Gender differences in open-field behavior as a function of age.

Male and female rats were observed in an open field at 30, 45, 60, 90, and 120 days of age. Thirty- and 45-day-old rats of both genders presented similar defecation, ambulation, and rearing scores. From 60 days on the male rats showed higher defecation scores and less ambulation and rearing than did the females. The gender difference observed in the adult rats reflected a decrease of defecation by females and a decrease of ambulation and rearing by males when compared to the earlier ages.