The role of self-administration in morphine withdrawal in rats

Rats assigned to a self-administration-of-morphine group (SA-M) could press a lever in an operant chamber to deliver an intravenous infusion of morphine to themselves and to a yoked morphine (Y-M) rat, and an infusion of Ringer’s solution to another yoked rat. Although rats assigned to SA-M and Y-M groups received the same drug doses at the same time, withdrawal symptoms were more pronounced in SA-M rats. Possible mechanisms for the differences in drug withdrawal between animals that self-administer morphine and animals that passively receive the drug are discussed.