A sgRNA (GGTTGAATGCTGTCCGCTGT) was used to insert a viral 2A oligopeptide (P2A) self cleaving peptide, to mediate ribosomal skipping, fused to a flpo recombinase sequence (flpo) at 2901 bp in the dopamine receptor D1 (Drd1) gene, immediately upstream of the stop codon in exon 2.