Figure 5.

NGF inactivates GSK-3β through a pathway different from PI-3 kinase activation. (A) GSK-3 activity was determined in extracts from cultured hippocampal neurons that were incubated for 1 h in the presence or absence of 100 ng/ml NGF, LY294002, a known inhibitor of PI-3 kinase, and 100 ng/ml NGF plus LY294002. Note that in the presence of the PI-3 kinase inhibitor, NGF was still capable of inhibiting GSK-3, suggesting an alternative pathway for NGF-induced GSK-3β inhibition. (B) NGF induced axon elongation is not prevented by inhibition of PI-3 kinase. Note that axon growth corresponds to the inhibition state of GSK-3.