[The effect of the age factor on open-field behavior in rats]

We examined the age-related behavior under open-field conditions using 925 Wistar-Imamichi rats of both sex ranging 21 to 695 days old. The mean score of ambulation and rearing increased between 28-56 days old, and both decreased after those ages. The coefficients of variation were stable and kept minimum values between 28-98 days old. Other parameters, except for ambulation and rearing, did not show the age-related change. Each parameter was divided into 3 one-minute-values in order to detect the change in minutes after exposure in open-field conditions. The chronological change in each behavioral parameter has its own specific pattern regardless of age and sex. Namely, it has been proved that a rat has an invariable natural behavioral pattern with regard to a time course in open-field conditions. It is important to detect a change of chronological pattern in each parameter, because an abnormal subject would be identified by an appearance of change in the chronological pattern. Sexual difference also was identified in all ages. It is necessary to evaluate separately parameters depending on sexual difference.