Figure 3.

Effect of levodopa on mitochondrial membrane potential (ΔΨ_M) in primary sensory neurons (DRGs) cultured in hypoxia. Data are normalized to percent of control cells treated with 0 µM levodopa and 0 nM rotenone in hypoxia. (A) A dose of 30 µM levodopa increases ΔΨ_M at 24 h in hypoxia; however, this effect is lost at 7 days and instead 300 µM levodopa inhibits ΔΨ_M. Photomicrographs show TMRM staining in DRG soma treated with 0 µM levodopa (left) or 300 µM levodopa (LD, right) in hypoxia. Scale bar = 10 µm, for both images. (B) (left) Beta III tubulin immunocytochemistry shows no effect of high-dose (300 µM) levodopa on soma size; however, mean percent fluorescence for ATP5b (right), a mitochondrial marker, was reduced. (C) No impact of levodopa is observed in the context of parkinsonism (rotenone) at 24 h. (D) At 7 days, the deleterious effect of 300 µM levodopa is maintained in mild ΔΨ_M inhibition (1 nM rotenone). Further, both 30 µM and 300 µM levodopa reduce ΔΨ_M caused by 10 nM rotenone. No additive effects of levodopa are observed at stronger ΔΨ_M inhibition caused by 500 nM rotenone. Data in (A–D) are shown as box plots of technical replicates with whiskers depicting 5–95% percentiles, black circles depicting remaining data points, lines depicting medians and “+” symbols depicting means. Light and dark orange circles show experiment means. (A,C,D): dashed lines show 100% (mean of control cells not treated with levodopa or rotenone) for reference. * p < 0.05, *** p < 0.001, **** p < 0.0001.