Regulation of the norepinephrine transporter by chronic administration of antidepressants

Background: Downregulation of serotonin transporter was observed previously after chronic treatment with selective serotonin reuptake inhibitors (SSRIs) but not selective norepinephrine reuptake inhibitors (NRIs). This study investigated if chronic treatment of rats with selective NRIs or SSRIs also affected the norepinephrine transporter (NET). Methods: Rats were treated for 3 to 6 weeks by osmotic minipumps with either the selective NRIs, desipramine, or the SSRI paroxetine. Results: [³H]nisoxetine binding sites as well as [³H]norepinephrine uptake were decreased in hippocampus and cortex after treatment with desipramine. By contrast, paroxetine-treated rats showed no alteration in either [³H]nisoxetine binding or [ ³H]norepinephrine uptake. NET messenger RNA levels in the locus coeruleus were unchanged by desipramine treatment. Conclusions: These results demonstrate that the marked decrease in NET density 1) is not a consequence of a decrease in gene expression; 2) was caused only by a selective NRI; and 3) was associated with a parallel decrease in norepinephrine uptake.