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Updated: May 15, 2026
Testing Animal Anxiety in Rats: Effects of Open Arm Ledges and Closed Arm Wall Transparency in Elevated Plus Maze Test
Published on: June 29, 2018
Effects of early protein malnutrition and environmental stimulation on behavioral and biochemical parameters in rats
Roberto O Soares1, Luiz M Oliveira, Julio S Marchini
1Department of Psychology, FFCLRP, University of São Paulo, Brazil.
Insights
Early protein malnutrition in rats led to lower anxiety and risk assessment behaviors in the elevated plus-maze (EPM). Environmental enrichment (EE), but not handling stimulation (H), reversed these malnutrition-induced effects.
Area of Science:
- Neuroscience
- Developmental Biology
- Nutritional Science
Background:
- Early life malnutrition can impact brain development and behavior.
- The hypothalamic-pituitary-adrenal (HPA) axis is sensitive to nutritional status and stress.
- Behavioral interventions like handling stimulation (H) and environmental enrichment (EE) may mitigate negative effects of malnutrition.
Purpose of the Study:
- To investigate the effects of tactile/handling stimulation (H) and environmental enrichment (EE) on the behavior of well-nourished (C) and malnourished (M) rats.
- To assess anxiety-like behaviors and risk assessment in the elevated plus-maze (EPM) following early protein malnutrition.
- To examine the impact of H and EE on corticosterone and hippocampal polyamine levels in malnourished rats.
Main Methods:
- Rats were assigned to well-nourished (16% protein) or malnourished (6% protein) diets.
- Animals received either handling stimulation (H) or environmental enrichment (EE) or no stimulation.
- Behavioral testing was conducted using the elevated plus-maze (EPM) at 36-37 days of age.
- Biochemical analyses included corticosterone and hippocampal polyamine levels.
Main Results:
- Malnourished (M) rats exhibited increased exploration of open arms and reduced risk assessment behaviors in the EPM compared to controls (C).
- Environmental enrichment (EE) reversed the behavioral alterations caused by malnutrition in the EPM; handling stimulation (H) did not.
- Malnourished rats showed higher corticosterone levels; non-stimulated animals had higher hippocampal polyamine levels.
Conclusions:
- Early protein malnutrition alters anxiety levels and risk assessment behaviors, potentially via HPA axis dysregulation.
- Environmental enrichment (EE) is effective in mitigating behavioral deficits associated with early protein malnutrition.
- The observed behavioral changes and hormonal alterations suggest a significant impact of early nutrition on neurodevelopment and stress response.
Abstract:
The objective of this study was to compare the effects of the tactile/handling stimulation (H) and environmental enrichment (EE) in well-nourished (C - 16% of protein) and malnourished (M - 6% of protein) rats tested in the elevated plus-maze (EPM) at 36 and 37 days of age. The results showed higher exploration of the open arms in the EPM in M as compared with C animals, as well as lower index of risk assessment behaviors, and EE, but not H, reversed the alterations produced by malnutrition in the EPM. Biochemical analysis showed higher levels of corticosterone in M when compared with C rats. The non-stimulated animals presented higher levels of polyamines in the hippocampus when compared with the stimulated ones in both diet conditions. It is suggested that both the lower anxiety levels and the lower risk-assessment behaviors in the EPM, as well as the higher levels of corticosterone, can be due to alterations in the activity of the hypothalamic-pituitary-adrenal axis as the result of early protein malnutrition.
