REM sleep distributions in post-addict rats relapsing to morphine self-administration: effects of naloxone subcutaneous pellets

Abstract

Female Sprague-Dawley rats were prepared with chronic cortical and temporalis muscle electrodes and i.v. cannulas. They were administered i.v. injections of morphine to produce tolerance and physical dependence, then trained to lever press for i.v. self-injections of morphine (10 mg/kg) to maintain dependence. They were subsequently withdrawn for two weeks, implanted subcutaneously with one or two pellets of naloxone base, 100 mg each, or placebo pellets, returned to the experimental cages and allowed to relapse to self-administration of either saline or morphine. Rats with placebo pellets relapsed to morphine self-administration and reestablished the dependence state. However, rats implanted with naloxone and then permitted to self-administer morphine extinguished their lever pressing ("drug-seeking behavior"). Similar results were obtained with rats implanted with placebo pellets and self-administering saline. The self-injections of morphine by rats implanted with placebo pellets severely suppressed REM sleep and altered its normal distribution. Rats implanted with naloxone pellets and that subsequently extinguished their lever pressing, however, did not exhibit a change in REM sleep distributions. Similarly, self-injections of isotonic saline did not exert an effect on REM sleep distributions. These findings suggest that a correlation between REM sleep distributions, drug-seeking behavior, and morphine-naloxone interaction prevailed.