Rats reared in litters of 4 and 12 pups did not differ in emotional reactivity, but plasma corticosterone levels were higher in the animals reared in the larger litters. Under 6-hr. immobilization there were no differences in the incidence of gastric erosions, whereas under 18-hr. immobilization, the incidence of gastric erosions was greater in the animals reared in litters of 12. This was attributed to a decrease in susceptibiliry among the rats reared in the smaller sized litters.
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