Negative affect as the primary emotional component in animal models of alcohol abuse and avoidance

Emotion plays a critical role in the development and maintenance of human substance abuse. Even though ultrasonic vocalizations (USVs) are a highly translational means of revealing affective state in preclinical models of substance abuse, difficulties in data management, including time-intensive methods used to tabulate and analyze multidimensional USV data has slowed the development of the field. To address this problem, we developed an automated USV analysis program (e.g., (WAV-file Automated Analysis of Vocalizations Environment Specific or “WAAVES”) that not only allows for rapid tabulation of USV counts, but assessment of a variety of USV acoustic characteristics (e.g. mean frequency, duration, bandwidth and power) for each individual USV as well. We used the WAAVES program to assess USV counts and acoustic characteristics to examine changes in affective state during a alcohol consumption paradigm (e.g., drinking-in-the-dark or “DID”) involving 7-hour daily sessions over 8 weeks. USV data analyses from lengthy, long duration experiments would not be feasible in the absence of automated analyses such as WAAVES. Thus our findings revealing that alcohol-naïve rats selectively bred to consume excessive levels of alcohol (e.g., alcohol-preferring “P” rats) have baseline bias toward negative affect and that alcohol consumption influences negative affect USVs and acoustic characteristics was entirely novel in the USV and alcohol addiction field.

In our next study, we decided to extend the examination of USV acoustic characteristics in divergent rat lines selectively bred for high alcohol consumption and alcohol avoidance (alcohol-preferring “P” and non-alcohol preferring “NP” rats, respectively) using advanced statistical techniques. Specifically, we applied a linear mixed model (LMM) to each acoustic characteristic (mean frequency, duration, bandwidth and power) separately and used linear discriminant analysis (LDA) to examine all four acoustic characteristics together to determine if acoustic characteristics could distinguish between these divergent rat lines. LMM findings revealed extensive differences in all four characteristics for the negative affect-related subtype of USVs, while the positive affect-related USVs displayed minimal differences between high- and low-alcohol preferring rat lines. The LDA analyses echoed these results, showing that negative, but not positive affect-related USV characteristics were capable of distinguishing these rat lines.