Salt (1.5 M) avoidance test with larvae under red and blue light (N=20)

Salt (1.5 M) avoidance test with larvae under red and blue light (N=14)

Salt (1.5 M) avoidance test in DAN-larvae under red and blue light (N=20)

Salt (1.5 M) avoidance test in DAN-larvae under red and blue light (N=10)

Finished salt (1.5 M) avoidance tests in larvae (Dop2R) under red and blue light

Salt (1.5 M) avoidance tests in larvae (Dop2R) under red and blue light (N=15)

Significant p-values:

Group A (RL <-> BL): 0.013

Group B (RL <-> BL): 0.044

Salt (1.5 M) avoidance tests in larvae (Dop2R) under red and blue light

Salt (1.5 M) avoidance tests in larvae (DANc1) under blue and red light (N = 20)

Salt (1.5 M) avoidance tests in larvae (DANc1) under blue and red light (N = 12)

Flexible Valence Coding by Dopaminergic PPM2 Neurons in Drosophila

Dopaminergic systems are involved in various physiological processes including motivation and valuation. Studies on Drosophila melanogaster imply that certain insect dopaminergic neurons (DANs) are central for the mediation of valuation, as activity in these neurons can substitute for teaching signals in classical conditioning. This view may oversimplify the complex circuitry of the fly’s dopaminergic system. We focus on an understudied population of DANs and their involvement in valence coding. Using a combination of optogenetics and different operant self-stimulating paradigms, we investigated whether flies expressing an optogenetic channel in DANs of the posterior protocerebral posterior medial cluster (PPM2) would approach or avoid optogenetic stimulation. Flies’ choice was not consistent over the course of our experiments: Initially, animals avoided the stimulating light but this avoidance weakened over time and shifted to mild approach behavior in the final stages. Pharmacologically impairing DA synthesis abolished both effects. Actively exposing flies to the stimulating light aimed to identify whether the valence shift was due to accumulating neural signaling/dopamine release during the experiments. However, exposing flies to light before testing did not induce any preference changes in one-minute choice, hinting that the behavioral change does not occur from prolonged signaling in these neurons. The observation that the very same dopaminergic neurons can mediate both, avoidance and approach behavior in our self stimulating experiments, challenges a central, dopamine-mediated valuation system. Additional findings from flies that express the optogenetic channel in heat-sensing neurons further weaken the claim of centralized dopaminergic punishment neurons, as heat-punishment was independent of dopamine.