CRH1 Receptor Knockout Mouse. A mouse mutant lacking a functional CRH1 receptor by using homologous recombination in embryonic stem cells was generated where the coding sequences of the transmembrane regions V, VI, and VII, including the G-coupling protein domain and the intracellular cytoplasmatic trial were deleted. Analysis of their behavioral phenotype employing the light-dark box revealed that these mice showed less anxiety-like behavior at basal and stress (alcohol withdrawal) conditions. (a) Latency to enter the lit compartment was increased during withdrawal from comparison of 20 wild-type, 18 heterozygous, and 19 null mutants under basal and 22 wild-type, 22 heterozygous, and 20 null mutants under stress conditions, significant (F1,115 = 8.4, p < .005) treatment effects emerged. (b) A similar effect of withdrawal stress was observed for animals avoiding the lit compartment. For latency, percent of time spent in the lit compartment and percent of entries into the lit compartment (genotype at F2,115 > 12.1, p < .0001). All these and data from Smith et al. (1998) are consistent with reduced anxiety-like behavior in the full or partial absence of CRH1 receptors. (From Timpl et al. 1998).