Experimental reorganization of the cerebellar cortex. IV. Parallel fiber reorientation following regeneration of the external germinal layer.

Abstract

AbstractThe heads of Long‐Evans hooded rats were irradiated with a schedule of low‐level x‐ray which allowed regeneration of the external germinal layer. In the subsequently regenerated molecular layer, parallel fibers were often reoriented. In some cerebella this was restricted to a single lobule, frequently several lobules were affected, rarely almost the entire vermis. It was postulated that the reorientation of parallel fibers was determined by the invasion route of multiplying cells from spared foci of the external germinal layer. Where parallel fibers were rotated transversely, the axons of basket cells and the arborizing dendrites of Purkinje cells became oriented longitudinally. This, and other considerations indicated that parallel fibers exert a guiding influence on the pattern of growth of the spiny branchlets of Purkinje cells.