SMITH, M.C.*; MILLARD, W.J.; CRAMER, C.P.; Mount Holyoke College, South Hadley, MA; Mount Holyoke College, South Hadley, MA; Dartmouth College, Hanover, NH: EFFECTS OF CROSS-FOSTERING ON DEVELOPMENT AND BEHAVIOR OF BALB/C AND C57BL/6 MICE

When mouse pups are reared with their biological mothers, prenatal and postnatal environments are confounded with genotype making it difficult to assess the contribution of environment. Cross-fostering allows assessment of whether the postnatal environment affects behavior. In the present study, mice of the BALB/c and C57BL/6 strains were cross-fostered to dams of the same or different strains. Postnatal bodyweight was measured and latency to eye opening noted. After weaning, pups were tested for emotionality in an open-field, the elevated plus-maze, and the Porsolt swim test. Consistent with strain difference found in previous studies, BALB mice were found to be more emotional than C57 mice. That is, they produced more boli in the open field, spent more time in the closed arm of the plus maze, and spent more time floating in the swim test. A Strain x Dam interaction was found for the number of boli in the open field. Regardless of strain, pups raised by BALB dams did not differ from one another in the number of boli produced. However, a difference was found between strains in those pups raised by C57 dams. BALB pups raised by C57 dams produced more boli than C57 pups raised by C57 dams. Mean bodyweight over Days 5 to 25 was higher for pups parented by BALB dams. Further studies will use embryo transplantation to unconfound the effects of prenatal and postnatal environment. Supported by NIH HD042131 to CPC and The Undergraduate Biological Sciences Education Program, Howard Hughes Medical Institute Grant 71100-505003 to Mount Holyoke College.