RESPONSE THRESHOLD TO AVERSIVE STIMULI IN STIMULATED EARLY PROTEIN-MALNOURISHED RATS

Two animal models of pain were used to study the effects of shortterm protein malnutrition and environmental stimulation on the response thr eshold to aversive stimuli. Eighty male Wistar rats were used. Half of the pups were submitted to malnutrition by feeding their mothers a 6% protein diet from 0 to 21 days of age while the mothers of the other half(controls) were well nourished, receiving 16% protein. From 22 to 70 days all rats were fed commercial lab chow. Half of the animals in the malnourished and control groups were maintained under stimulating conditions, including a 3-min daily handling from 0 to 70 days and an enriched living cage after weaning. The other half was reared in a sta ndard living cage. At 70 days, independent groups of rats were exposed to the shock threshold or to the tail-flick test. The results showed lower body and brain weights in malnourished rats when compared with c ontrols at weaning and testing. In the shock threshold test the malnou rished animals were more sensitive to electric shock and environmental stimulation increased the shock threshold. No differences due to diet or environmental stimulation were found in the tail-flick procedure. These results demonstrate that protein malnutrition imposed only durin g the lactation period is efficient in inducing hyperreactivity to ele ctric shock and that environmental stimulation attenuates the differen ces in shock threshold produced by protein malnutrition.