Direct connections of primary afferent fibers with spinal neurons projecting to the facial nucleus in the cat

Spinal neurons projecting to the facial nucleus, located in the lateral portion of lamina V from the C1 to C4 segments, had long dendrites extending into lamina IV. The detailed morphology of these spinal neurons was confirmed using the Golgi impregnation method. Dorsal root fibers were distributed mainly to lamina IV at the C1 and C2 segments. These findings indicated the possibility of direct connections between the primary afferent fibers and spinal neurons projecting to the facial nucleus in lamina IV of the upper cervical cords. In order to confirm the connections, electron microscopic observation was carried out on the dorsal horn after injections of horseradish peroxidase into the facial nucleus and dorsal root fibers.