Researchers at the John D. Dingell VA Medical Center and Wayne State University School of Medicine in Detroit have bred mice who cannot produce serotonin in their brains, which should theoretically make them chronically depressed. But researchers instead found that the mice showed no signs of depression, but instead acted aggressively and exhibited compulsive personality traits.
http://www.alternet....epression-wrong
Mice lacking the gene for TPH2 are genetically depleted of brain 5HT and were tested for a depression-like behavioral phenotype using a battery of valid tests for affective-like disorders in animals. The behavior of TPH2–/– mice on the sucrose preference test, tail suspension test, and forced swim test and their responses in the unpredictable chronic mild stress and learned helplessness paradigms was the same as wild-type controls. While TPH2–/– mice as a group were not responsive to SSRIs, a subset responded to treatment with SSRIs in the same manner as wild-type controls with significant reductions in immobility time on the tail suspension test, indicative of antidepressant drug effects. The behavioral phenotype of the TPH2–/– mouse questions the role of 5HT in depression.
http://pubs.acs.org/....1021/cn500096g
Mice without serotonin will respond to some SSRIs. So the mechanism of action may not be the expected one.
