Delvolvé I, Gabbay H, Lev-Tov A
Department of Anatomy and Cell Biology, The Hebrew University Medical School, Jerusalem 91120, Israel.
J Neurophysiol. 2001 May;85(5):2100-10. doi: 10.1152/jn.2001.85.5.2100.
The characteristics of the rhythmic motor output and behavior produced by intrinsic sacrocaudal networks were studied in isolated tail-spinal cord preparations of neonatal rats. An alternating left-right rhythm could be induced in the sacral cord by stimulus trains applied to sacrocaudal afferents at various intensities. Strengthening the stimulation intensity enhanced the rhythmic efferent firing and accelerated the rhythm by < or =30%. High stimulation intensities induced tonic excitation or inhibition and thereby perturbed the rhythm. Increasing the stimulation frequency from 1 to 10 Hz decreased the cycle time of the rhythm by 36%. The rhythm was blocked during prolonged afferent stimulation but could be restored by stimulation of contralateral afferents. Sacrocaudal afferent activation produced ventroflexion accompanied by either low- or high-amplitude rhythmic abduction of the tail. The low-amplitude abductions were produced by alternating flexor bursts during long stimulus trains. The activity of abductors and extensors was substantially reduced during these trains, their recruitment lagged after that of the flexors, and their activity bursts were much shorter. It is suggested that tail extensor/abductor motoneurons were suppressed during the stimulus train by inhibitory afferent projections. The high-amplitude abductions appeared after cessation of stimulus trains. Alternating left-right activation of the tail muscles, and coactivation of the principal muscles on each side of the tail were observed during these abductions. It is suggested that flexors and extensors assist the abductors to produce the high-amplitude abductions. This suggestion is supported by the finding that tail abduction could be produced by direct unilateral stimulation of any of the principal tail muscles. The relevance of the findings described in the preceding text to the use of regional sacral circuits in generation of stereotypic motor behaviors and to future studies of rhythmogenic sacrocaudal networks is discussed.
在新生大鼠的离体尾脊髓标本中，研究了骶尾内源性神经网络产生的节律性运动输出和行为特征。通过以不同强度刺激骶尾传入神经，可在骶髓诱发左右交替的节律。增强刺激强度可增强节律性传出放电，并使节律加快达30%或更低。高刺激强度会诱发强直兴奋或抑制，从而扰乱节律。将刺激频率从1Hz增加到10Hz，节律的周期时间缩短了36%。在长时间的传入刺激期间节律会被阻断，但可通过刺激对侧传入神经恢复。骶尾传入神经激活会产生腹屈，同时伴有低幅度或高幅度的尾部节律性外展。低幅度外展是在长时间刺激序列中由屈肌爆发交替产生的。在这些刺激序列中，外展肌和伸肌的活动大幅减少，它们的募集滞后于屈肌，且活动爆发持续时间短得多。提示在刺激序列期间，尾伸肌/外展肌运动神经元被抑制性传入投射所抑制。高幅度外展出现在刺激序列停止后。在这些外展过程中，观察到尾部肌肉左右交替激活以及尾部两侧主要肌肉的共同激活。提示屈肌和伸肌协助外展肌产生高幅度外展。这一提示得到以下发现的支持：直接单侧刺激任何一条主要尾部肌肉均可产生尾部外展。讨论了前文所述发现与骶部局部回路在刻板运动行为产生中的应用以及与节律性骶尾神经网络未来研究的相关性。
