BLI-3/Dopamine-Dependent Mn-Induced Neurotoxicity Figure 4. Increased extracellular, but not intracellular, dopamine levels confer hypersensitivity to Mn toxicity while decreased levels are protective. (A) Schematic representation of a generic dopaminergic synapse in C. elegans. (B) Total DA levels in selected mutants relevant to the study at the L1 larval stage. dat-1(ok157), dop-2(vs105);dop-1(vs100) dop-3(vs106) display significantly (p,0.001) higher dopamine levels than WT or other mutants, while dopamine measurement in cat-2(e1112) and dat-1(ok157);cat-2(e1112) did not reach a significant value compared to the background levels measured in our experiment. (C) dat-1(ok157) is hypersensitive (p,0.001) to Mn-induced lethality, with a LD50 = 9 mM. cat-2(e1112) is hyper-resistant (p,0.001) to Mn-induced lethality, with a LD50 = 95 mM. cat-2(e1112) rescues dat-1(ok157) hypersensitivity in the double-mutant cat-2(e1112); dat-1(ok157), which LD50 = 83 mM is not significantly different from cat-2(e1112) mutant. 10 mM DA pre-treatment restores Mn sensitivity (p,0.001) in both cat-2(e1112) and cat-2(e1112);dat-1(ok157), with respective LD50 of 34 mM and 40 mM. (D) The VMAT2 mutant cat-1(e1111) exhibits hyper-resistance to Mn (p,0.001), with a LD50 = 108 mM; while the DA receptor mutant dop- 2(vs105);dop-1(vs100) dop-3(vs106) is hypersensitive to Mn exposure (p,0.001), with a LD50 = 27 mM. doi:10.1371/journal.pgen.1001084.g004 mented cat-2(e1112) mutants with 10 mM DA exposure prior Mn treatment, which rendered those mutants hypersensitive (p,0.001) to Mn with a LD50 = 34 mM (Figure 4C). Pre-exposure to 10 mM DA of cat-2(e1112);dat-1(ok157) worms led to a comparable LD50 = 40 mM, not significantly different from cat-2(e1112) mutants pre-exposed to 10 mM DA, but significantly different PLoS Genetics | www.plosgenetics.org 6 August 2010 | Volume 6 | Issue 8 | e1001084