Earlier studies have shown that the dose of 55 mg/kg/day subcutaneously by pump in the rat results in a plasma level similar to that in patients seen in methadone maintenance.49 These studies showed that, although high doses

of methadone delivered by pump did not alter the direct reinforcing effects of cocaine as seen in self-administration, those doses of methadone did block both spontaneous and cocaine-induced “seeking” or “liking” 10 days after cocaine conditioning. Further, we have suggested that this may be through the mechanism of methadone attenuating or preventing the relative endorphin deficiency resulting from the increased mu-5 HT Receptor inhibitor opioid receptor density Inhibitors,research,lifescience,medical preceded by increased mu-opioid receptor gene expression, but with no concomitant increase Inhibitors,research,lifescience,medical in the endogenous opioids that bind to the mu receptor, that is, no increase in beta-endorphin or in the enkephalin peptides.46 These studies also build upon the early and also much more recent findings that, despite the fact that up to 70% of all persons in the Inhibitors,research,lifescience,medical middle Atlantic states, as well as currently in Tel Aviv, Israel, have concomitant dependence upon cocaine, when presenting for treatment for longstanding dependence on heroin, after 1 year or more of methadone treatment, as expected, the numbers using heroin dropped precipitously, to less than 20% of patients using heroin at any time (as contrasted to heroin use by all patients 3 to

6 times a day prior to entry). This was accompanied by the more surprising findings Inhibitors,research,lifescience,medical that during steady-dose methadone maintenance treatment, the percentage of persons dependent on cocaine drops down to less than 20%, and those using any cocaine to less than 30 %.47,48 Although these beneficial results of methadone maintenance on managing cocaine addiction were always attributed Inhibitors,research,lifescience,medical to the counseling and other psychosocial benefits derived from a good methadone maintenance program, we have, over the last decade, hypothesized that a pharmacological mechanism also

is in place, a hypothesis based on our findings that binge cocaine increases acutely mu-opioid receptor gene expression and on a chronic basis, mu-opioid Resminostat receptor density, and further, that a relative endorphin deficiency thus develops in humans, since there is no concomitant increase of beta-endorphin or enkephalins, as may be directly documented by stress-responsive metyrapone testing.50 These findings suggest that possibly an opioid agonist such as methadone, or possibly a partial agonist, such as buprenorphine, might be able to be effectively used to treat very severe, long-term, cocaine-dependent persons who have not responded to any other available current treatment. Since there are no effective targeted pharma-cotherapies for cocaine addiction, the potential target of the mu-opioid receptor, with now a neurobiological basis for such treatment, might be warranted.