Pre-synaptic dopamine D(3) receptor mediates cocaine-induced structural plasticity in mesencephalic dopaminergic neurons via ERK and Akt pathways

Abstract
Exposure to psychostimulants results in neuroadaptive changes of the mesencephalic dopaminergic system including morphological reorganization of dopaminergic neurons. Increased dendrite arborization and soma area were previously observed in primary cultures of mesencephalic dopaminergic neurons after 3-day exposure to dopamine agonists via activation of D3 autoreceptors (D3R). In this work, we showed that cocaine significantly increased dendritic arborization and soma area of dopaminergic neurons from E12.5 mouse embryos by activating phosphorylation of extracellular signal-regulated kinase (ERK) and thymoma viral proto-oncogene (Akt). These effects were dependent on functional D3R expression because cocaine did not produce morphological changes or ERK/Akt phosphorylation neither in primary cultures of D3R mutant mice nor following pharmacologic blockade with D3R antagonists SB-277011-A and S-33084. Cocaine effects on morphology and ERK/Akt phosphorylation were inhibited by pre-incubation with the phosphatidylinositol 3-kinase inhibitor LY294002. These observations were corroborated in vivo by morphometrical assessment of mesencephalic dopaminergic neurons of P1 newborns exposed to cocaine from E12.5 to E16.5. Cocaine increased the soma area of wild-type but not of D3R mutant mice, supporting the translational value of primary culture. These findings indicate a direct involvement of D3R and ERK/ Akt pathways as critical mediators of cocaine-induced structural plasticity, suggesting their involvement in psycho- stimulant addiction.