Static and dynamic analyses of reverberating neuronal within the brainstem.

在这项研究中，我们试图阐明猫脑干内反射神经元回路的存在及其在体位肌张力控制中的作用。我们用PHA-L免疫组织化学方法研究了左右侧桥脑网状核(NRPo)、NRPo与双侧巨细胞网状核(NRGc)之间的神经元联系。从NRGc发出的下行轴突穿过颈髓腹侧和腹外侧索。从下行轴突发出的单一轴突侧支主要终止于中间神经元所在的Rexed的VII和VIII板层。单侧NRPo内微量注射卡巴胆碱可引起NRPo和NRGc内一组细胞的紧张性激活。NRGc中的细胞被认为是由NRPo下行的神经元活动增加而突触激活的。这些NRGc细胞的下行轴突一直延伸到尾部，直到腰骶髓。这些NRGc细胞对支配伸肌和屈肌的后肢α运动神经元具有非互惠的突触后抑制作用。这些结果提示，在脑干内存在有回响的神经元回路，NRGc细胞是脑干的输出细胞，将球上持续的神经元活动传递到脊髓。这些NRGc细胞的紧张性激活导致对α运动神经元的紧张性抑制，从而导致姿势肌张力的紧张性抑制。

In this study, we have tried to elucidate the presence of reverberating neuronal circuits within the brainstem and the function of them on the control of postural muscle tone in the cats. Our immunohistochemical studies by using a PHA-L technique have demonstrated that there are neuronal connections between the left and the right nucleus reticularis pontis oralis (NRPo), and the NRPo and bilateral nucleus reticularis gigantocellularis (NRGc). Descending axons from the NRGc coursed bilaterally through the ventral and ventrolateral funiculi of the cervical cord. Single axon collaterals arising from the descending axons terminated mainly in the Rexed's laminae VII and VIII, where interneurons are located. Microinjections of carbachol into the unilateral NRPo resulted in tonic activation of a group of cells in the NRPo and in the NRGc. Cells in the NRGc were considered to be activated synaptically by the increased neuronal activity descending from the NRPo. Descending axons of these NRGc cells reached as far caudal as the lumbosacral cord. These NRGc cells were found to exert non-reciprocal postsynaptic inhibitory effects upon hindlimb alpha-motoneurons innervating extensor and flexor muscles. All these results suggested that there are reverberating neuronal circuits within the brainstem, and the NRGc cells are the output cells of the brainstem relaying suprabulbar sustained neuronal activity to the spinal cord. Tonic activation of these NRGc cells results in tonic inhibition of alpha-motoneurons, and consequently tonic suppression of postural muscle tone.