Psychosomatic Medicine 35:497-508 (1973)
© 1973 American Psychosomatic Society

Behavioral and Physiologic Effects of Littermate Removal on the Remaining Single Pup and Mother During the Pre-Weaning Period in Rats

¹ Departments of Psychiatry, Montefiore Hospital and Medical Center, Bronx, New York, and Yale University School of Medicine, New Haven, Connecticut

Wistar rat litters were reduced to a single pup shortly after birth. Prior to 10 days of age, this procedure generally resulted in inanition and death of the remaining pup, but by the 12th postnatal day 100% survived. Mothers increased the proportion of time spent with ‘singletons’ to 70-100% and showed more licking of the singleton and maintenance of a nursing posture than controls. Single pups showed increased stimulation of the mother, self-grooming and locomotion; they maintained weight gains indistinguishable from controls and developed cardiac acceleratory responses significantly greater than controls. We hypothesize that, with only a single pup present, the rat mother may not be stimulated to develop the normal changes in maternal behavior compatible with the growing age of her pup, resulting in altered development of her infant.

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