Mesolimbic dopaminergic decline after cannabinoid withdrawal

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Abstract
The mesolimbic dopamine system has recently been implicated in the long-term aversive consequences of withdrawal from major drugs of abuse. In the present study we sought to determine whether mesolimbic dopamine neurons are involved in the neurobiologic mechanisms underlying withdrawal from chronic cannabinoid exposure. Rats were treated chronically with the major psychoactive ingredient of hashish and marijuana, Δ9-tetrahydrocannabinol (Δ9-THC). Administration of the cannabinoid antagonist SR 141716A precipitated an intense behavioral withdrawal syndrome, whereas abrupt Δ9-THC suspension failed to produce overt signs of abstinence. In contrast, both groups showed a reduction in dopamine cells activity as indicated by extracellular single unit recordings from antidromically identified meso-accumbens dopamine neurons. The administration of Δ9-THC to spontaneously withdrawn rats restored neuronal activity. Conversely, SR 141716A produced a further decrease of spontaneous activity in cannabinoid-treated although it was ineffective in control rats. These data indicate that withdrawal from chronic cannabinoid administration is associated with reduced dopaminergic transmission in the limbic system, similar to that observed with other addictive drugs; these changes in neuronal plasticity may play a role in drug craving and relapse into drug addiction.