TIME-DEPENDENT EFFECTS OF INSULIN ON SCHWANN-CELL PROLIFERATION IN THE INVITRO REGENERATING ADULT FROG SCIATIC-NERVE

The present study showed that insulin (0.01 mug/ml, almost-equal-to 2 nM) inhibited [H-3]-thymidine incorporation in support cells, most lik ely Schwann cells, of the cultured frog sciatic nerve. A 25-35% inhibi tion took place in regenerating nerve preparations as well as in prepa rations devoid of neuronal protein synthesis, i.e., in isolated 5 mm n erve segments and in gangliectomized nerves, suggesting that the effec t was direct and not mediated via the neuronal cells. The inhibition b y insulin was time-dependent in that an effect was seen after 4 days b ut not at shorter or at longer periods of culturing. In separate exper iments biotinylated insulin was shown to be taken up by Schwann cells in the regenerating nerve. Addition of serum increased the [H-3]-thymi dine incorporation severalfold and abolished the inhibitory action of insulin. Our results suggest that insulin, at a certain stage of the r egeneration programme, exerts a direct, inhibitory effect on the proli feration of the Schwann cells in the cultured frog sciatic nerve.