| Summary: | 碩士 === 長庚大學 === 醫學影像暨放射科學系 === 102 === Introduction: The expression of Lewy body inclusions in dopaminergic neurons is a critical pathological hallmark of the idiopathic PD. These inclusions accumulate a wide range of proteins such as a-synuclein, ubiquitin and neurofilaments. The presence of a-synuclein inclusions in the brain of lactacystin-treated rodent models of PD has been reported. This study aimed to evaluate whether in-vivo [123I]FP-CIT SPECT could detect lactacystin-induced change of the dopamine transporter.
Methods: Twenty four adult male Sprague-Dawley rats were randomly divided into four groups: normal controls (receiving no treatment), sham controls (receiving intracranial injection of saline), group A (receiving intracranial injection of 2-g lactacystin), and group B (receiving intracranial injection of 5-g lactacystin). The PD animal model was prepared three weeks following a single intracranial injection of lactacystin to the medial forebrain bundle (MFB) in left hemisphere of the rat brain. 123I- and 125I-labeled FP-CIT were prepared by oxidative destannylation method and purified by reversed-phase solid extraction method. The tracer was administered intravenously into animals. Ex-vivo distributions of the radioactivity in striatum (ST) and cerebellum (CB) were measured by dissection 2 hr postinjection and were used to calculate the striatum-to-cerebellum (ST/CB) ratio for each rat. Dynamic [123I]FP-CIT brain SPECT imaging was performed on normal rats to verify the optimal imaging time window. Static brain SPECT imaging was performed 2 hr postinjection for 1 hr and the striatal standardized uptake ratio (SURST/CB) was determined in all rat groups using cerebellum as the reference region. Ex-vivo autoradiography and tyrosine hydroxylase immunohistochemistry (TH-IHC) staining were performed on striatal brain sections dissected immediately after SPECT scan. IHC staining for α-synuclein was performed on the sections of substantial nigra region in a 5-μg lactacystin-lesioned rat brain.
Results: The radioiodinated FP-CIT was obtained with high radiochemical purity (>98%). Dynamic scan verified that the optimal time window for [123I]FP-CIT SPECT in rat brain is from 2 to 3 hr postinjection. The ipsilateral striatum-to-cerebellum (I-ST/CB) ratios of ex-vivo [125I]FP-CIT uptake (1.82 and 1.73 for group A and group B, respectively) and ipsilateral striatal SURs (SURI-ST/CB) of in vivo [123I]FP-CIT binding (1.19 and 1.22 for group A and group B, respectively) were significantly lower than those of the normal and the sham controls (I-ST/CB: 3.83 and 3.35; SURI-ST/CB: 2.50 and 2.25, respectively). However, the difference of either I-ST/CB ratio or SURI-ST/CB between groups A and B rats was not statistically significant. The lactacystin-induced decline of DAT distribution shown in ex-vivo autoradiograms was corroborated with TH-IHC results on the adjacent brain sections. The Lewy body-like α-synuclein inclusions could be visualized in α-synuclein –IHC staining.
Conclusion: In-vivo DAT imaging with [123I]FP-CIT SPECT could be a feasible approach to evaluate the damage of dopaminergic neurons in lactacystin-lesioned rat model of PD. Further study will be proposed to evaluate the potential of [123I]FP-CIT DAT imaging for detecting early change of dopaminergic neuron using the rat model induced with improved lactacystin treatment protocol.
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