A neomycin resistance cassette replaced a 3.1 kb genomic fragment containing sequences encoding transmembrane domains 4-7, including the G-coupling protein domain and the intracellular cytoplasmic tail. Extracellular field potential measurements in the CA1 region of the hippocampus confirmed disruption of CRH signal transduction: application of CRH increased the population spike amplitudes in CA1 slices of wild-type mice, but not in slices of homozygous mutant mice.