Maggio, R., Vaglini, F., Rossi, M., Fasciani, I., Pietrantoni, I., Marampon, F., et al. (2019). Parkinson's disease and light: The bright and the Dark sides. Brain Res Bull, 150, 290–296.
Abstract: Light exerts a major influence on human behaviour and health, mainly owing to the importance of sight in our lives, but also due to its entrainment of daily rhythms via the suprachiasmatic nucleus, the master pacemaker. Light may also be a useful clinical medium, as in lumino-therapy for the improvement of depressed mood. Further, as discussed herein, local application of near infrared light to the substantia nigra exerts neuroprotective properties in models of Parkinson's disease. However, light also has a darker side. In general, as regards the growing problem to human health – and the natural world – of excess exposure to artificial light: both urban glow and ubiquitous screens. Moreover, over-exposure to light, in particular fluorescent light, disrupts circadian rhythms and sleep, and may damage dopaminergic neurons. Is it, then, a neglected risk factor for Parkinson's disease? The present article discusses epidemiological and experimental evidence supporting beneficial and potentially deleterious impact of light on dopaminergic neurons and highlights the mechanisms whereby light might influence neuronal tissue.
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Romeo, S. et al. (2013). Bright light exposure reduces TH-positive dopamine neurons: implications of light pollution in Parkinson's disease epidemiology. Scientific Reports, 3.
Abstract: This study explores the effect of continuous exposure to bright light on neuromelanin formation and dopamine neuron survival in the substantia nigra. Twenty-one days after birth, Sprague–Dawley albino rats were divided into groups and raised under different conditions of light exposure. At the end of the irradiation period, rats were sacrificed and assayed for neuromelanin formation and number of tyrosine hydroxylase (TH)-positive neurons in the substantia nigra. The rats exposed to bright light for 20 days or 90 days showed a relatively greater number of neuromelanin-positive neurons. Surprisingly, TH-positive neurons decreased progressively in the substantia nigra reaching a significant 29% reduction after 90 days of continuous bright light exposure. This decrease was paralleled by a diminution of dopamine and its metabolite in the striatum. Remarkably, in preliminary analysis that accounted for population density, the age and race adjusted Parkinson's disease prevalence significantly correlated with average satellite-observed sky light pollution.
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