A targeting vector was designed to remove the 3' region of exon 2 and a 600 bp intronic sequence common to all isoforms and replace it with a neomycin-resistance cassette and an in-frame stop codon after the last codon of the remaining exon 2. qPCR analysis of hippocampal and cortical mRNA from 50 day old heterozygous females indicates an approximate 50% reduction of mRNA and Western blot confirmed an approximate 50% reduction in protein.