A new actimetry-based test of photic sensitization in a murine photosensitive magnesium depletion model

Photic hypersensitivity may induce various signs of nervous hypersensitivity, including diurnal cephalalgias, anxiety, dyssomnia, seizures, fatigue and/or myalgias. The patients usually present both dishabituation and generalization in response to repetitive light stimuli instead of habituation as in normal subjects. These clinical manifestations appear when light intensity is maximum (daytime; spring and summer) in magnesium-depleted patients with hypofunction of the biological clock. The best photic hypersensitivity management involves darkness therapy, either darkness per se or darkness-mimicking agents. To detect efficiently the best drugs that may be used in the treatment of disorders due to photosensitive magnesium depletion, we are proposing a simple and reproducible actimetry-based test in a murine photosensitive magnesium depletion model. Photostimulation using a stroboscope (100 J, 50 Hz) was performed on magnesium-deficient and control mice. It led to habituation with a decreased activity in response to intermittent light stimulation in control mice, whereas it induced in magnesium-deficient mice both sensitization (or potentiation), with nervous hyperexcitability, and generalization, involving sound hypersensitivity, after visual stimulation. In preclinical evaluation, this test provides a valuable animal model to study the neuroprotective effect of drugs in photosensitive syndromes, which often associate sensitization and generalization to various stimuli.