Regeneration of central catecholamine fibers in young and aged rat brain.

Catecholamine histofluorescence patterns were examined in brains of young and aged rats, 1 to 14 days following neurosurgical transection of the medial forebrain bundle. At all ages examined, two phenomena were observed: degeneration of nerve fibers and vigorous regrowth of catecholamine-containing fibers in the lesion site. Regenerated catecholamine fibers invaded the area of scarred tissue. This invasion of the scarred area implies that the robust plasticity of catecholaminergic pathways, known to exist in young animals, persists in aged brain.