Effect of a single maternal separation at different pup ages on the corticosterone stress response in adult and aged rats.

Postnatal days (PNDs) 4-14 constitute the stress hyporesponsive period (SHRP) of the rat's pituitary-adrenal axis. The impact of manipulation of the pup-dam relationship during the SHRP on neuroendocrine and behavioural function has been the subject of considerable investigation. A single period of 24-h separation of the litter from the dam (maternal separation, MS) during the SHRP increases pup pituitary-adrenal activity and attenuates the SHRP. The MS manipulation also allows for the age-specific analysis of the chronic effects of early-life stress. Here we report on the effects of MS performed at the beginning of (PND 4), or about midway into (PND 9), or after (PND 18) the SHRP, on basal and stress-related blood corticosterone (CORT) titers in mature (month 5) and old (month 20) adult males. MS at PND 4, 9, or 18 did not affect basal CORT plasma titers. MS at each of these ontogenetic stages led to a similar and significant increase in the CORT response to restraint in adults but not in old adults. Therefore, whereas MS exerts a chronic impact on stress-related pituitary-adrenal activity in adult male rats, the effect of this postnatal experience does not depend upon the ontogenetic/SHRP status of the pup, and nor does it persist into senescence.