Assessing anxiety in C57BL/6J mice: a pharmacological characterization of the zero maze test.

INTRODUCTION: Anxiety disorders affect the quality of life and good health of millions of people over the world. Because clinical trials are expensive and frequently show high rates of placebo responses, animal models have become an important tool for drug discovery and brain research. Zero maze is a commonly used test to assess anxiety-like levels in mice, being the C57BL/6J strain one of the most widely used. However, only few studies have focused on the pharmacological characterization of this strain in the various anxiety tests.

METHODS: In this study, we analyzed the changes in the anxiety-like behaviors of mice exposed to chlordiazepoxide (CLZ), as an anxiolytic drug, at doses of 2.5, 5 and 10mg/kg, picrotoxine (PTX), as an anxiogenic drug, at doses of 0.5, 1 and 2mg/kg, and methylphenidate (MPH), as a psychomotor stimulant, at doses of 2.5, 5 and 10mg/kg. Data were hand recorded in situ by an observer and through a camcorder by computer software.

RESULTS: Results showed that CLZ and MPH had an anxiogenic effect at the two highest doses. Only CLZ at 2.5mg/kg reduced the anxiety-like levels of mice. Moreover, PTX exerted an anxiogenic effect in mice only at 2mg/kg. The drugs affecting the anxiety-like levels also affected the activity levels. Thus, the differences might have been mediated by changes in activity levels.

DISCUSSION: Globally, these data demonstrate that the results obtained from the zero maze test are difficult to interpret when the C57BL/6J strain is used. On the other hand, high doses of substances that interact with the GABAergic system, as CLZ, can produce sedation in these mice. In contrast, high doses of GABAA antagonists, as PTX, are necessary if anxiogenic effects should be observed. Further investigations with this strain are necessary in order to corroborate the results of the present study.