Shocking News: A Rat's Tail of Uncertainty

Type: Undergraduate
Author(s): Megan T Whittington Psychology Brenton G Cooper Psychology James O Taylor Psychology
Advisor(s): Brenton Cooper Psychology

The ultrasonic vocalizations (USVs) of rats are produced at frequencies above the level of human hearing. USVs are often used as a tool to assess the emotional state of rats. Previous research has identified two main call types for rats: 22 kHz (related to strongly negative emotion) and 50 kHz. 50 kHz calls can then be further broken down into constant frequency (CF) and frequency modulated (FM) subtypes. FM calls are produced with a bandwidth greater than 15 kHz; these calls are related to positive emotional states. Whereas, CF calls are produced with a constant frequency and a bandwidth less than 10 kHz. Our lab hypothesizes that CF 50 kHz calls are expressions of anxiety in rats. Our lab has previously explored the vocalizations of rats across a continuum of negative affective state (i.e., from anxiety to fear) within a single testing session using a sequence of temporally consistent mild footshocks. The current experiment explores USV production in male and female rats when the temporal predictability was reduced by randomizing the time between footshocks. We utilized an unpredictable footshock paradigm with the goal of increasing or prolonging a state of anxiety as compared to our previous procedure. In this paradigm, shocks were administered across three successive days: on Day 1, mild footshocks were administered in a pseudo-randomized pattern, on Day 2, subjects were returned to the same context but did not receive footshocks, and on Day 3, a single reinstatement shock was administered. In addition to USVs, rearing and freezing behavior were also recorded and used to assess anxiety and fear. To explore sex differences, both male and female rats were tested in this paradigm. Significant differences between sexes were found in both overt behavior (rearing and freezing) as well as USV production. Specifically, the male rats exhibited behavior that suggests a more strongly negative emotional state (i.e., fear). These results could aid in the construction of a more efficient animal model to use in research for the study of anxiety disorders and potential therapeutic interventions.