Serotonin System Impairment in Parkinson's Disease with Impulse Control Disorders
Overview
This study demonstrates that Parkinson’s disease patients with impulse control disorders (PDICD+) exhibit serotonergic dysfunction in sensorimotor and associative cortico-striato-pallido-thalamic circuits. Using PET imaging, increased presynaptic serotonin transporter (SERT) availability and elevated postsynaptic 5-HT2A receptor binding were observed in PDICD+ patients compared to PDICD− patients and healthy controls.
Background
Impulse control disorders (ICDs) such as hypersexuality, compulsive eating, shopping, and gambling are common and distressing in Parkinson’s disease (PD), affecting nearly half of patients within five years of diagnosis. Dopaminergic treatments, especially dopamine agonists, contribute to ICD development, but serotonergic mechanisms remain unclear. The serotonergic system is critical for behavioral inhibition and response control, with the prefrontal cortex receiving dense serotonergic innervation and expressing 5-HT2A receptors important for inhibitory control. Understanding serotonergic involvement in PDICD could identify new therapeutic targets.
Increased in posterior putamen and pallidum vs PDICD−
Increased in bilateral supplementary motor area, precentral gyrus, right dorsolateral prefrontal cortex
PDICD−
15
None
Lower presynaptic SERT availability in sensorimotor network
Lower cortical 5-HT2A receptor binding
Healthy Controls
15
None
Baseline
Baseline
Key Findings
PDICD+ patients show greater presynaptic serotonin transporter (SERT) availability in the posterior putamen and pallidum compared to PDICD− patients.
Increased postsynaptic 5-HT2A receptor binding is observed in PDICD+ patients in cortical regions including the supplementary motor area, precentral gyrus, and dorsolateral prefrontal cortex.
Serotonergic dysfunction in PDICD+ patients aligns with sensorimotor and associative fronto-striatal networks involved in inhibitory control.
PDICD+ patients exhibit greater choice impulsivity and urgency, with more severe depressive and anxious symptoms.
Serotonergic abnormalities contribute to ICD vulnerability and development beyond known dopaminergic dysregulation in limbic circuits.
Clinical Implications
These findings suggest that serotonergic dysfunction plays a significant role in impulse control disorders in Parkinson’s disease, highlighting potential new targets for therapeutic intervention. Clinicians should consider the involvement of serotonergic pathways when managing ICDs in PD, especially given the limitations of dopaminergic treatment adjustments. Future therapies targeting serotonergic receptors or transporters may improve inhibitory control and reduce ICD severity.
Conclusion
Serotonergic system impairment within sensorimotor and associative cortico-striato-pallido-thalamic circuits contributes to impulse control disorders in Parkinson’s disease. This expands the understanding of ICD pathophysiology beyond dopaminergic abnormalities and opens avenues for novel treatment strategies.
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