Withdrawal from chronic morphine administration causes prolonged enhancement of immobility in rat forced swimming test

Rationale: Opiate-dependent subjects experience severe depression as one of the subjective symptoms during withdrawal. No experimental work, however, has focused on the ability of opiate-withdrawal to produce depression-like behavior in dependent animal. Objectives. We therefore investigated whether withdrawal from chronic morphine treatment affects immobility in forced swimming test in rats. Methods: Morphine was administered in a dose escalation fashion using doses ranging from 20 to 140 mg/kg twice daily for 14 days, followed by 1-6 days of withdrawal, and their duration of immobility was assessed. Results: After the last morphine treatment, an increase in immobility occurred late on day 3 and persisted to at least day 6 of withdrawal without any change in ambulatory activity. Conclusions: The results suggest that the morphine withdrawal resulted in prolonged enhancement of depression-like behavior in drug-dependent laboratory animals.