RESUMEN
Early protein malnutrition produces structural and functional alterations in the brain and changes the organism-environment interactions. Rats from 26 to 76 days of age were used to study the effects of early postnatal protein malnutrition on the development of social play. During lactation phase the litters were fed diet containing 16% protein (well-nourished) or 6% protein (malnourished). From weaning to the end of behavioral tests well-nourished animals were fed a commercial lab chow diet (well-nourished--W) and the malnourished rats were divided into 2 groups: one was maintained on 6% protein diet (malnourished--M) and the other was fed a commercial lab chow diet (previously malnourished--PM). Pairs of male rats of same diet conditions were tested, at different ages, for three consecutive days. During sessions the following behaviors were recorded: pinning, wrestling, walk-over and rear. The frequency of wrestling and walk-over was significantly higher in malnourished as compared to well-nourished animals (p<0.05). Early protein malnutrition also changed the ontogeny of play behaviors (pinning and wrestling) with developmental retards in M and PM as compared with W animals, especially at 46 and 56 days of age. These results suggest that early protein malnutrition can affect the development of neural mechanisms underlying social play in rats.