GSK3B and Alzheimer disease: Furthermore, the administration of HPU (5 μg/animal/day) intraperitoneally for 7 days induced biochemical changes in the rat brain, resembling the prodromal phase of AD, such as the increased expression of Iba1 (marker of activated microglia) and the hyperphosphorylation of tau at Ser199, Thr205, and Ser396; however, no change in the total amount of tau or GSK-3β was observed (Figure 4) [6].