A sequence cassette composed of an attP site, T2A-GAL4, a loxP site and an FRT3 site has been inserted into the nAChRβ3 locus, into the part of the coding sequence that encodes the most C-terminal intracellular region of the polypeptide, resulting in the GAL4 driver being expressed as a separate protein under the control of the endogenous nAChRβ3 sequences.