Mild daily stressors in adulthood may counteract behavioural effects after constant presence of mother during early life.

This study investigated adult rat behaviour in three early life conditions, and how behaviour was affected after exposure to chronic mild stressors in later life. During postnatal days 2-14, male Wistar rats were exposed daily to either long or brief maternal separation, or were left undisturbed with their mothers (non-handled). As adults, non-handled and long maternally separated offspring demonstrated less object exploration than brief maternally separated offspring. Non-handled offspring also showed lower pre-pulse inhibition compared to both long and brief maternally separated offspring. Sucrose preference and open field behaviour as adults did not differ between the early life conditions. Exposure to four weeks of chronic mild stress in adulthood (mimicking daily hassles in humans) increased object exploration, increased pre-pulse inhibition and induced habituation of acoustic startle in non-handled offspring, similar to brief maternally separated offspring. Long maternally separated offspring exposed to chronic mild stress failed to show an increase in object exploration and enhanced pre-pulse inhibition, and did not show habituation of acoustic startle. In conclusion, different early life conditions have a different long-term impact on behaviour. Offspring from all three conditions differed from each other in terms of adult behaviour. Mild daily stressors in the adulthood counteracted the effects observed in the non-handled condition.