鳌虾口胃神经节神经元簇放电的动态离子流机制

Dynamic ion mechanism of bursting in the stomatogastric ganglion neurons of crayfish

为研究神经元自身的电活动特性(簇放电节律模式到峰放电节律模式的转迁,以及簇放电节律的离子流机制),本实验选取鳌虾口胃神经节(stomatogastric ganglion,STG)中功能上孤立的单个神经元,记录其在胞外钙离子浓度([Ca2+]o)变化和钙依赖钾离子通道阻断剂tetraethylammonium(TEA)作用下细胞内电活动的变化。当[Ca2+]o降低时,神经元膜电位水平升高,电活动模式表现为从低电位水平的静息(极化静息),到簇放电,再到峰放电,最后到高电位水平的静息(去极化静息)的转迁历程;当细胞外TEA浓度([TEA]o)增加时,神经元膜电位水平也升高,电活动模式表现为从极化静息,到簇放电,再到峰放电的转迁历程,且变化过程是可逆的。上述结果表明,不同生理状态下神经元电活动模式是复杂多样的,这种复杂多样的电活动模式随生理调节参数变化可以表现出规律性的转迁。另外,钙离子内流通过影响[Ca2+]i水平进而调节钙依赖钾电导,决定簇放电的起始与终止,这可能是簇放电产生的动态离子流机制。

The purpose of this study is to identify the electrical activity of neuron,the existence of the transition from bursting pattern to spiking pattern and the ion mechanism of the bursting pattern.The intracellular electrical activity patterns of single neurons in the stomatogastric ganglion（STG） of crayfish were recorded when the extracellular calcium concentration（[Ca2＋]o） or calcium-dependent potassium channel blocker tetraethylammonium concentration（[TEA]o） were changed,using intracellular recording method.These single neurons were also functionally isolated from the ganglion by application of atropine and picrotoxin which could block the inhibitory acetylcholine synapses and glutamatergic synapses respectively.When [Ca2＋]o was decreased by increasing EGTA,the membrane potential of the neuron was increased,and the electrical activity patterns were changed from the resting state with lower potential value（resting state of polarization） to the bursting pattern firstly,and then to the spiking pattern,at last to the resting state with higher potential value（resting state of depolarization）.When [TEA]o was increased,the membrane potential of the neuron was increased,and the electrical activity pattern was changed from the resting state with lower potential value（resting state of polarization） to the bursting pattern firstly,and then to the spiking pattern.The duration of the burst of the bursting pattern was increased.When [Ca2＋]o was increased or [TEA]o was decreased,an inverse procedure of the electrical activity pattern was exhibited.On one hand,the results indicate that a single neuron can generate various electrical activity patterns corresponding to different physiological conditions,and the regularity of the transitions between different electrical activity patterns.On the other hand,the results identify that the initiation and termination of the burst in bursting pattern are determined by calcium-activated potassium conductance,which is adjusted by intracellular calcium concentration influenced by inward calcium current.It may be the ionic mechanism of generation of the bursting pattern in a single neuron.