PET demonstrates reduced dopamine transporter expression in PD with dyskinesias

Area of Science:

• Neuroscience
• Neurology
• Pharmacology

Background:

• Dyskinesias are a common motor complication in Parkinson disease (PD).
• Presynaptic dopamine (DA) terminal adaptations are hypothesized to play a role in PD pathophysiology and treatment-related complications.
• Understanding these adaptations is crucial for managing PD symptoms.

Purpose of the Study:

• To investigate whether presynaptic dopamine transporter (DAT) expression, relative to DA nerve terminal density, is altered in Parkinson disease patients experiencing dyskinesias.
• To determine if these adaptations are associated with the development of treatment-related motor complications.

Main Methods:

• Positron Emission Tomography (PET) with [(11)C]-d-threo-methylphenidate (MP) and [(11)C]-(+/-) dihydrotetrabenazine (DTBZ) was used to assess 36 PD patients with motor fluctuations.
• The ratio of MP to DTBZ binding potentials (MP/DTBZ ratio) was calculated to estimate DAT expression relative to DA nerve terminal density.
• Statistical analyses were performed, accounting for age, treatment, and disease severity.

Main Results:

• Twenty-seven out of 36 patients exhibited dyskinesias; nine did not.
• No significant difference in the caudate MP/DTBZ ratio was observed between groups.
• A decreased putaminal MP/DTBZ ratio was found in patients with dyskinesias compared to those without, suggesting DAT downregulation in the putamen.

Conclusions:

• Presynaptic alterations, specifically dopamine transporter downregulation in the putamen, are implicated in the development of dyskinesias in Parkinson disease.
• While DAT downregulation might initially increase synaptic DA, it may lead to oscillating DA levels, potentially facilitating dyskinesias.
• These findings highlight the complex relationship between dopamine system adaptations and motor complications in PD.