Neuronal groups and fiber patterns in cerebellar tissue cultures

Abstract

Parasagittally oriented explants derived from newborn mouse cerebellum demonstrate a high degree of organization after 3–4 weeks in vitro. Structured cortical and subcortical nuclear groups of neurons are recognizable, with organized bundles of fibers coursing between them. the cortex is stratified and presents a range of laminar maturation varying from an essentially 2-layered structure consisting of outer granule and Purkinje cells to a 4-layered structure, composed of outer and internal granular layers, a molecular layer and a layer of Purkinje cells. Purkinje cell axons converge toward intracerebellar nuclei, and individual fibers can be traced to terminations near dendrites of intracerebellar nucleus neurons. Vestibular nucleus neurons are present near ependymal formations in more laterally derived explants, and a sparse fiber bundle often courses between the intracerebellar and vestibular nuclei. Axons of vestibular nuclear origin can be traced to almost all areas of the explant, and frequently contribute to the transverse band, a band of fibers in the margin of the cortex which follows the cortical curvature. This group of fibers also receives contributions from Purkinje axon collaterals, as they travel for short distances to terminate either freely or near the dendrites of other Purkinje cells, and from fibers of great length whose cells of origin could not be determined. The transverse band is augmented at the rostroventral and caudoventral cortical margins by Purkinje cell axons directed toward the intracerebellar nuclei. On the basis of the range and degree of cortical laminar maturation, the overall architecture of the mature cerebellum in vitro is comparable to that of an early postnatal animal.