The relationship between the efferents of the cortex and basal ganglia in the control of jaw movements

已知的是，小细胞网状结构(RFP)中含有三叉神经运动核的许多运动前神经元。我们已经发现，RFP接受黑质网状部背外侧部的黑质纤维，SNR是基底节的主要输出核团之一。此外，SNR的背外侧部向上丘(SC)的近外侧发出投射纤维，在那里分布有许多投射到RFP的神经元。在这种情况下，黑质轴突终末与红部神经元的胞体和近端树突进行对称性突触接触，将轴突发送到RFP。已知红核的背侧部分接受来自颌骨运动区的皮质纤维。第二，我们发现来自颌骨运动区的皮质纤维和投射到顶盖RFP(顶盖-RFP神经元)的顶盖神经元在SCC的后部几乎部分重叠分布。皮质轴突与顶盖-RFP神经元的树突不对称接触。在SC的后半部，SNR背外侧部和顶盖-RFP神经元的黑质纤维也有重叠分布，这一现象已有报道。黑质轴突终末与顶盖RFP神经元的胞体和树突对称接触。因此，本研究揭示了从颌骨运动皮质和基底节到顶盖神经元的会聚投射，这些神经元将轴突发送到RFP。

The parvicellular reticulr formation (RFp) has been known to contain many premotor neurons for the motor trigeminal nucleus. We has already indicated that the RFp receives nigral fibers from the dorsolateral part of the substantia nigra pars reticulata (SNr) which is one of the major output nuclei of the basal ganglia, and further that the dorsolateral part of the SNr sends projection fibers to the lateralmost part of the superior colliculus (SC), where many neurons projecting to the RFp are distributed.In the present study, we first showed that the dorsolateral part of the SNr sent projection fibers to the dorsal part of the red nucleus, where many neurons projecting to the RFp existed. In this case, the nigral axon terminals made symmetrical synaptic contacts with somata and proximal dendrites of the rubral neurons sending their axons to the RFp. The dorsal part of the red nucleus has been known to receive cortical fibers from the jaw motor area.Secondly, we indicated the overlapping distributions of the cortical fibers from the jaw motor area and the tectal neurons projecting to the RFp (tecto-RFp neurons) in the lateralmost part of the SC.The cortical axons were in asymmetrical contact with dendrites of the tecto-RFp neurons. In the lateralmost part of the SC,the overlapping distributions of the nigral fibers from the dorsolateral part of the SNr and the tecto-RFp neurons were also found, as reported previously. The nigral axon terminals made symmetrical contacts with somata and dendrites of the tecto-RFp neurons. Thus, the convergent projections from the jaw motor cortex and the basal ganglia to the tectal neurons sending their axons to the RFp were revealed by the present study.