Ascending somatosensory projections to the dorsal accessory olive: an anatomical study in cats.

The cells in the gracile nucleus that project to the dorsal accessory olive were identified in cats with retrograde tracing techniques. In the same animals, the retrograde labeling patterns in the lateral cervical nucleus and the lumbosacral spinal cord were also examined. Small injections of wheat germ agglutinin complexed to horseradish peroxidase were made in the ventrolateral portion of the dorsal accessory olive without involving the medial accessory olive and without damaging the medial lemniscus. The tissue was processed with tetramethyl benzidine. In each of the three relay nuclei, the neurons that project to the ventrolateral portion of the contralateral dorsal accessory olive are highly concentrated in small regions. In the gracile nucleus these cells are found almost exclusively in the transitional zone, just caudal to the obex and rostral to the clusters. In the lateral cervical nucleus they are concentrated in the dorsolateral tip. In the lumbosacral spinal cord in segments L5 and L6 the cells are found primarily in lamina V, while in segments L7 and S1 they are found along the ventromedial edge of the ventral horn. In the gracile and lateral cervical nuclei there is no segregation of neurons that project to the rostral and caudal portions of the dorsal accessory olive. Comparison of these results with physiological data suggests that each of the three sources of ascending somatic input conveys some distinct aspect of sensory information from the hindlimb to the dorsal accessory olive.