Pronounced increase in prolyl endopeptidase activity in primary cultures of rat cerebral cortex during neuronal differentiation.

The activity of prolyl endopeptidase (PEP), a cytosolic serine protease, was examined in developing primary cultures of the rat cerebral cortex between days 1 and 16, in vitro. Cells underwent remarkable differentiation during the first week in culture, as indicated by the formation of clusters and by the rapid development and fasciculation of neurites. The specific activity of PEP showed a rapid, about 5-fold increase by day 7. The morphology of cultures remained nearly unchanged and the activity of PEP slightly increased during the second week. Excitotoxic lesion of the neuronal component of mature cultures revealed that the majority (over 70%) of PEP activity is localised in glutamate-sensitive neurons. Our findings indicate that PEP may play some role during neuronal differentiation.