Effects of undernutrition during suckling on foot-shock escape behavior and of post-traini9ng beta-endorphin administration on inhibitory avoidance task test behavior of young rats

ABSTRACT

The hypothalamic beta-endorphin system of young Wistar rats of both sexes (21-day-old) responds in a distinct way to behavioral situations when compared to adult rats (90 to 120-day-old). In the present study we investigated whether the post-training amnestic effect of beta-endorphin previously demonstrated in Wistar adult rats is also observed young (21-day-old) well-nourished and undernourished rats. rats were undernourished since birth by feeding their dams an 8% casein diet, while well-nourished off spring were fed by dams maintained on a 20% caseindiet beta-endorphin was administered after training in a step-down inhibitory avoidance task using a 0.2 or 0.8 m-A footshock. Retention was tested 24 h later. We observed that the dose of beta-endorphin (1 ug/kg, ip) previously reported to have an amnestic effect on adult rats was ineffective in weanling rats of both nutritional groups. At a higher dose (2 ug/kg, ip) and using a 0.2-mA shock, beta-endorphin impaired the retention only of well-nourished rats. Test-to training difference (in s) in step-down latency for well-nourished beta-endorphin-treated rats was 7 vs 25 s for well-nourished rats treated with saline (P<0.05). Undernourished rats were hyperreactive to this shock intensity. Footshock escape latency (in s) for undernourished rats was 3.56 vs 5.80 for well-nourished rats (P<0.05, experiment 1) and 5.01 vs 10.89 (P<0.05 in experiment 2) and showed better retenmtion than did well-nourished rats. Test-totraining step down latency (in s) for saline-treated undernourished rats was abouth 108 vs 28 saline-treated well-nourished rats (P<0.05). At 0.8-m-A, neither beta-endorphin nor undernutrition affected performance. These resultssuggest that well-nourished rats respons in a distinct way to post-training beta-enmdorphin when compared to adult rats of both sexes. The absence of amnesia in weanling undernourished rats may be related to the enhacenced sensitivity of both sexes. The absence of amnesia in weanling undernourished rats may be related to the enhanced sensitivity of these animals to a 0.2-mA footshock