NORADRENERGIC INNERVATION OF THE EXTERNAL GRANULAR LAYER OF THE RAT FOLLOWING LOW-LEVEL X-IRRADIATION

The distribution of the noradrenergic system within the rat cerebellar cortex following low-level X-irradiation was studied using tyrosine hydroxylase immunocytochemistry. X-Irradiation treatments consisted of 1, 3, or 5 successive daily doses beginning on postnatal day 1. When studied 24 h after the last exposure, a dense plexus of tyrosine hydroxylase-like immunoreactive (THLR) fibers, not found in age-matched controls, was observed in the reduced external granular layer (EGL) in each treatment group. At 10 days of age, the THIR fibers were found in association with the reconstituted cells of the premigratory zone of the EGL. The rapid and abnormal innervation of the EGL by the THIR fibers suggests that the noradrenergic system could play a role in the regeneration of this layer.