Abstract

Depression is often related with memory impairment. The present study used the passive avoidance conditioning to evaluate the effects of fluoxetine on the retention of memory in an animal model of depression. Chronic exposure to a variety of mild unpredictable stress such as loud noise, flash light, or restriction of food and water, causes several behavioral symptoms correspondent to those of depression. Rats in experimental groups were exposed chronic mild stress(CMS) during 8 weeks, and monitored the consumption of 1% sucrose solution every week as a index of depression. After 4 weeks of CMS exposure they received the training trials of passive avoidance conditioning, and during next 4 weeks they received the retention tests weekly with drug treatment. On the basis of sucrose intake of 4th week they were devided two matched subgroups, and during latter 4 weeks each group daily treated with fluoxetine(15mg/kg) or saline. CMS exposure reduced the sucrose consumption gradually in the first 4 weeks. This effect was reversed after 3 weeks of fluoxetine treatment. In the training trials, experimental groups showed lower acquisition scores than control (no stress) groups and in the 3week-retention trial, saline-experimental group performed more poorly than saline-control group. This is, CMS exposure impaired the learning and memory processing of animals. Fluoxetine-experimental group showed better retention of memory than saline-experimental group in the 3week-retention trial, and fluoxetine-control group also performed better than saline-control group in the 4week-retention trial. These results suggest that fluoxetine, the representative selective serotonin reuptake inhibitor, has positive effects on memory improvement as well as antidepressant effects.