Spontaneous withdrawal in opiate-dependent Fischer 344, Lewis and Sprague-Dawley rats

► This study assessed the effects of chronic morphine in LEW and F344 rat strains. ► Termination of morphine induced withdrawal in both strains. ► There were no differences in severity of withdrawal (aversions and body weight). ► The strains did differ on one behavioral indicator of withdrawal (diarrhea). ► These results were discussed relative to acute morphine in these strains.