Lai H, Horita A, Guy AW (1994)

In previous research these authors reported that rats exposed for 45minutes to pulsed 2450 MHz microwaves showed a deficit in learning to perform in the radial-arm maze. This task involves spatial memory functions. The objective of the present research was to investigate the brain mechanisms involved in the previously observed spatial memory deficit.

Male rats were exposed for 45 minutes to 2450 MHz pulsed microwaves at an average power density of 1 mW/cm² (average whole body SAR of 0.6 W/kg). Control rats were sham-exposed. At the end of the exposure period the rats were placed in the central hub of a 12-arm radial maze and allowed to explore the maze and obtain food bait placed at the food wells. The animals were observed by an experimenter in an adjacent room via closed circuit television and were also videotaped. Before exposure in each of 10 training sessions the rats were given one of the following intraperitoneal injections: Saline, physostigmine, naltrexone, or naloxone.

The microwave-exposed rats learned significantly slower than the sham-exposed animals. Pre-treatment with physostigmine or naltrexone reversed this deficit, but naloxone did not. The authors hypothesize that the spatial memory deficits are caused by activation of central opioids, which in turn leads to a decrease in cholinergic activity in the hippocampus and frontal cortex. Physostigmine stimulates this cholinergic function and naltrexone blocks the action of the opioids. Naloxone only affects peripheral opioids, and, therefore, had no effect on the observed spatial memory deficit.