Prenatal development of rat primary afferent fibers: II. Central projections

Károly Mirnics, H. Richard Koerher

Research output: Contribution to journalArticle

86 Scopus citations

Abstract

These studies were designed to determine the pattern of initial afferent fiber ingrowth into the prenatal spinal gray matter and the establishment of the topographic organization of the presynaptic neuropil in the dorsal horn. A total of 113 lumbar dorsal root ganglia were labeled with carbocyanine fluorescent dye DiI or DiA in 67 rat embryos and neonatal pups aged embryonic day 13 to postnatal day O (E13–PO). The initial fiber penetration of the lumbar spinal gray began at E15 and was restricted to the segments of entry. Subsequent growth of fibers into gray matter of adjacent segments began approximately one day later, and this delay was continued, about one day for each successive segment. A second wave of ingrowth of putative small‐diameter afferents into the substantia gelatinosa began at E19 and also displayed the same rostrocaudal delay. Fiber ingrowth was specific and occupied the somatotopic area appropriate for the adult, from the earliest stages (E 18) in which dorsal horn laminae could be adequately defined. The somatotopic organization of the presynaptic neuropil in laminae III and IV did not change significantly throughout embryonic development as the amount of overlap between adjacent and non‐adjacent ganglion projections remained constant throughout embryonic development. In addition, it was found that fibers innervating the proximal and distal hindlimb entered the spinal gray simultaneously at E 15 before the innervation of the distal toes was established. The results of these studies indicate that the somatotopic organization of the presynaptic neuropil is established very early in development and requires little refinement to match that seen in the adult. The simultaneous penetration of the fibers originating from the proximal and distal areas of the limb before innervation is complete suggests that this ingrowth may be independent of the establishment of specific peripheral connections.

Original languageEnglish (US)
Pages (from-to)601-614
Number of pages14
JournalJournal of Comparative Neurology
Volume355
Issue number4
DOIs
StatePublished - May 15 1995

Keywords

  • dorsal root ganglion
  • fluorescent dye
  • somatosensory
  • somatotopy
  • spinal cord

ASJC Scopus subject areas

  • Neuroscience(all)

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