Figure 8.

Model for the Role of the Olfactory and Gustatory Modalities in the Biphasic Behavior of Adult Flies in Response to Ecc

Starved flies are first attracted by odors emanating from the Ecc-contaminated solution. This step requires both the olfactory receptor Gr63a, expressed by the CO₂-sensing neurons hosted by the antenna, and the Gαq1 transducer. Starved flies have reduced bitter sensitivity due to Gr66a/Gr33a-expressing neuron depotentiation. Feeding on the sucrose + Ecc-contaminated solution induces the re-potentiation of bitter neurons. No longer potentiated, the bitter neurons established an aversive behavior toward Ecc. The gustatory receptors Gr66a and Gr33a, expressed by the bitter neurons of the labellum and of the tarsae, are required for this second phase. The neuropeptide Lk expressed by the central nervous system is also required for optimal aversion.