Head-Shake distributions during self-maintained dependence on morphine, methadone, and l-alpha-acetylmethadol (LAAM) in the rat

Abstract

Adult female Sprague-Dawley rats were prepared with chronic cortical and muscle electrodes and i.v. cannulas, made tolerant to and physically dependent on morphine, and trained to lever press for i.v. morphine self-injections to maintain dependence. Methadone or l-alpha-acetylmethadol (LAAM) was then substituted for morphine in some of these rats. During self-maintained dependence on either morphine or methadone, head shakes appeared and increased in frequency before lever pressing for selfinjections. In contrast, there were fewer head shakes during LAAM dependence, which were evenly distributed over the entire duration of the interinjection interval. These findings suggest a relationship between head-shake distributions, drug-seeking behavior, and the pharmacodynamics of these three narcotics.