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Ontogeny of stress effects on ornithine decarboxylase activity in rats
Insights
Different stressors impact developing rats uniquely. Maternal deprivation (MD) decreases enzyme activity, while immobilization (IMM) and cold stress increase it, with mechanisms changing with age.
Area of Science:
- Developmental Biology
- Neuroendocrinology
- Physiology
Background:
- Stress responses vary significantly based on stressor type and animal age.
- Ornithine decarboxylase (ODC) activity is a key indicator of cellular response to stimuli.
- Previous research indicated maternal deprivation (MD) impacts ODC activity.
Purpose of the Study:
- To investigate the distinct organ-specific responses to different stressors (MD, immobilization, cold) in developing rats.
- To determine how age influences these stress-induced changes in ODC activity and serum growth hormone (GH).
- To elucidate the underlying mechanisms (hormonal vs. neural) mediating immobilization-induced ODC changes during development.
Main Methods:
- Administering maternal deprivation (MD), immobilization (IMM), and cold stress to rats at different developmental stages (neonatal, preweaning, adult).
- Measuring ornithine decarboxylase (ODC) activity in various organs (liver, heart, kidney).
- Quantifying serum growth hormone (GH) levels.
- Utilizing the ganglionic antagonist chlorisondamine to probe neural pathways.
Main Results:
- MD decreased ODC activity in many tissues, while IMM and cold stress increased ODC activity in the liver and heart of neonatal rats.
- Serum GH decreased with MD and IMM, but was unaffected by cold stress.
- Stress-induced ODC elevation intensified with age, MD effects diminished post-weaning, and IMM/cold increased ODC in adult organs.
- Chlorisondamine blocked IMM effects in adults but not neonates, indicating a shift from hormonal to neural mechanisms.
Conclusions:
- Maternal deprivation and classical stress paradigms (IMM, cold) elicit divergent organ ODC response patterns in neonatal rats.
- The mechanism underlying immobilization-induced ODC activity shifts from hormonal in neonates to neural in adults.
- These findings highlight the complex interplay between stress type, age, and physiological response during development.
Abstract:
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.
