The Suok Test of Anxiety — the New Rodent Behavioral Paradigm Which Opens Minds

Proceedings of the 9th International Multidisciplinary Conference «Stress and Behavior» Saint-Petersburg, Russia, 16–19 May 2005.In a series of our pilot studies (Kalueff, Tuohimaa, 2005), we have introduced the Suok test (ST) — a long elevated horizontal rod (mice) or alley (rats) and the light-dark ST modification (LDST) for behavioral characterization in small rodents, including simultaneous assessment of their anxiety, activity, and neurological phenotypes. The unique feature of this test is its ability to simultaneously assess these three distinct behavioral domains. To establish the ST and the LDST as murine models of anxiety, we used several different mouse strains which differ markedly in their anxiety and activity (C57BL/6, 129S1/SvImJ, NMRI, and BALB/c), showing that our tests are able to ethologically discriminate between high and low anxiety mouse strains, as assessed by horizontal and directed exploration, stops, and defecation boli (Kalueff, Tuohimaa, 2005). The spatial distribution of the LDST behaviors is also sensitive to these strain-specific anxiety phenotypes, showing clear avoidance of the brightly lit part of the test in stressed vs. non-stressed mice. In addition, we validated the ST in 129S1/SvImJ and BALB/c mice by assessing the behavioral consequences of acute stress such as rat exposure. We also showed that our test is able to detect high anxiety and poorer motor coordination in 129S1/SvImJ (vs. C57BL/6) mice (Kalueff, Tuohimaa, 2005). Similar, although not identical, behavioral results were obtained in rats using different types of stress (light exposure, novelty, chemical challenge, etc). The results of our studies show that the ST emerges as an experimental tool to analyze anxiety, motor-vestibular anomalies, as well as anxiety-induced motor impairments in mice and rats. In general, it may be suggested that the ST represent a hybrid model combining several well-validated behavioral models: 1) open field test (open unknown area), 2) elevated plus maze (elevated platform), 3) rotarod test (horizontal confined bar). In addition, the LDST is the combination of features of these three tests with the light-dark box paradigm. Recently, the ST was used in both mice and rats in order to pharmacologically validate this method using reference GABAergic drugs — anxiolytic diazepam (DZ, 0.5–1 mg/kg i.p.) and axiogenic pentylenetetrazole (PTZ, 10–15 mg/kg i.p.). We showed that the ST works consistently in both species, predictably increasing anxiety and motor incoordination in PTZ-treated animals, and showing the opposite effects after DZ. Overall, we suggest that the ST can be a useful protocol in neurobehavioral stress research including modeling stress-evoked states, pharmacological screening of potential anti-stress drugs, or behavioral phenotyping of genetically modified animals. Here we will review different behavioral features of the rat and mouse ST, critically overview species-specific behavioral differences in these tests, and discuss potential utility of this new model for behavioral pharmacology and biological psychiatry