Two experiments studied the open-field behaviors of rat mothers as a function of offspring manipulation. In the first experiment mothers whose offspring were "handled" were compared with mothers whose offspring were not handled. Mothers of handled offspring were found to be less emotional in the open field than control mothers. In the second experiment control litters and litters handled during their first week were fostered to mothers of nonhandled litters. The foster mothers and their new litters were not disturbed again until weaning 2 weeks later. Again, mothers which reared handled litters were less emotional than those which reared nonhandled litters. It was concluded that mothers are affected by early handling of their offspring, that the direction of influence can be from infant to mother, and that the effects of mother-infant interactions are likely to be extremely complex.
Many investigators have studied the effects of early "handling" on later behavior (Ader, 1968;Levine, Haltmeyer, Karas & Denenberg, 1967;Denenberg & Whimbey, 1968). The general finding has been that early handling reduces later emotionality. That is, when exposed to an unfamiliar open field as adults, early handled rats generally respond with higher activity, lower defecation scores, and lower plasma adrenocortical levels than nonhandled controls. In these studies, as in most other studies of the effects of early experience, the experimental manipulation of the young organisms either took place in the presence of the mother or unavoidably resulted in some disturbance of the