DISRUPTION OF A PUTATIVE WORKING-MEMORY TASK AND SELECTIVE EXPRESSIONOF BRAIN C-FOS FOLLOWING MICROWAVE-INDUCED HYPERTHERMIA

To discern the effects of hyperthermia on working memory, we recorded the ability of rats to discriminate between objects following microwav e radiation exposure. Memory changes were evaluated by measuring relat ive exploration time of a familiar vs. a new stimulus object. A subjec t that extensively reexplores a stimulus with which it has previous ex perience is presumed to exhibit memory loss associated with that objec t. Between training and testing, rats were exposed to various doses: o f microwave radiation, were sham irradiated, or remained in their home cage. Brain (dural) and rectal temperatures were recorded. To discern brain regions activated or possibly damaged by microwave exposure, we also used immunocytochemistry techniques to identify sites of c-fos p rotein expression in the brains of several irradiated/sham-irradiated subjects. Rats exposed to > 5 W/kg exhibited hyperthermia when compare d to nonirradiated controls. Normothermic control subjects (sham-irrad iated rats and rats exposed to 0.1 W/kg) showed a distinct preference for the new object although other microwave-exposed rats (1, 5, 8.5, 9 .3, 10 W/kg) did not. Microwave hyperthermia evoked prominent c-fos ex pression in periventricular strata, hypothalamic nuclei, amygdala, and several areas of the cortex. These data suggest that performance on a putative working memory task may be disrupted by a sufficiently inten se microwave-induced hyperthermia. The pattern of expression of the ea rly proto-oncogene c-fos may suggest candidate brain nuclei that media te the behavioral changes we observed.