favorisait les comportements de recherche du toucher et avait des influences prosociales sur la dynamique de groupe. Ce travail fournit la première preuve empirique que des entrées périphériques spécifiques peuvent à elles seules conduire à des comportements sociaux complexes. Ils démontrent l'existence d'un circuit neuronal spécialisé, provenant de la peau, conçu pour favoriser les interactions avec d'autres individus

Discussion de l'article 3 du projet de décret du comité d’agriculture et de commerce sur les droits à imposer sur les denrées coloniales, lors de la séance du 18 mars 1791

Moreau de Saint-Méry Louis-Elie, Roussillou Pierre-Augustin, Begouën Jacques-François. Discussion de l'article 3 du projet de décret du comité d’agriculture et de commerce sur les droits à imposer sur les denrées coloniales, lors de la séance du 18 mars 1791. In: Archives Parlementaires de 1787 à 1860 - Première série (1787-1799) Tome XXIV - Du 10 mars 1791 au 12 avril 1791. Paris : Librairie Administrative P. Dupont, 1886. p. 187