Hyperbaric oxygen treatment suppresses withdrawal signs in morphine-dependent mice

•Physical dependence was induced by twice-daily morphine injections over 4 days.•Naloxone precipitated jumping, tremors, wet-dog shakes, rearing and defecation.•Withdrawal signs were suppressed by treatment with hyperbaric oxygen (HBO2).

Hyperbaric oxygen (HBO2) therapy reportedly reduces opiate withdrawal in human subjects. The purpose of this research was to determine whether HBO2 treatment could suppress physical signs of withdrawal in opiate-dependent mice. Male NIH Swiss mice were injected s.c. with morphine sulfate twice a day for 4 days, the daily dose gradually increasing from 50 mg/kg on day 1 to 125 mg/kg on day 4. On day 5, withdrawal was precipitated by i.p. injection of 5.0 mg/kg naloxone. Mice were observed for physical withdrawal signs, including jumping, forepaw tremor, wet-dog shakes, rearing and defecation for 30 min. Sixty min prior to the naloxone injection, different groups of mice received either a 30-min or 60-min HBO2 treatment at 3.5 atm absolute. HBO2 treatment significantly reduced naloxone-precipitated jumping, forepaw tremor, wet-dog shakes, rearing and defecation. Based on these experimental findings, we concluded that treatment with HBO2 can suppress physical signs of withdrawal syndrome in morphine-dependent mice.