Acute Effects of Local Exposure to Radio-frequency Electro- Magnetic Fields with a Loop Antenna on the Cerebral Microcirculation in Rats

A cranial window method modified for our experiment enabled to observe the cerebral microcirculation including the hemodynamic changes, the leukocyte behavior, and the blood-brain barrier(BBB) function during preand postexposure to radio-frequency electromagnetic fields (EMF) with a loop antenna in rats. No noticeable changes in the BBB function, the diameter of venule, and the number of sticking leukocyte were recognized under the present conditions due to EMF exposure. However, further investigation of plasma velocity and the number of rolling leukocyte, which were partially altered after due to EMF exposure, are needed. INTRODUCTION Biological effects of radio-frequency electromagnetic fields(EMF) on the blood-brain barrier (BBB) function has been extensively studied in experimental animals. Most of these studies, however, have been performed by the histological or morphological investigations due to postmortem examination. Besides these, little information are available about the *This study was financially supported by the committee to Promote Research on the Possible Biological Effects of Electromagnetic Fields, Ministry of Pablic Management, Home Affairs, Posts and Telecommunications, Japan. exposure effects of EMF on cerebral microcirculation. A closed cranial window (CW) method have been widely used among many researchers as a beneficial method to investigate the cerebral microcirculation including BBB function [1]. We partially modified this method for evaluating the exposure effect to EMF on the cerebral microcirculation. Our previous results from acute exposure effects of EMF using a monopole antenna showed that no noticeable changes have been recognized due to EMF exposure [2]. The present study aims to investigate the acute exposure effect of EMF on the cerebral microcirculation in rats using the loop antenna that enabled more local exposure to the brain than the monopole antenna does. MATERIAL AND METHODS Nineteen male Sprague-Dawley rats (B.W. 426±19 g) were used in the study. Both CW implantation and the intravitalmicroscopic observation were performed under anesthesia with a cocktail (100mg/kg i.m.) of Ketamine hydrochloride and Xylazine hydrochloride (10:1, w/w). EMF exposure system consisted of a small anechoic chamber and a loop antenna. The head of rat was positioned 2mm under the loop antenna and was locally exposed to 1,439MHz electromagnetic near-field TDMA (time division multiple access) signal for PDC (Personal Digital Cellular, Japanese cellular telephone standard) system. The intensity of EMF exposure was controlled by average specific absorption rate (SAR) of the brain at 0.2, 2.0, and 7.5W/kg as shown in Table 1. The EMF exposure duration was 10 minutes. After exposure to EMF, the animal’s head was immediately positioned in a stereotactic frame for microscopic observations. The exposure for 10 min and the observation for 20 min were performed sequentially from 0.2W/kg SAR. The pial microcirculation within a CW was investigated by a fluorescent microscope equipped with an SIT camera and a confocal scanning laser microscope. In order to measure hemodynamic changes, plasma velocities, leukocyte behavior and BBB-function, two-types of fluorescent dye and fluorescent microparticles were administered via the tail vein. Results are given as means±s.e. mean. The statistical analysis was performed by Student’s t-test or ANOVA.