Classifying Ultrasonic Vocalization Subtypes During Oxycodone Self-Administration in Male Rats
Opioid abuse is a rampant problem in the United States, claiming the lives of over 47,000 individuals in 2018 alone. Understanding opioid abuse – how and why individuals administer substances to the point of dependence – remains critically important in the development of treatments for opioid use disorders. Opioids are known to produce subjectively positive feelings from humans, underscoring their abuse potential, however this has been difficult to study in animals. Intriguingly, rats make high-pitched vocal emissions called ultrasonic vocalizations (USVs), and previous work suggests that USVs act as both a communication tool and an emotional marker. Specifically, numerous studies support that USVs ~22-kHz in frequency are emitted in situations evoking a negative emotional state, whereas USVs ~50-kHz mark a positive emotional state. More recently, researchers in the addiction field have come to realize that within the 50-kHz range of USVs, there are numerous subtypes with potential functional relevance. Thus, the question is whether these subtypes represent more specific emotions that can then be used to further understand the forces behind addiction. Using male rats in an oxycodone self administration experiment, we studied if and how different 50-kHZ USV subtypes changed in frequency at different timepoints in the acquisition phase. These timepoints were before the lever (used for drug infusion) extended, after the lever extended, and then 20 seconds after the first 10 infusions on Days 1, 7 and 13. Our preliminary data suggests two major trends during the pre-lever timepoint: 1) there is a decrease in the number of fixed frequency (FF) USVs throughout the sessions and 2) on Days 7 and 13, the majority of the USVs belong to the Sweep with 1 modulation (SW1) and Step with 1 modulation (ST1) subtypes.