Cytoarchitectonic arrangement and intracortical circuits of hamster cerebellum. A study by means of confocal scanning laser microscopy.

The FM4-64, a member of the family of fluorescent dyes, has been applied to the cerebellar cortex to study its cytoarchitectonic arrangement and intracortical course of mossy and climbing fibers. Slabs of hamster cerebellum, 1-2 mm thick, were incubated in 10, 30 and 100 microM solutions of FM4-64 in 0.1 M sodium phosphate buffer and observed in a slow scan confocal laser scanning microscope. Cellular tomography of cerebellar cortex allowed us to follow the course of mossy and climbing fibers in the cerebellar white and gray substance. They exhibited high fluorescence signal at the level of myelin sheath. Mossy fibers were identified only in the granular layer by their typical rosette formations and dichotomous bifurcation pattern. Climbing fiber bundles were observed crossing the granular layer and giving off collateral branches in the granular and molecular layers in a crossing-over pattern. They ascend to the Purkinje cell layer in their way to the molecular layer. Cerebellar macroneurons (Golgi and Purkinje cells) and microneurons (granule, basket and stellate cells) showed optimal intracellular staining of cell soma, axonal and proximal dendritic processes. The montage of z-series of stacked optodigital sections allowed us to explore in depth the cytoarchitectonic arrangement, nerve and glial cell morphology, and the topographic relationship of intrinsic cerebellar neurons with the afferent mossy and climbing fibers.