Medical/biological study (experimental study)

Disruption of a putative working memory task and selective expression of brain c-fos following microwave-induced hyperthermia med./bio.

By: Mickley GA, Cobb BL, Mason PA, Farrell S

Published in: Physiol Behav 1994; 55 (6): 1029-1038

To study the effects of hyperthermia on working memory, the ability of rats to discriminate between objects following microwave exposure was recorded. Furthermore, the expression of the early proto-oncogene c-fos in the brain was used as a tool to indicate which brain regions were activated or possibly damaged by microwave exposure.

Exposure	Parameters
Exposure 1: 600 MHz Modulation type: CW Exposure duration: 20 min	SAR: 10 mW/g mean (whole body) (9.3 W/kg, 8.5 W/kg, 5 W/kg, 1 W/kg and 0.1 W/kg)

Modulation type	CW

Exposure source	90? corner reflector
Distance between exposed object and exposure source	1 m
Chamber	Anechoic chamber maintained at 24?C
Setup	rats were irradiated individually in 3 mm thick plastic restraint holders
Additional info	The rats remained for 20 min in their home cages (cage control). Electric field was parallel to the long axis of the rats.

Measurand	Value	Type	Method	Mass	Remarks
SAR	10 mW/g	mean	determined by power loss	whole body	9.3 W/kg, 8.5 W/kg, 5 W/kg, 1 W/kg and 0.1 W/kg

Exposed system:

molecular biosynthesis: see "effects on the neurological system"
effects on the neurological system: expression of the early proto-oncogene c-fos in the brain (immunocytochemical measurement)
cognitive/behavioral endpoints: working memory (relative exploration time of a familiar versus a new stimulus object)
thermoregulation: brain and rectal temperature

Investigated system:

Investigated organ system:

Time of investigation:

Animals irradiated by more than 5 W/kg exhibited hyperthermia when compared to nonirradiated control animals. Normothermic control rats (sham-irradiated rats and rats exposed to 0.1 W/kg) showed a distinct preference for the new object although other microwave-irradiated animals with brain hyperthermia (1, 5, 8.5, 9.3, 10 W/kg) did not. These findings suggest a disruption of the memory of the previously explored object.
Microwave hyperthermia evoked significant expression of the early proto-oncogene c-fos in periventricular strata, hypothalamic nuclei, amygdala, and several areas of the cortex. The pattern of c-fos expression may suggest candidate brain nuclei that mediate the behavioral changes observed.
These results indicate that performance on a putative working memory task may be disrupted by a sufficiently intense microwave-induced hyperthermia.

Study character:

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