Ethopharmacological analysis of behaviour of rats using variations of the elevated plus-maze

Besides allowing better observation and recording of the behaviour of rodents, we have shown that the elevated plus-maze with transparent walls is as sensitive to anxiolytic and anxiogenic drug effects as a traditional apparatus with opaque walls. In this study we extend these observations with an ethopharmacological analysis of the behaviour of rats in the elevated plus-maze with transparent walls. A factor analysis of the behaviour of control (saline-treated) rats on the modified maze and on a standard maze revealed a characteristic distribution of the behavioural categories in six factors. For the modified maze, the first three factors, representing standard indices of anxiety, locomotion and risk assessment, were similar to the factor distribution reported by this and other studies using the standard elevated plus-maze test. Distinct features appeared on Factor 4, with the loading of rears in the modified maze together with the occurrence of the percentage of centre time and flat-back approach common to both mazes. Scanning and grooming, which are generally grouped on Factor 5 in the standard maze, appeared as isolated behavioural elements loading on Factors 5 and 6, respectively, in the modified maze. An ethopharmacological analysis of behaviour in the modified maze showed that midazolam (1 and 2 mg/kg) produced an anxioselective profile, whereas pentylenetetrazol (5 and 10 mg/kg) produced an anxiogenic-like profile. These results point to the distinct features of the elevated plus-maze with transparent walls, which may be beneficial in the study of the different facets of anxiety and the mode of action of anxiolytic drugs in rats.