The effects of xylazine on locomotion and motor behaviour in a planarian model

In recent years, the recreational use of xylazine has increased dramatically in the USA. Although xylazine has been used as an anesthetic in veterinary medicine for decades, little is known about its behavioral effects. We took advantage of the planarian's innate negative phototaxis, the reliable movement from the light side to the dark side of a Petri dish, to explore the organism's suitability as an animal model for investigating the preclinical pharmacology of xylazine. In two experiments, we tested the effects of several doses of xylazine on locomotion by recording the latency to transition into an opaque area. Xylazine disrupted locomotion in a dose-dependent fashion. Larger doses first produced a period of hyperkinesia without forward motion. This was followed by a period of sedation. Physical stimulation disrupted sedation and evoked the resumption of locomotion. Data on the behavioral effects of xylazine outside of anesthesia and sedation are limited; therefore, the current study adds to a relatively small literature on the behavioral effects of xylazine.