The influence of postnatal handling on adult neuroendocrine and behavioural stress reactivity

Environmental stimuli during early stages of life can influence the develop ment of an organism and may result in permanent changes in adult behaviour and physiology. In the present study we investigated the influence of early postnatal handling on adult neuroendocrine and behavioural stress reactivi ty in Wistar rats. Pups were subjected to handling from postnatal day 1-21. The young were taken from the nest every day for 15 min and each of the pu ps was handled separately. Control nests were left undisturbed. When the an imals had reached an adult age of 3-4 months they were individually housed and subjected to a series of tests to measure their stress reactivity. In t he first experiment we established adult behavioural coping with stressors and anxiety in the following series of tests: open field test, shock prod d efensive burying test, elevated plus maze and conditioned fear test. Collec tively, the data clearly indicate that handled animals are characterized by a lower stress-induced anxiety. Yet, handled and control animals do not di ffer in their general way of coping with stressors. Although the lower anxi ety in handled animals is often reflected in a higher activity, they are no t more active per se. In a second experiment, animals were provided with a permanent jugular vein canula for repeated blood sampling to determine stre ss hormones: noradrenaline, adrenaline, prolactin and corticosterone. Anima ls were subjected to a novelty test and a conditioned fear test. The neuroe ndocrine response profile is consistent with the conclusion that handled an imals are less anxious than controls but are not different in their general strategy of coping with stressors. The handled animals showed an attenuate d adrenaline, prolactin and corticosterone response. Yet, in neither of the two tests there was a difference in noradrenaline response, a typical mark er for an active coping strategy. Interestingly, the differences in neuroen docrine reactivity already appeared in response to a mild novelty challenge when there were no clear behavioural differences yet. The neuroendocrine m easures are in line with the behavioural data but more sensitively reflect the differences between handled and control animals.