Résumé
Objective: The hippocampus has an important role in the acquisition and recall of aversive memories. The objective of this study was to investigate the relationship among hippocampal rhythms. Methods: Microeletrodes arrays were implanted in the hippocampus of Wistar rats. The animals were trained and tested in a contextual fear conditioning task. The training consisted in applying shocks in the legs. The memory test was performed 1 day (recent memory) or 18 days (remote memory) after training. We proposed a measure based on the FFT power spectrum, denominated "delta-theta ratio", to characterize the different behaviors (active exploration and freezing) and the memories types. Results: The delta-theta ratio was able to distinguish recent and remote memories. In this study, the ratio for the 18-day group was smaller than for the 1-day group. Moreover, this measure was useful to distinguish the different behavior states - active exploration and freezing. Conclusions: The results suggest delta-theta oscillations could reflect the demands on information processing during recent and remote memory recalls.
Objetivo: O hipocampo tem um importante papel na aquisição e evocação das memórias aversivas. Pretendeu-se, neste trabalho, investigar a dinâmica entre os ritmos hipocampais durante a evocação das memórias aversivas recente e remota. Métodos: Foram implantadas matrizes de microeletrodos em ratos Wistar. Os animais foram treinados e testados numa tarefa de condicionamento contextual de medo. O treino consistiu em aplicações de choques nas patas. O teste de memória foi realizado 1 dia (memória recente) ou 18 dias (memória remota) após o treino. Nesse trabalho, foi proposta uma medida baseada no espectro de potências, denominada "razão delta-theta", para caracterização dos diferentes comportamentos observados (vigília exploratória e congelamento) e tipos de memórias. Resultados: A razão delta-theta mostrou-se capaz de distinguir os grupos testados para as memórias recente e remota. Neste caso, observou-se, para o grupo testado 18 dias após, um valor menor do que para o grupo testado 1 dia após. Além disso, essa medida mostrou-se útil para distinguir os diferentes estados comportamentais. Conclusões: Os resultados sugerem que a dinâmica entre os ritmos delta e theta pode refletir o processamento da informação durante a evocação das memórias recente e remota.
Sujets)
Amnésie rétrograde , Hippocampe , Mémoire , Peur/physiologieRésumé
Objective To investigate the effects of propofol on learning and amnesia in the old miceMethods The normal Kunming mice were trained in a one-trial, step-through, light-dark passive avoidance paradigm Propofol (50 or 100 mg/kg) was administered intraperitoneally 15 min before training ,and propofol (100 or 200 mg/kg) separately 30 min and 6 h in the immediate post-training period The latency of escaping into a darkened chamber and the wrong number of entering darkened chamber were recorded Animals were tested for recall at 24th h post-training time The activity of acetyltransferase was determined with radiommunoassay in the brain 3h after administrationResults All control animals were liable to learn the task as judged by their increased latencies to enter the darkened chamber at 24th h post-training time After administration with propofol 50 mg/kg or 100 mg/kg, the latencies were reduced (246 and 208,repectively), compared with control (P