title: Eyes as gateways for environmental light to the substantia nigra: relevance in Parkinson's disease.
abstract: Recent data indicates that prolonged bright light exposure of rats induces production of neuromelanin and reduction of tyrosine hydroxylase positive neurons in the substantia nigra. This effect was the result of direct light reaching the substantia nigra and not due to alteration of circadian rhythms. Here, we measured the spectrum of light reaching the substantia nigra in rats and analysed the pathway that light may take to reach this deep brain structure in humans. Wavelength range and light intensity, emitted from a fluorescent tube, were measured, using a stereotaxically implanted optical fibre in the rat mesencephalon. The hypothetical path of environmental light from the eye to the substantia nigra in humans was investigated by computed tomography and magnetic resonance imaging. Light with wavelengths greater than 600 nm reached the rat substantia nigra, with a peak at 709 nm. Eyes appear to be the gateway for light to the mesencephalon since covering the eyes with aluminum foil reduced light intensity by half. Using computed tomography and magnetic resonance imaging of a human head, we identified the eye and the superior orbital fissure as possible gateways for environmental light to reach the mesencephalon.
authors.affiliation: Biotechnological and Applied Clinical Sciences Department, University of L'Aquila, 67100 L'Aquila, Italy.
authors.forename: Stefania
authors.initials: S
authors.lastname: Romeo
authors.affiliation: Department of Physical and Chemical Sciences, University of L'Aquila, 67100 L'Aquila, Italy.
authors.forename: Daniela
authors.initials: D
authors.lastname: Di Camillo
authors.affiliation: Biotechnological and Applied Clinical Sciences Department, University of L'Aquila, 67100 L'Aquila, Italy.
authors.forename: Alessandra
authors.initials: A
authors.lastname: Splendiani
authors.affiliation: Biotechnological and Applied Clinical Sciences Department, University of L'Aquila, 67100 L'Aquila, Italy.
authors.forename: Marta
authors.initials: M
authors.lastname: Capannolo
authors.affiliation: Biotechnological and Applied Clinical Sciences Department, University of L'Aquila, 67100 L'Aquila, Italy.
authors.forename: Cristina
authors.initials: C
authors.lastname: Rocchi
authors.affiliation: Biotechnological and Applied Clinical Sciences Department, University of L'Aquila, 67100 L'Aquila, Italy.
authors.forename: Gabriella
authors.initials: G
authors.lastname: Aloisi
authors.affiliation: Biotechnological and Applied Clinical Sciences Department, University of L'Aquila, 67100 L'Aquila, Italy.
authors.forename: Irene
authors.initials: I
authors.lastname: Fasciani
authors.affiliation: Department of Translational Research and New Technology in Medicine, University of Pisa, 56126 Pisa, Italy.
authors.forename: Giovanni U
authors.initials: GU
authors.lastname: Corsini
authors.affiliation: Biotechnological and Applied Clinical Sciences Department, University of L'Aquila, 67100 L'Aquila, Italy.
authors.forename: Eugenio
authors.initials: E
authors.lastname: Scarnati
authors.affiliation: Department of Physical and Chemical Sciences, University of L'Aquila, 67100 L'Aquila, Italy.
authors.forename: Luca
authors.initials: L
authors.lastname: Lozzi
authors.affiliation: Biotechnological and Applied Clinical Sciences Department, University of L'Aquila, 67100 L'Aquila, Italy.
authors.forename: Roberto
authors.initials: R
authors.lastname: Maggio
mesh_terms: D000818:Animals; D002940:Circadian Rhythm / Q000502:physiology; D005123:Eye / Q000000981:diagnostic imaging; D006801:Humans; D008027:Light; D008279:Magnetic Resonance Imaging; D009799:Ocular Physiological Phenomena; D011859:Radiography; D051381:Rats; D013378:Substantia Nigra / Q000000981:diagnostic imaging / Q000502:physiology*; D015898:Tomography Scanners, X-Ray Computed