Dopamine D-3 receptor agents as potential new medications for drug addiction

All drugs abused by humans increase dopamine in the shell of nucleus accumbens, which implicate the neurons of this structure in their hedonic and reinforcing properties. Among the various dopamine receptor subtypes, the D-1 (D1R) and D-3 (D3R) receptors co-localise in accumbal shell neurons. Synergistic D1R/D3R interactions at this level were found on gene expression and during induction and expression of behavioral sensitisation to levodopa in rats bearing unilateral lesions of dopamine neurons. Behavioral sensitisation to abused drugs is a component of their long-term effects, converging pharmacologic, human postmortem and genetic studies suggest the involvement of the D3R in reinforcing effects of drugs; D3R agonists reduced cocaine self-administration in rats, without disrupting the maintenance of self-administration. These data suggest the use of D3R agonists as partial substitutes to treat cocaine dependence, by affecting its reward component. However, substitution therapies maintain dependence and may be inefficient on drug craving and relapse, which are the unsolved and critical problems in the treatment of drug addiction. Recently, a highly selective and partial D3R agonist was shown to reduce cocaine-associated cue-controlled behaviour in rats, without having any primary intrinsic effects. As drug-associated cues maintain drug-seeking in animals and elicit craving and relapse in humans, such D3R agents have potential therapeutic applications. (C) 2000 Editions scientifiques et medicales Elsevier SAS.