"Exposure Equipment and Dosimetry

The exposure system consisted of two identical anechoic chambers (3 3 3 3 3 m). One was fitted with a GSM-900 base-station antenna located 1.8 m above the animal cages. The second chamber was used for sham exposure. Both chambers had independent temperature, ventilation and lighting controls. Room temperature was maintained at 22 ± 28C. Rats were exposed to plane-wave microwaves emitted from the base-station antenna. The animal cages for exposure were constructed of Plexiglast, divided into 20 separate compartments (6 cm wide, 17 cm long, 6 cm high) in two rows that kept the animals parallel to the electric field. Gel phantoms were placed in the four outermost compartments to provide uniform exposure for the 16 exposed rats. The stress due to confinement of the animals was minimal, since the rats were able to turn around. However, their heads were kept facing outward most of the time by painting the outer part of the compartment lids black. Neither food nor water was provided to the animals during the daily 2-h exposure.

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Based on these data and the GSM generator settings used in the various runs, the final evaluation of SARs, averaged over the compartments and the rat body, were 0.1, 0.7, 1.4, 2.2 and 3.5 6 0.2 W/kg.

Exposure Protocol

Two experiments were conducted. In the first experiment, after DMBA treatment, 64 rats were randomly divided into four groups: three exposed groups with 16 rats in each group (1.4, 2.2 and 3.5 W/kg) and one sham exposed group (16 rats). Another untreated cage-control group included eight rats. In the second experiment, an identical number of groups and animals per group were used and the SARs were 0.1, 0.7 and 1.4 W/kg. Except for the SAR levels and the starting dates, the protocols were identical in both experiments. In each experiment, 10 mg of DMBA dissolved in 1 ml sesame oil was administered to the animals by a single gastric intubation without anesthesia. All treated rats were 55 days old. Exposure started 10 days 4 G. Thuroczy, Budapest, private communication. after DMBA treatment, i.e. at 65 days of age, to allow for initiation of carcinogenesis in the absence of exposure. Rats were exposed or sham exposed in groups of 16 for 2 h per day (between 09:00 and 17:00), 5 days/week for 9 weeks, with a rotation among groups to minimize circadian effects.

Tumor Monitoring

Animals were examined, always by the same researcher, every 3 days from day 20 after DMBA treatment to detect tumor appearance and localization and to determine tumor numbers. The total tumor volume was measured once per week. Tumor volume was calculated as (length 3 width2)/2. Body weight was monitored once a week. Three weeks after the end of exposure, all rats were killed humanely after anesthesia for autopsy. For evaluation of mammary tumors, the skin was opened by a midline incision to expose the six pairs of mammary glands extending from the salivary glands to the perianal region. All macroscopic mammary tumors were removed and recorded. Tumors were fixed in Bouin’s solution, embedded in paraffin, sectioned (6 mm thick), stained with hematoxylin and eosin, and examined histologically to confirm the macroscopic diagnosis. A full histopathological evaluation of all mammary tumors was performed blindly at the Veterinary School of Maisons- Alfort by a single biologist (FLC). Histopathology of mammary glands without macroscopically observed tumors was not examined, and no other gross pathology observations were performed. The malignant or benign nature of the tumors was assessed on the basis of classification (3) and the macroscopic and histological observations.

Statistical Analysis

Daily weights (not shown) were analyzed using non-parametric statistical methods (ANOVA on repeated measurements). The time profiles of tumor latency and incidence were analyzed as survival curves using the logrank test (Kaplan-Meier), while multiplicity was analyzed using ANOVA on repeated measurements. All statistical analyses were performed using the StatView software."

experiment 1 SD rats, female

HAWC