Effects of early protein malnutrition and environmental stimulation on behavioral and biochemical parameters in rats submitted to the elevated plus-maze test

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.

Keywords:

• Protein malnutrition
• Environmental enrichment
• Tactile stimulation
• Elevated plus-maze
• Corticosterone
• Polyamines

Acknowledgments

The authors express gratitude to Dalmo Presta Nicola, technician at the Laboratory of Nutrition and Behavior of the University of São Paulo, for the assistance in the animal care and behavioral tests; Maria Valci Aparecida dos Santos, technician at the Laboratory of Neuroendocrinology of the University of São Paulo, for the assistance in the analysis of corticosterone; Gilberto João Padovan, chemist of the Laboratory of Mass Spectrometry at the University of São Paulo, for the assistance in the chromatography analysis; and Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) for the financial support of this study (Grant Number 2007/51380-7).