Dopamine and serotonin imbalances in the left anterior cingulate and pyriform cortices following the repeated intermittent administration of cocaine

Studies on the neurobiology of cocaine abuse suggest that cocaine directly modifies the activity of dopamine neurons projecting from the dopaminc-synthesizing cells of the ventral tegmental area to the nucleus accumbens. The repeated use of cocaine produces persistent adaptations within the mesocorticolimbic system and the resulting changes in monoamine neurotransmission may lead to behavioral sensitization. The present series of experiments sought to determine the effects of the repeated, intermittent administration of cocaine for five days on (i) the expression of locomotor activity in response to a cocaine challenge that took place two days after discontinuation of the pretreatment regimen; (ii) the ex vivo levels of biogenic monoamines, choline and acetylcholine in the nucleus accumbens, the dorsolateral caudate nucleus, as well as the anterior cingulate, frontal motor, frontal somatosensory and pyriform cortices; and (iii) the degree of neurochemical relationship between the left and right hemispheres. The repeated administration of cocaine produced sensitized behavioral responses to a subsequent challenge. Neurochemical correlates of repeated cocaine administration were observed at the cortical level and included a significant decrease in serotonin levels in the left anterior cingulate and pyriform cortices and an increase in dopamine metabolism in the left pyriform cortex. Furthermore, a shift in the interhemispheric coupling coefficient matrix for dopamine neurotransmission was observed in both the pyriform cortex and nucleus accumbens of cocaine-sensitized animals suggesting that, in these structures, the two hemispheres are operating independently. These results demonstrate that cocaine produces alterations in specific dopaminergic and serotonergic pathways that arise from the mesencephalon and project towards both the anterior cingulate and pyriform cortices. (C) 1999 IBRO. Published by Elsevier Science Ltd.