Synaptic and molecular mechanisms that control the excitability of spinal interneurons

本研究旨在阐明刺激延髓网状结构(MRF)所产生的全身性运动抑制所涉及的脊髓神经元间机制。对76只体重2.1~4.3 kg的急性去大脑猫在磁流变液刺激前后后肢α运动神经元(MN)兴奋性、反射通路向MNS的神经元间传递、反射通路中的中间神经元(INS)和腰骶段初级传入终末(L5-S1)的变化进行了观察。刺激MRF可在支配后肢肌肉的伸肌和屈肌MN产生抑制性突触后电位(IPSP)，并且大多数INS介导相互抑制、非相互I组抑制、反复抑制和屈肌反射传入通路。也产生Ia、Ib和皮肤传入纤维的初级传入去极化(PAD)。MNS和INS中的IPSP以及…在初级传入神经元中，更多的PAD被FRA的抽动所抑制，而刺激MRF则兴奋被FRA抑制的INS，其中四分之一的INS也接受I组传入的单突触兴奋。这些INS位于VII板的腹内侧部，棘波触发平均显示它们在MNS和INS产生单突触IPSP，在初级传入产生PAD。这些结果表明，这种普遍的运动抑制不仅是由于MNS和INS插入反射通路的突触后抑制，也是对初级传入终末兴奋性的抑制。这种抑制作用可能是通过INS接受兴奋性MRF输入和抑制性FRA输入介导的。实验结果还提示延髓网状脊髓通路和FRA通路在脊髓神经元间存在协同抑制作用。它可以作为一个功能门，整合来自高级运动中心的下行信号和外周感觉信号，以调节正在进行的运动。较少

This study was aimed at elucidating the spinal interneuronal mechanisms involved in the generalized motor inhibition produced by stimulating the medullary reticular formation (MRF). Changes in the excitability of hindlimb alpha-motoneurons (MNs), interneuronal transmission of reflex pathways to MNs, interneurons (INs) in reflex pathways and primary afferent terminals in lumbosacral segments (L5-S1) were examined before and after the MRF stimulations in acute decerebrate cats.Seventy-six cats weighing of 2.1-4.3 kg were decerebrated at precollicular-postmammilarly level. The MRF stimulation induced inhibitory postsynaptic potentials (IPSPs) in both extensor and flexor MNs innervating hindlimb muscles as well as most INs mediating reciprocal Ia inhibition, non-reciprocal group I inhibition, recurrent inhibition, and flexor reflex afferent (FRA) pathways. It also produced primary afferent depolarization (PAD) of Ia, Ib and cutaneous afferent fibers. Both the IPSPs in MNs and INs, and the … More PAD in primary afferents were suppressed by volleys in FRA.However, the MRF stimulation excited INs that received inhibition from FRA.One-fourth of them also received monosynaptic excitation from group I afferent. These INs were located in ventro-medial portion of lamina VII.Spike-triggered averaging revealed that they produced monosynaptic IPSPs in MNs as well as INs, and produced PAD in primary afferents.These results suggest that the generalized motor inhibition is due to not only the postsynaptic inhibition of MNs and INs interposed in reflex pathways but also suppression of excitability of primary afferent terminals. Such inhibitory effects are possibly mediated by INs receiving excitatory MRF input and inhibitory FRA input. The results also proposed the co-inhibitory interaction at spinal interneuronal level between the medullary reticulospinal pathway and FRA pathways. It may operate as a functional gate that integrate descending signals from higher motor centers and peripheral sensory signals to modify ongoing movements. Less