Haj-Dahmane S, Andrade R
Department of Psychiatry and Behavioral Neurosciences, Wayne State University School of Medicine, Detroit, Michigan 48201, USA.
J Neurophysiol. 1998 Sep;80(3):1197-210. doi: 10.1152/jn.1998.80.3.1197.
The mammalian prefrontal cortex receives a dense cholinergic innervation from subcortical regions. We previously have shown that cholinergic stimulation of layer V pyramidal neurons of the rat prefrontal cortex results in a depolarization and the appearance of a slow afterdepolarization (sADP). In the current report we examine the mechanism underlying the sADP with the use of sharp microelectrode and whole cell recording techniques in in vitro brain slices. The ability of acetylcholine (ACh) and carbachol to induce the appearance of an sADP in pyramidal cells of layer V of prefrontal cortex is antagonized in a surmountable manner by atropine and is mimicked by application of muscarine or oxotremorine. These results indicate that ACh acts on muscarinic receptors to induce the sADP. In many cell types afterpotentials are triggered by calcium influx into the cell. Therefore we examined the possibility that calcium influx might be the trigger for the generation of the sADP. Consistent with this possibility, buffering intracellular calcium reduced or abolished the sADP but had little effect on the direct muscarinic receptor-induced depolarization also seen in these cells. These results, coupled to the previous observation that calcium channel blockers inhibit the sADP, indicated that the sADP results from a rise in intracellular calcium secondary to calcium influx into the cell. The ionic basis for the current underlying the sADP (IsADP) was examined with the use of ion substitution experiments. The amplitude of IsADP was found to be reduced in a graded fashion by replacement of extracellular sodium with N-methyl-D-glucamine (NMDG). In contrast no clear evidence for the involvement of potassium or chloride channels in the generation of the sADP or IsADP could be found. This result indicated that IsADP is carried by sodium ions flowing into the cell. However, the dependence of IsADP on extracellular sodium was less pronounced than expected for a pure sodium current. We interpret these results to indicate that the sADP is most likely mediated by nonselective cation channels. Examination of the current underlying the sADP at different voltages indicated that this current was also voltage dependent, turning off with hyperpolarization. We conclude that the sADP elicited by muscarinic receptor activation in rat cortex is mediated predominantly by a calcium- and voltage-sensitive nonselective cation current. This current could represent an important mechanism through which ACh can regulate neuronal excitability in prefrontal cortex.
哺乳动物的前额叶皮质接受来自皮质下区域的密集胆碱能神经支配。我们之前已经表明，对大鼠前额叶皮质第V层锥体神经元进行胆碱能刺激会导致去极化，并出现缓慢的后去极化（sADP）。在本报告中，我们使用锋利微电极和全细胞记录技术，在体外脑片中研究了sADP的潜在机制。乙酰胆碱（ACh）和卡巴胆碱在前额叶皮质第V层锥体细胞中诱导sADP出现的能力，可被阿托品以可克服的方式拮抗，而毒蕈碱或氧化震颤素的应用则可模拟这种作用。这些结果表明，ACh作用于毒蕈碱受体以诱导sADP。在许多细胞类型中，后电位是由钙离子流入细胞触发的。因此，我们研究了钙离子流入可能是sADP产生触发因素的可能性。与这种可能性一致的是，缓冲细胞内钙离子可减少或消除sADP，但对这些细胞中也可见的直接毒蕈碱受体诱导的去极化影响很小。这些结果，再加上之前观察到钙通道阻滞剂抑制sADP，表明sADP是由钙离子流入细胞后细胞内钙离子升高导致的。我们使用离子替代实验研究了sADP（IsADP）电流的离子基础。发现用N - 甲基 - D - 葡糖胺（NMDG）替代细胞外钠会以分级方式降低IsADP的幅度。相比之下，没有发现明确证据表明钾离子或氯离子通道参与sADP或IsADP的产生。这一结果表明，IsADP是由流入细胞的钠离子携带的。然而，IsADP对细胞外钠的依赖性不如纯钠电流预期的那么明显。我们将这些结果解释为表明sADP最有可能由非选择性阳离子通道介导。在不同电压下对sADP电流的研究表明，该电流也是电压依赖性的，随着超极化而关闭。我们得出结论，大鼠皮质中由毒蕈碱受体激活引发的sADP主要由钙和电压敏感的非选择性阳离子电流介导。这种电流可能代表了ACh调节前额叶皮质神经元兴奋性的一种重要机制。
