Open-Field Behavior as a Function of Age, Sex, and Repeated Trials

Unhandled male and female rats, 28, 56, and 112 days old, received 10 trials in an open-field. All groups showed a decline in ambulation in the early trials, followed by an increase later in the series. 28-day-old animals showed no change in defecation across trials, whereas the 56- and 112-day groups showed an increase in defecation on the middle trials. Further ambulation and defecation were negatively correlated at 56 and 112 days but not at 28 days. As such, the changes in ambulation and defecation in the 56- and 112-day groups were both seen as reflecting the differential habituation of approach and avoidance tendencies. The results also show that defecation is not a reliable measure of emotionality in 28-day-old rats.