Figure 3

Deletion mutants in gpa-14 and dop-2 display limited associative learning that is rescued by exogenous dopamine. Associative learning chemotaxis assay. Three-day-old synchronized worms were conditioned with 3 μl of isoamyl alcohol on freshly prepared chemotaxis plates and tested with 1:100 isoamyl alcohol in the absence of food, as described previously [8, 24]. Plates were left undisturbed for one hour and then kept at −10°C for 3 minutes. Chemotaxis index was calculated by subtracting the number of worms at the diluent sector from the number of worms at the chemical gradient sector and dividing by the total number of worms on the plate. Tests were then repeated in the presence of plates supplemented with 60 μl of 5 mM exogenous dopamine. (A) While naïve strains [wild type, dop- 2(vs105) and gpa-14(pk347)] are equally attracted to isoamyl alcohol but after conditioning, wild type worms display significantly greater decrease in attraction towards isoamyl alcohol than dop- 2(vs105) and gpa-14(pk347) (p = 0.35 for naive and p < 0.05 for conditioned animals, ANOVA). Additionally, the conditioned response of the gpa-14;dop- 2 double mutant is the same as either single mutant (p = 0.46, One-Way ANOVA). (B) When conditioned in the presence of exogenous dopamine, no statistical significance was noted between the wild types and the mutants (p = 0.65 for naives and p = 0.88 for conditioned, One Way ANOVA). (C) As a control, 3-day-old synchronized worms were exposed to 3 μl of isoamyl alcohol in the presence of E. coli for 90 minutes and tested for their attraction to 1:100 isoamyl alcohol. No significant difference in attraction was observed for wild type or either of the mutants [dop-2(vs105) and gpa-14(pk347)] before or after treatment (p = 0.85 for naives and p = 0.89, One Way ANOVA). Bars represent SEM values n ≥ 3 assays for each strain.