Central projections of the normal and 'regenerate' infraorbital nerve in adult rats subjected to neonatal unilateral infraorbital lesions: a transganglionic horseradish peroxidase study.

Application of horseradish peroxidase (HRP) to the proximal stump of the transected infraorbital (IO) nerve in the orbit was employed in normal adult rats to demonstrate the ganglionic representation of and brainstem innervation by the trigeminal (V) branch which supplies primarily the mystacial vibrissae. In the V ganglion, somal clusters resembling the barrels or barreloids which comprise the central representations of the whiskers were not visible. In the trigeminal brainstem nuclear complex (TBNC), however, barrel-like aggregates of HRP-labeled terminals could be clearly seen throughout subnucleus interpolaris and, to a lesser extent, in the principal sensory nucleus, subnucleus caudalis and the first cervical segment. In adult rats subjected to neonatal IO nerve section and vibrissae follicle cauterization, transganglionic HRP transport from the 'regenerate' IO nerve indicated an almost exclusive projection to the marginal layer of the medullary and rostral cervical dorsal horn.