Long‐term effects of infant learning on adult conditioned odor aversion are determined by the last preweaning experience

We recently showed that odorizing mother's nipples from birth to weaning attenuated adult conditioned odor aversion (COA). The present study evaluated whether shorter durations of preweaning olfactory experiences could induce similar long‐term effects. We first showed that late preweaning odorization (PN13–PN25) impaired adult COA similarly to odorization from birth to weaning (PN0–PN25) whereas early odorization (PN0–PN12) had no effect on adult COA. As early odorization was followed by an odorless suckling period, we evaluated whether this odorless suckling could have interfered with early associative learning. We therefore weaned the animals either immediately after early odorization or 7 days later. Early odorization (PN0–PN18) followed by late odorless suckling (PN19–PN25) had no effect on adult COA. However, pups with early odorization (PN0–PN18) but without late odorless suckling (weaned at PN18) showed attenuated COA. These results support the hypothesis that interference between early and late preweaning experiences with the mother determines the long‐term impact on adult COA. © 2009 Wiley Periodicals, Inc. Dev Psychobiol 51: 389–398, 2009.