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

通过轴突回溯和顺行追踪技术，已经确定了与姿势抑制有关的桥髓和脊柱系统。它起源于口脑桥网状核(Po0)的细胞，下行轴突沿其中线穿过桥脑尾侧被盖区(DTF)的背侧部分。它们终止于巨细胞网状核(GC)细胞的胞体，这些细胞将它们的下行轴突投射到腰髓。GC核中的细胞也将其上升轴突投射到Po0核，表明Po0核和GC核之间存在“反射神经元回路”。对DTF区的一次刺激可反向激活Po0核的细胞。同样的刺激可顺向激活GC核中的细胞，而刺激脊髓则可逆行激活GC核中的细胞。在反射性站立去大脑的猫，局灶性注射卡巴胆碱(抗乙酰胆碱酯酶的长效拟胆碱剂)到Po0核，导致后肢伸肌张力的抑制。注射该药后，Po0核和GC核的细胞均开始强直放电，支配伸肌的α运动神经元(MN)膜电位超极化。对α-MN的影响与对DTF区的列车脉冲刺激对它们的影响非常相似。由GC核细胞外记录的动作电位触发的细胞内记录的α-MN膜电位的平均值显示，支配后肢的伸肌和屈肌的α-MN均有突触后抑制电位。这些结果表明，Po0核和GC核的细胞在姿势抑制中分别起“触发神经元”和“传递神经元”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.