Low-Anxiety Rat Phenotypes Can Be Further Reduced through Genetic Intervention

BACKGROUND: A previous study using an intercross between the inbred rat strains Lewis (LEW) and Spontaneously Hypertensive Rats (SHR) identified a locus on chromosome 4, named Anxrr16, influencing an experimental index of anxiety and showing a transgressive effect, with alleles from the LEW strain (more anxious) decreasing rather than increasing anxiety. OBJECTIVE: To confirm the location and isolate the effect of a rat genome region named Anxrr16 through a planned genomic recombination strategy, where the target locus in SHR rats was replaced with LEW genetic material. METHODS: A new congenic strain, named SHR.LEW-Anxrr16 (SLA16), was developed from a cross between LEW (donor) and SHR (receptor) rats and then evaluated in several anxiety-related tests. The activity and attention levels of the new strain were also evaluated, since hyperactivity was observed during its construction and because SHR is a model of attention deficit hyperactivity disorder. RESULTS: Significant effects of Anxrr16 were found for open field central locomotion, as well as for other indices of anxiety from the light/dark box, triple test and T-maze. In all cases, the low-anxiety levels of SHR rats were further reduced by the insertion of LEW alleles. Differences in locomotor activity were found only in unfamiliar (hence stressful) environments and no genetic effects were observed in indices of attention. CONCLUSION: The SLA16 strain can help in the identification of the molecular pathways involved in experimental anxiety and it demonstrates how apparently extreme phenotypes sometimes hide major opposite-acting genes.