EVIDENCE FOR SURVIVAL OF THE CENTRAL ARBORS OF TRIGEMINAL PRIMARY AFFERENTS AFTER PERIPHERAL NEONATAL AXOTOMY - EXPERIMENTS WITH GALANIN IMMUNOCYTOCHEMISTRY AND DI-I LABELING

Studies employing axoplasmic transport techniques have suggested that the central arbors of vibrissae-related primary afferents are rapidly and permanently lost from the trigeminal (V) brainstem complex after t ransection of the intraorbital nerve (ION). The present study reexamin ed this issue using immunocytochemistry for galanin (GAL) and anterogr ade labelling with Di-I to evaluate V brainstem organization in rats t hat sustained damage to the ION or individual vibrissae follicles in i nfancy or adulthood. After adult nerve damage, GAL-positive fibers are increased in layers I and II of V subnucleus caudalis (SpC). This was apparent by 3 days after the lesion. In rats that sustained nerve dam age at birth (P0), GAL immunoreactivity (IR) appeared throughout the V brainstem complex and had a patchy distribution similar to that of vi brissae-related V primary afferents in normal rats. Increased GAL-IR i n rostral portions of the V brainstem complex was observed in rats tha t sustained ION damage as late as P14. Additional experiments in which nerve damage was followed by destruction of the V ganglion demonstrat ed that this GAL-IR was contained in primary afferents. Damage to sing le vibrissa follicles or to a row of follicles produced a single patch or row of GAL-IR terminals in the somatotopically appropriate portion of the ipsilateral V brainstem complex. Di-I labelling in neonatally nerve-damaged rats demonstrated that primary afferent axons filled the central territory normally innervated by this nerve and that their te rminal distribution was patchy. These results suggest that the V gangl ion cells that survive neonatal axotomy may retain somatotopically org anized projections to the V brainstem complex for at least a limited p ostnatal period. (C) 1994 Wiley-Liss, Inc.