Drugs of abuse preferentially increase dopamine transmission in the shell of the nucleus accumbens. This area is considered as a transition between the striatum and the extended amygdala a complex neural system that includes the central amygdala and the bed nucleus of stria terminalis, areas that, like the nucleus accumbens shell, are heavily innervated by mesolimbic dopamine neurons originating in the ventral tegmental area. Given the anatomical and neurochemical relationships and similarities with the nucleus accumbens shell it was of interest to investigate whether the dopamine transmission of the bed nucleus of stria terminalis shares with the accumbens shell the peculiar responsiveness to drugs of abuse. To this end we studied by microdialysis with concentric probes, the effect of drugs of abuse on extracellular dopamine in the bed nucleus of stria terminalis. We report that morphine, nicotine, cocaine, ethanol, and the selective dopamine uptake inhibitor GBR 12909 increase effectively and dose dependently extracellular dopamine in the bed nucleus of stria terminalis. These results indicate that the bed nucleus of stria terminalis shares with the nucleus accumbens shell a peculiar sensitivity to the dopamine stimulant actions of drugs of abuse.

Dopamine reuptake by norepinephrine terminals can occur in brain areas such as the prefrontal cortex, the nucleus accumbens shell, and the bed nucleus of stria terminalis that are innervated, although unevenly, by both dopamine and norepinephrine neurons. Therefore the antidepressants that bind selectively the norepinephrine transporter might produce their therapeutic effect by raising the extracellular concentration of dopamine besides that of norepinephrine. Moreover, cocaine can be reinforcing even in knock-out mice for the dopamine transporter because it might raise synaptic dopamine in the nucleus accumbens shell by preventing its uptake by the norepinephrine transporter, an effect that could take place even in wild animals. Recently, it has also been suggested that dopamine can be co-released with norepinephrine by norepinephrine neurons, although it is not clear whether this feature might be related to a previous nonspecific uptake of dopamine by the norepinephrine transporter. In this review we discuss the potential role of the nonspecific uptake of dopamine by norepinephrine transporter in the mechanism of action of drugs of abuse, antipsychotics, and antidepressants.

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.