ACQUISITION AND EXTINCTION OF JUMPING, 2-WAY SHUTTLE-BOX AND BAR PRESS AVOIDANCE RESPONSES IN MALNOURISHED RATS - EFFECTS OF SHOCK-INTENSITY

1. In order to investigate the role of avoidance response and shock in tensity in avoidance learning in malnourished rats, three avoidance re sponses (jumping, two-way shuttle-box and bar press) and three shock i ntensities (0.4, 0.6 and 1.0 mA) were used. Independent groups of 6 ra ts were used for each response topography and shock intensity. 2. Maln ourished male Wistar rats were suckled by mothers fed a 12% casein die t during the lactation period (0-21 days of age) while the mothers of well-nourished controls received a 25% casein diet. After weaning (21s t day), all animals received a commercial lab chow diet until 70 days of age, when the avoidance training started. 3. Malnutrition did not a ffect the acquisition of the avoidance response, but malnourished grou ps required more trials to extinguish jumping and two-way shuttle-box. During the acquisition phase all animals learned the jump response fa ster in comparison to bar press and shuttle-box avoidance responses. B oth groups in the acquisition phase responded faster with 1.0 mA when compared to lower intensities (0.6 and 0.4 mA). The malnourished anima ls showed lower latency of avoidance in the jumping response when comp ared with well-nourished animals. During the extinction phase there wa s a significant effect of diet, response topography and shock intensit y in the latency to respond and trials to criterion. The increased res istance to extinction in malnourished rats was particularly evident wi th 1.0 mA in the two-way shuttle-box response. 4. These results sugges t that contradictory data related to the acquisition of the avoidance response in malnourished animals cannot be attributed to response topo graphy or variations in shock intensity. Furthermore, our results also indicate that resistance to extinction and latency to respond are app ropriate parameters for detecting differences between well-nourished a nd malnourished animals.