Neuroendocrine correlates of chronic stress in human infants have not been established.
The goal of the present study was to create an animal model of continuous chronic
stress using the immature rat to measure basal plasma corticosterone, and secretion
of plasma corticosterone in response to an acute stress. This was achieved by modulation
of the cage environment for rat pups and their mothers. During postnatal days 2-9,
pups were maintained in three groups: (1) handled, (2) not handled and with ample
bedding; and (3) not handled with limited bedding. On postnatal day 9, some pups from
each group were subjected to acute cold-separation stress and were killed 90, 240,
or 360 min later along with unstressed controls. The group not handled and with limited
bedding manifested increased plasma corticosterone output even without cold exposure
and a sustained increase of plasma corticosterone after cold-separation stress. Plasma
corticosterone interanimal variability was increased and body weight was decreased
in these pups, typical of a state of chronic stress. The first model of continuous
stress in infant rats in which upregulation of hypothalamic-pituitary-adrenal axis
is achieved without maternal separation is presented. This paradigm may more closely
approximate the human situation of chronically stressed, neglected infants.