Martin Michelle M
Department of Biology, Marquette University, Milwaukee, Wisconsin 53233, USA.
J Neurophysiol. 2002 Nov;88(5):2463-76. doi: 10.1152/jn.00725.2001.
Electrophysiological properties of lamprey spinal motoneurons were measured to determine whether their cellular properties change as the spinal cord goes from a quiescent state to the active state of fictive swimming. Intracellular microelectrode recordings of membrane potential were made from motoneurons in the isolated spinal cord preparation. Electrophysiological properties were first characterized in the quiescent spinal cord, and then fictive swimming was induced by perfusion with D-glutamate and the measurements were repeated. During the depolarizing excitatory phase of fictive swimming, the motoneurons had significantly reduced rheobase and significantly increased input resistance compared with the quiescent state, with no significant changes in these parameters during the repolarizing inhibitory phase of swimming. Spike threshold did not change significantly during fictive swimming compared with the quiescent state. During fictive swimming, the slope of the spike frequency versus injected current (F-I) relationship decreased significantly as did spike-frequency adaptation and the amplitude of the slow after-spike hyperpolarization (sAHP). Serotonin is known to be released endogenously from the spinal cord during fictive swimming and is known to reduce the amplitude of the sAHP. Therefore the effects of serotonin on cellular properties were tested in the quiescent spinal cord. It was found that, in addition to reducing the sAHP amplitude, serotonin also reduced the slope of the F-I relationship and reduced spike-frequency adaptation, reproducing the changes observed in these parameters during fictive swimming. Application of spiperone, a serotonin antagonist, significantly increased the sAHP amplitude during fictive swimming but had no significant effect on F-I slope or adaptation. Because serotonin may act in part through reduction of calcium currents, the effect of calcium-free solution (cobalt substituted for calcium) was tested in the quiescent spinal cord. Similar to fictive swimming and serotonin application, the calcium-free solution significantly reduced the sAHP amplitude, the slope of the F-I relationship, and spike-frequency adaptation. These results suggest that there are significant changes in the firing properties of motoneurons during fictive swimming compared with the quiescent state, and it is possible that these changes may be attributed in part to the endogenous release of serotonin acting via reduction of calcium currents.
测量七鳃鳗脊髓运动神经元的电生理特性，以确定随着脊髓从静止状态转变为模拟游泳的活动状态，其细胞特性是否发生变化。在分离的脊髓标本中，用细胞内微电极记录运动神经元的膜电位。首先在静止的脊髓中表征电生理特性，然后通过灌注D-谷氨酸诱导模拟游泳，并重复测量。在模拟游泳的去极化兴奋期，与静止状态相比，运动神经元的基强度显著降低，输入电阻显著增加，而在游泳的复极化抑制期，这些参数没有显著变化。与静止状态相比，模拟游泳期间动作电位阈值没有显著变化。在模拟游泳期间，动作电位频率与注入电流（F-I）关系的斜率显著降低，动作电位频率适应性和慢后峰超极化（sAHP）的幅度也显著降低。已知在模拟游泳期间血清素从脊髓内源性释放，并且已知其可降低sAHP的幅度。因此，在静止的脊髓中测试了血清素对细胞特性的影响。结果发现，除了降低sAHP幅度外，血清素还降低了F-I关系的斜率并减少了动作电位频率适应性，重现了在模拟游泳期间这些参数中观察到的变化。应用血清素拮抗剂螺哌隆，在模拟游泳期间显著增加了sAHP幅度，但对F-I斜率或适应性没有显著影响。因为血清素可能部分通过减少钙电流起作用，所以在静止的脊髓中测试了无钙溶液（用钴替代钙）的效果。与模拟游泳和应用血清素类似，无钙溶液显著降低了sAHP幅度、F-I关系的斜率和动作电位频率适应性。这些结果表明，与静止状态相比，模拟游泳期间运动神经元的放电特性有显著变化，并且这些变化可能部分归因于血清素通过减少钙电流的内源性释放。
