Frazier C J, Buhler A V, Weiner J L, Dunwiddie T V
Neuroscience Program, University of Colorado Health Sciences Center, Denver, Colorado 80262, USA.
J Neurosci. 1998 Oct 15;18(20):8228-35. doi: 10.1523/JNEUROSCI.18-20-08228.1998.
Exogenous application of acetylcholine elicits inward currents in hippocampal interneurons that are mediated via alpha-bungarotoxin-sensitive nicotinic acetylcholine receptors, but synaptic responses mediated via such receptors have never been reported in mammalian brain. In the present study, EPSCs were evoked in hippocampal interneurons in rat brain slices by electrical stimulation and were recorded by using whole-cell voltage-clamp techniques. Nicotinic EPSCs were isolated pharmacologically, using antagonists to block other known types of ligand-gated ion channels, and then were tested with either alpha-bungarotoxin or methyllycaconitine, which are selective antagonists for nicotinic acetylcholine receptors that contain the alpha7 receptor subunit. Each antagonist proved highly effective at reducing the remaining synaptic current. Evoked alpha7-mediated nicotinic EPSCs also were desensitized by superfusion with 1 microM nicotine, had extrapolated reversal potentials near 0 mV, and showed strong inward rectification at positive potentials. In several interneurons, methyllycaconitine-sensitive spontaneous EPSCs also were observed that exhibited a biphasic decay rate very similar to that of the alpha7-mediated evoked response. These studies provide the first demonstration of a functional cholinergic synapse in the mammalian brain, in which the primary postsynaptic receptors are alpha-bungarotoxin-sensitive nicotinic acetylcholine receptors.
外源性应用乙酰胆碱可在海马中间神经元中引发内向电流，该电流由α-银环蛇毒素敏感的烟碱型乙酰胆碱受体介导，但在哺乳动物大脑中，尚未有通过此类受体介导的突触反应的报道。在本研究中，通过电刺激在大鼠脑片的海马中间神经元中诱发兴奋性突触后电流（EPSCs），并使用全细胞电压钳技术进行记录。通过使用拮抗剂阻断其他已知类型的配体门控离子通道，从药理学角度分离出烟碱型EPSCs，然后用α-银环蛇毒素或甲基lycaconitine进行测试，这两种物质是含有α7受体亚基的烟碱型乙酰胆碱受体的选择性拮抗剂。每种拮抗剂在降低剩余突触电流方面都被证明非常有效。诱发的α7介导的烟碱型EPSCs也会因用1μM尼古丁灌流而脱敏，其外推反转电位接近0 mV，并且在正电位时表现出强烈的内向整流。在几个中间神经元中，还观察到了甲基lycaconitine敏感的自发性EPSCs，其表现出与α7介导的诱发反应非常相似的双相衰减率。这些研究首次证明了哺乳动物大脑中存在功能性胆碱能突触，其中主要的突触后受体是α-银环蛇毒素敏感的烟碱型乙酰胆碱受体。
