Simultaneously, the expression of PKA and DRD1 brown yellow-stained particles, as well as PKA mRNA, was significantly downregulated in the PFC and striatum of SHRs, indicating that inactivation of DRD1 and the cAMP/PKA signaling pathway in SHRs resulted in behavioral manifestations similar to those of ADHD. This evidence concerns the gene DRD1 and attention deficit-hyperactivity disorder.