Tau is an important microtubule-stabilizing protein in neurons. In its hyperphosphorylated form, tau-protein loses its ability to bind to microtubules, accumulates and is part of pathological lesions characterizing tauopathies, e.g. Alzheimers disease (AD). Glycogen synthase kinase-3beta (GSK-3beta), antagonized by phosphatase 2A (PP2A), regulates tau-phosphorylation at many sites. Diabetes mellitus is linked to an increased risk of developing AD. This could be partially caused by dysregulated GSK-3 beta. In a long-term experiment (- 16h) using primary murine neuron cultures, we interfered in the insulin/PI3K- (LY294002-treatment, insulin-boost) and mTor- (AICAR-, rapamycin-treatment) signaling pathways and examined consequent changes in the activities of PP2A, GSK-3beta-, and tau-phosphorylation. We found that the coupling of PI3K- with mTor-signaling, in conjunction with a regulatory interaction between PP2A and GSK-3beta, changed activities of both enzymes always in the same direction. These balanced responses seem to ensure the steady tau-phosphorylation at GSK/PP2A-dependent sites observed over a long period of time (³ 6h). This may help in preventing severe changes in tau-phosphorylation under conditions when neurons undergo transient fluctuations either in insulin or nutrient supply. On the other hand, the investigation of tau protein at Ser262 showed that interferences in the insulin/PI3K- and mTor-signaling potentially influenced the tau-phosphorylation status at sites where only one of the both enzymes (in this case PP2A) is involved in the regulation.