Are large, fluorescent spots in aged mouse brain due to lesioning of catecholamine neurons?

Age-related, large intensely fluorescent (LIF) catecholamine-containing spots were discovered in mouse brain. The similarity of their appearance to "piled-up" fluorescent material observed in catecholamine (CA) nerve tracts after 6-hydroxydopamine (6-OHDA) lesions suggests that LIF spots may be due to accumulation of CA in neurons whose distal portions are undergoing degeneration. When senescent mouse brain were examined longitudinal to monoaminergic tracts by the Falck-Hillarp histofluorescence method, some elongated, large fluorescent structures were observed. This suggests an axonal swelling and accumulation of CA proximal to a lesion. One month after lesioning by intraventricular injections of 6-OHDA, the number of large fluorescent accumulations was significantly reduced. CA accumulations due to lesioning, thus, do not generally remain for the life of the animal. Hence if LIF spots are caused by lesioning, they may be turning over, and the number of LIF spots present at any one time represents only newly formed spots.