A cDNA open reading frame encoding a dominant-negative mutant NR1 subunit of the NMDA receptor with an asparagine-to-arginine substitution at amino acid 616 (N616R), a hemagglutinin (HA) epitope tag 27 aa from the N terminus and a polyadenylation signal, followed by a loxP-flanked SV40-neo cassette, has replaced the first ~130 base pairs of the endogenous Drd1a gene. (J:121750)