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STUDY DESIGN
Five treatment groups:
1. Control
2. Low DQ 12.5 ppm DQ∙Br2 in diet (~1.5 mg DQ ion / mg BW / day)
3. High DQ...
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Dietary Administration of Diquat for 13 Weeks Does Not Result in a Loss of Dopaminergic Neurons in the Substantia Nigra Pars Compacta (SNpc) of C57BL/6J Mice

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Dietary Administration of Diquat for 13 Weeks Does Not Result in a Loss of Dopaminergic Neurons in the Substantia Nigra Pars Compacta (SNpc) of C57BL/6J Mice

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Dietary Administration of Diquat for 13 Weeks Does Not Result in a Loss of Dopaminergic Neurons in the Substantia Nigra Pars Compacta (SNpc) of C57BL/6J Mice

  1. 1. STUDY DESIGN Five treatment groups: 1. Control 2. Low DQ 12.5 ppm DQ∙Br2 in diet (~1.5 mg DQ ion / mg BW / day) 3. High DQ 62.5 ppm DQ∙Br2 in diet (~7.5 mg DQ ion / mg BW / day) 4. Low MPTP 4 x 10 mg/kg/dose i.p. at 2-hr intervals during week 12 5. High MPTP 4 x 16 mg/kg/dose i.p. at 2-hr intervals during week 12 Three Assessment Subsets / Group: Subset I: Pathology (after 4, 8 and 13 weeks of DQ exposure) Subset II: Stereology (after 13 weeks of DQ exposure) Subset III: Neurochemistry (after 13 weeks of DQ exposure) STUDY OBJECTIVE This study assessed the potential effects of diquat (DQ) on the nigrostriatal dopaminergic system of male and female C57BL/6J mice continuously exposed to DQ in the diet for 13 weeks. Neuropathology, stereology, and neurochemistry endpoints were evaluated for effects of DQ by comparison to control and MPTP. CONCLUSIONS Mice exposed to DQ in their diets for up to 13 weeks showed no evidence of effects on the nigrostriatal dopaminergic system based on stereological, neuropathological and neurochemical assessments. MPTP, the positive control, produced changes in all three assessment endpoints (stereology, neuropathology and neurochemistry). The achieved DQ dose level in the study (~7.5 mg DQ ion / mg BW / day at 62.5 ppm) was approximately 15 times the chronic DQ reference dose of 0.5 mg DQ ion / kg BW / day. Dietary Administration of Diquat for 13 Weeks Does Not Result in a Loss of Dopaminergic Neurons in the Substantia Nigra pars compacta (SNpc) of C57BL/6J Mice Daniel J. Minnema 1, Nicholas C. Sturgess 2, Kim Z. Travis 2, Charles B. Breckenridge1, Mark T. Butt 3, Jeffrey C. Wolf 4, Dan Zadory 4, Andrew Cook 2, and Philip A. Botham 2 1 Syngenta Crop Protection LLC, Greensboro, NC, US; 2 Syngenta Limited, Bracknell, UK; 3 Tox Path Specialists, Frederick, MD, US; 4 EPL, Sterling, VA, US Abstract #2745 NEUROPATHOLOGY – SNpc and Striatum Brains were block-randomly assigned to matrices/slides (25 sections/slide). A qualitative grading system was used by the pathologist who was blinded to treatment group during the evaluation. Neuropathology Results DQ: Exposure to DQ was not associated with any morphological (neuronal, astrocytic or microglial) changes in the SNpc or the striatum. MPTP: The SNpc &/or striata of the MPTP-treated mice displayed: • reduced TH immunostaining intensity (decreased dopamine neurons) • increased AmCuAg staining (neuronal degeneration) • increased IBA-1 immunoreactivity (microglial activation) • increased GFAP immunoreactivity (astrocytic activation) Mean severity scores STRIATUM SNpc STEREOLOGY – SNpc Following in situ perfusion fixation, sections of midbrain (SNpc) were prepared and stained at EPL (Sterling VA). • Section thickness: 40 μm • Section frequency: every third section through SNpc region • Staining: TH immunostain - avidin-biotin complex (ABC) and diaminobenzidine (DAB) chromogen • Stereology: optical fractionator [Stereo Investigator (Micro-Brightfield)] • Disector