DEVELOPMENTAL ORGANIZATION OF PRIMARY AFFERENT FIBERS IN THE DORSAL HORN OF THE MOUSE LUMBAR SPINAL CORD / 神经解剖学杂志

ABSTRACT

The present study was designed to examine the morphological pattern of primary afferent projections into the spinal dorsal horn by labeling the lumbar dorsal root ganglia with carbocyanine fluorescent dye DiI in mouse embryos and neonatal pups aged embryonic day 12 to postnatal day 3 (E12-P3). Primary afferent fibers projected into dorsal funiculus at E13, but did not penetrated into gray matter of dorsal horn until E15. The afferent projections became dense and entered the spinal gray matter more deeply at E16 and E17. By E18 the intensity of primary afferent in the deep part of the dorsal horn increased and their branching patterns became more complicated. Some of these primary fibers were also observed to ramify extensively in the superficial laminae. The projection pattern of primary afferent remained unchanged after birth, but the intensity of afferent terminals increased in the superficial laminae. In addition, afferent fiber collaterals that projected into the contralateral dorsal horn were also observed. They were first examined at E16 and mainly originated from the medial and deep part of the dorsal horn. Around birth, the contralateral projections were also found to originate from the lateral part of dorsal horn. Our results indicate that laminar organization of primary afferents in the spinal dorsal horn is established during the late embryonic and early postnatal stages.This organization then undergoes further refinement to match the pattern seen in the adult.