Background: The age at weaning programs life history adaptively. Shorter infancy resulted in longer/thinner animals with a reproductive-strategic shift to earlier physical and sexual development (BMC Med, 2013).
Hypotheses: The length of infancy impacts also the stress-response and has behavioural consequences.
Method: Sprague-Dawley pups (generation F1), which usually are weaned at age 21 days, were weaned by cross-fostering at age day (d) 16, 21 or 26, and separated from their foster mothers at d30. At d60 females (F) and males (M) were mated within the weaning groups and generation F1, F2 and F3 animals were tested weekly in an open field maze from age 2260 days for motor activity, anxiety/curiosity, short-term memory and stress-related corticosterone (CS) levels.
Results: Motor activity in an open field was similar in the three groups at generation F1, but increase in d16 vs d26 animals by a mean 19% in F and 27% in M rats at F2 (P<0.05) and 16% (F and M) in F3 (P<0.02). Anxiety, measured as time spent next to the maze walls, was similar at F1, but smaller by 58% and 68% in d16 vs d26 young animals at F2 (P<0.05) and F3 (P<0.05). Anxiety was associated with greater CS levels in d16-weaned (25.3±4.6 μg%) as compared to d26-weaned animals (11.6±0.8 μg%, P<0.01). Curiosity, measured as time spent in the maze centre was greater in d16 F2 and F3 rats vs d26-weaned rats (P<0.05). Short-term memory, measured as object recognition, was similar between groups in F1 but greater in d16 as compared to d26-weaned rats by a mean 25% in M and 19% in F (P<0.05) at F2 and 10% in both F and M at F3.
Conclusion: The age at weaning programs the stress-response and behaviours adaptively. In line with a faster reproductive strategy, shorter infancy resulted in a shift to greater motor activity, short-term memory and curiosity, and smaller anxiety but greater associated CS response. M were affected more than F animals and these traits built up trans-generations.