Avoidance Learning Deficits in Prenatally Gamma‐Ray Irradiated Rats

Pregnant female rats of the Fischer344 (F344/Du Crj) strain were exposed to gamma‐ray radiation of 1.46Gy on day 15 of gestation (vaginal plug = day 0). When male offspring of control and irradiated dams matured, they were trained with various avoidance conditioning paradigms. In the avoidance acquisition paradigm in which one of the tone‐on and lights‐off signals was presented with predetermined random sequences, the irradiated group had lower overall rates of active avoidance responding than controls. In the go/no‐go (active‐passive) discrimination avoidance paradigm after rats learned only active avoidance responses to these two different signals, irradiated rats established stable active avoidance rates under the go (tone‐on) signal, while they decreased gradually the rate of passive avoidance responding to the no‐go (lights‐off) signal as the amount of discrimination training increased. In the standard avoidance acquisition paradigm in which only the lights‐off signal was used, the irradiated group also was inferior in active avoidance learning to controls. However, the irradiated group showed a high level of anticipatory responding, which was maintained in avoidance conditioning paradigms even though no shock‐avoidance contingency was operating. These results indicated that poor associative ability for the warning signal and the shock might result in the active avoidance learning deficits in irradiated rats, and that active responding was more persistent and passive responding declined due to response excitation within a shock paradigm over the subsequent further training.