Biró Zoltán, Hill Russell H, Grillner Sten
The Nobel Institute for Neurophysiology, Department of Neuroscience, Karolinska Institutet, SE 171 77 Stockholm, Sweden.
J Neurophysiol. 2008 Aug;100(2):716-22. doi: 10.1152/jn.90206.2008. Epub 2008 May 28.
Commissural interneurons in the lamprey coordinate activity of the hemisegmental oscillators to ensure proper left-right alternation during swimming. The activity of interneuronal axons at the ventral commissure was studied together with potential target motoneurons during fictive locomotion in the isolated lamprey spinal cord. To estimate the unperturbed activity of the interneurons, axonal recordings were chosen because soma recordings inevitably will affect the level of membrane depolarization and thereby spike initiation. Of 227 commissural axons recorded during locomotor activity, 14 produced inhibitory and 3 produced excitatory postsynaptic potentials (PSPs) in target motoneurons. The axons typically fired multiple spikes per locomotor cycle, with approximately 10 Hz sustained frequency. The average shortest spike interval in a burst corresponded to an instantaneous frequency of approximately 50 Hz for both the excitatory and inhibitory axons. The maximum number of spikes per locomotor cycle was inversely related to the locomotor frequency, in accordance with previous observations in the spinal hemicord preparation. In axons that fired multiple spikes per cycle, the mean interspike intervals were in the range in which the amplitude of the slow afterhyperpolarization (sAHP) is large, providing further support for the role of the sAHP in spike timing. One hundred ninety-five axons (86%) fired rhythmically during fictive locomotion, with preferred phase of firing distributed over either the segmental locomotor burst phase (40% of axons) or the transitional phase (between bursts; 60%). Thus in lamprey commissural interneurons, we found a broad distribution of firing rates and phases during fictive locomotion.
七鳃鳗的连合中间神经元协调半节段振荡器的活动，以确保游泳过程中左右交替正常进行。在分离的七鳃鳗脊髓进行虚拟运动期间，研究了腹侧连合处中间神经元轴突的活动以及潜在的靶运动神经元。为了估计中间神经元未受干扰的活动，选择了轴突记录，因为胞体记录不可避免地会影响膜去极化水平，从而影响动作电位的起始。在运动活动期间记录的227条连合轴突中，有14条在靶运动神经元中产生抑制性突触后电位（PSP），3条产生兴奋性突触后电位。这些轴突通常在每个运动周期发放多个动作电位，持续频率约为10Hz。兴奋性和抑制性轴突在爆发中的平均最短动作电位间隔对应的瞬时频率约为50Hz。每个运动周期的最大动作电位数量与运动频率呈负相关，这与之前在脊髓半横切标本中的观察结果一致。在每个周期发放多个动作电位的轴突中，平均动作电位间隔处于慢后超极化（sAHP）幅度较大的范围内，这进一步支持了sAHP在动作电位时间调控中的作用。195条轴突（86%）在虚拟运动期间有节律地发放，其发放的偏好相位分布在节段性运动爆发期（40%的轴突）或过渡阶段（爆发之间；60%）。因此，在七鳃鳗连合中间神经元中，我们发现虚拟运动期间发放频率和相位分布广泛。
