An Evaluation of the Relative Behavioral Toxicity of Heavy Particles

As astronauts leave the magnetic field of the earth, they will be exposed to radiation qualities and doses that differ from those experienced in low-earth orbit. Research using low LET radiation (gamma rays or high-energy electrons) indicates that large doses of these types of radiations (> 20–40 Gy) are needed to produce significant decrements in performance (Bogo et al., 1989; Hunt, 1983; Micldey et al., 1988). It is unlikely that astronauts will be exposed to such high doses (Mullen et al., 1988; McCormack, 1988). However, the extent to which exposure to heavy particles outside the magnetosphere can affect behavior has not been extensively studied. In contrast, recent research suggests that exposure to low doses of HZE particles can produce effects on behavior. Exposing rats to 56Fe particles (600 MeV/amu) at doses as low as 10 cGy, produces significant alterations in dopaminergic function in the striatum and in the motor behavior that depends upon the proper functioning of these neurons (Joseph et al., 1988; Hunt et al., 1988, 1989, 1990). Similarly, exposure to 50 cGy of 56Fe particles produces destruction of hippocampal neurons and an associated decrease in the speed of maze running (Philpott & Miguel, 1986).