Egorov Alexei V, Angelova Plamena R, Heinemann Uwe, Müller Wolfgang
AG Molekulare Zellphysiologie, Neurowissenschaftliches Forschungszentrum der Charitè, Humboldt Universität zu Berlin, Schumannstrasse 20/21, D-10117 Berlin, Germany.
Eur J Neurosci. 2003 Dec;18(12):3343-51. doi: 10.1111/j.1460-9568.2003.03050.x.
Cholinergic activation of entorhinal cortex (EC) layer V neurons plays a crucial role in the medial temporal lobe memory system and in the pathophysiology of temporal lobe epilepsy. Here, we demonstrate that muscarinic activation by focal application of carbachol depolarizes EC layer V neurons and induces epileptiform activity in rat brain slices. These seizure-like bursts are associated with a somatic [Ca2+]i increase of 293 +/- 82 nm and are blocked by the glutamate receptor antagonists CNQX and APV. Muscarinic activation did not directly evoke a [Ca2+]i increase, but subthreshold and suprathreshold depolarization did. Functional axon mapping revealed local axon branching as well as axon collaterals ascending to layers II and III. During blockade of ionotropic glutamatergic AMPA and NMDA receptors, carbachol depolarized layer V neurons by +7.5 +/- 3.4 mV. This direct muscarinic depolarization was associated with a conductance increase of 35 +/- 10.3% (+4.3 +/- 1.25 nS). Intracellular buffering of [Ca2+]i changes did not block this depolarization, but prolonged action potential duration and reduced adaptation of action potential firing. The muscarinic depolarization was neither blocked by combining intracellular Ca2+-buffering (EGTA or BAPTA) with non-specific Ca2+-channel inhibition by Ni+ (1 mm), nor by Ba2+ (1 mm) nor during inhibition of the h-current by 2 mm Cs+. In whole-cell patch-clamp recording, reversal of the muscarinic current occurred at about -45 mV and -5 mV with complete substitution of intrapipette K+ with Cs+. Thus, muscarinic depolarization of EC layer V neurons appears to be primarily mediated by Ca2+-independent activation of non-specific cation channels that conduct K+ about three times as well as Na+.
内嗅皮层（EC）第V层神经元的胆碱能激活在颞叶内侧记忆系统以及颞叶癫痫的病理生理学中起着至关重要的作用。在此，我们证明，通过局部应用卡巴胆碱进行毒蕈碱激活可使EC第V层神经元去极化，并在大鼠脑片中诱导癫痫样活动。这些癫痫样爆发与体细胞内[Ca2+]i增加293±82 nM相关，并被谷氨酸受体拮抗剂CNQX和APV阻断。毒蕈碱激活并未直接引起[Ca2+]i增加，但阈下和阈上 depolarization 却能引起。功能性轴突映射显示了局部轴突分支以及向上延伸至第II层和第III层的轴突侧支。在离子型谷氨酸能AMPA和NMDA受体被阻断期间，卡巴胆碱使第V层神经元去极化了+7.5±3.4 mV。这种直接的毒蕈碱去极化与电导增加35±10.3%（+4.3±1.25 nS）相关。细胞内对[Ca2+]i变化的缓冲并未阻断这种去极化，但延长了动作电位持续时间并减少了动作电位发放的适应性。毒蕈碱去极化既未被细胞内Ca2+缓冲（EGTA或BAPTA）与Ni+（1 mM）对非特异性Ca2+通道的抑制相结合所阻断，也未被Ba2+（1 mM）阻断，在2 mM Cs+抑制h电流期间也未被阻断。在全细胞膜片钳记录中，当吸管内的K+被Cs+完全替代时，毒蕈碱电流的反转发生在约-45 mV和-5 mV。因此，EC第V层神经元的毒蕈碱去极化似乎主要由非特异性阳离子通道的Ca2+非依赖性激活介导，这些通道对K+的传导能力约为Na+的三倍。
