Opiate Withdrawal and Conditioned Withdrawal Enhance Consolidation of Object Memory in Male Sprague-Dawley Rats

Abstract

The present study explored the effects of acute precipitated and conditioned withdrawal on object memory. Using the object recognition task, it was first demonstrated that 3 mg/kg naltrexone enhanced memory in morphine-maintained (osmotic mini-pumps;10 mg/kg/day) rats when administered immediately but not 6 h post-sample. Importantly, post-sample naltrexone enhanced memory in the same animals 7 days later following removal of mini pumps. To establish that conditioned withdrawal could also alter memory, morphine-maintained animals received naltrexone in a distinctive context (CS+) and vehicle in a separate context (CS-) alternatively over 10 days. At the end of conditioning, confinement to this CS+ produced a conditioned locomotion suppression. More important, immediate but not delayed post-sample exposure to CS+ enhanced memory. These experiments indicate that both acute precipitated and conditioned withdrawal have significant facilitatory effects on memory consolidation and thus can play a role in the development of addictive behaviours.