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首页> 外文期刊>Journal of Neurophysiology >Investigation into non-monosynaptic corticospinal excitation of macaque upper limb single motor units.
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Investigation into non-monosynaptic corticospinal excitation of macaque upper limb single motor units.

机译：猕猴上肢单个运动单位的非单突触皮质脊髓兴奋的研究。

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There has been considerable recent debate as to relative importance, in the primate, of propriospinal transmission of corticospinal excitation to upper limb motoneurons. Previous studies in the anesthetized macaque monkey suggested that, compared with the cat, the transmission of such excitation via a system of C3-C4 propriospinal neurons may be relatively weak. However, it is possible that in the anesthetized preparation, propriospinal transmission of cortical inputs to motoneurons may be depressed. To address this issue, the current study investigated the responses of single motor units (SMUs) to corticospinal inputs in either awake (n = 1) or lightly sedated (n = 3) macaque monkeys. Recordings in the awake state were made during performance of a precision grip task. The responses of spontaneously discharging SMUs to electrical stimulation of the pyramidal tract (PT) via chronically implanted electrodes were examined for evidence of non-monosynaptic, presumed propriospinal, effects. Single PT stimuli (up to 250 microA; duration, 0.2 ms, 2 Hz) were delivered during steady discharge of the SMU (10-30 imp/s). SMUs were recorded from muscles acting on the thumb (adductor pollicis and abductor pollicis brevis, n = 18), wrist (extensor carpi radialis, n = 29) and elbow (biceps, n = 9). In all SMUs, the poststimulus time histograms to PT stimulation consisted of a single peak at a fixed latency and with a brief duration [0.74 +/- 0.25 (SD) ms, n = 56], consistent with the responses being mediated by monosynaptic action of cortico-motoneuronal (CM) impulses. Later peaks, indicating non-monosynaptic action, were not present even when the probability of the initial peak response was low and when there was no evidence for suppression of ongoing SMU activity following this peak (n = 20 SMUs). Even when repetitive (double-pulse) PT stimuli were used to facilitate transmission through oligosynaptic linkages, no later peaks were observed (16 SMUs). In some thumb muscle SMUs (n = 8), responses to PT stimulation were compared with those evoked by transcranial magnetic stimulation, using a figure-eight coil held over the motor cortex. Responses varied according the orientation of the coil: in the latero-medial position, single peak responses similar to those from the PT were obtained; their latencies confirmed direct excitation of CM cells, and there were no later peaks. In the posterio-anterior orientation, responses had longer latencies and consisted of two to three subpeaks. At least under the conditions that we have tested, the results provide no positive evidence for transmission of cortical excitation to upper limb motoneurons by non-monosynaptic pathways in the macaque monkey.
机译：在灵长类动物中，皮质脊髓兴奋的脊柱螺旋传递至上肢运动神经元的相对重要性在最近有相当大的争论。先前在麻醉的猕猴中进行的研究表明，与猫相比，这种兴奋通过C3-C4脊椎神经元系统的传递可能相对较弱。但是，在麻醉的准备过程中，可能会抑制皮层输入到运动神经元的脊柱脊柱传输。为了解决这个问题，本研究调查了清醒（n = 1）或轻度镇静（n = 3）猕猴中单个运动单位（SMU）对皮质脊髓输入的反应。在执行精确抓握任务期间以清醒状态进行记录。检查了通过慢性植入电极自发放电的SMU对锥体束（PT）的电刺激的反应，以寻找非单突触，假定的脊椎前突作用的证据。在SMU稳定放电期间（10-30 imp / s）传递了单个PT刺激（最高250 microA;持续时间0.2 ms，2 Hz）。从拇指（内收肌和外展短肌，n = 18），手腕（radial腕伸肌，n = 29）和肘部（二头肌，n = 9）的肌肉记录SMU。在所有SMU中，刺激刺激后的时间直方图由PT刺激的固定时间和短暂持续时间[0.74 +/- 0.25（SD）ms，n = 56]组成，与单突触作用介导的反应一致皮质运动神经元（CM）脉冲。即使初始峰响应的可能性很低，并且没有证据表明在此峰之后仍抑制正在进行的SMU活动（n = 20 SMU），也不会出现后来的峰，表明非单突触作用。即使使用重复（双脉冲）PT刺激促进通过突触连接的传递，也未观察到更高的峰（16个SMU）。在一些拇指肌肉SMU（n = 8）中，使用保持在运动皮层上的八字形线圈，比较了对PT刺激的反应与经颅磁刺激引起的反应。响应根据线圈的方向而变化：在后中位置，获得了与PT相似的单峰响应;它们的潜伏期证实了CM细胞的直接激发，并且以后没有峰值。在后-前方向，反应具有更长的潜伏期，由两到三个亚峰值组成。至少在我们测试的条件下，结果没有提供积极的证据证明猕猴通过非单突触途径将皮质兴奋传递至上肢运动神经元。

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