The extremely low-frequency magnetic field exposure differently affects the AMPAR and NMDAR subunit expressions in the hippocampus, entorhinal cortex and prefrontal cortex without effects on the rat spatial learning and memory

Abstract

In the present study, we investigated the effects of chronic exposure (14 and 28 days) to a 50Hz, 0.5mT extremely low-frequency magnetic field (ELF-MF) on the NMDAR and AMPAR subunit expressions and rat spatial learning and memory. Using the Western blotting method, we found ELF-MF exposure specifically decreased the expressions of GluA2 in the EC post 28 day exposure and GluA3 of AMPAR subunits in the PFC after 14 day exposure, while it did not affect the AMPAR subunit expression in the hippocampus at both time points. As for NMDAR subunits, 14 day ELF-MF exposure significantly increased the levels of GluN2A and GluN2B in the hippocampus. Moreover, the levels of GluN1 and GluN2A were enhanced in the EC and PFC after two weeks of ELF-MF exposure. Interestingly, 28 day ELF-MF exposure induced a different expression pattern for NMDAR subunits. The increased GluN2A expression observed at 14 day post ELF-MF exposure was recovered after prolonged exposure in the hippocampus and PFC. In the EC, the increased expression of GluN1 achieved to control level and, specifically, a decrease in GluN2A level was observed. Surprisingly, neither 14 nor 28 day ELF-MF did affect the rat spatial reference memory as assessed by water maze. These results indicate that the dynamic and brain-region specific changes in ionotropic glutamate receptor expression induced by ELF-MF are insufficient to influence the rat spatial learning ability.