Chronic exposure to ultrasonic frequencies results in selective increase of aggression level in rats

We studied aggression in male Sprague-Dawley rats in a model of a depressive-like state induced by unpredictable treatment with ultrasonic waves with the frequencies of 20-45 kHz for 1, 2 or 3 weeks. We did not find any increase in the number of animals exhibiting aggression in the “Resident- intruder” test after the treatment of any chosen duration. However, the aggressive animals exposed to ultrasound exhibited increased number of attacks and their total duration as well as decreased latency of the first attack compared to the respective scores in the animals of the control group. Taking this into account, we suggest that the initial level of aggression increases in a model of ultrasonic chronic stress.