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Neonatal isolation alters stress hormone and mesolimbic dopamine release in juvenile rats
Cheryl M McCormick1, Priscilla Kehoe, Kathy Mallinson
1Neuroscience Program and Department of Psychology, Bates College, Lewiston, ME 04240, USA. cmccormi@abacus.bates.edu
Insights
Neonatal isolation in rats impairs stress responses and dopamine levels postweaning. Isolated rats showed altered corticosterone and locomotor activity when stressed compared to controls.
Area of Science:
- Neuroscience
- Developmental Biology
- Stress Physiology
Background:
- Neonatal isolation is a significant environmental stressor impacting neurodevelopment.
- Early life stress can lead to long-term alterations in stress response systems and behavior.
Purpose of the Study:
- To investigate the lasting effects of neonatal isolation on stress reactivity and neurochemical changes in juvenile rats.
- To compare the behavioral and neuroendocrine responses to acute stress between neonatally isolated and nonhandled control rats.
Main Methods:
- Rat pups underwent daily 1-hour isolation from postnatal days 2-9.
- Juvenile rats (PND 26-30) were subjected to 1-hour restraint stress.
- Locomotor activity, plasma corticosterone, brain dopamine, and allopregnanolone levels were measured.
Main Results:
- Neonatally isolated rats did not increase locomotor activity or dopamine levels in response to restraint stress, unlike controls.
- Both groups showed increased corticosterone, but isolated rats had higher levels.
- Brain allopregnanolone increased with stress, with no difference between groups.
Conclusions:
- Neonatal isolation induces persistent changes in stress response and dopamine regulation evident postweaning.
- The impact of early life stress is most pronounced under acute stress conditions.
- Sex differences were observed in corticosterone levels, with females exhibiting higher responses.
Abstract:
Rat pups were individually isolated from the mother and nest for 1 h/day from postnatal days (PND) 2 to 9 and tested as juveniles (PND 26-30) compared to nonhandled (NH) controls. In response to 1 h of restraint stress, NH rats increased locomotor activity and dopamine (DA) levels, but neonatally isolated (ISO) rats did not. Both groups had increased plasma corticosterone levels in response to restraint, but corticosterone levels were higher in ISO than in NH. Brain allopregnanolone (3alpha,5alpha-THP) levels also increased in response to stress, but NH and ISO did not differ. Sex of the rats was not a factor for any of the measures except plasma corticosterone levels, where females had higher levels than males. These data indicate that the effects of neonatal isolation persist postweaning and that the effects are most evident in response to stress as opposed to under baseline conditions.