DOPAMINE TRANSPORTER GENE-EXPRESSION IN RAT MESENCEPHALIC DOPAMINERGIC-NEURONS IS INCREASED BY DIRECT INTERACTION WITH TARGET STRIATAL CELLS IN-VITRO

By using a semi-quantitative reverse transcriptase-PCR assay (RT-PCR) we have analyzed dopamine transporter (DAT), tyrosine hydroxylase (TH) and synaptic vesicle monoamine transporter (VMAT2) gene expression in rat mesencephalic (MES) primary cultures. Consistent with previous da ta obtained during rat MES ontogeny, the onset of DAT transcription in vitro is delayed in embryonic day (E)13, but not in E16, MES neurons when compared to that of TH and VMAT2. In co-culture, the addition of target striatal cells (STR) to E13 MES selectively increases DAT mRNA level in DA neurons during the first 3 days in vitro; cortical cells a re ineffective. On the contrary, DAT gene does not appear up-regulated in E16 MES co-cultured with target STR cells, indicating that MES DA neurons respond to STR stimulation only at defined developmental stage s. Up-regulation of DAT mRNA level by STR in E13 MES seems to require direct cell interactions since target cells do not exert their effect on DAT transcription when are separated from MES cells by a porous bar rier, which only allows diffusion of soluble molecules. Thus maturatio n of DA neurotransmission in vitro appears to follow a developmental p rogram which can be specifically modulated by their target STR cells.