raclopride and Neurodegenerative-Diseases

Existing technologies permit the detection of changes in neurotransmitter and/or neuroreceptor expression. This may be useful for diagnosis, for monitoring disease progression, and for assessing the pathogenesis of complications associated with long-term treatment. Although the binding of [11C]raclopride to D2 receptors is subject to competition from endogenous dopamine, this can be exploited to estimate changes in synaptic levels of dopamine. Assessment of processes downstream to the receptor will require the development of new approaches.

Topics: Carbon Radioisotopes; Cell Transplantation; Diagnostic Imaging; Disease Progression; Dopamine; Dopamine Antagonists; Humans; Neurodegenerative Diseases; Neurotransmitter Agents; Raclopride; Receptors, Dopamine D2; Sensory Receptor Cells

The partial saturation approach (PSA) is a simple, single injection experimental protocol that will estimate both B(avail) and appK(D) without the use of blood sampling. This makes it ideal for use in longitudinal studies of neurodegenerative diseases in the rodent. The aim of this study was to increase the range and applicability of the PSA by developing a data driven strategy for determining reliable regional estimates of receptor density (B(avail)) and in vivo affinity (1/appK(D)), and validate the strategy using a simulation model.. The data driven method uses a time window guided by the dynamic equilibrium state of the system as opposed to using a static time window. To test the method, simulations of partial saturation experiments were generated and validated against experimental data. The experimental conditions simulated included a range of receptor occupancy levels and three different B(avail) and appK(D) values to mimic diseases states. Also the effect of using a reference region and typical PET noise on the stability and accuracy of the estimates was investigated.. The investigations showed that the parameter estimates in a simulated healthy mouse, using the data driven method were within 10±30% of the simulated input for the range of occupancy levels simulated. Throughout all experimental conditions simulated, the accuracy and robustness of the estimates using the data driven method were much improved upon the typical method of using a static time window, especially at low receptor occupancy levels. Introducing a reference region caused a bias of approximately 10% over the range of occupancy levels.. Based on extensive simulated experimental conditions, it was shown the data driven method provides accurate and precise estimates of B(avail) and appK(D) for a broader range of conditions compared to the original method.

Topics: Algorithms; Animals; Brain; Computer Simulation; Dopamine Antagonists; Injections; Male; Mice; Mice, Inbred C57BL; Neurodegenerative Diseases; Positron-Emission Tomography; Raclopride; Radiopharmaceuticals; Receptors, Dopamine D2; Reproducibility of Results

Spinocerebellar ataxia type 17 (SCA17) is a rare autosomal dominantly inherited neurodegenerative disorder presenting with a variable phenotype including ataxia, dystonia, chorea, and parkinsonism, as well as cognitive impairment. We evaluated morphologic and functional imaging characteristics to elucidate evidence of neurodegeneration in SCA17, even in the presymptomatic stage of the disease.. Nine individuals of 3 large SCA17 pedigrees, including 4 presymptomatic mutation carriers, underwent cranial 3-dimensional MRI volumetry, as well as multitracer PET with (18)F-FDG, (11)C-d-threo-methylphenidate, and (11)C-raclopride. Healthy subjects showing no signs of a neurologic or psychiatric disease served as controls.. MRI volumetry revealed atrophy of the cerebellum and caudate nucleus in manifesting patients (P = 0.04 and 0.05, respectively) and in presymptomatic mutation carriers (P = 0.04 and 0.01, respectively). PET demonstrated decreased glucose metabolism in the striatum, as well as in the cuneus, cingulum, and parietal lobe, in all SCA17 patients and presymptomatic mutation carriers. In addition, PET was closely correlated with motor performance as assessed by the Scale for the Assessment and Rating of Ataxia (P = 0.037) and Unified Parkinson Disease Rating Scale (P = 0.05) and with cognitive function as assessed by the Mini-Mental Status Examination (P = 0.037). Furthermore, (11)C-raclopride PET showed impairment of the postsynaptic dopaminergic compartment of the putamen and caudate nucleus not only in manifest SCA17 patients (P = 0.04 and 0.008, respectively) but also in yet-unaffected mutation carriers (P = 0.05 and 0.05, respectively). The degree of postsynaptic dopaminergic dysfunction was associated with impairment of motor performance. In contrast, significant presynaptic dopaminergic deficits assessed with (11)C-d-threo-methylphenidate PET were not detected.. MRI volumetry, as well as (11)C-raclopride and (18)F-FDG PET, reveal neuronal dysfunction and neurodegeneration even in the presymptomatic stage and may serve as markers for disease activity in upcoming interventional trials on SCA17.

Topics: Adult; Age of Onset; Brain; Dopamine Agents; Dopamine Antagonists; Dopaminergic Neurons; Female; Fluorodeoxyglucose F18; Glucose; Heterozygote; Humans; Image Processing, Computer-Assisted; Magnetic Resonance Imaging; Male; Methylphenidate; Middle Aged; Mutation; Neurodegenerative Diseases; Neuropsychological Tests; Positron-Emission Tomography; Raclopride; Radiopharmaceuticals; Spinocerebellar Ataxias