Chronic desipramine alters stress-induced behaviors and regional expression of the immediate early gene, c-fos.

This experiment examined the effects of acute or chronic administration of the antidepressant drug desipramine on conditioned stress-induced behaviors and regional c-fos expression in the brain. To this end, rats were exposed to three sequential daily sessions of uncontrollable foot-shock and matched, on the basis of crouching, into one of four groups. Two of these groups were exposed to saline injections twice daily and two were exposed to injections of desipramine (5 mg/kg, SC) twice per day, for 9 days. On the 10th day one of the saline groups received saline and the other received desipramine before being exposed to the shock chamber without shock. Likewise, on the 10th day one of the desipramine groups received saline and the other received desipramine before being exposed to the shock chamber without shock. Detailed behavioral analysis showed that compared to the saline-treated controls only the group treated chronically with desipramine, including on the test day, exhibited statistically significant reductions in crouching and increases in exploration during the test session. Similarly, Fos immunohistochemistry revealed that the chronic desipramine group showing positive behavioral effects was the only group in which there were significant reductions in the number of stress-induced Fos-positive neurons in five of 60 structures surveyed. These structures included the anterior cingulate cortex, anterior claustrum, central nucleus of the amygdala, dentate gyrus of the dorsal hippocampus, and paraventricular nucleus of the thalamus. To the extent that repeated exposure to uncontrollable stress is an animal model of depression, these and previous results suggest that these structures are potentially important neural targets for the antidepressant effects of desipramine.