The modulation of 4-aminopyridine sensitive potassium channel to bifurcation scenario of the spontaneous neural firing rhythms / 生理学报

Neuronal firing is crucial to the information processing in the nervous system. In order to make a further study of bifurcation scenarios, experiments were performed on neural pacemakers formed at the injured site of rat sciatic nerve subjected to chronic ligatures. We chose the conductance of voltage-dependent potassium ion channels as conditional parameter, and the extracellular calcium concentration as bifurcation parameter, to give a demonstration of how the firing pattern of neural pacemaker responses to dual parameter adjusting. Among 28 preparations observed, 21 were insensitive to dual parameter adjusting since no change of bifurcation scenario structure was detected. On the contrary, the residual 7 preparations showed dramatic bifurcation scenario shifting corresponding to different dual parameter configuration. Briefly, when concentration of 4-aminopyridine (4-AP), a voltage-dependent potassium ion channels blocker, was kept at different level and extracellular Ca2+ concentration was decreased gradually, different bifurcation scenarios of firing patterns were exhibited in an identical neural pacemaker. The two-parameter bifurcation scenarios of experimental neural pacemaker with different parameter configuration were also different. The results show that neural firing pattern is different when the parameter configuration is different, and the bifurcation scenario is a fundamental framework to identify the transitions between firing patterns.

Dynamic ion mechanism of bursting in the stomatogastric ganglion neurons of crayfish / 生理学报

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 ([Ca(2+)](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 [Ca(2+)](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 [Ca(2+)](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.