Effects of illumination and handling upon rat open field activity.

Eighty male rats (Crj:CD, 4 weeks old), were randomly assigned to four groups in a 2 x 2 (brightness x handling) factorial design. Ambulation and three types of defecations [pre-open-field defecation (PRD), post-open-field defecation (POD), and testing defecation (TD)] were examined for 3 consecutive days, for 3 min per day. In this study, the effects of handling treatment were illumination dependent. The changes in TD and POD were opposite in relation to the trial day, whereas the changes during the trial, the sum of the TD and POD, were invariable. Considering the invariable changes of the sum of TD and POD, time per trial may be an important factor to measure emotional activity. The TD-POD inversion may reflect the strength of the stress response against a novel placement in open field, because of the change of the time for evoking defecation behavior.