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.

Measuring emotional memory in the elevated T-maze using a training-to-criterion procedure.

The elevated T-maze, an ethologically based test, has been used to investigate the effects of anxiolytic drugs on memory and the relationships between neural systems involved in such modulation. This test allows the measurement in the same rat of two kinds of aversively motivated behaviors--inhibitory avoidance and one-way escape. The apparatus consists of three arms of equal dimensions, elevated 50 cm from the floor. One arm is enclosed by walls and stands perpendicular to the two open arms. Placing the rat at the end of the enclosed arm and recording the time to withdraw from this arm during three consecutive trials assesses inhibitory avoidance. Soon afterwards, the rat is placed at the end of one of the open arms and the time to leave this arm recorded as escape response. Three days later memory is assessed by reexposing the rats to the maze. One critical question raised by these studies is whether the anterograde amnesia induced by anxiolytic drugs could be due to insufficient learning during training or to amnesia. The present work investigated whether the introduction of a multitrial training-to-criterion procedure could overcome this question. For this purpose, rats were tested as many times as needed to stay in the enclosed arm continuously for 300 s (avoidance learning to criterion). Results from Experiment 1 showed that rats trained to a learning criterion shows significantly better retention performance. Experiment 2 evaluated the effects of pretraining diazepam (DZP) treatment on this training-to-criterion protocol. The results indicate that DZP did not affect acquisition performance but induced a dose-dependent impairment of the inhibitory avoidance in the memory test. One-way escape (latency to enter the enclosed compartment from the open arms) was not affected by DZP. These results rule out the possibility that the impairment of inhibitory avoidance memory in the elevated T-maze could be due to lack of learning during training, and support the hypothesis that the disruptive effects of DZP are on processes involved in long-term storage of information.