Effects of undernutrition during suckling and of post-training beta-endorphin administration on avoidance performances of adult rats.

1. The effects of undernutrition during suckling and of post-training beta-endorphin administration on avoidance task were investigated in adult rats. 2. Young rats were undernourished from delivery until weaning (21 days) by feeding their mothers a diet containing 8% protein (w/w). Mothers of well-nourished rats were fed a 20% protein diet. After weaning, both groups of rats were fed a 20% protein diet until 90-120 days of age, when they were subjected to behavioral sessions. 3. Acquisition was measured in training sessions and retention in test sessions 24 h after training. Beta-endorphin or saline (control) was injected ip immediately after training. Rats were subjected to shuttle and step-down inhibitory avoidance sessions using footshock of 0.2 or 0.8 mA intensity. 4. Undernutrition during suckling caused hyperreactivity to 0.2 mA footshocks. Beta-endorphin caused amnesia to shuttle avoidance task only in normal rats trained with 0.8 mA footshocks. In the step-down inhibitory avoidance task, beta-endorphin was amnesic only for normal rats and only for 0.2 mA footshocks. Beta-endorphin was not amnesic in undernourished rats.