Hypertrophic A10 dopamine neurones in a rat model of attention-deficit hyperactivity disorder (ADHD)

To clarify whether a hypo or hyperfunctioning mesocorticolimbic system is the neural substrate of Attention-Deficit Hyperactivity Disorder (ADHD), we carried out a morphometric analysis on an animal model, the Naples high excitability rat (NHE). Male adult NHE and control rats were used for tyrosine hydroxylase (TH) immunocytochemistry in the ventral tegmental area and substantia nigra in coronal cryostat sections. PC-assisted image analysis showed larger DA neurones in the ventral tegmental area but not in the substantia nigra of NHE rats than in controls, associated with a higher expression of TH in the neuropil. Thus, the increased activity and impaired attention of NHE rats are associated with a hyperfunctioning mesocorticolimbic system in this ADHD model.