Efeito do estrogênio na memória para objetos em ratas Wistar: estampa temporal

Abstract

Previous studies have demonstrated an effect of the estrogen in hippocampus dependent memory. For example, proestrous rodents outperforming diestrous rodents, estrogen high levels and estrogen low levels, respectively. Besides its circadian modulation, memory is also subjected to the 24-h time stamp phenomenon, in which memory recall is best when the circadian times of the testing and training match. The aim of this study was investigated the effect of estrogen on memory recall on matching times or non matching times in an object recognition task, and identify if changes which ocurr during the estrous cycle on locomotor activity rhythm modulate the cognitive performance. We used 59 young adult female Wistar rats, arranged in 3 groups: intact (n = 34), sham-operated (n = 10) and ovariectomized (n = 15). Animals were trained and tested in matching times (ZT 14 - ZT 14) or non matching times (ZT 14 - ZT 18), testing made on proestrous or estrous phase. The results demonstrated that rats tested in proestrous phase explore more the new object than the old object, independent of the circadian coincidence between training and testing phases. Whatever, when the tests were made during estrous phase, we found the time stamp memory in na object recognition task. In ovariectomized groups, rats failured in memory recall of new object on matching times and non matching times in na object recognition task. Moreover, the acrophase of the locomotor activity rhythm changed according to the phase of estrous cycle, later on proestrous. But no correlations were found between acrophase and c ognitive performance in an object recognition task. We suggest that high levels of estrogen facilitate memory recall regardless of time of the day. Additionally, changes on locomotor activity rhythms according to the estrous cycle in Wistar rats that is exclusively in acrophase, don’t influence cognitive performance on object recognition task.