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Keywords:

  • cocaine;
  • dopamine;
  • drugs of abuse;
  • reward;
  • synuclein

Abstract

Synucleins have attracted much attention because of their involvement in several neurodegenerative disorders. In a screening for genes differentially expressed after high-dose cocaine exposure, we found γ-synuclein as a major upregulated candidate in the tegmentum. Overexpression of both α- and γ-synuclein after drug treatment was confirmed by means of microarrays, yielding an increase in the hippocampus, the striatum and the tegmentum (2.65 ×, 1.96 × and 3.5 ×, respectively, for α-synuclein vs. 2.7 ×, 1.96 × and 7.16 × for γ-synuclein), but no change in the nucleus accumbens. Investigation of the distribution of mRNA (by in situ hybridization) and of the proteins (by immunocytochemistry) shows in both cases a clearly distinct pattern of expression for α- and γ-synuclein. α-synuclein displays a very characteristic distribution, confined to specific nuclei, whereas γ-synuclein is more widely expressed throughout the brain. mRNA of both α- and γ-synucleins display a complementary pattern of expression all over the cortex. In contrast to γ-synuclein, α-synuclein is neuronal, being only found in NeuN-expressing cells, and is expressed in the basal ganglia (faintly) and in the substantia nigra compacta where it is highly correlated with tyrosine hydroxylase. Immunocytochemistry shows that γ-synuclein generally colocalizes with glial fibrillary acidic protein-expressing cells and is abundant in the red nucleus, the substantia nigra reticulata and the anterior commissure, while γ-synuclein mRNA labels the matrix compartments of the caudate-putamen. The role of synucleins in relation to cocaine-induced plasticity or neurotoxicity is discussed.