Ontogeny of stress effects on ornithine decarboxylase activity in rats.

This study demonstrates that "stress" elicits a specific pattern of organ response in developing rats that is determined by the particular "stress" and by the age of the animal. Maternal deprivation (MD) of preweanling rat pups decreases ornithine decarboxylase (ODC) activity in many tissues, as reported previously, while immobilization (IMM) and cold stress increase ODC activity in liver and heart of neonatal rat. Serum GH is decreased by MD and by IMM, but is not affected by cold stress. Stress-induced ODC elevation increases with age, while MD effects disappear at weaning. IMM and cold increase ODC activity in kidney, liver and heart of adult rats. These effects of IMM are blocked by the ganglionic antagonist chlorisondamine in adult but not in neonatal rats. The results of this study suggest that MD and the "classical" stress paradigms IMM and cold evoke different patterns of organ ODC response in neonatal rats. Furthermore, these findings suggest that the mechanism by which immobilization increases ODC activity changes from a hormonal to a neural mechanism during ontogeny.