Department of Anatomy, Histology and Embryology, Faculty of Medicine, Medical and Health Science Center, University of Debrecen, Debrecen, Hungary.
Glia. 2012 Sep;60(9):1316-29. doi: 10.1002/glia.22351. Epub 2012 May 9.
It is generally accepted that the endocannabinoid system plays important roles in spinal pain processing. Although it is documented that cannabinoid-1 receptors are strongly expressed in the superficial spinal dorsal horn, the cellular distribution of enzymes that can synthesize endocannabinoid ligands is less well studied. Thus, using immunocytochemical methods at the light and electron microscopic levels, we investigated the distribution of diacylglycerol lipase-alpha (DGL-α) and N-acylphosphatidylethanolamine-specific phospholipase D (NAPE-PLD), enzymes synthesizing the endocannabinoid ligands, 2-arachidonoylglycerol (2-AG) and anandamide, respectively. Positive labeling was revealed only occasionally in axon terminals, but dendrites displayed strong immunoreactivity for both enzymes. However, the dendritic localization of DGL-α and NAPE-PLD showed a remarkably different distribution. DGL-α immunolabeling in dentrites was always revealed at membrane compartments in close vicinity to synapses. In contrast to this, dendritic NAPE-PLD labeling was never observed in association with synaptic contacts. In addition to dendrites, a substantial proportion of astrocytic (immunoreactive for GFAP) and microglial (immunoreactive for CD11b) profiles were also immunolabeled for both DGL-α and NAPE-PLD. Glial processes immunostained for DGL-α were frequently found near to synapses in which the postsynaptic dendrite was immunoreactive for DGL-α, whereas NAPE-PLD immunoreactivity on glial profiles at the vicinity of synapses was only occasionally observed. Our results suggest that both neurons and glial cells can synthesize and release 2-AG and anandamide in the superficial spinal dorsal horn. The 2-AG can primarily be released by postsynaptic dendrites and glial processes adjacent to synapses, whereas anandamide can predominantly be released from nonsynaptic dendritic and glial compartments.
人们普遍认为内源性大麻素系统在脊髓疼痛处理中发挥着重要作用。尽管有文献记载大麻素-1 受体在脊髓背角浅层强烈表达，但能合成内源性大麻素配体的酶的细胞分布研究得还不够充分。因此，我们使用免疫细胞化学方法在光镜和电镜水平上，研究了二酰基甘油脂肪酶-α（DGL-α）和 N-酰基磷酸乙醇胺特异性磷酯酶 D（NAPE-PLD）的分布，这两种酶分别合成内源性大麻素配体 2-花生四烯酸甘油（2-AG）和大麻素。只有偶尔在轴突末梢中发现阳性标记，而树突显示出两种酶的强烈免疫反应性。然而，DGL-α 和 NAPE-PLD 的树突定位显示出明显不同的分布。DGL-α 在树突中的免疫标记总是在靠近突触的膜隔室中显示。与此相反，树突状 NAPE-PLD 标记从未在与突触接触相关的情况下观察到。除了树突，相当一部分星形胶质细胞（对 GFAP 免疫反应阳性）和小胶质细胞（对 CD11b 免疫反应阳性）也对 DGL-α 和 NAPE-PLD 进行免疫标记。DGL-α 免疫染色的神经胶质突起经常在突触附近被发现，其中突触后树突对 DGL-α 呈免疫反应性，而在突触附近的神经胶质突起上的 NAPE-PLD 免疫反应性只是偶尔观察到。我们的结果表明，神经元和神经胶质细胞都可以在脊髓背角浅层合成和释放 2-AG 和大麻素。2-AG 主要可以由突触后树突和与突触相邻的神经胶质突起释放，而大麻素可以主要从非突触的树突和神经胶质隔室中释放。
