Skin samples of 51 rats were collected at 6 and 24 h after exposure for microarray analysis. For histopathology analysis the skin of 36 was harvested from a separate group of rats at 3-6 h or 24-48 h after exposure.
Temperature control (42°C) was also performed.
Exposure duration: continuous for about 60 min
Rats were subjected to sham exposure, to 42°C environmental heat, or to 35 GHz millimeter waves at 75 mW/cm². Animal exposures were performed as described previously [Millenbaugh et al., 2006] with some modifications. Preliminary experiments indicated that a colonic temperature of 41-42°C would provide a dose close to the maximum dose used in previous studies of MMW overexposure in this animal model [Millenbaugh et al., 2006; Ryan et al., 1997 and 1996].
|Setup||Rats were placed on a custom-designed Styrofoam stand and were exposed to MMW until the colonic temperature reached 41-42°C which took a total of 58.6 ± 4.7 min including a 5-min pre-exposure control period.|
|Sham exposure||A sham exposure was conducted.|
|Additional info||During the 60-min sham exposure in the same setup, colonic temperatures were maintained at 37 ± 0.5°C using a water-perfused pad set at 37°C. Environmental heat control rats were exposed to warm air at 42°C in a custom-designed environmental chamber until the colonic temperature reached 41-42°C.|
|power density||75 mW/cm²||-||-||-||-|
Changes were detected in 56 genes at 6 h and 58 genes at 24 h in the millimeter wave exposed rats. Genes associated with regulation of transcription, protein folding, oxidative stress, immune response, and tissue matrix turnover were affected at both times. At 24 h, more genes related to extracellular matrix structure and chemokine activity were altered. Up-regulation of some genes at 24 h was confirmed by RT-PCR.
In addition, the authors identified significant microscopic changes in skin induced by millimeter wave exposure and thus demonstrated that the detected changes in gene transcription may be associated with observable alterations in cell behavior and tissue structure.
The data are indicative of thermally induced injury to skin tissue. The observed responses to millimeter wave exposure differ significantly from those induced by warm air and from the sham exposure. This suggests that the differences in temperature gradients within the skin are the cause of the observed histological and molecular changes.