Noradrenergic innervation of ectopic granule cells following low-level X-irradiation

The distribution pattern of the noradrenergic system within the cerebellar cortex following low-level X-irradiation was studied using immunocytochemistry. Following one X-irradiation exposure on postnatal day 1, the laminar distribution of tyrosine hydroxylase-like immunoreactive (THIR) fibers was similar to controls at postnatal day 30, but the orientation of the fibers in the molecular layer (ML) was slightly changed. Successive daily doses, however, produced alterations in both the pattern and concentration of THIR fibers within the ML of the cerebellar cortex. In addition, THIR fibers were found among ectopic cell clusters within the ML. This relationship suggests a potential role for the noradrenergic system in the development and/or maintenance of the ectopic cell clusters.