[17]

THE EFFECTS OF LOW-DOSE PROTON RADIATION ON PREPULSE INHIBITION OF THE ACOUSTIC STARTLE REFLEX IN C57BL/6 MICE.  C.N. Zuccarelli^1,2, P.E. Haerich², G.A. Nelson^1, and M.J. Pecaut¹. Depts of ¹Radiation Medicine, Radiobiology Program and ²Department of Psychology.  Loma Linda University and Medical Center, Loma Linda, CA.

   Many studies have shown that radiation influences behavior.  Roughly 85% of radiation in Solar Particle Events and Galactic Cosmic Rays are made up of high-energy protons.  Because the long-term effects of proton radiation may have implications to the behavior of astronauts on extended missions in space, this study examines the effects of several doses of proton radiation on prepulse inhibition of the acoustic startle response (PPI), one of the classical measurements of behavior in rodent models.  

   100 male C57BL/6 mice were irradiated with various doses of head-only proton radiation (n=20/group, 0, 1, 2, 3 and 5 Gy, 250 MeV, unmodulated).  Animals were then tested with the PPI protocol two days post irradiation.  The protocol consisted of a five minute acclimation period, followed by 8 bins of 8 semi-randomized trials (two of each of four trial types).  There was one trial with only a main burst (120 dB), and three trials with differing prepulse burst intensities (80, 85, and 90 dB).  Prepulse onset to main pulse onset was 125 ms.  Prepulse and main pulse burst lengths were 100 and 25 ms, respectively.

   Results indicated that there were no significant differences in baseline startle reflex amplitude between 0, 1, 3, and 5 Gy.  However, 2 Gy differed significantly from 0 Gy in producing a reliable reduction in baseline response as well as a decreased inhibition of the response due to the prepulse (p<0.05).  This suggests some specific population of cells that influences startle behavior is activated at 2 Gy.  At lower doses, these cells may not be activated at all, whereas at higher doses these cells may be compromised or in the process of recovery.

(Supported by NASA: Coop. Agreement NCC9-149.)