A combined study of behavior and Fos expression in limbic structures after re-testing Wistar rats in the elevated plus-maze.

The elevated plus-maze is an animal model used to study anxiety. In a second session, rats show a reduction in the exploratory behavior even when the two sessions are separated by intervals as large as 7 days. The aim of the present study was to investigate whether the reduction in the exploratory behavior is maintained after intervals larger than 7 days. Additionally, we aimed at investigating eventual correlations between behaviors in the plus-maze and activation of limbic structures as measured by Fos protein expression after the second session. Rats were tested for 5 min in the elevated plus-maze and re-tested 3, 9 or 33 days later. Other groups were tested only once. The rat brains were processed for immunohistochemical detection of Fos protein. The results show a decrease in the open arms exploration in the second trial with intervals of 3, 9 and 33 days. The expression of Fos protein in the piriform cortex, septal nucleus and paraventricular hypothalamic nucleus in the groups tested with intervals of 9 and 33 days were statistically different from the other groups. The alterations observed in exploratory behavior in the second session in the plus-maze did not correlate with Fos expression. In conclusion, although the specific test conditions were sufficient to evoke behavioral alterations in exploration in the elevated plus-maze, they were enough to induce significant Fos protein expression in piriform cortex, septal nucleus and thalamic and hypothalamic paraventricular nuclei but not in other areas such as dorsomedial nucleus of the hypothalamus and amygdala nuclei, known to be also active participants in circuits controlling fear and anxiety.

Thermal stress decreases general motor activity of rats in the elevated plus-maze but does not alter aversion to the open arms.

Environmental temperature is known to affect a variety of biological processes ranging from simple chemical reactions up to ecological distribution of animal species. To our knowledge, however, there are no studies relating environmental temperature and exploration in the elevated plus-maze. The present study was aimed at investigating the influence of animal house temperature on the exploration of an elevated plus-maze. Fifty-seven male Wistar-derived rats were divided into five groups which were kept for 96-h in an animal house with different temperatures (18, 22, 26, 30 or 34 degrees C) and then tested in the elevated plus-maze. Results showed that the animals submitted to the higher temperatures decreased body weight, frequency of entries into both the open and closed arm, time spent in the open arm extremities, distance run in the closed arms and frequency of rearing while increasing the mean duration of each entry into both the open and closed arms. There were no significant effects on the time spent in the open arms and the percentage of entries into the open arms. These effect are probably due to thermal stress and do not relate to emotional changes but rather to modifications in general activity. The frequency of stretching and head-dipping exhibited different profile reactions to temperature when compared to the above measures. These behavioral modifications are also consistent with the effects of thermal stress rather than alterations in emotionality.