Effects of age, sex, and brightness of rield on open-field behaviors of rats.

48 male and 48 female Holtzman rats, ages 50, 100, and 150 days, were tested in a black or white open field to determine the effect of varying brightness of the field upon ambulation and defecation scores. There were significant negative correlations between all ambulation and defecation scores, except for the 50-day-old animals. Ambulation scores decreased over trials for all animals; defecation scores remained the same. Trials did not interact with age, sex, or brightness on either measure. In both fields females crossed more squares than males at ages 100 and 150 days, but there were no sex differences in ambulation at age 50 days. Most notable was a sex difference as a function of brightness of field; whereas male scores did not differ, females ambulated significantly more and tended to defecate less in the white field. Results are described in terms of the need for standardization of the open field.