Moreover, in the ADHD model, the retinal levels of the inducible nitric oxide synthase (iNOS) protein, which is also involved in inflammatory processes, were similar to the control rats (Figure 6D), but the MPH treatment led to a downregulation in the ADHD rats (SHR MPH, 66.7 ± 7.7% of the control). This evidence concerns the gene NOS2 and attention deficit-hyperactivity disorder.