Functional role of nicotinic receptor in striato-nigral dopaminergic pathway using patch clamp method.

在本研究中，我尝试用膜片钳法研究烟碱乙酰胆碱受体在静-黑质多巴胺能系统中的功能作用。先前用水合氯醛麻醉大鼠的体内实验表明，尼古丁离子传导增加纹状体神经元接受黑质兴奋性多巴胺能输入的放电，而多潘立酮抑制尼古丁诱导的放电。因此，我使用大鼠纹状体切片进行膜片钳研究，以阐明尼古丁诱导纹状体神经元兴奋的机制。尼古丁对静息膜电位没有任何影响，但确实增加了微型突触后电位的频率。多潘立酮（多巴胺D2受体拮抗剂）和/或GDEE（非选择性谷氨酸受体拮抗剂）抑制尼古丁的这种兴奋作用。这些结果表明，尼古丁作用于神经末梢，释放多巴胺和/或谷氨酸等神经递质，从而激活纹状体神经元。另一方面，一项使用黑质切片制备的膜片钳研究显示，尼古丁诱导多巴胺能神经元的剂量依赖性去极化，并伴有放电增加。即使在无Ca^<2+> /高Mg^<2+>溶液中，也观察到尼古丁诱导的去极化现象。这些结果表明，尼古丁在突触后激活黑质多巴胺能神经元，促进纹状体多巴胺释放，并引起多巴胺能末端的突触前效应。

In this study, I tried to investigate the functional role of nicotinic acetylcholine receptor in the stiato-nigral dopaminergic system using patch clamp method. Previous in vivo experiments using rats anesthetized with chloral hydrate have revealed that nicotine applied iontophoretically increased firing of striatal neurons receiving exicitatory dopaminergic input from the substantia nigra, and nicotine-induced firing was inhibited by domperidone. Therefore, I performed the patch-clamp study using slice preparations of the rat striatum to elucidate the mechanisms underlying nicotine-induced excitation of striatal neurons. Application of nicotine to the bath did not produce any effect on the resting membrane potential, but did increase the frequency of miniature postsynaptic potentials. Domperidone (a dopamine D2 receptor antagonist) and/or GDEE (a non-selective glutamate receptor antagonist) inhibited this excitatory effect of nicotine. These results suggest that nicotine acts on the nerve terminals to release neurotransmitters such as dopamine and/or glutamate, thereby activating the striatal neurons.On the other hand, a patch-clamp study using slice preparations of the substantia nigra revealed that nicotine induced a dose-dependent depolarization of dopaminergic neurons accompanying by an increase in firing. The nicotine-induced depolarization was observed even in a Ca^<2+>-free / high Mg^<2+> solution. These results suggest that nicotine postsynaptically activates dopaminergic neurons in the substantia nigra to facilitate dopamine release in the striatum beside eliciting presynaptic effects on the dopaminergic terminals.