Height: entire depth of section • Stereologist: blinded to treatment group • Statistical Analysis: one-sided two-sample t-test Stereology Results DQ: There were no statistically-significant decreases in the mean number of TH+ (dopamine) neurons in the SNpc after 13 weeks of dietary exposure to DQ∙Br2 at either 12.5 or 62.5 ppm. MPTP: The mean number of TH+ (dopamine) neurons in the SNpc was significantly decreased in MPTP-treated mice. Mean number of TH+ neurons at each depth of SNpc sections Effect of treatment on mean number of TH+ neurons in SNpc of male mice ** p ≤ 0.01 ACKNOWLEDGEMENTS Sielken and Associates Consulting Inc. (Bryan, TX) performed the statistical analyses of the stereological data. Scott Watson and Jim Mathews (RTI International, Research Triangle Park, NC) provided technical assistance for the striatal neurochemical analysis. Melissa Beck, Pragati Coder and Mark Herberth (WIL Laboratories, Ashland, OH) provided direction for the in-life and necropsy phases of the study. Stain: Diagnosis Grade: Normal (0) Slight (1) Minimal (2) Mild (3) Moderate (4) Severe (5) AmCuAg: Necrosis No necrotic neurons/ terminals < 1% 1 – 5% 5 – 15% 15 – 40% >40% TH+: Decreased TH+ neurons / synaptic terminals Densely stained neurons or synaptic terminals 1 – 20% ↓ staining 20 – 40% ↓ staining 40 – 60% ↓ staining 60 – 80% ↓ staining 80 – 100% ↓ staining GFAP: Reactive Astrocytosis No reactive astrocytes 1 – 20% 20 – 40% 40 – 60% 60 – 80% 80 – 100% IBA-1: Reactive Microgliosis No reactive gliosis 1 – 20% 20 – 40% 40 – 60% 60 – 80% 80 – 100% + + + + + + + + + + + + + + 0 1 2 3 4 5 6 7 8 9 10 11 12 13 weeks Pathology 5 mice/sex/group 48 hrs after MPTP Group 1: Control (basal diet) Group 2: Low DQ 12.5 ppm DQ·Br2∙H2O Group 3: High DQ 62.5 ppm DQ·Br2∙H2O Group 4: Low MPTP Group 5: High MPTP MPTP ip 4x16mg/kg MPTP ip 4x10mg/kg Pathology 5 mice/sex in Groups 1 – 3 Pathology 5 mice/sex in Groups 1 – 3 Stereology 20 mice/sex/group 1 week after MPTP Striatal Neurochemistry 6 mice/sex/group 1 week after MPTP NEUROPATHOLOGY – SNpc and Striatum Following in situ perfusion fixation, sections of striatum and/or SNpc were stained (or immuno-stained, as appropriate) at Neuroscience Associates, Inc. Stain Pathologic Assessment Parameter • amino cupric silver necrosis of neurons / synaptic terminals • GFAP astrocytic responses • IBA-1 microglial responses • TH (tyrosine hydroxylase) dopamine neuronal processes • Caspase 3 apoptotic cell death • TUNEL DNA fragmentation • Thionine nuclear changes NEUROCHEMISTRY – STRIATUM Flash-frozen striatal tissues were analyzed at RTI (RTP, NC). Striatal concentrations of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), and homovanillic acid (HVA) were determined by HPLC coupled with electrochemical detection. DA turnover was calculated: [DOPAC+HVA] / [DA]. Neurochemistry Results DQ: There were no DQ-related effects on striatal dopamine concentration, dopamine metabolite (DOPAC, HVA) concentrations or dopamine turnover. MPTP: Statistically-significant reductions in mean striatal concentrations of dopamine and its metabolites (DOPAC, HVA) and a statistically-significant increase in mean dopamine turnover (relative to controls) was noted for the mice dosed with MPTP. Representative photomicrographs of sections of the SNpc AmCuAg GFAP IBA-1 TH MPTPControl MeanSeverityScoreMeanSeverityScore MeanSeverityScoreMeanSeverityScore DQ·Br2 AmCuAg+ Terminals Decreased TH AmCuAg+ Neurons Decreased TH Increased GFAP Increased IBA-1 Increased GFAP Increased IBA-1 WEEK 4 WEEK 8 WEEK 13 WEEK 4 WEEK 8 WEEK 13 WEEK 4 WEEK 8 WEEK 13 WEEK 4 WEEK 8 WEEK 13 WEEK 4 WEEK 8 WEEK 13 WEEK 4 WEEK 8 WEEK 13 WEEK 4 WEEK 8 WEEK 13 WEEK 4 WEEK 8 WEEK 13 ** p ≤ 0.01

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