Predator Odor Stressor, 2,3,5-trimethyl-3-thiazoline (TMT): Assessment of stress reactive behaviors during an animal model of traumatic stress in rats

Abstract

Animal models utilizing predator odor stress are important in understanding implications for post-traumatic stress disorder. 2,5-dihydro-2,4,5-trimethylthiazoline (TMT) has been used to measure stress reactive behaviors during TMT exposure, indicative of stress coping behaviors. In addition, long-term consequences of stress including contextual-induced stress memory, anxiety-like and hyperarousal behaviors, and subsequent increases in alcohol self- administration can also be examined after TMT exposure. In this article, we describe the TMT exposure protocol used in our lab and how we measure different stress-reactive behaviors that rats engage in during the TMT exposure. Rats are placed in Plexiglas chambers that contains white bedding on the bottom of the chamber and a metal basket in the top right corner that contains a filter paper on which 10 {micro}L of TMT is pipetted onto. During the 10 min exposure, rats can move around the chamber freely. Exposures are recorded by a video camera for later analysis. During TMT exposure, rats engage in a variety of stress-reactive behaviors, including digging and immobility behavior. These are two distinctly different types of stress-induced behavioral coping strategies to measure individual differences in stress responsivity. To examine individual differences, we group rats into TMT-subgroups based on time spent engaging in digging or immobility behavior. We calculate a digging/immobility ratio score in which we divide the total time spent digging by the total time spent immobile. A cut-off strategy is used such that rats with a criterion ratio score below 1.0 are classified as TMT-1 (i.e., low digging/high immobility; greater passive coping) and rats with a ratio score above 1.0 are classified as TMT-2 (i.e., high digging/low immobility; greater active coping). In the present paper, we provide a detailed description of the TMT exposure protocol and step- by-step process in evaluation of stress-reactive behaviors. Basic Protocol 1: Predator Odor Stressor Exposure using TMT Basic Protocol 2: Description of Stress-Reactive Behaviors during TMT Exposure and Formation of TMT-subgroups