Roux Julien, Wanaverbecq Nicolas, Jean André, Lebrun Bruno, Trouslard Jérôme
Centre de Recherche en Neurobiologie-Neurophysiologie de Marseille, Université Paul Cézanne, Université de la Méditerranée, CNRS UMR, USC-INRA, Département de Physiologie Neurovégétative, Faculté des Sciences et Techniques St Jérôme, Marseille, France.
Neuropharmacology. 2009 Jun;56(8):1106-15. doi: 10.1016/j.neuropharm.2009.03.009. Epub 2009 Mar 28.
Numerous studies, focused on the hypothalamus, have recently implicated endocannabinoids (EC) as orexigenic factors in the central control of food intake. However, the EC system is also highly expressed in the hindbrain autonomic integrator of food intake regulation, i.e. the dorsal vagal complex (DVC). Previous studies have shown that exogenous cannabinoids, by acting on cannabinoid 1 receptor (CB1R), suppress GABAergic and glutamatergic neuronal transmission in adult rat dorsal motor nucleus of the vagus nerve (DMNV), the principal efferent compartment of the DVC. However, no endogenous release of EC has been demonstrated in DVC to date. Using patch-clamp techniques on mouse coronal brainstem slices, we confirmed that both inhibitory and excitatory neurotransmission were depressed by WIN 55,212-2, a CB1R agonist. We demonstrated that DMNV neurons exhibited a rapid and reversible depolarization-induced suppression of electrically evoked GABAergic IPSCs (eIPSCs), classically known as DSI (depolarization-induced suppression of inhibition), while spontaneous or miniature IPSCs activity remained unaltered. Further, no depolarization-induced suppression of glutamatergic eEPSCs (DSE) occurred. Our results indicate that DSI was blocked by SR141716A (Rimonabant), a selective CB1R antagonist, and was dependent on calcium elevation in DMNV neurons, suggesting a release of EC in the DVC. Moreover, the analysis of the paired-pulse ratio, of the coefficient of variation and of the failure rate of eIPSCs support the fact that EC-mediated suppression of GABAergic inhibition takes place at the presynaptic level. These results show for the first time that DMNV neurons release EC in an activity-dependent manner, which in turn differentially regulates their inhibitory and excitatory synaptic inputs.
最近，众多聚焦于下丘脑的研究表明，内源性大麻素（EC）是食物摄入中枢控制中的促食欲因子。然而，EC系统在后脑食物摄入调节自主整合器即迷走背核复合体（DVC）中也有高表达。先前的研究表明，外源性大麻素通过作用于大麻素1受体（CB1R），抑制成年大鼠迷走神经背运动核（DMNV）（DVC的主要传出部分）中的GABA能和谷氨酸能神经元传递。然而，迄今为止，尚未在DVC中证实有EC的内源性释放。通过对小鼠冠状脑干切片使用膜片钳技术，我们证实CB1R激动剂WIN 55,212-2可抑制抑制性和兴奋性神经传递。我们证明，DMNV神经元表现出快速且可逆的去极化诱导的电诱发GABA能抑制性突触后电流（eIPSCs）抑制，即经典的去极化诱导的抑制抑制（DSI），而自发性或微小IPSCs活动保持不变。此外，未发生去极化诱导的谷氨酸能兴奋性突触后电流（eEPSCs）抑制（DSE）。我们的结果表明，DSI被选择性CB1R拮抗剂SR141716A（利莫那班）阻断，并且依赖于DMNV神经元中的钙升高，提示DVC中有EC释放。此外，对eIPSCs的双脉冲比率、变异系数和失败率的分析支持了EC介导的GABA能抑制在突触前水平发生的事实。这些结果首次表明，DMNV神经元以活动依赖的方式释放EC，进而差异性地调节其抑制性和兴奋性突触输入。
