Fentanyl and Alcohol Co-Exposure Induce Robust, Sustained Hyperlocomotion and Neural Circuit Disruption in Larval Zebrafish

The constantly evolving trends in substance abuse are a major concern for health authorities worldwide, and these trends include an increasing prevalence of poly-substance misuse. For instance, opioid overdoses are frequently accompanied by alcohol co-use, yet the combined effects of these substances remain poorly understood. Using zebrafish as a highly relevant vertebrate model of neuropharmacology, we investigated the interactions between fentanyl and alcohol, uncovering a unique and robust hyperlocomotor response characterized by initial locomotor suppression followed by persistent, erratic hyperlocomotion. Alcohol was found to be critical to this phenomenon, as substitution with other GABAA modulators failed to replicate the effect. However, the response was replicable with heroin and remifentanil, suggesting an opioid-class wide effect. In vivo whole brain imaging further demonstrated dysregulated neuronal activity, with co-administration with alcohol causing potentiated neuronal activity compared to individual drug exposures and controls. Collectively, these findings suggested an integral role of ethanol and fentanyl co-administration in dysregulated neuronal responses and reveals a complex neurobehavioral mechanism. These observations suggest further investigation is warranted into the use of the larval zebrafish model for studying the neuropharmacological interactions of multiple substances of abuse.