Abstract: Microtubule associated protein tau from Alzheimer disease(PHF-tau)and fetal brains(F-tau)are known to be hyperphosphorylated, though PHF-tau usually has been considered as an abnormally phosphorylated form of tau, calcineurin(CaN)is the only Ca²⁺/CaM dependent phosphatase for tau, which is enriched in human brain, might dephosphorylate PHF tau and F tau in vitro. In the present study, P nitrophenyl phosphate was used as substrate to measure CaN activities in 15 fresh fetal and infant brains, 2 brains from adult and one from Alzheimer disease. All these samples were dissected from 5 regions, i. e. frontal, hippocampal, occipital, basal ganglia and cerebellum. The results showed that the topographical difference of CaN might correlate with their physiological functions. The specific activity of CaN in one week newborn infan't brain appeared to have a higher level which was consistent with the time interval that F-tau was dephosphorylated. In the Alzheimer's brain, the specific activity of CaN decreased approximately to the respective level of those fetal brains of 17～20 weeks, suggesting that the formation of PHF tau might result from the decreasing CaN activity. Also, the hyperphosphorylation of the neuronal proteins might be the result of augmented activity of protein kinase, of reduced activity of CaN and other phosphatase, or both.

Key words: fetal brains, Alzheimer disease, calcineurin