An elevated plus-maze was used to study the ontogeny of the exploratory behaviors of earlyprotein-malnourished animals in an experimental aversive situation. Rats were malnourished by feeding their dams a 6% protein diet during the lactation period (0-21 days of age); controls received a 16% protein diet. From 21 to 100 days of age, all rats received a balanced lab chow diet. At 21,30, 40, 50, 60, 70, 80, 90, and 100 days of age, independent groups of malnourished and control animals were exposed to the elevated plus-maze and allowed to explore for 5 min. During this period, 12 behavioral categories (number of entries and time spent in the open and enclosed arms, total arms entries, attempts to enter open and closed arms, closed-arm returns, latency of fIrst closed-arm entry, total immobility time, total grooming time, total reatings, total head-dippings, and total stretch attend posture) were recorded. The results showed that anxiety increased with age and that protein malnutrition produced alterations in the ontogeny of exploratory behaviors. It was shown that malnourished rats maintained or increased exploration in the maze with age, in contrast to wellnourished animals, which exhibited a steady decrease in exploration as they matured. The higher number of entries and time spent in the open arms suggest that the protein malnutrition causes a permanent increase in the impulsiveness and/or an increased drive to explore open-arm novelty, leading to a behavior consistent with lower anxiety in malnourished animals, relative to that in wellnourished animals, in this naturalistic animal model of anxiety. Protein malnutrition early in life causes long-lasting structural and neurochemical changes in the central nervous system, as well as behavioral abnormalities (Dob-

In order to study the effects of the protein--calorie malnutrition on the behavior of rats submitted to the elevated plus-maze, an ethopharmacological analysis was used. Litters (dam plus 6 male pups) were fed ad lib (control) or were fed 5091> of the amount of diet consumed by the control group (malnourished) from birth to 49 days of age. From Day 50 on, all rats were fed ad lib. At 70 days of age, the animals were pharmacologically treated (vehicle or diazepam, 1.5 and 3.0 mg/kg) and were placed, 30 min later, in the center of the elevated plus-maze for a 5-min session. During this session, 11 behaviors believed to indicate anxiety or exploration were measured. The results showed that protein--calorie malnutrition results in increased exploration of the open arms of the maze, higher latency offrrst arm entry, and lower closed-arm returns, indicating lower anxiety or higher impulsiveness. In addition, the protein--calorie-malnourished rats were hypo reactive to the anxiolytic effects of diazepam, indicating possible alterations in the GABA-benzodiazepine system as result of the malnutrition procedure.Protein malnutrition early in life results in morphological, neurochemical, and behavioral changes that persist even after a long period of nutritional rehabilitation (

An increased number of visits and time spent in the open arms of the elevated plus-maze by malnourished rats has been used as indicative of lower anxiety or higher impulsiveness. In order to study how this behavior profile responds to an anxiogenic procedure (short-term social isolation), control (16% protein) and malnourished (6% protein) rats were socially isolated prior to the test in the maze. Litters (dam plus 6 male and 2 female pups) were fed the diets from birth to 49 days of age. From 50 days on, all rats were fed a lab chow diet. Social isolation consists in removing the rats from the group and placing them in individual cages for 2 h before the test. During the test each rat was individually placed on the center of the maze and allowed to explore for 5 min. The results showed higher open arms exploration and lower attempts to enter open arms by the malnourished rats than by the controls. Social isolation decreased open arm exploration and increased time spent on the central platform in control animals, but had no effect on the malnourished rats. The results reinforce the lower anxiety or higher impulsiveness of malnourished rats, as well as the anxiogenic effect of social isolation in control rats. However, the malnourished rats were unresponsive to the anxiogenic effects of social isolation, indicating that protein deficiency early in life not only induces lower anxiety or higher impulsiveness in the maze, but also changes the behavior of these animals in response to another environmentally-induced procedure of anxiety (social isolation).