Dissociation between activation of higher nervous system and postural muscle tone in cats.

一个脑桥延髓和脊髓系统，参与姿势抑制，已被确定通过轴索流技术的逆行和顺行追踪。它起源于脑桥口侧网状核（Po 0）内的细胞，下行轴突沿脑桥中线沿着穿过脑桥尾侧被盖区（DTF）背侧部。它们终止于网状核（Gc）细胞的胞体，这些细胞将其下行轴突投射到腰髓。Gc核中的细胞也将它们的上行轴突投射到Po 0核，这表明在Po 0核和Gc核之间存在“反射神经元回路”。传递到DTF区域的单个刺激在核Po 0中逆向激活细胞。同样的刺激可使Gc核中的细胞顺向激活，而刺激脊髓可使其逆向激活。在反射性站立去脑猫，局部注射卡巴胆碱（长效拟胆碱药耐乙酰胆碱酯酶）到核Po 0导致在后肢伸肌张力的抑制。通过这种注射，Po 0核和Gc核中的细胞都开始紧张性地放电，并且支配伸肌的α运动神经元（MN）的膜电位超极化。施加在α-MN上的效果与传递到DTF区域的序列脉冲刺激对它们诱导的效果非常相似。细胞内记录的α-MN的膜电位的平均值，触发细胞外记录的动作电位的细胞在核Gc，揭示突触后抑制电位在伸肌和屈肌α-MN支配后肢。这些结果表明，Po 0核和Gc核的细胞在姿势抑制中分别起着“触发神经元”和“中继神经元”的作用。

A ponto-medullary and spinal system, that is involved in postural suppression, has been identified by means of axonal flow techniques for both retro- and antero-grade tracing. It originated from cells in the nucleus reticularis pontis oralis (Po0) and the descending axons coursed through the dorsal portion of the caudal tegmental field (DTF) in the pons along its midline. They terminated on somata of cells in the nucleus reticularis gigantocellularis (Gc), and these cells projected their descending axons to the lumbar spinal cord. The cells in the nucleus Gc also projected their ascending axons to the nucleus Po0 suggesting an existence of "reverberating neuronal circuits" between the nucleus Po0 and the nucleus Gc. A single stimulation delivered to the DTF area activated antidromically cells in the nucleus Po0. Cells in the nucleus Gc were activated orthodromically by the same stimulation and were activated antidromically by stimulating the spinal cord. In reflexively standing decerebrate cats, focal injection of carbachol (long-acting cholinomimetic agent resistant to acethylcholinesterases) into the nucleus Po0 resulted in the suppression of extensor muscle tone in the hindlimbs. With this injection, cells both in the nucleus Po0 and the nucleus Gc started to fire tonically, and the membrane potential of alpha-motoneurons (MNs) innervating extensor muscles were hyperpolarized. The effects exerted upon alpha-MNs were quite similar to those induced upon them by a train pulse stimulation delivered to the DTF area. Averaging of intracellularly recorded membrane potentials of alpha-MNs, triggered by the extracellularly recorded action potentials of the cells in the nucleus Gc, revealed postsynaptic inhibitory potentials both in extensor and flexor alpha-MNs innervating hindlimbs. All these results clearly demonstrated that cells in the nucleus Po0 and those in the nucleus Gc play the roles of "trigger neurons" and "relay neuron", respectively, in postural suppression.