Original research paper Effects of early protein malnutrition and environmental stimulation on behavioral and biochemical parameters in rats submitted to the elevated plus-maze test Roberto O. Soares 1 , Luiz M. Oliveira 1 , Julio S. Marchini 2 , José Antunes- Rodrigues 3 , Lucila L.K. Elias 3 , Sebastião S. Almeida 1 1 Department of Psychology, FFCLRP, University of São Paulo, Brazil, 2 Department of Internal Medicine, FMRP, University of São Paulo, Brazil, 3 Department of Physiology, FMRP, University of São Paulo, Brazil 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 Introduction When early protein malnutrition occurs in newborns and children during the most vulnerable stages of their cerebral development, it can lead to several maturational events causing impairments on morpho- logical, neurochemical, behavioral, and cognitive pro- cessess. 1,2 Studies in rats indicate that when the malnutrition is imposed during the prenatal period it can alter the development of the central nervous system (CNS), especially the plasticity of the hippocampus. 3–5 During the postnatal period it was shown that the protein malnutrition alters the levels of the glucocorti- coid as well as the plasmatic corticosterone (CORT), 6,7 suggesting a modification in the response of the adrenocorticotropin to the stress. Protein malnutrition can cause a decrease on the number of glucocorticoid receptors in the hippocampus, 3,8,9 altering the sensibil- ity of the hypothalamic-pituitary-adrenal axis (HPA) and consequently the response of the organism to the stress. 3,5,7 The CORT participates in the synthesis of the ornithine decarboxylase (ODC), being essential in the polyamines synthesis processes [ putrescine, spermine (SPM), and spermidine (SPD)]. 10–13 The polyamines can present changes in the anabolic/cata- bolic process during aversive stimulation, a pheno- menon known as the polyamine response to stress. 12 As the result of an increase of CORT, there is a response of the polyamines with a decrease of its levels, evidencing an increase in the anabolic/catabolic processes and producing decreases in the intracellular level of polyamines. 13 Has been shown that among hippocampal neurons, dentate granule cells are selectively vulnerable to food restriction, 9 more specifically, in the CA1 region, the protein malnutrition resulted a decrease of total neurons. 9 This change observed in the granule cells of hippocampus may change the behavior observed during of elevated plus-maze (EPM) test. Protein malnutrition imposed early in life can alter some responses in animal models of behavior. Thus, it Correspondence to: Sebastião S. Almeida, Laboratório de Nutrição e Comportamento, Departamento de Psicologia, Faculdade de Filosofa, Ciências e Letras de Ribeirão Preto, Avenida dos Bandeirantes, 3900 - Ribeirão Preto - São Paulo, Brazil 14040-901. Email: sebasalm@usp.br © W.S. Maney & Son Ltd 2012 DOI 10.1179/1476830512Y.0000000036 Nutritional Neuroscience 2012 VOL. 0 NO. 0 1