Preweaning Handling and Later Open-Field Behavior in the White Rat

Abstract

2 litters (10 males and 8 females) of Wister strain rats received daily handling stimulation in the handling box (Plate 1) for 20 consecutive days from days 2 to 21, while two other litters (5 males and 6 females) received no handling experience. All animals were weaned at 22 days of age and reared in individual cages thereafter. At 60 days of age, the animals were tested in an open-field apparatus for 3 minutes daily over 10 consecutive days. The results are summarized as follows : (1) Females ambulated significantly more in the open field than males (Fig. 1, Table 1).(2) Preweaning handling stimulation showed no significant effect on ambulation when an average was taken regardless of sex difference (Fig. 1, Table 1).(3) However, handled males ambulated more than non-handled ones, while non-handled females ambulated more than handled ones. Thus, a significant Sex×Handling interaction was found for ambulatory activity (Fig.1, Table 1).(4) As the 10 day test period proceeded, ambulation increased from test day 1 up to its peak on test days 2-4, showing little change or a tendency to decrease slightly on subsequent test days (Fig. 1).(5) On day 1 no significant difference appeared between handled and nonhandled rats, but on day 2 the former showed both a much greater amount of ambulation in the inner area (i. e. 9 sections in the center) and in the ratio of this to that in the whole area (Fig. 3).(6) Males showed significantly more elimination on two points, the number of days defecating and the frequency of urination (Table 2, Fig. 4-5).(7) The handling treatment appeared to increase elimination (Table 2, Fig. 4-5).(8) Neither handling treatment nor sex appeared to have any relationship to rearing responses (Fig. 6).