Synaptically driven endocannabinoid release requires Ca2+-assisted metabotropic glutamate receptor subtype 1 to phospholipase C β4 signaling cascade in the cerebellum
Synaptically driven endocannabinoid release requires Ca2+-assisted metabotropic glutamate receptor subtype 1 to phospholipase C β4 signaling cascade in the cerebellum
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DOI：
10.1523/jneurosci.0945-05.2005
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发表时间：
2005-07-20
影响因子：
5.3
通讯作者：
Kano, M
中科院分区：
文献类型：
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作者：
Maejima, T;Oka, S;Kano, M
内源性大麻素介导逆行信号传导并调节中枢神经系统各个区域的突触传递。去极化诱导的细胞内 Ca2+ 浓度升高会导致内源性大麻素介导的兴奋性/抑制性突触传递抑制。 G(q/11) 偶联受体（包括 I 类代谢型谷氨酸受体 (mGluR)）的激活也会导致内源性大麻素介导的突触传递抑制。然而，由生理相关突触活动引发的内源性大麻素产生的精确机制仍有待确定。为了解决这个问题，我们对小鼠小脑切片中的浦肯野细胞（PC）进行了全细胞记录，并检查了它们由攀爬纤维（CF）和平行纤维（PF）产生的兴奋性突触。我们首先通过分析 CF 到 PC 突触来表征诱导内源性大麻素释放的三种不同模式。第一种模式是强烈激活 mGluR 亚型 1 (mGluR1)-磷脂酶 C (PLC)-4 级联，而没有检测到 Ca2+ 升高。第二种模式是 Ca2+ 升高至微摩尔范围，而不激活 mGluR1-PLC beta 4 级联。第三种模式是 Ca2+ 辅助的 mGluR1-PLC beta 4 级联，需要弱 mGluR1 激活和 Ca2+ 升高至亚微摩尔范围。通过分析 PF 到 PC 突触，我们表明第三种模式对于通过兴奋性突触活动从 PC 有效释放内源性大麻素至关重要。此外，我们的生化分析表明，PC 中 mGluR1 的弱激活和轻度去极化相结合，可有效产生 2-花生四烯酰甘油 (2-AG)（内源性大麻素的候选物），而单独的任何刺激均不会产生可检测到的 2-AG。我们的结果强烈表明，在生理条件下，PC 的兴奋性突触输入激活 Ca2+ 辅助的 mGluR1-PLC beta 4 级联，从而产生 2-AG，逆行调节 PC 的突触传递。
Endocannabinoids mediate retrograde signaling and modulate synaptic transmission in various regions of the CNS. Depolarization-induced elevation of intracellular Ca2+ concentration causes endocannabinoid- mediated suppression of excitatory/ inhibitory synaptic transmission. Activation of G(q/11)-coupled receptors including group I metabotropic glutamate receptors (mGluRs) also causes endocannabinoid- mediated suppression of synaptic transmission. However, precise mechanisms of endocannabinoid production initiated by physiologically relevant synaptic activity remain to be determined. To address this problem, we made whole-cell recordings from Purkinje cells (PCs) in mouse cerebellar slices and examined their excitatory synapses arising from climbing fibers (CFs) and parallel fibers (PFs). We first characterized three distinct modes to induce endocannabinoid release by analyzing CF to PC synapses. The first mode is strong activation of mGluR subtype 1 (mGluR1)-phospholipase C (PLC)-4 cascade without detectable Ca2+ elevation. The second mode is Ca2+ elevation to a micromolar range without activation of the mGluR1-PLC beta 4 cascade. The third mode is the Ca2+ assisted mGluR1-PLC beta 4 cascade that requires weak mGluR1 activation and Ca2+ elevation to a submicromolar range. By analyzing PF to PC synapses, we show that the third mode is essential for effective endocannabinoid release from PCs by excitatory synaptic activity. Furthermore, our biochemical analysis demonstrates that combined weak mGluR1 activation and mild depolarization in PCs effectively produces 2-arachidonoylglycerol (2-AG), a candidate of endocannabinoid, whereas either stimulus alone did not produce detectable 2-AG. Our results strongly suggest that under physiological conditions, excitatory synaptic inputs to PCs activate the Ca2+-assisted mGluR1-PLC beta 4 cascade, and thereby produce 2-AG, which retrogradely modulates synaptic transmission to PCs.