may be traced to body's tissues
Light therapy to relieve winter depression and regulate sleep and wake cycles might work by triggering a reaction in certain tissues of the body, according to a study by a Yale researcher.
"For the last 15 years it has been known that light therapy can help seasonal affective disorder and can shift the biological clock in people and mammals, but no one knew how," says Dr. Dan Oren, associate professor of psychiatry and lead author of the study published in a recent issue of Biological Psychiatry. "Conventional wisdom had been that light triggers the vision system and sent a signal to the brain causing the anti-depressant and clock-shifting effects in people. But experimental data has been failing to support that conventional wisdom."
Oren says a more recent theory is that the therapeutic light can cause reactive oxygen species (ROS) production in various biological tissues. Excess concentrations of ROS can cause cell death, but controlled concentrations of ROS stimulate signal transduction processes for transcription factor activation, gene expression, muscle contraction and cell growth.
Production of ROS is known to maintain antibacterial systems of the body and may also mediate inflammation. Also, given the role of oxy radicals as neurotransmitters and signaling molecules, the demonstration that visible light produces such molecules reinforces the more recent hypothesis, Oren says.
He conducted the experiment using a standard light box for treating winter seasonal depression. The tissue, known as fibroblasts, was irradiated. Electron spin resonance, which is a physical technique used for detection of "free radical" molecules with energetic electrons, was measured before and after the light exposure. The tissue showed evidence of production of reactive oxygen species after 10 minutes of irradiation.
"The implication of the experiment is that it provides evidence that the body is able to detect light independent of the visual system and produce free radicals, or energized gas molecules, from a human cell culture," Oren says. "For many people, the idea that light could stimulate production of neuroactive gases was dismissed as a fanciful theory. This provides some evidence this model should be taken seriously and needs to be taken further."
Oren theorizes that the energized gas molecules, because they convey energy, carry a signal of energy to the biological clock. "They converge the light signal from the outside into a chemical signal to the brain," Oren says.
-- By Jacqueline Weaver
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