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Light-induced Hormone Surge Points To Benefits Of Light TherapyA report in the November Cell Metabolism reveals powerful effects of light on the adrenalglands, a finding that might explain the broad benefits of bright light therapy for a variety ofconditions, including sleep and depressive disorders, according to researchers. The body'stwo adrenal glands sit atop each kidney, where they secrete hormones that regulate stressresponse and metabolism.The researchers found in mice that light sparks a cascade of gene activity in the adrenal gland through

its effects on the suprachiasmatic nucleus (SCN). Located in the brain region called the hypothalamus,the SCN is the seat of the circadian clock, the body's internal clock that regulates the roughly 24-hourcycle of biological processes.Moreover, the researchers report, the gene expression changes accompany a massive surge of thesteroid hormone corticosterone in the animals' blood and brain. That hormonal response increased withlight intensity, they found.Glucocorticoids--including cortisone in humans and corticosterone in mice--play many roles throughoutthe body, including metabolic response to starvation, antiinflammatory immune response, and thetiming of circadian rhythms in peripheral organs. Therefore, light-induced secretion of glucocorticoidsmay play a key role in physiological changes in the body and the brain evoked by light, reported studyauthor Hitoshi Okamura of Kobe University Graduate School of Medicine in JapanFirst introduced in the early 1980s for the treatment of seasonal affective disorder, bright light therapy

has been applied to many sleep disorders, including jet lag syndrome and shift work sleep disorder, thereseachers said. Shift work sleep disorder, which affects people who frequently rotate shifts or work atnight, is often accompanied by metabolic symptoms, including hypertension, cancer, and diabetes."In these patients, light therapy improves not only psychiatric status, but also disordered hormones andmetabolisms," Okamura said. "However, effects of light had only been established on melatonin, andthe remaining powerful and broad effects of light on body metabolism and hormones remained to beclarified."The researchers examined the activity of the clock gene Per1 in the organs of living animals. The teamfound that nighttime light exposure induced Per1 expression in the adrenal gland. Further analysis ofthe gland revealed numerous changes in the activity of almost 200 genes, followed by the delayedrelease of corticosterone.When the researchers severed the SCN, light's effect on the gland was lost, indicating that the

phenomenon is closely linked to the circadian clock, they said."The surge of blood corticosterone after light exposure indicates that environmental signals areinstantly converted to glucocorticoid signals in the blood and cerebrospinal fluid," Okamura reported."The present light-induced corticosterone release may entrain metabolically peripheral clocks to theenvironmental light-dark cycle through its prevailing receptors located in virtually all cells in the body."The findings could prove of great clinical and physiological interest, wrote Ueli Schibler and StevenBrown in an accompanying commentary."If a light-induced pathway were also operative in humans, a question that could readily be examinedby recording blood cortisone levels after light exposure, it would be tempting to speculate thatcortisone-mediated synchronization of peripheral circadian clocks would be one of the beneficial effectslight therapy has on patients with seasonal affective disorder," Schibler and Brown said."It might also explain why bright light therapy can aid patients with other disorders--such as majordepressive disorder and bipolar disorder--not typically associated with the circadian clock," theycontinued.

###The researchers include Atsushi Ishida, Tatsushi Mutoh,Tomoko Ueyama,Satoru Masubuchi, andHitoshi Okamura of the Kobe University Graduate School of Medicine in Kobe, Japan; Hideki Bando ofKobe University Graduate School of Medicine in Kobe and of Kyoto Prefectural University of Medicinein Kyoto, Japan; Daiichiro Nakahara of Hamamatsu University School of Medicine, Hamamatsu, Japan;and Gozoh Tsujimoto of Kyoto University Graduate School of Pharmaceutical Sciences in Kyoto,Japan. This work was supported by Scientific Grants from the Ministryof Health, Welfare, and Labor,The Special Coordination Funds and the Scientific Grants of the 21st Century COE Program fromMinistry of Education, Culture, Sports, Science, and Technology of Japan, SRF, and Hyogo Science

and Technology Association.Ishida et al.: "Light activates the adrenal gland: Timing of gene expression and glucocorticoid release."Publishing in Cell Metabolism Volume 2, November 2005, pages 297 - 307. DOI10.1016/j.cmet.2005.09.009www.cellmetabolism.org

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