The transgene contains the entire Ca2+/calmodulin-dependent protein kinase II alpha locus, ~110 kbp 5' flanking region (including the Arsi locus and a portion of the Tcof1 locus) and ~50 kbp 3' flanking region (including the Slc6a7 and Cdx1 loci) from BAC RP23-221H5. The P2X2-YC3.1 fusion gene was inserted immediately upstream of the CaMKIIalpha translation initiation codon in exon 1 via homologous recombination/BAC recombineering. The P2rx2/YC3.1 fusion gene encodes rat P2rx2 fused at its carboxy terminus to the fluorescence resonance energy transfer (FRET)-based optical reporter Yellow Cameleon 3.1 (YC3.1).