Figure 5. Sources of Dopaminergic Reinforcement Signals.

(A) Action-contingent photoactivation of P2X₂ in dopaminergic neurons under TH-GAL4 control produces conditioned odor avoidance (columns a and b). Optically reinforced flies achieve the same level of performance as animals trained conventionally via electric shock (horizontal shaded band; mean ± SEM). Effective conditioning requires a functional rutabaga gene product (column c) and contingency between olfactory choice behavior and optically evoked dopamine release; learning does not occur when this contingency is broken by randomizing reinforcement (column d). Activation of P2X₂ in dopaminergic neurons under HL9-GAL4 control (column e) or ATP uncaging in flies lacking P2X₂ expression (columns f–h) are equally ineffective. p < 0.0001; Kruskal-Wallis ANOVA; **, significantly different from electric shock conditioning in post-hoc comparison (n = 20–68 flies per condition; means ± SEM).

(B) Temperature-induced expression of Kir2.1 in dopaminergic neurons under TH-GAL4 control (dark gray columns), but not under HL9-GAL4 control (medium gray columns), blocks action-contingent conditioning (column b). p = 0.0062; Kruskal-Wallis ANOVA; **, significantly different from permissive temperature in post-hoc comparison (n = 19–58 flies per condition; means ± SEM).

(C) Temperature-induced expression of Kir2.1 in dopaminergic neurons, under either TH-GAL4 control (dark gray columns) or HL9-GAL4 control (medium gray columns), inhibits locomotion (columns b and d). p < 0.0001; Kruskal-Wallis ANOVA; **, significantly different from permissive temperature in post-hoc comparison (n = 82–120 flies per condition; means ± SEM).