Opposite influences of dopaminergic pathways to the prefrontal cortex or the septum on the dopaminergic transmission in the nucleus accumbens. An in vivo voltammetric study.

Modulation of dopaminergic transmission in the nucleus accumbens by the dopaminergic pathways reaching the prefrontal cortex (anteromedian and the suprarhinal parts) and the lateral septum was investigated. Changes in dopaminergic transmission in the nucleus accumbens were assessed by in vivo voltammetry using pretreated carbon fiber electrodes. This technique allows the selective detection of 3,4-dihydroxyphenylacetic acid, the main presynaptic metabolite of dopamine. Dopaminergic transmission in the prefrontal cortex (anteromedian and suprarhinal parts) and the lateral septum was altered by local injection of the dopaminergic agonist (d-amphetamine) and the dopaminergic antagonists (alpha-flupenthixol and sulpiride). Pharmacological interventions, either stimulation or blockade, in the anteromedian and suprarhinal parts of the prefrontal cortex induced, respectively, a decrease or an increase in extracellular 3,4-dihydroxyphenylacetic acid in the nucleus accumbens. The same pharmacological interventions in the lateral septum had exactly opposite effects in the nucleus accumbens. The inhibitory action of the mesocortical and mesorhinal dopaminergic projections and the facilitatory action of the mesoseptal dopaminergic projection on dopaminergic input in the nucleus accumbens were shown to rely on the activity of inhibitory fugal pathways which could be blocked by local injection of tetrodotoxin in the three structures. In a previous work, it was demonstrated that dopaminergic projections in the amygdala exert an inhibitory influence on dopaminergic transmission in the nucleus accumbens. Thus the present results suggest that functional interdependence between the different dopaminergic pathway arising in the ventral mesencephalon is a general property of this neuronal group. Data obtained after manipulation of dopaminergic transmission in these various projection areas may need to be interpret in a different light. Similarly, neurological and psychiatric observations may need to be reconsidered in view of the interdependence of the dopaminergic mesencephalic pathways.