A sequence cassette encoding, 1. a B2RT transcription stop cassette and 2. a 'spaghetti monster' (sm) FLAG tag (10 copies of the Tag:FLAG epitope in the backbone of a fluorescently inactivated mRuby2), has been inserted into the endogenous VGlut locus, immediately upstream of the translation start codon. The presence of the B2RT stop cassette prevents expression of VGlut.