Abstract
The elevated plus maze test is a widely used test for assessing anxiety-like behavior and screening novel therapeutic agents in rodents. Previous studies have shown that a variety of internal factors and procedural variables can influence elevated plus maze behavior. Although some studies have suggested a link between behavior and plasma corticosterone levels, the relationships between them remain unclear. In this study, we investigated the effects of experience with a battery of behavioral tests, the wall color of the closed arms, and illumination level on the behavior and plasma corticosterone responses in the elevated plus maze in male C57BL/6J mice. Mice were either subjected to a series of behavioral tests, including assessments of general health and neurological function, a light/dark transition test, and an open field test, or left undisturbed until the start of the elevated plus maze test. The mice with and without test battery experience were allowed to freely explore the elevated plus maze. The other two independent groups of naïve mice were tested in mazes with closed arms with different wall colors (clear, transparent blue, white, and black) or different illumination levels (5, 100, and 800 lx). Immediately after the test, blood was collected to measure plasma corticosterone concentrations. Mice with test battery experience showed a lower percentage of open arm time and entries and, somewhat paradoxically, had lower plasma corticosterone levels than the mice with no test battery experience. Mice tested in the maze with closed arms with clear walls exhibited higher open arm exploration than mice tested in the maze with closed arms with black walls, while there were no significant differences in plasma corticosterone levels between the different wall color conditions. Illumination levels had no significant effects on any measure. Our results indicate that experience with other behavioral tests and different physical features of the maze affect elevated plus maze behaviors. Increased open arm time and entries are conventionally interpreted as decreased anxiety-like behavior, while other possible interpretations are considered: open arm exploration may reflect heightened anxiety and panic-like reaction to a novel situation under certain conditions. With the possibility of different interpretations, the present findings highlight the need to carefully consider the test conditions in designing experiments and drawing conclusions from the behavioral outcomes in the elevated plus maze test in C57BL/6J mice.
Highlights
The elevated plus maze test has been widely used to measure anxiety-like behavior and evaluate potential therapeutic agents for anxiety-like traits in rats and mice [1,2,3,4,5,6]
The present study investigated the influences of experience with a battery of behavioral tests that did not include the elevated plus maze test, closed-arm wall color, and illumination level on elevated plus maze behavior during a 10-min period from the elevated plus maze test and plasma corticosterone levels immediately after exposure to the maze in male C57BL/6J mice
The results showed that experience with some types of behavioral tests induced decreases in both exploration of the open arms of the maze and plasma corticosterone response, while testing in closed arms of different wall colors affected behavior but not plasma corticosterone levels, and illumination level had no significant effects on any measures
Summary
The elevated plus maze test has been widely used to measure anxiety-like behavior and evaluate potential therapeutic agents for anxiety-like traits in rats and mice [1,2,3,4,5,6]. Previous reports showed that Swiss mice subjected to a holeboard test immediately before being tested in the elevated plus maze exhibited increased exploration of open arms [2], while repeated handling and exposure to an open field induced reduced exploratory behavior in the elevated plus maze in C57BL/6JOlaHs mice [24]. These findings suggest that such behavioral changes in the elevated plus maze may not necessarily require the learning and memory processes for previous experience in the same maze and can be induced by experience with different testing situations
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