A gating mechanism by acetylcholine : a facilitatory effect on thalamic input to barrel cortex

大脑皮层胆碱能投射的广泛神经支配表明，乙酰胆碱(ACh)在信息处理中起着重要作用，但它的工作原理仍然是个谜。嗅皮层和海马区的实验和理论工作表明，ACh通过M受体将皮质网络的动力学转变为以传入影响为主的状态，而不是皮质内影响。最近的实验表明，尼古丁受体也可以在相同的背景下调节皮质功能。为了更好地了解ACh在皮质中的作用，我们使用小鼠的丘脑皮质脑片，研究了尼古丁对小鼠桶状皮质对丘脑刺激的丘脑皮质传递的影响。尼古丁(1-10 mM，通过浴液)可增强IV层细胞记录到的场电位(125.7±44.8%，n=8)。电压钳记录显示尼古丁降低了IV层细胞EPSCs的失败率，这表明尼古丁促进了递质的释放。光学记录表明，尼古丁不仅增强了跨各层的兴奋，而且还招募了一种晚期抑制(&gt；150ms)，这种抑制是第IV层桶状中空区所特有的。这一结果进一步证实了尼古丁在促进丘脑大脑皮层输入方面的作用。

Wide innervation of cholinergic projections throughout the cortex implies that acetylcholine (ACh) plays an essential role in information processing, but how it works is still enigmatic.Experimental as well as theoretical work in the olfactory cortex and hippocampus suggests that ACh, via the muscarinic receptors serves to shift the dynamics of the cortical networks into a state where afferent influence predominates over intracortical influence. Recent experiments suggest that nicotinic receptors could also be incorporated in the same context in regulating the cortical functions.To better understand the role of ACh in the cortex, nicotinic effects on thalamo-cortical transmission were studied in the mouse barrel cortex in response to thalamic stimulation using thalamocortical slices from mice. Nicotine, (1-10 mM, through bath) application enhanced field potentials recorded from layer IV (125.7 + 44.8 % of control, n=8).Voltage-clamp recordings demonstrated that nicotine reduced the failure rate of EPSCs from layer IV cells, which suggested nicotine enhanced the transmitter release. Optical recording indicated that nicotine not only enhanced excitation across the layers but also recruited a late inhibition (> 150 ms), which was specific to barrel hollow area in layer IV.This results further substantiate the role of nicotine in facilitating thalamic inputs in the cerebral cortex.