3 The use of intraspecific groups of

animals that differ in their genetic backgrounds and/or their responses to environmental challenges has gained more and more interest. The selection of divergent rat or mouse strains that differ in their behavioral responses to well-defined stressors, such as the Maudsley strains of rat,4 provides an example of such a strategy. Interestingly, the use Inhibitors,research,lifescience,medical of divergent strains of rats to understand the physiology (including the neurochemistry) of stress responses has recently been complemented by genetic studies of quantitative trait loci, leading to a precise genomic location underlying or associated with these inherited differences in stress responses.5 Eight years ago, we decided to adopt a complementary approach through detection of the most divergent strains with respect to anxiety-related LY294002 behaviors Inhibitors,research,lifescience,medical among commercially available inbred rat strains. Given the amount of evidence linking stress-related behaviors, and particularly anxiety, to central serotonergic systems, some of the key features of these systems in the divergent strains selected were compared under basal and stress conditions. We complemented this strategy by comparing the behavioral and neurochemical effects of psychotropic drugs, especially serotonergic and/or

noradrenergic antidepressants, with and without repeated stress exposure. Inhibitors,research,lifescience,medical Finally, our most recent work, which will also be presented below, somewhat differed from our initial studies in that the inbred Inhibitors,research,lifescience,medical rat strains were selected on the basis of a neurochemical trait,

ie, the serotonin transporter (5-HTT), rather than a behavioral trait. Anxiety-related behaviors in inbred rat strains Male and female rats were selected from six inbred strains (the Fischer 344 rat [F344], the Lewis rat [LEW], the Brown Norway rat, the Wistar-Kyoto rat [WKY], the spontaneously hypertensive rat [SHR], and the Wistar-Furth rat) and the behaviors of these animals in several stressful environments were recorded.6 These included the open field, the elevated plus-maze, the social interaction test, and the black and white box, ie, models thought to allow a correct estimation Inhibitors,research,lifescience,medical of independent behavioral dimensions such as anxiety and locomotion.7 A principal component (multivariate) analysis allowed us to dissect the ethological meaning of the behaviors Ketanserin measured in each test. In addition, our study allowed us to select two strains of rats (SHR and LEW), which differed selectively for anxiety-related behaviors in the elevated plus-maze (open arm visits), the black and white box (visits to the white compartment), and the open field (visits to the central squares), but not for locomotor-related behaviors in any test (a finding that was later confirmed by locomotion monitoring in activity cages). Thus, SHR and LEW were found to display low and high anxiety, respectively, and the difference between them was devoid of any contamination by activity-related inputs.