Avaliação dos efeitos do estresse e da administração de corticosterona em diferentes modelos de memória

• Ano de defesa: 2016
• Autor(a) principal: Raya, Juliana [UNIFESP]
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de São Paulo (UNIFESP)
• Palavras-chave em Português: Memory; Stress; Corticosterone; Oral administration; Memória; Estresse; Corticosterona; Administração oral
• Link de acesso: https://sucupira.capes.gov.br/sucupira/public/consultas/coleta/trabalhoConclusao/viewTrabalhoConclusao.jsf?popup=true&id_trabalho=3614664; http://repositorio.unifesp.br/handle/11600/47265

Memory can be affected by several factors, among them stress. Acute stress, depending on the moment it is applied, may facilitate or impair memory. Chronic stress may affect memory according to their duration and intensity, causing deficit, improvement or no effect. Thus, the objective of this study was to investigate the effects of chronic stress and acute and chronic administration of corticosterone (CORT) in different memory tasks in rats. First, chronic mild stress (ECB) was performed, and animals were evaluated in the Multiple Trial Inhibitory Avoidance task (EIMT). ECB induced an anhedonic behavior in rats, noticed by reduction of sucrose consumption, yet there were no changes in the EIMT performance. We suggest that sucrose may be acting as an attenuator of stress effects. In the second experiment chronic restraint stress was conducted and animals were evaluated in the Morris Water Maze task (TLAM). Rats submitted to chronic restraint stress showed better performance in TLAM than those who did not. Thus, we speculate that stress has not been enough to cause a deficit in memory, but that was moderate to facilitate performance on the task. In other experiments, CORT was administered (40 mg/kg) for 21 days by two routes: orally or subcutaneously, and animals were evaluated in TLAM. It was observed that rats which received vehicle or CORT through voluntary orally path (in a piece of bread) performed the task properly, while animals that received vehicle or CORT subcutaneously showed impairment. We suggest that this discrepancy may be related to the route of administration, since there was no drug effect on any of the experiments. We also evaluated plasmatic CORT 30 minutes after oral administration, and there was a significant increase in the concentration of CORT. Then we found no behavioral changes in the Elevated Plus Maze and Open Field after acute ingestion of CORT (10 and 40 mg/kg). We speculate that this lack of behavioral changes could be explained by the evaluation time on the tasks. In the last experiment, we evaluated the effects of subcutaneous acute administration of CORT in three moments in the EIMT task: pre-training (40 m/kg), after training (40 mg/kg) and pre-test (3, 15 and 40 mg/kg). There were no changes in the performance of animals, and we suggest that the shock employed may have been too high. Furthermore, in the EIMT task animals undergo several training sessions to reach the learning criterion, however, studies commonly use the inhibitory avoidance task with a single session. In conclusion, in this study we present a series of independent experiments that may help in the development of future work involving the effects of stress and CORT administration on memory. We also proposed a refined method of CORT oral administration, which does not present stressors and reduces animal discomfort, contributing to the ethics policy of the 3 R's.