Investigation into non-monosynaptic corticospinal excitation of macaque upper limb single motor units.
Investigation into non-monosynaptic corticospinal excitation of macaque upper limb single motor units.
复制标题
猕猴上肢单运动单位非单突触皮质脊髓兴奋的研究。
作者：
E. Olivier;S. Baker;Koji Nakajima;T. Brochier;R. Lemon
关于在灵长类动物中，皮质脊髓兴奋的固有脊髓传递到上肢运动神经元的相对重要性，最近有相当大的争论。以往对麻醉猕猴的研究表明，与猫相比，这种兴奋通过C3-C4固有脊髓神经元系统的传递可能相对较弱。然而，在麻醉准备过程中，皮质传入到运动神经元的固有脊髓传递可能受到抑制。为了解决这个问题，目前的研究调查了清醒(n=1)和轻度镇静(n=3)猕猴的单运动单位(SMU)对皮质脊髓输入的反应。清醒状态下的记录是在执行精确抓握任务期间进行的。通过长期植入的电极，检测自发放电的SMU对电刺激锥体束(PT)的反应，以寻找非单突触、假定为固有脊髓效应的证据。单次PT刺激(高达250微安，持续时间0.2ms，2 Hz)在SMU稳定放电(10-30 imp/S)。分别记录拇指(拇内收肌和拇短展肌，n=18)、腕(腕伸肌，n=29)和肘肌(二头肌，n=9)的SMU。在所有SMU中，对PT刺激的刺激后时间直方图由固定潜伏期和短暂持续时间的单峰组成[0.74+/-0.25(SD)ms，n=56]，这与皮层运动神经元(CM)冲动的单突触作用所介导的反应一致。即使当初始峰值反应的概率很低，并且没有证据表明在该峰值之后正在进行的SMU活动受到抑制时(n=20 SMU)，也不存在表明非单突触作用的后来的峰值。即使使用重复的(双脉冲)PT刺激来促进通过寡突触连接的传递，也没有观察到后来的峰值(16个SMU)。在一些拇指肌肉SMU(n=8)中，用一个8字线圈固定在运动皮质上，将PT刺激的反应与经颅磁刺激的反应进行比较。反应因线圈方位不同而不同：在外侧内侧位置，可获得与PT相似的单峰反应；其潜伏期证实了CM细胞的直接兴奋，没有后续的峰。在后-前定向，反应潜伏期较长，由两到三个亚峰组成。至少在我们所测试的条件下，这些结果没有提供猕猴皮质兴奋通过非单突触通路传递到上肢运动神经元的积极证据。
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.