Cumulative effect of norepinephrine and dopamine carrier blockade on extracellular dopamine increase in the nucleus accumbens shell, bed nucleus of stria terminalis and prefrontal cortex.

We investigated, by microdialysis in various brain areas, the possibility that dopamine could be captured by the norepinephrine transporter when the dopamine transporter is pharmacologically blocked. Administration of reboxetine, a selective blocker of the norepinephrine transporter, 20 min after the administration of GBR 12909, a selective blocker of the dopamine transporter, produced an increase of dopamine output in the nucleus accumbes shell (+408% above basal) greater than that obtained by GBR 12909 alone (+308% above basal). On the contrary, reboxetine did not increase further the dopamine output produced by GBR 12909 in the nucleus accumbens core or in the dorsal caudate, areas lacking a consistent noradrenergic innervations. A cumulative effect of dopamine and norepinephrine transporter blockade on the output of dopamine in dialysates was also observed in the bed nucleus of stria terminalis and in the prefrontal cortex. This study shows that dopamine extracellular concentration can be elevated by norepinephrine transporter blockade, even in areas where the dopamine transporter is predominant, when the latter is pharmacologically blocked. This phenomenon may have relevance in psychostimulant dependence as well as in antidepressant pharmacology.