The interaction of housing condition and acute immobilization stress on the elevated plus-maze behaviors of protein-malnourished rats

Abstract

Protein malnutrition induces structural, neurochemical and functional alterations in the central nervous system, leading to behavioral alterations. In the present study, we used the elevated plus-maze (EPM) as a measure of anxiety to evaluate the interaction between acute immobilization and housing conditions on the behavior of malnourished rats. Pups (6 males and 2 females) were fed by Wistar lactating dams receiving a 6% (undernourished) or 16% (well-nourished) protein diet. After weaning, the animals continued to receive the same diets ad libitum until 49 days of age when they started to receive a regular lab chow diet. From weaning to the end of the tests on day 70, the animals were housed under two different conditions, i.e., individual or in groups of three. On the 69th day, half of the animals were submitted to immobilization for 2 h, while the other half were undisturbed, and both groups were tested 24 h later for 5 min in the EPM. Independent of other factors, protein malnutrition increased, while immobilization and social isolation per se decreased, EPM exploration. Analysis of the interaction of diet vs immobilization vs housing conditions showed that the increased EPM exploration presented by the malnourished group was reversed by acute immobilization in animals reared in groups but not in animals reared individually. The interaction between immobilization and housing conditions suggests that living for a long time in social isolation is sufficiently stressful to reduce the responses to another anxiogenic procedure (immobilization), while living in groups prompts the animals to react to acute stress. Thus, it is suggested that housing condition can modulate the effects of an anxiogenic procedure on behavioral responses of malnourished rats in the EPM.