Acquisition and extinction of jumping, two-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 intensity in avoidance learning in malnourished rats, three avoidance responses (jumping, two-way shuttle-box and bar press) and three shock intensities (0.4, 0.6 and 1.0 mA) were used. Independent groups of 6 rats were used for each response topography and shock intensity. 2. Malnourished male Wistar rats were suckled by mothers fed a 12% casein diet during the lactation period (0-21 days of age) while the mothers of well-nourished controls received a 25% casein diet. After weaning (21st day), all animals received a commercial lab chow diet until 70 days of age, when the avoidance training started. 3. Malnutrition did not affect the acquisition of the avoidance response, but malnourished groups required more trials to extinguish jumping and two-way shuttle-box. During the acquisition phase all animals learned the jump response faster in comparison to bar press and shuttle-box avoidance responses. Both groups in the acquisition phase responded faster with 1.0 mA when compared to lower intensities (0.6 and 0.4 mA). The malnourished animals showed lower latency of avoidance in the jumping response when compared with well-nourished animals. During the extinction phase there was a significant effect of diet, response topography and shock intensity in the latency to respond and trials to criterion. The increased resistance to extinction in malnourished rats was particularly evident with 1.0 mA in the two-way shuttle-box response. 4. These results suggest that contradictory data related to the acquisition of the avoidance response in malnourished animals cannot be attributed to response topography or variations in shock intensity. Furthermore, our results also indicate that resistance to extinction and latency to respond are appropriate parameters for detecting differences between well-nourished and malnourished animals.