The Coffin-Lowry syndrome, a rare syndromic form of X-linked mental retardation, is caused by loss-of-function mutations in the hRSK2 (RPS6KA3) gene. To further investigate RSK2 (90-kDa ribosomal S6 kinase) implication in cognitive processes, a mrsk2_KO mouse has previously been generated as an animal model of Coffin-Lowry syndrome. The aim of the present study was to identify possible neurochemical dysregulation associated with the behavioral and morphological abnormalities exhibited by mrsk2_KO mice. A cortical dopamine level increase was found in mrsk2_KO mice that was accompanied by an over-expression of dopamine receptor of type 2 and the dopamine transporter. We also detected an increase of total and phosphorylated extracellular regulated kinase that may be responsible for the increased level of tyrosine hydroxylase phosphorylation also observed. By taking into consideration previously reported data, our results strongly suggest that the dopaminergic dysregulation in mrsk2_KO mice may be caused, at least in part, by tyrosine hydroxylase hyperactivity. This cortical hyperdopaminergia may explain some non-cognitive but also cognitive alterations exhibited by mrsk2_KO mice.