Restraint-induced hypoactivity in an elevated plus-maze

Rodents submitted to restraint stress show decreased activity in an elevate d plus-maze (EPM) 24 h later. The objective of the present study was to det ermine ifa certain amount of time is needed after stress for the developmen t of these changes. We also wanted to verify if behavioral tolerance of rep eated daily restraint would be detectable in this model. Male Wistar rats w ere restrained for 2 h and tested in the EPM 1, 2, 24 or 48 h later. Anothe r group of animals was immobilized daily for 2 h for 7 days, being tested i n the EPM 24 h after the last restraint period. Restraint induced a signifi cant decrease in the percent of entries and time spent in the open arms, as well as a decrease in the number of enclosed arm entries. The significant effect in the number of entries and the percentage of time spent in the ope n arms disappeared when the data were submitted to analysis of covariance u sing the number of enclosed arm entries as a covariate. This suggests that the restraint-induced hypoactivity influences the measures of open arm expl oration. The modifications of restraint-induced hypoactivity are evident 24 or 48 h, but not 1 or 2 h, after stress. In addition, rats stressed daily for seven days became tolerant to this effect.