Impact of the time in an animal model of mood disorder.

The objective of the study is to evaluate whether intervening and testing in different rest-activity periods of the day would produce different measurements in animal behavior studies.Thirty-five, 60-day-old male Wistar rats were submitted to an inescapable foot shock (IFS) stress model and behavioral tests (Light-Dark Box test). The animals received intervention and were tested in both light and dark phases, resulting in the following groups: control L (tested in the light), control D (tested in the dark), LL (IFS and tested in the light), LD (IFS in the light and tested in the dark), DL (IFS in the dark and tested in the light), and DD (IFS and tested in the dark).The Light-Dark Box test showed that control L was not significantly different from other groups in any of the parameters. However, when comparing control D with the intervention groups, we observed a difference in the mean length of time spent in the light compartment (t=2.56; p=0.045). A significant difference in the number of crossings into the light compartment was only observed between the control D and the LL and LD groups (t=-2.608; p=0.028; t=-2.571; p=0.030, respectively). The latency time for the control D group was significantly lower than that of the DD group (t=-2.556; p=0.043).These results show that behavior testing during the animal's period of highest activity (dark period) revealed differences caused by the intervention, whereas no differences were apparent when the control group was observed during the day.