Figure 1. Low doses of H₂O₂ promote osmotic avoidance behavior.

(a) Low doses of H₂O₂ promote osmotic avoidance behavior while high concentrations of H₂O₂ inhibit it. Worms were pre-incubated with varying concentrations of H₂O₂ for 2 h. After a brief recovery on seeded NGM plates (up to 2 h), worms were tested for avoidance response to glycerol. To avoid a ceiling effect which would mask behavioral potentiation, a non-saturating concentration of glycerol (0.5 M) was used to challenge the worm. n≥20; *P<0.05, **P<0.005 (ANOVA with Dunnett's test); Error bars: s.e.m. (b) Exposing worms to H₂O₂ for one hour is sufficient to induce behavioral potentiation. Worms were pre-treated with 0.1 μM of H₂O₂ for varying durations of time. n≥20; *P<0.05, **P<0.005, ***P<0.0005 (t test); Error bars: s.e.m. (c) The antioxidants NAC and BHA block H₂O₂-induced behavioral potentiation. BHA (butylated hydroxyanisole, 25 μM) and NAC (N-acetyl-cysteine, 1 mM) were included during H₂O₂ (0.1 μM ) treatment. n≥10; ***P<0.0005 (ANOVA); Error bars: s.e.m. (d) Transgenic expression of the catalase gene ctl-2 in ASH neurons blocks H₂O₂-induced behavioral potentiation. H₂O₂: 0.1 μM. The sra-6 promoter was used to drive expression of ctl-2 in ASH neurons. n≥10; **P<0.005 (ANOVA); Error bars: s.e.m. (e) Reducing the level of endogenous H₂O₂ suppresses osmotic avoidance behavior. Worms were treated with BHA or NAC for 2 h, and right after the treatment, they were assayed for osmotic avoidance behavior. n≥10; *P<0.05 (ANOVA); Error bars: s.e.m. (f) Reducing the level of endogenous H₂O₂ in ASH neurons suppresses osmotic avoidance behavior. Transgenic expression of the catalase gene ctl-2 in ASH neurons suppressed osmotic avoidance behavior. H₂O₂: 0.1 μM. n≥10; *P<0.05 (ANOVA); Error bars: s.e.m. Note: 0.1 μM H₂O₂ was used to induce potentiation of osmotic avoidance behavior and ASH neuron sensory response throughout the paper unless otherwise indicated.