Objective      To determine the effect of electromagnetic radiation on tau protein phosphorylation in primarily cultured cortical neurons.       Methods      Primarily cultured rat cortical neurons were divided into sham radiation group and radiation group. Rats in radiation group were radiated with electromagnetic wave at the average power density

of 90 mW/cm

2

for 10 min. Tissue samples were taken at 0

1

3

6 and 12 h after radiation. Viability of neurons was assayed with CCK-8

tau protein phosphorylation in primarily cultured neurons at ser199/202

ser396 and ser404 was detected by Western blotting

and effect of cyclin-dependent kinase5 (CDK5) inhibitor Roscovitine

glycogen synthase kinase-3β(GSK-3β）inhibitor lithium chloride (LiCl)

and calpain inhibitor PD150606 on tau protein phosphorylation was detected after radiation.       Results      The viability of primarily cultured neurons was 19% and 30% lower respectively at 6 and 12 h after radiation in radiation group than in sham radiation group (P0.05

P0.01). The tau protein phosphorylation level in primarily cultured neurons at ser404 was 89% and 46% higher respectively at 1 and 3 h after radiation in radiation group than in sham radiation group (P0.05). No significant difference was found in tau protein phosphorylation level in primarily cultured neurons at ser199/202 and ser396 after radiation (P 0.05). The inhibitory effect of Roscovitine

LiCl and PD150606 on tau protein phosphorylation in primarily cultured neurons at ser404 was lower in radiation group than in sham radiation group after radiation (P0.01).       Conclusion      Electromagnetic radiation induces over tau protein phosphorylation in primarily cultured neurons at ser404 with involvement of CDK5

GSK-3β and calpain.