Objective       To investigate the effects of low-intensity microwave (900 MHz) electro-magnetic field (EMF) on the spatial memory

  permeability of blood-brain barrier and ultrastructural changes of related rat brain regions.       Methods       Male SD rats were randomly divided into 4 groups (n=12 for each group) and separately underwent EMF exposure for 14 d (EMF 14 d group)

EMF exposure for 28 d (EMF 28 d group)

sham-exposure for 14 d (sham 14 d group) and sham-exposure for 28 d (sham 2

8 d group). Continuous microwave EMF exposure (900 MHz

power density=1 mW/cm

2

) was conducted to the head of rats for 3 h per day in the EMF groups. Then

behavioral changes were examined using the Morris water maze. The permeability of the blood-brain barrier and signs of neuronal damage in hippocampal region were assessed by immunohistochemical staining for albumin. The ultrastructural changes of the brain tissue were observed by transmission electron microscopy (TEM).       Results       Compared with the sham exposure groups (0 mW/cm

2

)

the EMF exposure groups (1 mW/cm

2

) showed obviously changed intracellular ultrastructure of brain tissue

damaged structure of blood-brain barrier

and significant increased albumin extravasation and uptake into neurons (

P

0.05). The percentage of target quadrant and the times of crossing platform were significantly decreased (

P

0.05) in the EMF 28 d group.       Conclusion       Exposure to 900 MHz microwaves (1 mW/cm

2

) may alter the ability of spatial memory

change blood-brain barrier permeability

and induce the ultrastructural changes in rat hippocampal neurons.