Effects of different shock intensities during the contextual fear conditioning training on plasma corticosterone levels and the contextual memory specificity in rats

Abstract

Stressful or emotional events modulate how memory is consolidated in humans and animals. Contextual fear conditioning (CFC) tasks elicit the release of corticosterone, adrenal hormone associated with the consolidation of memories. In the training of this task, an aversive unconditioned stimulus, such as a foot-shock, according to its intensity, leads to increasing plasma corticosterone levels, variable that also shows a correlation with the freezing response of animals exposed to the same training context during the test. To evaluate how precise the aversive memory consolidation is, the animals will be exposed to the training context and to a novel context during the test and a discrimination index will be calculated according with the freezing time of these animals in both contexts. This discrimination index allows investigating memory specificity. However, up to this point, there are no studies investigating how different foot-shock intensities during the training affect the discrimination between contexts. This project will investigate how increasing shock intensities relate to the release of plasma corticosterone and memory specificity. The CFC task will happen in conditioning chambers where Wistar rats will receive, during the training, 3 foot-shocks of one intensity (0, 0.3, 0.6 or 1.0 mA). Right after the tests, a discrimination index will be calculated. Possible correlations between these variables will be analised. The results obtained in this experiment will contribute to a better understanding of how precise are the memories modulated by glucocorticoids. (AU)