NEONATAL DAMAGE TO THE RATS INFRAORBITAL NERVE UP-REGULATES BOTH GALANIN AND NEUROPEPTIDE-Y IN INDIVIDUAL VIBRISSAE-RELATED PRIMARY AFFERENT AXONS

Previous studies in adult animals have suggested that the peptides gal anin and neuropeptide Y (NPY) may be upregulated in the same primary a fferent neurons after peripheral axotomy. The present study was undert aken to determine whether such upregulation occurred in vibrissae-rela ted primary afferent neurons and their axons after damage to the infra orbital nerve [ION; the trigeminal (V) branch that innervates the vibr issae follicles]. Double-labelling experiments demonstrated that appro ximately 75% of axotomized V ganglion cells and the central arbors of vibrissae-related primary afferents expressed both galanin and NPY aft er perinatal, but not adult, nerve damage. However, additional experim ents demonstrated that the sensitive periods for lesion-induced upregu lation of the two peptides and the period over which they were express ed after neonatal ION transection differed substantially. Staining for both peptides was increased after ION damage on P-O through P-14, but only galanin staining was increased in vibrissae-related primary affe rents after lesions on P-21. Galanin expression was elevated in vibris sae-related primary afferents in rats killed 3,8, and 15 days after ne onatal ION transection, while increased NPY was observed at only the m iddle time point. The lesion-induced increases in galanin and NPY in v ibrissae-related ION primary afferents suggest that these peptides may modulate central V reorganization after such damage.