Alstermark B, Isa T, Ohki Y, Saito Y
Department of Integrative Medical Biology, Umeå University, S-901 87 Umeå, Sweden.
J Neurophysiol. 1999 Dec;82(6):3580-5. doi: 10.1152/jn.1999.82.6.3580.
In contrast to findings in the cat, it recently has been shown that disynaptic pyramidal EPSPs only rarely are observed in forelimb motoneurons of the macaque monkey in the intact spinal cord or after a corticospinal transection in C(5). This finding has been taken to indicate that the disynaptic pyramidal excitatory pathway via C(3)-C(4) propriospinal neurons (PNs) is weakened through phylogeny when the monosynaptic cortico-motoneuronal connection has been strengthened. We reinvestigate this issue with special focus on the possibility that the inhibitory control of the C(3)-C(4) PNs may be stronger in the macaque monkey than in the cat. The effect in forelimb motoneurons of electrical stimulation in the contralateral pyramid was investigated in anesthetized macaque monkeys (Macaca fuscata). We confirmed the low frequency of disynaptic pyramidal EPSPs in forelimb motoneurons. However, after intravenous injection of strychnine, disynaptic EPSPs could be evoked in 39 of 41 forelimb motoneurons recorded after lesion of the corticospinal fibers in C5. After a corresponding lesion in C(2), disynaptic pyramidal EPSPs were observed in 2 of 25 motoneurons. In contrast to previous reports, we conclude that C(3)-C(4) PNs can mediate disynaptic pyramidal excitation in high frequency of occurrence to forelimb motoneurons in the C(6)-C(8) segments and that this transmission is under a stronger inhibitory control than in the cat. Thus, the hypothesis that the disynaptic excitatory cortico-motoneuronal pathway via the C(3)-C(4) PNs is weakened in parallel with the strengthened monosynaptic connection through phylogeny is not supported by the present findings.
与猫的研究结果相反，最近有研究表明，在完整脊髓或C5水平皮质脊髓束横断后的猕猴前肢运动神经元中，很少观察到双突触锥体兴奋性突触后电位（EPSP）。这一发现表明，当单突触皮质-运动神经元连接增强时，通过C3-C4脊髓 propriospinal 神经元（PNs）的双突触锥体兴奋性通路在系统发育过程中被削弱。我们重新研究了这个问题，特别关注C3-C4 PNs的抑制性控制在猕猴中可能比在猫中更强的可能性。在麻醉的猕猴（食蟹猴）中研究了对侧锥体电刺激对前肢运动神经元的影响。我们证实了前肢运动神经元中双突触锥体EPSP的低频出现。然而，静脉注射士的宁后，在C5皮质脊髓纤维损伤后记录的41个前肢运动神经元中的39个中可诱发双突触EPSP。在C2进行相应损伤后，在25个运动神经元中的2个中观察到双突触锥体EPSP。与先前的报道相反，我们得出结论，C3-C4 PNs可以在高频率下介导对C6-C8节段前肢运动神经元的双突触锥体兴奋，并且这种传递受到比猫更强的抑制性控制。因此，目前的研究结果不支持通过C3-C4 PNs的双突触兴奋性皮质-运动神经元通路在系统发育过程中与增强的单突触连接平行减弱的假设。
