Axonal branching and termination of cervical reticulospinal neurons in the cat brachial segments

Axonal branching patterns in the brachial segments of cervical reticulospinal neurons (C-RSNs) were examined in cats using intraaxonal injection of horseradish peroxidase (HRP). Axons of these neurons were electrophysiologically identified by their projection to the lower cervical but not to the lumbar segments and monosynaptic activation after tectal and pyramidal stimulation. Six axons were stained up to terminals. Their stem axons descended in the ventral funiculus near the boundary of the spinal gray. The majority of collateral axons crossed lamina VIII and distributed terminals in the whole area of lamina VIII, the middle part of lamina VII, the lateral 2/3 of lamina VI, the ventral part of lamina V, and sparsely in the limb motor nuclei. Their possible functional role in head orienting movements is discussed.