Abstract
The goal of the present study was to investigate the role of thigmotaxis (the tendency to remain close to vertical surfaces) in rat exploratory behavior in an open-field. Thigmotaxis was investigated in a parametric way, using 24 experimentally adult naive male Wistar rats (210-230 g). Exploratory behavior was studied in an open-field (N = 12) in 5-min sessions and behavior was analyzed in terms of where it occurred: in areas surrounded by two, one, or no walls. Another group of rats (N = 12) was studied in an open-field with blocks placed near two of the corners so as to make these corner areas surrounded by three walls. The floor of the open-fields was divided into 20-cm squares in order to locate the exact place of occurrence of each behavior. The following behaviors were recorded: entries into the squares, rearings, and groomings. In both types of open-field the rats chose to remain longer in the squares surrounded by the largest possible number of walls. In one of the open-fields, the mean time (seconds) spent in squares surrounded by two walls was longer than the time spent in squares surrounded by one or no walls (37.2, 7.7, and 1.8 s, respectively). In the other open-field, the mean time spent in squares surrounded by three walls was longer than the time spent in squares surrounded by two, one or no walls (41.7, 20.4, 7.0, and 2.6 s, respectively). Other measures presented a similar profile. These results indicate that rats are sensitive to the number of walls in an environment and prefer to remain close to them.
Highlights
The role played by different aversive stimuli in behavioral tasks that take advantage of the rat’s natural tendency to explore, like the open-field or the elevated plusmaze, is not fully understood
The t-test (t [22] = -2.358, P = 0.028) showed that the rats in the 3W open-field groomed more often (13.08 ± 2.12) than those in the 2W open-field (7.75 ± 0.79) but did www.bjournal.com.br. The rats in both open-fields exhibited no differences in locomotor activity, as shown by the almost identical distances run in both apparatuses during the sessions
When squares with three adjacent walls were available to the animals they preferred to remain in them at the expense of the time allocated to squares with two adjacent walls, but not at the expense of squares with no or just one adjacent wall
Summary
The role played by different aversive stimuli in behavioral tasks that take advantage of the rat’s natural tendency to explore, like the open-field or the elevated plusmaze, is not fully understood. For long it has been assumed that the innate fear of open spaces was the most important anxiety-triggering stimulus [1], an assumption that later received experimental support (e.g., 2). The mechanisms by which rodents perceive the openness of an environment are still unclear. Barnett [1] states that “rats, like other small mammals, tend to move in contact with a vertical surface; they eat in a corner rather than in an open space” Grossen and Kelley [3] narrowed this assumption to aerial predators
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