COMMENTS: Depletion of frontal cortex dopamine (which happens in addiction), resulted in greater and greater dopamine response to food and sex. Another finding is that frontal cortex dopamine will inhibit reward circuit activity.
Mitchell JB, Gratton A.
Douglas Hospital Research Center, Department of Psychiatry, McGill University, Montreal, Quebec, Canada.
High-speed chronoamperometry was used to monitor the extracellular concentration of dopamine within the nucleus accumbens, a terminal field of the mesolimbic dopamine system, in freely behaving rats exposed daily, on 6 consecutive days, to one of two naturally reinforcing stimuli; a highly palatable food or sex-related olfactory cues.
The animals either were intact or had previously received microinjections of 6-hydroxydopamine into prefrontal cortex to lesion dopamine terminals. Food reliably elicited increases in dopamine levels within the nucleus accumbens, and if prefrontal cortical dopamine had been depleted, the response to food increased with repeated testing. Animals exposed to the sexually relevant olfactory stimulus showed progressively enhanced dopamine release with repeated testing, and this enhancement was potentiated by prefrontal cortical dopamine depletion.
These results indicate that repeated exposure to naturally reinforcing events can lead to a hyperresponsiveness of the mesolimbic dopamine system upon future activation, and suggest that the dopamine projection to prefrontal cortex exerts an indirect, inhibitory influence on mesolimbic dopamine neurotransmission.