Berg Allison P, Sen Neil, Bayliss Douglas A
Department of Pharmacology, University of Virginia, Charlottesville, Virginia 22908, USA.
J Neurosci. 2007 Aug 15;27(33):8845-56. doi: 10.1523/JNEUROSCI.0551-07.2007.
Large aspiny cholinergic interneurons provide the sole source of striatal acetylcholine, a neurotransmitter critical for basal ganglia function; these tonically active interneurons receive excitatory inputs from corticostriatal glutamatergic afferents that act, in part, via metabotropic glutamate receptors (mGluRs). We combined electrophysiological recordings in brain slices with molecular neuroanatomy to identify distinct ion channel targets for mGluR1/5 receptors in striatal cholinergic interneurons: transient receptor potential channel 3/7 (TrpC3/C7) and Slo2.1. In recordings obtained with methanesulfonate-based internal solutions, we found an mGluR-activated current with voltage-dependent and pharmacological properties reminiscent of TrpC3 and TrpC7; expression of these TrpC subunits in cholinergic interneurons was verified by combined immunohistochemistry and in situ hybridization, and modulation of both TrpC channels was reconstituted in HEK293 (human embryonic kidney 293) cells cotransfected with mGluR1 or mGluR5. With a chloride-based internal solution, mGluR agonists did not activate interneuron TrpC-like currents. Instead, a time-dependent, outwardly rectifying K(+) current developed after whole-cell access, and this Cl(-)-activated K(+) current was strongly inhibited by volatile anesthetics and mGluR activation. This modulation was recapitulated in cells transfected with Slo2.1, a Na(+)- and Cl(-)-activated K(+) channel, and Slo2.1 expression was confirmed histochemically in striatal cholinergic interneurons. By using gramicidin perforated-patch recordings, we established that the predominant agonist-activated current was TrpC-like when ambient intracellular chloride was preserved, although a small K(+) current contribution was observed in some cells. Together, our data indicate that mGluR1/5-mediated glutamatergic excitation of cholinergic interneurons is primarily a result of activation of TrpC3/TrpC7-like cationic channels; under conditions when intracellular NaCl is elevated, a Slo2.1 background K(+) channel may also contribute.
大型无棘胆碱能中间神经元是纹状体乙酰胆碱的唯一来源，乙酰胆碱是一种对基底神经节功能至关重要的神经递质；这些持续活跃的中间神经元接受来自皮质纹状体谷氨酸能传入神经的兴奋性输入，这些传入神经部分通过代谢型谷氨酸受体（mGluRs）发挥作用。我们将脑片电生理记录与分子神经解剖学相结合，以确定纹状体胆碱能中间神经元中mGluR1/5受体的不同离子通道靶点：瞬时受体电位通道3/7（TrpC3/C7）和Slo2.1。在用甲磺酸盐基内液进行的记录中，我们发现一种mGluR激活电流，其电压依赖性和药理学特性让人联想到TrpC3和TrpC7；通过免疫组织化学和原位杂交相结合，证实了这些TrpC亚基在胆碱能中间神经元中的表达，并在与mGluR1或mGluR5共转染的HEK293（人胚肾293）细胞中重建了对两种TrpC通道的调节。使用基于氯化物的内液时，mGluR激动剂不会激活中间神经元的TrpC样电流。相反，在全细胞接入后会出现一种时间依赖性的外向整流钾电流，这种氯离子激活的钾电流受到挥发性麻醉剂和mGluR激活的强烈抑制。在用Slo2.1（一种钠和氯激活的钾通道）转染的细胞中重现了这种调节，并且在纹状体胆碱能中间神经元中通过组织化学证实了Slo2.1的表达。通过使用短杆菌肽穿孔膜片钳记录，我们确定当细胞内氯离子保持在环境水平时，主要的激动剂激活电流是TrpC样电流，尽管在一些细胞中观察到有少量钾电流贡献。总之，我们的数据表明，mGluR1/5介导的胆碱能中间神经元的谷氨酸能兴奋主要是TrpC3/TrpC7样阳离子通道激活的结果；在细胞内氯化钠升高的情况下，Slo2.1背景钾通道也可能起作用。
