The development of primary afferents to the lumbar spinal cord in Xenopus laevis.

The development of dorsal root ganglia (DRG) and the primary afferent system of the hindlimb was studied during metamorphosis in Xenopus laevis larvae. The first DRG cells appeared at stage 40 and at stage 48 the first primary afferent fibers entered the lumbar spinal cord where they bifurcated into ascending and descending branches. Primary afferent fibers and the dendrites of the secondary motoneurons contacted first in a lateral (state 56) and later (stage 58) in a dorsomedial terminal field. Reflexogenic hindlimb behaviour at stage 56 concurred with the presence of the lateral terminal field and many unipolar dorsal root ganglion cells.