Cervetto Chiara, Frattaroli Daniela, Venturini Arianna, Passalacqua Mario, Nobile Mario, Alloisio Susanna, Tacchetti Carlo, Maura Guido, Agnati Luigi Francesco, Marcoli Manuela
Department of Pharmacy, Section of Pharmacology and Toxicology, University of Genova, Viale Cembrano 4, 16148 Genova, Italy; Centre of Excellence for Biomedical Research CEBR, University of Genova, Viale Benedetto XV, 5, 16132 Genova, Italy.
Department of Pharmacy, Section of Pharmacology and Toxicology, University of Genova, Viale Cembrano 4, 16148 Genova, Italy.
Neuropharmacology. 2015 Dec;99:396-407. doi: 10.1016/j.neuropharm.2015.08.011. Epub 2015 Aug 7.
The Bergmann glia is equipped with Ca2+-permeable AMPA receptors for glutamate, indispensable for structural and functional relations between the Bergmann glia and parallel/climbing fibers-Purkinje cell synapses. To better understand roles for the Bergmann AMPA receptors, herein we investigate on gliotransmitter release and Ca2+ signals in isolated Bergmann glia processes obtained from adult rat cerebellum. We found that: 1) the rat cerebellar purified astrocyte processes (gliosomes) expressed astrocytic and Bergmann markers and exhibited negligible contamination by nerve terminals, microglia, or oligodendrocytes; 2) activation of Ca2+-permeable AMPA receptors caused Ca2+ signals in the processes, and the release of glutamate from the processes; 3) effectiveness of rose bengal, trypan blue or bafilomycin A1, indicated that activation of the AMPA receptors evoked vesicular glutamate release. Cerebellar purified nerve terminals appeared devoid of glutamate-releasing Ca2+-permeable AMPA receptors, indicating that neuronal contamination may not be the source of the signals detected. Ultrastructural analysis indicated the presence of vesicles in the cytoplasm of the processes; confocal imaging confirmed the presence of vesicular glutamate transporters in Bergmann glia processes. We conclude that: a vesicular mechanism for release of the gliotransmitter glutamate is present in mature Bergmann processes; entry of Ca2+ through the AMPA receptors located on Bergmann processes is coupled with vesicular glutamate release. The findings would add a new role for a well-known Bergmann target for glutamate (the Ca2+-permeable AMPA receptors) and a new actor (the gliotransmitter glutamate) at the cerebellar excitatory synapses onto Purkinje cells.
伯格曼神经胶质细胞配备有对谷氨酸具有钙离子通透性的AMPA受体，这对于伯格曼神经胶质细胞与平行/攀缘纤维-浦肯野细胞突触之间的结构和功能关系不可或缺。为了更好地理解伯格曼AMPA受体的作用，我们在此研究了从成年大鼠小脑中分离出的伯格曼神经胶质细胞突起中的神经胶质递质释放和钙离子信号。我们发现：1）大鼠小脑纯化的星形胶质细胞突起（胶质小体）表达星形胶质细胞和伯格曼标记物，并且神经末梢、小胶质细胞或少突胶质细胞的污染可忽略不计；2）钙离子通透性AMPA受体的激活导致突起中的钙离子信号以及突起中谷氨酸的释放；3）孟加拉玫瑰红、台盼蓝或巴弗洛霉素A1的作用表明，AMPA受体的激活引发了囊泡性谷氨酸释放。小脑纯化的神经末梢似乎没有释放谷氨酸的钙离子通透性AMPA受体，这表明神经元污染可能不是检测到的信号来源。超微结构分析表明突起的细胞质中存在囊泡；共聚焦成像证实了伯格曼神经胶质细胞突起中存在囊泡性谷氨酸转运体。我们得出结论：成熟的伯格曼突起中存在释放神经胶质递质谷氨酸的囊泡机制；钙离子通过位于伯格曼突起上的AMPA受体进入与囊泡性谷氨酸释放相关联。这些发现将为谷氨酸的一个著名靶点（钙离子通透性AMPA受体）以及小脑浦肯野细胞兴奋性突触处的一个新参与者（神经胶质递质谷氨酸）增添新的作用。
