Behavioral and biochemical characterization of elevated “I-maze” as animal model of anxiety

The elevated I-maze is a modification of the elevated plus-maze model of anxiety in mice. The design of I-maze comprises a straight wooden passage, resembling the English letter “I,” divided equally into three areas; two enclosed areas (close arms) at both ends of the “maze” and an open area in the center of two enclosed areas. The I-maze completely avoids the central platform of elevated plus-maze, removing any ambiguity in time spent on central platform and allowing uninterrupted animal exploration. In this model, diazepam (1 mg/kg) and gabapentin (10 mg/kg) significantly increased the percentage of time spent in the open areas (%TO) and the number of unprotected head dips (uHDIPS), and reduced the number of protected head dips (pHDIPS) and stretch attend postures (SAP) from close to open arm. Similarly, fluoxetine (5 mg/kg) significantly increased %TO and uHDIPS, and significantly decreased SAP from close to open arm, but it did not have any significant effect on pHDIPS. The 5-HT3 receptor antagonist, ondansetron (0.1 mg/kg), did not produce any significant change in all the behaviors, observed, as compared to vehicle-treated control mice. On the other hand, the anxiogenic agent, caffeine (15 mg/kg), did produce a significant decrease in %TO and uHDIPS, and significantly increased pHDIPS and SAP from close to open arm. Mice confined in open area of I-maze bring the relevant biochemical changes associated with anxiety behavior, showing significant increase in the levels of plasma nitrate and plasma corticosterone. These data indicate that a combination of novel design of elevated I-maze and a detailed behavioral analysis provides a sensitive model for the measurement of anxiety.