In this week’s issue of Journal of Neuroscience, Austrian neuroscientists used a wide array of molecular, endocrinal, and behavioral techniques and a novel animal model of depression to lend credence to the role of circadian rhythms in the etiology of mood disorders. To date, there are some nice reviews on this subject matter from a human and animal perspective by Drs. Anna Wirz-Justice and Colleen McClung, respectively.

ResearchBlogging.orgIn this particular study, housing under constant darkness induced depressive-like behaviors, including decreased ambulation, increased defeat, and decreased sensitivity to pleasurable stimuli. Neurobiologically, constant darkness prevented cell regeneration in the hippocampus, which could lead to severe cognitive decline, and physiologically, it was associated with elevated central and peripheral expression of proinflammatory cytokines (IL-6, TNF-alpha).

In addition to characterizing behavioral and physiological phenotypes associated with constant darkness, these neuroscientists went one step further and used pharmacology (antagonism) to understand the mechanisms,  responsible for the behavioral and physiological pathologies. It turns out that these phenotypes result from disturbances of the NF-kB signaling pathway, which is a protein complex that gates DNA transcription and cellular responses to stress, free radicals, and ultraviolet irradiation. Once this pathway is blocked, the behavioral and physiological markers of depression induced by constant darkness disappear (but of course, remain in the saline controls). These depressive phenotypes were also absent in knockdown IL-6 mice housed under constant darkness. Moreover, this eloquent study not only substantiates the role of circadian behavioral and physiological systems in the etiology of psychiatric illness, but advances our understanding of the broad effects the immune system can have on underlying physiology and behavior.

Francisco J. Monje,1 Maureen Cabatic,1 Isabella Divisch,1 Eun-Jung Kim,1,3 Kurt R. Herkner,3 Bernd R. Binder,2†, & and Daniela D. Pollak1 (2011). Constant Darkness Induces IL-6-Dependent Depression-Like
Behavior through the NF-B Signaling Pathway Journal of Neuroscience, 31 (25), 9075-9083 : 10.1523/JNEUROSCI.1537-11.2011