Excessive GABAergic activity in striatal and frontal cortical regions more than dopaminergic functions are related to daytime sleepiness in Parkinson's disease: An exploratory 11C-flumazenil PET study
Abstract
Aims: Increased gamma-aminobutyric acid type A (GABAA) receptor activity has been identified in hypersomnolence syndromes, but its role and regional cerebral topography of receptor occupancy in excessive daytime sleepiness (EDS) in Parkinson's disease (PD) is unknown. Dopaminergic functions or medications may contribute to EDS. Neuroimaging shows evidence of increased brain GABAergic activity in PD. We investigated the relationship between EDS, GABAA receptor binding, striatal dopamine and dopaminergic medication use in PD.
Methods: Six PD patients underwent [11C]flumazenil GABAA receptor and [11C]dihydrotetrabenazine (DTBZ) dopaminergic positron emission tomography (PET), clinical and Epworth Sleepiness Scale (ESS) assessments.
Results: Mean ESS score was 12.7 ± 4.5. Mean levodopa equivalent dose (LED) was 1,170 ± 616 mg. There was no significant correlation between nigrostriatal [11C]DTBZ PET (R = 0.138, p = 0.792) or disease duration (R = 0.209, p = 0.902) and ESS scores. In contrast, there was a significant inverse relationship between striatal GABAA receptor activity and ESS scores (β = -0.942, p = 0.024), more prominent in the caudate head (β = -0.949, p = 0.011). Therefore, frontal cortex binding was explored. A significant inverse relationship between frontal cortical GABAA receptor activity and ESS (R = -0.884, p = 0.042) was found. A trend toward positive association between LED and ESS (R = 0.773, p = 0.053), was weakened (β = -0.128, p = 0.738) by the addition of…
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