Mossy fiber and Purkinje cell axon collateral arborization patterns in normal and X-irradiated rat cerebellum: a light microscopic study using horseradish peroxidase fiber filling techniques.

The horseradish peroxidase neuronal staining technique was applied to reveal through anterograde and retrograde staining the detailed morphology of fiber arborization patterns in the cerebella of normal adult rats as well as those treated with neonatal X-irradiation. Morphological features of anterogradely-filled mossy fibers including the axonal arborization and glomerular-type synaptic specializations were found to be similar in all groups studied. In addition, retrogradely-filled Purkinje cell axon collaterals in the cerebella degranulated by X-irradiation exhibited much more elaborate branching and arborization of recurrent collaterals than those labeled in the normal cerebellar cortex. The presence of glomerular-type specializations in the degranulated cerebellum suggested that mossy fibers develop and maintain their normal features independent of major influences from granule cells. The hypertrophy observed after destruction of the cerebellar interneurons suggests the hypothesis that the growth of the normal Purkinje cell collateral system is normally suppressed by extrinsic factors within the neuronal circuit.