Evaluation of Candidates for Systemic Analgesia and General Anesthesia in the Emerging Model Cephalopod, Euprymna berryi

SIMPLE SUMMARY: Analgesia and anesthesia in aquatic animals can be challenging, and are exceptionally difficult to implement and evaluate in invertebrate species. In this study we test multiple analgesic candidates in the small Hummingbird Bobtail Squid, to identify drugs that may be effective at enhancing welfare in cephalopods. Cephalopods are growing in popularity as comparative neuroscience models, and there is a pressing need to refine procedures to permit their ethical use. In addition to identifying analgesic candidates for cephalopods for the first time, we also validate a general anesthesia protocol for E. berryi that has been tested in other cephalopods. ABSTRACT: Cephalopods’ remarkable behavior and complex neurobiology make them valuable comparative model organisms, but studies aimed at enhancing welfare of captive cephalopods remain uncommon. Increasing regulation of cephalopods in research laboratories has resulted in growing interest in welfare-oriented refinements, including analgesia and anesthesia. Although general and local anesthesia in cephalopods have received limited prior study, there have been no studies of systemic analgesics in cephalopods to date. Here we show that analgesics from several different drug classes may be effective in E. berryi. Buprenorphine, ketorolac and dexmedetomidine, at doses similar to those used in fish, showed promising effects on baseline nociceptive thresholds, excitability of peripheral sensory nerves, and on behavioral responses to transient noxious stimulation. We found no evidence of positive effects of acetaminophen or ketamine administered at doses that are effective in vertebrates. Bioinformatic analyses suggested conserved candidate receptors for dexmedetomidine and ketorolac, but not buprenorphine. We also show that rapid general immersion anesthesia using a mix of MgCl(2) and ethanol was successful in E. berryi at multiple age classes, similar to findings in other cephalopods. These data indicate that systemic analgesia and general anesthesia in Euprymna berryi are achievable welfare enhancing interventions, but further study and refinement is warranted.