Effects of acute stress on learning and memory processes of malnourished rats

The aim of the study was to investigate the effects of acute stress on the processes of learning and memory in malnourished rats tested in the Morris water maze. The animals were divided into eight groups according to nutritional status (malnourished or well nourished) and stress (stressed or unstressed). In Experiment I the animals were subjected to immobilization stress procedure before the learning session and in Experiment II after the learning sessions. The test consisted of two daily sessions, and a memory test after four weeks. There was loss of learning and memory in malnourished rats. In Experiment I the malnourished group was positively affected by acute stress, with significant improvement of performance. No effects of stress on the animals' performance in Experiment II were observed. In the memory test, the malnourished rats showed deficits in consolidation and recall, regardless of the occurrence of stress. The stress imposed 24 hours before the learning task improved performance of malnourished animals with a protective effect of stress. However there was no improvement in the processes of retention or recall from memory (previously learned information) assessed four weeks later, during the memory retention test