Regrowth of lesioned dorsal root nerve fibers into the spinal cord of neonatal rats.

In postnatal rat pups the L4 and L5 dorsal roots were lesioned. After 3-6 months the spinal cord of the rats was subjected to tracing studies of regenerated dorsal root axons with transganglionically transported horseradish peroxidase (HRP) and immunohistochemistry with antibodies to calcitonin gene-related peptide (CGRP). In rats operated at birth (0-2 days old) HRP-filled profiles as well as CGRP staining were found in the outer lamina of the spinal cord dorsal horn. Signs of dorsal root nerve fiber regrowth in the spinal cord could not be found in rats which had been operated at the end of the first postnatal week or later.