The dopaminergic system in attention deficit/hyperactivity disorder

Area of Science:

• Neuroscience
• Psychiatry
• Pharmacology

Background:

• The mesocorticolimbic dopamine system is implicated in attention deficit/hyperactivity disorder (ADHD) pathophysiology.
• Existing research presents inconsistent findings regarding dopamine system function in ADHD, leading to debate over hypofunction versus hyperfunction.

Purpose of the Study:

• To review and clarify conflicting findings from neuroimaging and functional neuroimaging studies on the dopaminergic system in ADHD.
• To analyze animal models and psychostimulant therapy mechanisms to understand dopamine's role in ADHD-related behaviors.

Main Methods:

• Review of neuroimaging studies (functional and non-functional).
• Analysis of experimental studies using animal models (genetic manipulation, brain lesions, dopamine depletion, dopamine transporter knockout/knockdown).
• Consideration of psychostimulant therapy mechanisms in ADHD.

Main Results:

• Neuroimaging and animal studies offer contradictory evidence, with some supporting dopamine hypofunction (basal ganglia, dopamine-depleted animals) and others suggesting hyperfunction (dopamine transporter knockout/knockdown mice).
• Inconsistencies in findings and interpretations highlight potential heterogeneity in ADHD pathogenesis.

Conclusions:

• The precise role of the dopaminergic system (hypo- or hyperfunctioning) in ADHD remains unclear due to conflicting evidence.
• Heterogeneity in the underlying pathological, biochemical, and physiological mechanisms may explain the varied symptoms and research findings in ADHD.