Is slow-onset long-acting monoamine transport blockade to cocaine as methadone is to heroin? Implication for anti-addiction medications.

The success of methadone in treating opiate addiction has suggested that long-acting agonist therapies may be similarly useful for treating cocaine addiction. Here, we examined this hypothesis, using the slow-onset long-acting monoamine reuptake inhibitor 31,345, a trans-aminotetralin analog, in a variety of addiction-related animal models, and compared it with methadone's effects on heroin's actions in the same animal models. Systemic administration of 31,345 produced long-lasting enhancement of electrical brain-stimulation reward (BSR) and extracellular nucleus accumbens (NAc) dopamine (DA). Pretreatment with 31,345 augmented cocaine-enhanced BSR, prolonged cocaine-enhanced NAc DA, and produced a long-term (24-48  h) reduction in cocaine self-administration rate without obvious extinction pattern, suggesting an additive effect of 31,345 with cocaine. In contrast, methadone pretreatment not only dose-dependently inhibited heroin self-administration with an extinction pattern but also dose-dependently inhibited heroin-enhanced BSR and NAc DA, suggesting functional antagonism by methadone of heroin's actions. In addition, 31,345 appears to possess significant abuse liability, as it produces dose-dependent enhancement of BSR and NAc DA, maintains a low rate of self-administration behavior, and dose-dependently reinstates drug-seeking behavior. In contrast, methadone only partially maintains self-administration with an extinction pattern, and fails to induce reinstatement of drug-seeking behavior. These findings suggest that 31,345 is a cocaine-like slow-onset long-acting monoamine transporter inhibitor that may act as an agonist therapy for cocaine addiction. However, its pattern of action appears to be significantly different from that of methadone. Ideal agonist substitutes for cocaine should fully emulate methadone's actions, that is, functionally antagonizing cocaine's action while blocking monoamine transporters to augment synaptic DA.