The effects of a mild stressor on spontaneous alternation in mice

Adult mice of the C57BL/6J strain were subjected to an acute mild stress at different periods before the choice trial of a spontaneous alternation tes t. The stressful event was either inescapable (forced exploration in a brig htly lit open field) or escapable (temporary entries into an adjacent dark chamber). While unstressed control mice alternated above chance:ln each con dition, mice subjected to inescapable stress did not alternate when forced exposure to the open field occurred during the entire retention interval. T he same effect was seen when forced exposure to the open held occurred afte r a post-forced trial delay period. However, no change in the alternation r ate was observed when the inescapable stress occurred before the forced tri al, or if the delay intervened between the stressful event and the choice t rial. The escapable stressful event had no effect on spontaneous alternatio n. These results indicate the role of cognitive mediation in the behavioral effects of inescapable stress, causing either a retrieval deficit or neoph obia. (C) 2001 Elsevier Science B.V. All rights reserved.