Cat‐Exposure Results in Significantly More Elicited Alarm Calls (22kHz Ultrasonic Vocalizations, USVs) Compared to Snake‐, Ferret‐, or Sham‐Exposure During a Rodent Model of Traumatic Stress

Ultrasonic vocalizations (USVs) in rodents can be used as a method of measuring the affective state of the animal during a wide range of experiences. Adult rats generally emit two types of USVs: “alarm” calls (22kHz) and calls during “nonaggressive” behavioral situations (50kHz). Rat USVs can therefore be measured and classified when a rat is in the presence of a natural predator. In humans, PTSD results from exposure to a traumatic event(s) which evoke a level of fear, helplessness, or horror with a threat of physical harm. In this study, a rodent model of traumatic stress was used to elicit a traumatic event via (a single protected) exposure to a predator species (snake, ferret, or cat). To determine the impact of these animals as a natural predator species, we examined each one individually and assessed USVs to determine the impact on ultrasonic communication by these predator species. Rats (~11–12 weeks old) were behaviorally assessed pre‐ and post‐predator exposure on several behavioral tasks. USVs were recorded during the open field task and on predator exposure days (pre‐ and post‐exposure, in transfer cages, and during predator exposure, in the predator home cage). To record the USVs, an Avisoft‐Ultra SoundGate electret 116Hnb microphone and Recorder USGH program (Avisoft Bioacoutistc, Germany) were used. Rats were placed in a protective predator tube, and then placed in the predator home cage. These tubes allow for visual and olfactory cues; however, prevent the rat from gross physical contact. The rats were exposed to one of the predators or sham (using a predator tube free of predator scent). Sham‐exposed rats emitted significantly more 50kHz USVs than any of the predator‐ exposed rats (F(3,44)= 9.12, p < .0001). Cat‐exposed rats did not emit any 50kHz USVs during exposure, but emitted the most 22kHz USVs, significantly more than any other predator or sham (F(3,44)= 3.29, p < .05). 22kHz USVs were emitted by 75% of cat‐exposed rats and only 2 of 12 snake‐exposed rats. Rats exposed to the ferret and sham did not emit any fear‐induced 22kHz vocalizations, only 50kHz vocalizations. Based on emitted ultrasonic calls, the cat appears to be the most impactful, eliciting the most fear‐induced vocalizations. To the contrary, the ferret did not cause any fear‐inducing vocalizations. This study has provided the ground work for the recording of USVs during our laboratory's rodent model of traumatic stress. For future research, this method can be used as an additional measure, along with assessing overt behavior measures, to identify candidate therapeutic compounds for the prevention and/or treatment of PTSD. Support or Funding Information Material has been reviewed by the Walter Reed Army Institute of Research. There is no objection to its presentation and/or publication. The opinions or assertions contained herein are the private views of the author, and are not to be construed as official, or as reflecting true views of the Department of the Army or the Department of Defense. Research was conducted in an AAALACi accredited facility in compliance with the Animal Welfare Act and other federal statutes and regulations relating to animals and experiments involving animals and adheres to principles stated in the Guide for the Care and Use of Laboratory Animals , NRC Publication, 2011 edition. Supported by the Military Operational Medicine Research Program, US Army Medical Research and Materiel Command.