Use of a shuttle box model to assess the behavioral and analgesic effects of opioid injections in goldfish (Carassius auratus)

OBJECTIVE To evaluate if opioid-induced behavioral effects, such as sedation, can be detected using a shuttle box experimental apparatus and whether thermal preference following noxious stimulation using mustard oil is reversed by morphine administration in fish. METHODS 5 goldfish ( Carassius auratus) underwent 2 randomized blinded experimental trials, with a crossover study design. First, opioid effects were tested in a shuttle box without painful stimulus. Fish were injected 5 days apart with butorphanol at 0.4 or 10 mg/kg, morphine at 5 or 10 mg/kg, or saline IM. After 30 minutes, each fish was placed in a shuttle box for 2 hours with a temperature gradient of 26 to 28 degrees C. Temperature preference, time spent immobile, and swimming velocity were assessed. The second trial consisted of cutaneous noxious stimulation using mustard oil immersion for 5 minutes followed by an assessment of thermal preference for 4 minutes in the shuttle box after either morphine at 10 mg/kg or saline IM injections. Linear mixed models were used to compare treatment groups. RESULTS Before noxious stimulation, a low dose of morphine caused sedation compared with control group and high-dose morphine and butorphanol treatments. Immersion in mustard oil caused fish to spend more time in the cold area in the control group. Morphine administration reversed this pattern. CONCLUSIONS The sedative and analgesic effects of opioids were detected through this model. CLINICAL RELEVANCE The shuttle box model could be used to assess the analgesic effects of other opioids in goldfish while reducing biases associated with the sedative and stimulatory effects of these drugs.