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EFFECTS OF HIGH-LET RADIATION ON DOPAMINE-INFLUENCED PRE-PULSE INHIBITION. C.N. Zuccarelli^1,2, P.E.  Haerich², M.J. Pecaut¹, A.L. Smith¹, and G.A. Nelson¹. Depts of ¹Radiation Medicine, Radiobiology Program and ²Department of Psychology.  Loma Linda University and Medical Center, Loma Linda, CA.

     Radiation has consistently been shown to influence behavior.  Because the long-term effects of radiation on behavioral responses may have serious implications to astronauts on extended missions in space, this pilot study examines the acoustic startle response, one of the classical measurements of behavior in rodent models. The acoustic startle reflex and associated pre-pulse inhibition have been shown to be dopamine (DA)-dependent behaviors. Apomorphine and haloperidol are known to have opposing effects on dopaminergic systems. The major goal of this study was to examine the synergistic effects of high-LET radiation and the above pharmaceutical agents upon the startle model.  Thus, this study examines radiation effects on two behavioral endpoints: a) the immediate effects of radiation exposure in a perceptual learning/memory task (habituation) and b) the brainstem/midbrain level sensory gating task (pre-pulse inhibition). Female C57BL/6 mice were irradiated with iron ions (⁵⁶Fe, Z = 26, LET = 146 KeV/mm) at doses of 1, 2, and 3 gray (Gy) at Brookhaven National Laboratory. The animals were shipped to Loma Linda University and tested 54 days later. While the responses to the drugs were as expected, there were no significant effects of radiation. These data contrast with previous studies showing an acute decrease in startle activity after proton radiation at similar doses. This suggests that radiation effects on startle behavior may only occur within several weeks post-irradiation. 

     (Supported by NASA: Coop. Agreement NCC9-79.)