Cytosolic sialidase from the nerve endings of developing rat forebrain

The developmental profile of cytosolic sialidase from the nerve ending and the nerve ending-free compartments of rat forebrain was studied from birth to 150 days. Soluble extracts containing the cytosol from nerve endings and nerve ending-free tissue were separately prepared; the recovery of cytosol in the two extracts was followed by assaying lactate-dehydrogenase. In both cytosolic extracts the content of sialidase and lactate-dehydrogenase had a marked and progressive enhancement from the 5th to the 20th day of life and then maintained a constant level through adult life. However the rate of lactate-dehydrogenase and sialidase increase in the two cytosolic compartments was different. Lactate-dehydrogenase increased at a very similar rate in the two cytosols. Instead the rate of sialidase increase was greater in the cytosol from nerve endings from the 5th to the 10th day of life, and, inversely, in the cytosol from nerve ending-free tissue from 10 to 20 days. Between the 5th and 10th day of life the nerve ending cytosol underwent an enrichment of sialidase which was several times higher than that of lactate-dehydrogenase; in the other periods of forebrain development sialidase and lactatedehydrogenase moved in parallel. The variations with age of cytosolic sialidase from the nerve ending-free tissue seemed to follow the overall process of brain development. The nerve ending soluble sialidase would more specifically reflect formation of synaptic junctions in some brain regions in a well defined period of brain maturation.