Effects of protein kinase inhibitors on regeneration in vitro of adult frog sciatic sensory axons

The effects of protein kinase inhibitors on regeneration in vitro of adult frog sciatic sensory axons were tested. Regeneration of crush‐injured nerves for 8 days in serum‐free medium was inhibited by staurosporine (100 nM) and H‐7 (100 μM), which are both known to inhibit protein kinase C. With the use of a compartmented culture system it could be shown that H‐7 exerted both local (outgrowth region) and central (ganglia) effects, the latter being more pronounced. The local effects could be due to reduction of Schwann cell proliferation by H‐7. Immunohisto‐chemistry demonstrated the presence of protein kinase C in neuronal cell bodies but not in axonal processes. Proliferation of Schwann cells was accompanied by increased protein kinase C immunoreactivity at the site of injury. H‐7 caused a selective inhibition in the incorporation of radioactive phosphate into one 74 kDa protein of both ganglia and nerve but also a more general decrease in protein labelling. The results show that protein phosphorylations, possibly mediated by protein kinase C, are involved in regeneration‐related mechanisms operating at both local and central levels in the adult frog sciatic sensory axons.