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Proton Irradiation Effects a Neurobehavioral Response in the Fruit Fly, Drosophila melanogaster.  Irene M. Choi¹, M.E. Sanchez², O. Marcu³, F. Selch¹, O. Inan⁴, S. Bhattacharya³.

¹Education Associates Program, ²Lockheed Martin Mission Services, ³NASA Ames Research Center, Moffett Field, CA, ⁴Bioengineering Department, Stanford University, CA.

   Extended space travel affects human performance through deficits in visuomotor and visuoperceptual tasks.  Performance deficits may be triggered by exposure to proton and high-energy particle radiation in the space environment.  We assessed the effects of proton irradiation on the behavior and motor function of the fruit fly, D. melanogaster.  Fruit flies were exposed to 250 MeV protons at the Loma Linda University Medical Center.  Increasing doses between 2-30 Gy protons were delivered at a rate of 0.5 Gy/minute.  A distinct locomotor impairment of adult flies was proportional to the dose of irradiation received at the larval stage and resulted in decreased survival.  The behavior was monitored in three different assays.  In a climbing assay the vertical movement of a pool of 10-20 flies was measured as a function of distance traveled in 10 seconds.  The relative speed of transient movements in a horizontal plane was determined by an ultra-low bandwidth circuit, which integrates the video signal from a monochrome camera using a sharp low-pass filter.  The absolute speed of the flies was tracked on individual animals in a behavioral chamber, using the Noldus Ethovision software.  All three assays identified a quantifiable decrease in movement, detectable as low as 5 Gy protons.  The speed of locomotion decreased progressively with the irradiation dose and age.  This effect was differentially rescued by the expression of transgenic Wnt5, a ligand involved in axon guidance, in specific regions of the mushroom body, the part of the brain involved in olfactory learning and memory.  We are currently mapping the precise neurons in the brain involved in the radiation-induced behavior impairment and defining the associated signaling pathway.  The identified effect of ground proton irradiation suggests that the fruit fly can be used as a biodosimeter for radiation in the space environment. 

   (Supported by NASA: FIT - Fly/Fungal Immunity and Tumorigenesis)