Spontaneous Vs. Naloxone-induced Abstinence in Dependent Rats Self-administering L-alpha-acetylmethadol (LAAM) or Morphine

Rats maintained dependence by the self-administration of LAAM or morphine. Following the substitution of saline for LAAM, REM sleep was not disrupted, and the frequency of lever pressing for saline self-injections peaked at about 24 hr. In contrast, following the substitution of saline for morphine, REM sleep was suppressed for 24 hr while the frequency of lever pressing for saline self-injections peaked within 8 hr. When abstinence was induced by hourly iv naloxone injections, REM sleep occurrences were suppressed to a similar degree and for similar durations during naloxone-induced abstinence from both morphine and LAAM. These results suggest that the level of physical dependence maintained during self-administration of LAAM and morphine was similar. The relatively mild abstinence syndrome that was seen during saline substitution in LAAM-dependent rats was most likely related to the long plasma half-lives of the pharmacologically active N-demethylated metabolites of LAAM.