An analysis of connexions between 2nd and 3rd order of relay neurones in the spinal reflex.

刺激猫的顶盖和锥体后，支配脾背侧运动神经元(SPL)和颈复合肌(BCC)的运动神经元产生双突触兴奋效应。这些效应是由脑桥尾侧网状核(NRPC)和巨细胞网状核(NRG)内的网状脊髓神经元(RSN)介导的。NRPC内多数RSNs接受来自顶盖的输入多于来自锥体的输入，并在C3节段下行至同侧腹索。相反，NRG的RSNs一般来自锥体的输入比来自顶盖的更强，并在同侧腹外侧索或对侧索下行。对C2-C3节段RSNs逆行发放的系统阈值标测和对C1-C3节段RSNs下行轴突的轴突内染色研究表明：在RSNs中，降至臂段(C6-Th1)而不向下至腰段(C-RSNs)的RSNs向C_1~C3节段的前角发出侧支，而降至腰段的RSN在C_1~C3节段很少发出侧支。用棘波触发平均法证实了NRPC和NRG内C-RSNs与SPL和BCC运动神经元的直接单突触兴奋性联系。它们的联系是肌肉特有的。皮质网状投射的起源被检查。在NRPC注射HRP后，逆行标记神经元位于前额叶皮质(PF)、6区和4区的内侧半部，而在NRG注射HRP后，它们分布在4区的外侧2/3和6区。皮质内刺激在6区和4区内侧半侧RSNs中诱发出以EPSP为主的EPSP，在Pf区诱发出少量EPSP，而在NRG中从4区外侧2/3处诱发出大的EPSP，在6区诱发出小的EPSP，但不诱发Pf。

Dorsal neck motoneurones innervationg splenius (SPL) and biventer cervicis and complexus (BCC) muscles receive disynaptic excitatory effects after stimulation of the tectum and the pyramid in the cats. These effects were mediated by reticulospinal neurones (RSN) in the nucleus reticluaris pontis caudalis (NRPC) and the nucleus reticularis gigantocellularis (NRG). The majority of RSNs in NRPC received larger inputs from the tectum than from the pyramid, and descended in the ipsilateral ventral funiculus in the C3 segment. RSNs in the NRG, in contrast, had a stronger inputs in general from the pyramid than from the tectum, and descended in the ventrolateral or lateral funiculus of the ipsilateral side or in the contralateral funiculi.Studies of systematic threshold mapping for evoking antidromic spikes of RSNs in C2-C3 segments and intra-axonal staining of their descending axons in C1-C3 segments with horseradish peroxidase(HRP) revealed the following. Among RSNs, those descending to the brachial segments (C6-Th1) but not down to lumbar segments (C-RSNs) issued collaterals to the ventral horn of C1-C3 segments, while RSNs descended to the lumbar segments gave off collaterals rarely in C1-C3 segments. Direct monosynaptic excitatory connexions of C-RSNs in NRPC and NRG with SPL and BCC motoneurones were demonstrated by spike triggered averaging methods. Their connexions were muscle specific.The origin of corticoreticular projections was examined. Retrogradely labelled neurones were located, following injection of HRP in NRPC, in the prefrontal cortex(PF), areas 6 and medial half of area 4. In contrast, they were distributed in the lateral 2/3 of area 4 and area 6 following injection in the NRG. Intracortical stimulation evoked dominant EPSPs in RSNs in NRPC from area 6 and the medial half of area 4 and small EPSPs from PF, while it evoked large EPSPs in RSNs in NRG from the lateral 2/3 of area 4 and small EPSPs from area 6 but not from PF.