Morphological evidence for 6-hydroxydopamine-induced sprouting or noradrenergic neurons in the cerebellum

Intracisternal injection of 6-hydroxydopamine (6-OHDA) into young rats during the first 24 hours after birth resulted in a significant elevation of cerebellar norepinephrine by day 9. This elevation continued through 120 days. Fluorescence microscopy demonstrated an increased fluorescence in all layers of the cerebellar cortex in treated rats from 9 days after treatment through 120 days. This was considerably greater than the normal developmental change observed in control rats and appeared to be due to an increased number of fluorescent terminals. Quantitative electron-microscopic analysis indicated that all layers of the cerebellar cortex of treated rats contained significantly more boutons with small dense-cored vesicles (SGV), a morphologic marker for catecholamines, than controls. No significant difference in the number of SGVs per bouton was observed in 6-OHDA treated rats.