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

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

Undernutrition during suckling does not change the specific or total activity of hypothalamic proline endopeptidase in adult rats

Undernutrition during suckling causes a decrease in hypothalamic beta-endorphin-like immunoreactivity in rats. Since proline endopeptidase (E.C. 3.4.21.26) has been proposed to play a role in the processing of Beta-endorphin, we examined the effects of undernutrition during suckling on the enzyme activity. Rats were undernourished by feeding their dams an 8% casein diet from the day of birth until weaning (21 days). Dams of well-nourished rats were fed a 25% casein diet during the same period. After weaning, all rats received a 20% protein diet until 90 to 120 days of age when they were killed for the enzyme assay. The specific and total activity of hypothalamic proline endopeptidase was not altered by undernutrition followed by nutritional rehabilitation(2.37 + or - 0.24 nmol sulphamethoxazole min-1 mg-1 for well-nourished rats vs 2.68 + or - 0.24 nmol sulphamethoxazole min-1 mg-1 for undernourished rats). This lack of correlation suggests that proline endopeptidase is probably not responsible for the low levels of hypothalamic Beta-endorphin found in adult rats submitted to undernutrition during suckling

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

1. The effects of undernutrition during suckling and of post-training ß-endorphin administration on avoidance task were invstigated in adult rats. 2. young rats were undernourished from delivery until weaning (21 days) by feeding their mothers a diet conatining 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 if age, when they were subjected to behavioral sessions. 3. Acquistion was measured in training sessions and retention in test sessions 24 h after training. Beta-endorphin or salina (control) was injected ip immdiately 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. Foor-shocks. In the step-down inhibitory avoidance task, ß-endorphin was amnesic only for normal rats and only for 0.2-mA footshocks. Beta-endorphin was not amnesic in undernourished rats