HRH3 and major depressive disorder: These data accumulating from rodent models and clinical settings underpin the idea that modulation of H3R represents a novel therapeutic target for the treatment of ADHD especially due to its wider therapeutic role in CNS and the fact that ADHD is frequently co-morbid with sleep disorders, learning difficulties, substance abuse, anxiety, depression and other neuropsychiatric disorders (Cortese, 2012).