Impairment of spatial learning and memory induced by learned helplessness and chronic mild stress.

This study examined the influence of learned helplessness (LH) and chronic mild stress (CMS) on spatial learning and memory in mice.  Researchers indicate that the hippocampal complex plays an important role in many common psychiatric disorders, spatial awareness, and is also involved in LH which is similar to depression in humans.  

There were 6 groups of mice with 12 mice in each group.  One control group for each independent (LH, CMS, or no stressor) variable and then each group has a similar a group that would receive an anti-depressant, “Imi” or “Flu”, to evaluate its effect.  Researchers induced LH using traditional shuttle box electric shock method. To induce CMS they used a variety of stressors that were presented at unpredictable times. Mice were also evaluated for plasma corticosterone levels and BDNF and CREB levels in the hippocampus were evaluated to asses stress and LH effects.

The research indicated that both Imi and Flu significantly reduced the number of escape failures in LH mice over the course of 18 days.  It also indicates that Imi and Flu reduced corticosterone in CMS mice over the course of 18 days. Additionally, both BDNF and CREB were improved with Imi and Flu.  Its notable that even though the drugs improved these measures, the levels never reached the same as the non-conditioned non-stressed mice.  

Lastly researchers evaluated mice in a Morris water maze.  Stressed mice performed significantly worse on escape times.  However, both Imi and Flu improved escape times. Interestingly mice who were not stressed but received Flu anyways did even better regarding escape times than mice who did not receive Flu.  

Song, L., Che, W., Min-wei, W., Murakami, Y., & Matsumoto, K.  (2006) Impairment of the spatial learning and memory induced by learning helplessness and chronic mild stress.  Pharmacology Biochemestry And Behavior.  83, 186-193.