Gosgnach S, Quevedo J, Fedirchuk B, McCrea D A
Department of Physiology, University of Manitoba, 730 William Avenue, Winnipeg, Canada R3E 3J7.
J Physiol. 2000 Aug 1;526 Pt 3(Pt 3):639-52. doi: 10.1111/j.1469-7793.2000.00639.x.
The effects of fictive locomotion on monosynaptic EPSPs recorded in motoneurones and extracellular field potentials recorded in the ventral horn were examined during brainstem-evoked fictive locomotion in decerebrate cats. Composite homonymous and heteronymous EPSPs and field potentials were evoked by group I intensity (<= 2T) stimulation of ipsilateral hindlimb muscle nerves. Ninety-one of the 98 monosynaptic EPSPs were reduced in amplitude during locomotion (mean depression of the 91 was to 66 % of control values); seven increased in amplitude (to a mean of 121 % of control). Twenty-one of the 22 field potentials were depressed during locomotion (mean depression to 72 % of control). All but 14 Ia EPSPs were smaller during both the flexion and extension phases of locomotion than during control. In 35 % of the cases there was < 5 % difference between the amplitudes of the EPSPs evoked during the flexion and extension phases. In 27 % of the cases EPSPs evoked during flexion were larger than those evoked during extension. The remaining 38 % of EPSPs were larger during extension. There was no relation between either the magnitude of EPSP depression or the locomotor phase in which maximum EPSP depression occurred and whether an EPSP was recorded in a flexor or extensor motoneurone. The mean recovery time of both EPSP and field potential amplitudes following the end of a bout of locomotion was approximately 2 min (range, < 10 to > 300 s). Motoneurone membrane resistance decreased during fictive locomotion (to a mean of 61 % of control, n = 22). Because these decreases were only weakly correlated to EPSP depression (r 2 = 0.31) they are unlikely to fully account for this depression. The depression of monosynaptic EPSPs and group I field potentials during locomotion is consistent with the hypothesis that during fictive locomotion there is a tonic presynaptic regulation of synaptic transmission from group Ia afferents to motoneurones and interneurones. Such a reduction in neurotransmitter release would decrease group Ia monosynaptic reflex excitation during locomotion. This reduction may contribute to the tonic depression of stretch reflexes occurring in the decerebrate cat during locomotion.
在去大脑猫的脑干诱发的模拟运动过程中，研究了模拟运动对运动神经元中记录的单突触兴奋性突触后电位（EPSP）以及脊髓腹角中记录的细胞外场电位的影响。通过对同侧后肢肌肉神经进行I组强度（<=2T）刺激，诱发复合的同名和异名EPSP以及场电位。98个单突触EPSP中有91个在运动期间幅度降低（91个的平均降低幅度为对照值的66%）；7个幅度增加（平均为对照值的121%）。22个场电位中有21个在运动期间降低（平均降低至对照值的72%）。除14个Ia类EPSP外，所有EPSP在运动的屈曲和伸展阶段均比对照期间小。在35%的情况下，屈曲和伸展阶段诱发的EPSP幅度差异<5%。在27%的情况下，屈曲期间诱发的EPSP大于伸展期间诱发的EPSP。其余38%的EPSP在伸展期间更大。EPSP降低的幅度或出现最大EPSP降低的运动阶段与EPSP是在屈肌还是伸肌运动神经元中记录之间没有关系。一阵运动结束后，EPSP和场电位幅度的平均恢复时间约为2分钟（范围，<10至>300秒）。在模拟运动期间，运动神经元膜电阻降低（平均为对照值的61%，n = 22）。由于这些降低与EPSP降低的相关性较弱（r2 = 0.31），它们不太可能完全解释这种降低。运动期间单突触EPSP和I组场电位的降低与以下假设一致，即在模拟运动期间，从Ia类传入神经到运动神经元和中间神经元的突触传递存在强直的突触前调节。这种神经递质释放的减少会降低运动期间Ia类单突触反射兴奋性。这种减少可能有助于去大脑猫在运动期间出现的牵张反射的强直抑制。
