Thirdly, as substantia nigra and striatum are crucial parts of dopamine signaling and play a major role in motor control and attention, examining TH-ir neurons in the substantia nigra and TH-ir fibers in the striatum would provide in-depth information about the usefulness of the SHR as a suitable animal model for hyperactive/impulsive subtype of ADHD as defined in DSM-5-TR. This evidence concerns the gene TH and attention deficit-hyperactivity disorder.