SLC6A3 and attention deficit-hyperactivity disorder: Our study has some limitations: firstly, the sample size of the animal experiment was low due to the limitation of experimental funding, which may have some bias on the expression of the results; secondly, although WKY rats are often used as natural controls for SHRs, the addition of SD rats as a control would make the results more convincing; finally, the study did not conduct the DAT, the target of first-line drugs for the treatment of ADHD, to in-depth study was not conducted to compare with MPH to further reveal the mechanism of DA neurotransmission.