Three-dimensional morphology of cerebellar protoplasmic islands and proteoglycan content of mossy fiber glomerulus: a scanning and transmission electron microscope study.

The present review summarizes the outer and inner surface features of mossy fiber glomeruli in vertebrate cerebellar granular layer as seen by conventional scanning electron microscopy (SEM) and SEM freeze-fracture method. The intracortical trajectory of mossy fibers and their synaptic contacts with granule cell dendrites were traced by the slicing and freeze-fracture techniques revealing the radial distribution of granule cell dendrites around the central mossy rosette. The "en passant" nature of mossy fiber synaptic contacts and the participation of Golgi cell axonal ramifications were demonstrated. The results obtained were compared with available light and transmission electron microscopy data. The freeze-etching technique disclosed the true extension of glomerular neuroglial investment. The proteoglycan content of mossy fiber rosette has been also studied by Alcian Blue staining, enzymatic digestion with testicular hyaluronidase and neuraminidase and Os-DMEDA staining method resulting in the presence of an electron dense material at the mossy fiber axoplasmic matrix and some synaptic vesicles, pre-and postsynaptic densities and cleft substance. The axoplasmic material appears to be constituted by proteoglycans with hyaluronic acid or chondroitin sulphate in their composition. The possible role of proteoglycans in synaptic functions is also discussed. Scanning electron microscopy is a promising methodology for analysis of short intracortical circuits and for the study of complex multisynaptic arrangements.

Transient accumulations of glycosaminoglycans in rat and chicken cerebellar cortex during development.

Modifications of glycosaminoglycans at neuropile of rat and chicken cerebellum during development were histochemically studied. The application of Alcian Blue staining techniques and enzymatic degradations permitted to reveal in both species that in earlier stages of cerebellar development hyaluronic acid is present throughout neuropile of entire cerebellum but it accumulated preferentially at the medullary region and around precursory Purkinje cells where it showed a mucoid-like appearance. This substance was related with cell migration and aligning processes. At the middle of cerebellar development, around 2nd postnatal week in rat and 12-16 embryonary days in chick, a new polyanionic transient accumulation, presumably chondroitinsulphate, became present at the medullary region following the longitudinal axis of folium and limiting the forming granular layer, being this substance mainly related with polarity processes by controlling or guiding the growing cones of afferent fibers, which enter massively to cerebellar cortex. It disappeared as myelination progressed. Also from the middle stage of development onward, beside glycosaminoglycans, other polyanionic substances were present at the molecular and granular layer neuropile and at the cytoplasm of some nerve cells. These macromolecules were rather related with nerve cell differentiation and maturation.