Objective: In this study, we employed heterozygous knockout (vmat2+/-) mice to investigate the influence of reduced vesicular storage of catacholamines on 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-impaired dopaminergic neurons in locus coeruleus and olfactory bulb.

Background: Cytosolic dopamine (DA) is sequestered by VMAT2 into synaptic vesicle for consequent neurotransmission. Previous studies have shown that mice with a 95% genetic reduction in Vmat2 display motor and nonmotor features of PD and exhibit progressive nigrostriatal degeneration. In addition, reduced vesicular storage of catacholamines mice are more susceptible than WT littermates to MPTP- and amphetamine-induced nigrostriatal neurotoxicity.

Methods: Vmat2+/- mice were provided by professor Uhl GR and bred in SPF Laboratory Animal Center. Genotypes were confirmed by PCR of genomic DNA extracted from tail. 6- month-old Vmat2+/- and WT littermates were investigated in the study and injected MPTP (30mg/kg/day) for 7 days. Two weeks after the last injection, locomotor activity was assessed by total distance moved in the open field test and total time consumed in pole test. TH expression in dopaminergic neurons including substantia nigra, striatum, locus coeruleus and olfactory bulb were demonstrated by westernblot, immunohistochemistry staining and immunofluorescent staining. DA and its metabolites were analyzed via liquid chromatography with electrochemical detection.

Results: At 6 months old, total distance moved in the open field test and total time consumed in pole test were similar between WT littermates and Vmat2+/- group. In comparision with MPTP-treated WT mice, MPTP-treated vmat2+/- mice display a decrease in traveled distance and a increase in time spent in pole test. The number of TH positive cells in substantia nigra, striatum, locus coeruleus of vmat2+/- mice did not differ from WT mice. However, MPTP-treated vmat2+/- mice showed more obvious decrease in TH positive cells in substantia nigra, striatum and locus coeruleus. Remarkably, MPTP didn’t induce decrease in TH positive cells in olfactory bulb in WT mice while MPTP-treated vmat2+/- mice did show a decrease in TH positive cells in olfactory bulb. In the striatum of vmat2+/- mice, we observed a decrease in DA and increase in DA metabolites in comparision with WT mice. MPTP treatment increased DOPAC:DA in both genotype but more obvious in vmat2+/-, indicating increased DA turn over by MPTP.

Conclusions: Our data demonstrated that Vmat2+/- mice are also more susceptible than WT littermates to MPTP-induced death of dopaminergic neurons in locus coeruleus and olfactory bulb except nigrustriatal system.

References: 1. Taylor, T.N., W.M. Caudle, and G.W. Miller, VMAT2-Deficient Mice Display Nigral and Extranigral Pathology and Motor and Nonmotor Symptoms of Parkinson’s Disease. Parkinsons Dis, 2011. 2011: p. 124165. 2. Wimalasena, K., Vesicular monoamine transporters: structure-function, pharmacology, and medicinal chemistry. Med Res Rev, 2011. 31(4): p. 483-519. 3. Fukui, M., et al., Vmat2 heterozygous mutant mice display a depressive-like phenotype. J Neurosci, 2007. 27(39): p. 10520-9. 4. Taylor, T.N., et al., Reduced vesicular storage of catecholamines causes progressive degeneration in the locus ceruleus. Neuropharmacology, 2014. 76 Pt A: p. 97-105.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/reduced-vesicular-storage-of-catacholamines-enhance-mptp-induced-death-of-dopaminergic-neurons-in-locus-coeruleus-and-olfactory-bulb/