A REEVALUATION OF THE ULTRASTRUCTURAL-LOCALIZATION OF 5'-NUCLEOTIDASEACTIVITY IN THE DEVELOPING RAT CEREBELLUM, WITH A CERIUM-BASED METHOD

The membrane ectoenzyme 5'-nucleotidase converts 5'-AMP into adenosine which, in the nervous tissue, plays an important role as intercellula r messenger. Moreover, during histogenesis, 5'-nucleotidase seems to b e related to cell proliferation and migration. Conflicting data are re ported in the literature about the localization (neuronal or glial) of 5'-nucleotidase in the rat cerebellum. In the present report we have analyzed the distribution of 5'-nucleotidase activity with electron mi croscopy, using a cerium-based method, at different postnatal histogen etic stages (postnatal days (PND) 11, 17, 28). On PND 11 and 17, rims of reaction product outlined the plasma membranes of some neuroblasts in the external granular layer and of parallel fibers and some migrati ng cells in the developing molecular layer. Positivity was frequently observed on membranes of adjacent neuronal cells and glial processes. Moderate activity was also present on the membranes of granule cells a nd of messy fiber rosettes and granule cell dendrites constituting the cerebellar glomeruli within the internal granule cell layer. At PND 2 8, the reaction product was slightly reduced in some localizations. Cy tochemical patterns prove that the cerium-based method is suitable for demonstration of 5'-nucleotidase-specific activity. In fact, a contin uous and fine reaction product appears strictly linked to the cell mem branes, and no unevenly scattered precipitates can be observed. Data s uggest that, during cerebellar histogenesis, 5'-nucleotidase may be in volved in the mechanisms of cell migration and proliferation. However, in adulthood, prominent localization of the reaction product on neuro nal elements suggests a major role in neuromodulation processes for th e enzyme.