title: Interaction of (12)C ions with the mouse retinal response to light.
abstract: Astronauts in orbit reported phosphenes varying in shape and orientation across the visual field; incidence was correlated with the radiation flux. Patients with skull tumors treated by (12)C ions and volunteers whose posterior portion of the eye was exposed to highly ionizing particles in early studies reported comparable percepts. An origin in radiation activating the visual system is suggested. Bursts (∼ 4 ms) of (12)C ions evoked electrophysiological mass responses comparable to those to light in the retina of anesthetized wild-type mice at threshold flux intensities consistent with the incidence observed in humans. The retinal response amplitude increased in mice with ion intensity to a maximum at ∼ 2000 ions/burst, to decline at higher intensities; the inverted-U relationship suggests complex effects on retinal structures. Here, we show that bursts of (12)C ions presented simultaneously to white light stimuli reduced the presynaptic mass response to light in the mouse retina, while increasing the postsynaptic retinal and cortical responses amplitude and the phase-locking to stimulus of cortical low frequency and gamma (∼ 25-45 Hz) responses. These findings suggest (12)C ions to interfere with, rather than mimicking the light action on photoreceptors; a parallel action on other retinal structures/mechanisms resulting in cortical activation is conceivable. Electrophysiological visual testing appears applicable to monitor the radiation effects and in designing countermeasures to prevent functional visual impairment during operations in space.
authors.affiliation: Department of Neuroscience, Ophthalmology and Genetics, University, Genova, Italy.
authors.forename: Simone
authors.initials: S
authors.lastname: Carozzo
authors.affiliation: Cleveland VA Medical Center, Cole Eye Institute, Cleveland Clinic Foundation, Cleveland, OH, USA.
authors.forename: Sherry L
authors.initials: SL
authors.lastname: Ball
authors.affiliation: Department of Physics, University Tor Vergata, and INFN, Roma2, Roma, Italy.
authors.forename: Livio
authors.initials: L
authors.lastname: Narici
authors.affiliation: Biophysik, GSI Helmholtzzentrum für Schwerionenforschung GmbH, Darmstadt, FRG Germany.
authors.forename: Dieter
authors.initials: D
authors.lastname: Schardt
authors.affiliation: Department of Neuroscience, Ophthalmology and Genetics, University, Genova, Italy; Department of Psychiatry, State University of New York, Stony Brook, NY, USA. Electronic address: wgs@dism.unige.it.
authors.forename: Walter G
authors.initials: WG
authors.lastname: Sannita
mesh_terms: D000818:Animals; D002244:Carbon; D004596:Electroretinography; D005260:Female; D007477:Ions; D008027:Light; D008810:Mice, Inbred C57BL; D010719:Phosphenes / Q000502:physiology; D012160:Retina / Q000502:physiology / Q000528:radiation effects*
chemical_list: D007477:Ions; D002244:Carbon
keywords: ERG; Electroretinogram; Heavy ions irradiation; OPS; Phosphenes in space; Retinal gamma response; VEP; Visual evoked potentials; Wild-type mice