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Updated: Aug 20, 2026
Restraint to Induce Stress in Mice and Rats
Published on: December 6, 2024
Adrenocortical response to stress in fasted and unfasted artificially reared 12-day-old rat pups
Glenn Ward1, Hua Cheng Xing, Nancy Carnide
1Department of Health Studies and Gerontology, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1. gward@healthy.uwaterloo.ca
Insights
Artificial rearing (AR) in rats does not impair the stress hyporesponsive period (SHRP) if nutrition is adequate. However, food deprivation in AR or dam-reared pups increases corticosterone levels and stress response, though less so in AR rats.
Area of Science:
- Neuroscience
- Developmental Biology
- Endocrinology
Background:
- The impact of artificial rearing (AR) on the stress response during the stress hyporesponsive period (SHRP) in rats is not well understood.
- AR rats are deprived of maternal care during a critical developmental window.
Purpose of the Study:
- To investigate the effects of AR on the corticosterone (CORT) response to stress during the SHRP.
- To compare CORT responses in artificially reared (AR) and dam-reared (DR) rat pups under conditions of maternal/food deprivation and non-deprivation.
Main Methods:
- AR and DR rat pups were assessed for CORT levels at baseline and after acute stress (saline injection) on postnatal Day 12.
- Experimental groups included non-deprived AR, food-deprived AR, non-deprived DR, and maternally deprived (food-deprived) DR pups.
- Corticosterone levels were measured to assess the HPA axis activity and stress responsiveness.
Main Results:
- In non-deprived conditions, AR and DR pups showed similar low CORT levels, characteristic of the SHRP.
- Food deprivation in both AR and DR pups led to elevated baseline CORT and increased stress-induced CORT response.
- The CORT elevation in response to stress was significantly lower in food-deprived AR pups compared to food-deprived DR pups.
Conclusions:
- Long-term artificial rearing with adequate nutrition does not abolish the SHRP in rats.
- Food deprivation significantly impacts the stress response in both AR and DR pups, but AR pups show a blunted response compared to DR pups.
- Adequate nutrition is crucial for maintaining the normal development of the stress response system during the SHRP in artificially reared rats.
Abstract:
Recent studies have compared artificially reared (AR) rats with dam-reared rats on behavioral outcomes but, despite the fact that they are deprived of their mothers during the stress hyporesponsive period (SHRP), little is known about the effects of AR on the development of the stress response. In this study, the corticosterone (CORT) response to a stressor (saline injection ip) on postnatal Day 12 was assessed in rat pups that had been either dam-reared (DR) or artificially reared since Day 5. In the preceding 24 hr, half the pups in the DR group were maternally deprived (DEP). To control for the food deprivation consequent to maternal deprivation in these groups, half the pups in the AR groups also underwent 24-hr food deprivation (DEP). In the nondeprived condition AR pups did not differ from DR pups on untreated CORT levels or on levels at 1-hr poststress (i.e., all rats demonstrated low levels of CORT characteristic of the SHRP). In contrast, both maternally deprived DR pups and food-deprived AR pups exhibited increased untreated CORT levels as well as a significant increase at 30-min poststress, but CORT elevations were lower in the AR groups than in the DR groups. Thus, long-term maternal deprivation through artificial rearing in rats does not affect the reduced CORT levels and reduced CORT responsiveness associated with the SHRP; however, if animals are food deprived, then all show increased basal CORT levels and a greater CORT response to stress, although this response is lower in AR groups than in DR groups. These results suggest that rat pups artificially reared with adequate nutrition will still exhibit the SHRP.
