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）产生广泛性运动抑制的脊髓神经元间机制。在急性去脑猫上，观察了MRF刺激前后后肢α运动神经元（MN）兴奋性、反射通路向MN的神经元间传递、反射通路中的中间神经元（IN）和腰骶段（L5-S1）初级传入终末的变化。MRF刺激在支配后肢肌肉的伸肌和屈肌MN中诱导抑制性突触后电位（IPSP），以及大多数IN介导相互Ia抑制、非相互I组抑制、复发性抑制和屈肌反射传入（FRA）通路。它也产生初级传入去极化（PAD）的Ia，Ib和皮肤传入纤维。MN和IN中的IPSP以及 ...更多信息 FRA的齐射抑制初级传入的PAD，而MRF刺激则兴奋受FRA抑制的IN，其中1/4的IN还接受I组传入的单突触兴奋。这些神经元位于第VII层的腹内侧部。棘波触发平均法显示，它们在MN和INs中产生单突触IPSP，在初级传入中产生PAD。这些结果表明，广泛性运动抑制不仅是由于MN和INs介导的反射通路的突触后抑制，而且也是由于初级传入终末兴奋性的抑制。这种抑制作用可能是通过接受兴奋性MRF输入和抑制性FRA输入的INs介导的。本研究结果还提示延髓网状脊髓通路和FRA通路在脊髓神经元间水平存在协同抑制作用。它可以作为一个功能门，整合来自高级运动中枢的下行信号和外周感觉信号，以修改正在进行的运动。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