Upper cervical afferents to the motor trigeminal nucleus and the subnucleus oralis of the spinal trigeminal nucleus in the rat: an anterograde and retrograde tracing study.

Upper cervical afferents to the motor trigeminal nucleus (Vmo) and the subnucleus oralis (Vo) neurons projecting contralaterally to the cervical cord were demonstrated in the rat. Axon-terminals were labeled with biotinylated dextran and neurons with cholera toxin subunit B. Axons from the C2 and C3 segments terminated ipsilaterally on the somata and proximal dendrites of Vmo neurons. In the Vo, terminals of axons from the C2 and C3 segments were densely distributed on the somata, and proximal to distal dendrites of neurons projecting contralaterally to the cervical cord. The ipsilateral cervical input to the Vmo would modulate the activity of motoneurons of masticatory muscles while that to the Vo neurons subserves the feedback control of the trigemino-spinal reflex.