Repeated restraint stress facilitates fear conditioning independently of causing hippocampal CA3 dendritic atrophy

This study investigated whether 21 days of restraint stress (6 hr/day) and the subsequent hippocampal dendritic atrophy would affect fear conditioning , a memory task with hippocampal-dependent and hippocampal-independent comp onents. Restraint-stressed rats were injected daily (21 days) with tianepti ne (10 mg/kg; to prevent hippocampal atrophy) or vehicle then tested on fea r conditioning (Days 23-25, with 2 tone-shock pairings) and open field (Day 25). Restraint stress enhanced freezing to context (hippocampal-dependent behavior) and tone (hippocampal-independent) and decreased open-field explo ration, irrespective of whether tianeptine was given. Results confirmed tha t stress produced CA3 dendritic atrophy and tianeptine prevented it. Moreov er, CA3 dendritic atrophy was not permanent but reversed to control levels by 10 days after the cessation of restraint stress. These data argue that d ifferent neural substrates underlie spatial recognition memory and fear con ditioning.