Figure 10.

Sugar-sensing inhibition simplifies the processing of conflicting messages. Sweet molecules alone are activating S cells (orange dot) that express sugar receptors such as Gr64f. Bitter molecules alone are activating L2 cells (blue dots) that express Gr66a on the labellum. These neurons project in separate areas in the subesophageal ganglion (SOG). In the presence of a mixture of sugar and bitter molecules, if these two detection channels were independent, one would expect the two populations of cells to be activated simultaneously. Our data show that bitter molecules inhibit the detection of sugar molecules. This suggests that, in flies, the detection of bitter molecules within mixtures is encoded in two ways: (1) activating bitter-sensitive cells; and (2) inhibiting sugar sensing through the sugar-sensitive cells, thereby making appetitive stimuli less attractive when mixed with bitter substances.