One loxP sequence was added 260 bp upstream from the translational initiation codon of Slc18a3 (within the first intron of Chat), and a second loxP was added approximately 1.5 kb downstream from the stop codon. This flanking region included the second exon of Chat. The TK-Neo cassette was added immediately after the second loxP and was followed by a third loxP (all in the same direction). The floxed region (including the TK-Neo cassette) was excised from mice by in vivo cre mediated recombination. No Slc18a3 mRNA was detected in homozygous mouse brain by qPCR. Slc18a3 protein was undetected in homozygous mutant mice by Western blot analysis of spinal cord extracts and immunostaining of the neuromuscular junction. Chat protein level was increased in E18.5 spinal cords and Chat mRNA level was increased as detected by qPCR from E18.5 mouse brains.