Effects of weekly or daily exposure to the elevated plus-maze in male mice.

The elevated plus-maze is an animal model where the behavioural repertoire of rodents is used to detect effects on anxiety. Repeated testing is a procedural variable where contradictory results have been reported. Some laboratories have found stable test-retest profiles, although other studies have reported reduced open arm exploration. The objective was to further discern behavioural changes in the behaviour of the mouse after either weekly or daily tests. Behaviour was videotaped and later analysed. Behavioural patterns were encoded from an ethological point of view, a nine-pattern ethogram being employed. Other parameters such as percent time on the different sections of the maze were evaluated as well. Descriptive analysis revealed a progressive decrease in percent time spent on open arms (in weekly-tested mice), percent time on central platform, open arm entries, percent open entries, unprotected stretched attention posture (uSAP) and unprotected head-dipping (uDip), together with an augmented number of closed arm returns and percent time spent on closed arms. Taken together, these findings are consistent with an enhanced anxiety level across the tests. It is worth noting that percent time on open arms, a traditional anxiety-related parameter, was not progressively decreased in daily-tested mice. Other than expected, exploratory and locomotor elements such as sniffing, rearing, closed arm entries, and total arm entries remained quite similarly elicited throughout the tests, suggesting that locomotor habituation was not developed. However, grooming, considered a displacement response, habituated across the tests. In conclusion, the findings of the present study support the hypothesis that anxiety is enhanced after test repetition, and indicate that test-retest profiles are far from stable, except for exploratory locomotor activity.