Department of Neurobiology, Physiology and Behavior, and Center for Neuroscience, University of California Davis, 95616-8519, USA.
J Exp Biol. 2009 Nov;212(Pt 22):3605-11. doi: 10.1242/jeb.033621.
The crayfish swimmeret system undergoes transitions between a silent state and an active state. In the silent state, no patterned firing occurs in swimmeret motor neurons. In the active state, bursts of spikes in power stroke motor neurons alternate periodically with bursts of spikes in return stroke motor neurons. In preparations of the isolated crayfish central nervous system (CNS), the temporal structures of motor patterns expressed in the active state are similar to those expressed by the intact animal. These transitions can occur spontaneously, in response to stimulation of command neurons, or in response to application of neuromodulators and transmitter analogues. We used single-electrode voltage clamp of power-stroke exciter and return-stroke exciter motor neurons to study changes in membrane currents during spontaneous transitions and during transitions caused by bath-application of carbachol or octopamine (OA). Spontaneous transitions from silence to activity were marked by the appearance of a standing inward current and periodic outward currents in both types of motor neurons. Bath-application of carbachol also led to the development of these currents and activation of the system. Using low Ca(2+)-high Mg(2+) saline to block synaptic transmission, we found that the carbachol-induced inward current included a direct response by the motor neuron and an indirect component. Spontaneous transitions from activity to silence were marked by disappearance of the standing inward current and the periodic outward currents. Bath-application of OA led promptly to the disappearance of both currents, and silenced the system. OA also acted directly on both types of motor neurons to cause a hyperpolarizing outward current that would contribute to silencing the system.
螯虾游泳肢系统在静止状态和活动状态之间发生转变。在静止状态下，游泳肢运动神经元中没有模式性放电。在活动状态下，动力冲程运动神经元中的爆发性尖峰与返回冲程运动神经元中的爆发性尖峰周期性交替。在分离的螯虾中枢神经系统（CNS）的制剂中，在活动状态下表达的运动模式的时间结构与完整动物表达的运动模式相似。这些转变可以自发发生，响应于命令神经元的刺激，或响应于神经调质和递质类似物的施加。我们使用动力冲程激发器和返回冲程激发器运动神经元的单电极电压钳来研究自发转变期间和通过施加 carbachol 或章鱼胺（OA）引起的转变期间膜电流的变化。从静止到活动的自发转变以两种类型的运动神经元中出现的静止内向电流和周期性外向电流为标志。 carbachol 的施加也导致这些电流的产生和系统的激活。使用低 Ca(2+)-高 Mg(2+)盐溶液阻断突触传递，我们发现 carbachol 诱导的内向电流包括运动神经元的直接反应和间接成分。从活动到静止的自发转变以静止内向电流和周期性外向电流的消失为标志。OA 的施加迅速导致两种电流的消失，并使系统沉默。OA 还直接作用于两种类型的运动神经元，引起会导致系统沉默的超极化外向电流。
