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

Abstract

Abstr actThe 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 signifi cant improvement of performance. No effects of stress on the animals' performance in Experiment II were observed. In the memory test, the malnourished rats showed defi cits 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. Keywords: Protein malnutrition, acute stress, learning, spatial memory. ResumoO objetivo do estudo foi investigar os efeitos do estresse agudo sobre os processos de aprendizagem e memória em ratos desnutridos testados no labirinto aquático de Morris. Os animais foram divididos em oito grupos de acordo com a condição nutricional (desnutridos ou bem nutridos) e estresse (não estressados ou estressados). No Experimento I os animais foram submetidos ao procedimento de estresse por imobilização antes da sessão de aprendizagem e no Experimento II após as sessões de aprendizagem. O teste consistiu de duas sessões diárias e um teste de memória após quatro semanas. Houve prejuízos de aprendizagem e memória em ratos desnutridos. No Experimento I o grupo desnutrido foi positivamente afetado pelo estresse agudo, apresentando melhora signifi cativa de desempenho. Não foram observados efeitos do estresse sobre o desempenho dos animais no Experimento II. No teste de memória os ratos desnutridos apresentaram défi cits de consolidação e evocação, independentemente da ocorrência de estresse. O estresse imposto 24 horas antes da tarefa de aprendizagem melhorou o desempenho de animais desnutridos com um efeito protetor do estresse. Entretanto não houve melhora nos processos de retenção ou evocação da memória (informações previamente aprendidas), avaliados quatro semanas mais tarde, durante o teste de retenção de memória. Palavras-chave: Desnutrição proteica, estresse agudo, aprendizagem e memória espacial. Mailing address:

Sinais sugestivos de estresse infantil em escolares com transtorno de aprendizagem

“…On the other hand, the information from this study about the high frequency of warning stress signs among children with adequate school performance elicits the reflection that such children could present even better results, further developing their potential in the absence of stressors. Another study 26 investigated the stress and malnutrition effect on learning in rats. The results showed no effects of isolated stress on learning, however, in previously undernourished rats, an episode of acute stress, before the execution of learning tasks and spatial memory, positively affects the acquisition of learning.…”

The effects of post-encoding stress and glucocorticoids on episodic memory in humans and rodents

“…Moreover, they have been observed in studies of object recognition (Guercio et al, 2014;Li et al, 2012;Maroun & Akirav, 2008;Segev, Ramot, & Akirav, 2012) and spatial water maze tasks (Kogan & Richter-Levin, 2010;Li et al, 2012;Vales, Fukuda, & Almeida, 2014). In addition, post-encoding stress impairments on memory were found across various stressors, including restraint (Guercio et al, 2014;Li et al, 2012;Vales et al, 2014), elevated platform (Maroun & Akirav, 2008;Segev et al, 2012), foot shock (Busquets-Garcia et al, 2016;Kogan & Richter-Levin, 2010), and tail suspension (Busquets-Garcia et al, 2016) stress paradigms. However, note that the only study to use predator odor as the stress manipulation did not find an effect of postencoding stress on memory (Homiack et al, 2017).…”