Three groups of rats were tested in different types of elevated plus-mazes, a normal one (two closed and two open arms), a totally closed one (four closed arms) and a totally open (four open arms). Closed arms were Surrounded by 40-crn high wooden walls and open arms were Surrounded by 0.5-cm high transparent Plexiglas ledges. As expected, in the closed maze rats explored equally all the arms. both in terms of time and frequency of entries, as well as in exploration of the extremities. Rats in the totally open maze also presented a similar pattern of exploration, that is, no significant differences were found between the results obtained with the closed and the open mazes in terms of central and extremities exploration. It is suggested that the typical behavior of rats in the conventional elevated plus-maze is caused by the contrasting characteristics of open and closed arms rather than by the physical aversive characteristics of the open arms per se. Results also confirm a prediction made by a computer model sinudating rat exploratory behavior in virtual mazes, normal, totally open and totally closed. (C) 2003 Elsevier Science B.V. All rights reserved.
