Up- and down-expression of the dopamine transporter by plasmid DNA transfer in the rat brain

The functional role of the dopamine transporter (DAT) in central dopaminerg ic neurotransmission was assessed further by investigating the consequences on dopamine (DA) turn-over of up- and down-regulation of this protein indu ced by a non-viral gene transfer approach. For this purpose, expression pla smids containing the sense or antisense coding sequence of DAT complexed wi th the cationic polymer, polyethylenimine (PEI), were injected into the rat substantia nigra, the brain region containing the majority of DA cell bodi es. Before in vivo injection, the efficacies of the different DNA constructs we re assessed by transfection studies into LLC-PK1 cells. Stereotaxic adminis tration of the sense plasmid complexed to PEI induced, 3 days later, a sign ificant increase in the immunoautoradiographic labelling by anti-DAT antibo dies of the substantia nigra and various DA projection areas. These effects were associated with a significantly enhanced capacity of striatal synapto somes to take up [H-3]-DA and lasted up to 14 days postinjection. In contra st, 7 days after intranigral administration of the antisense plasmid comple xed to PEI, we observed a significant decrease of DAT immunolabelling in th e substantia nigra and [H-3]-DA uptake by striatal synaptosomes. Whereas DA turnover in the striatum was unaltered 3 days after intranigral administration of the sense plasmid, it was increased 7 days after intranig ral administration of the antisense construct. These data indicate that non-viral transfer of the sense or antisense codin g sequence of DAT can be used as a novel approach to induce long-term chang es in central DA neurotransmission.