Although GABA release is known to be inhibitory, there are both stimulatory and inhibitory 5HT
receptors in the Drosophila brain and it is unknown whether Gαs-coupled 5HT receptors, such as
5HT7, are expressed in the MBs. To test whether 5HT could be stimulatory in the MBs, we used
5HT7-GAL4 to drive expression of Epac1-camps, a FRET-based cyclic nucleotide sensor. There was no expression evident in the MBs, although there was strong fluorescence in the central complex as reported previously. We bath-applied 5HT and saw increased cAMP in the labeled cells of the ellipsoid body, confirming the efficacy of the drug as well as the positive coupling to cyclase in 5HT7-GAL4+ cells.