(A) Mice that were X-irradiated at 4 weeks of age, prior to experiencing footshock stress (FSS) were examined behaviorally at 20 weeks of age. (B, C) Activity in a novel environment was comparable between 0 and 10 Gy irradiated mice. However, mice irradiated with 10 Gy and subjected to FSS showed decreased motion time and rearing. (D) In the prepulse inhibition (PPI) test, 10 Gy plus FSS mice showed significant decreases in PPI following both 68 dB and 71 dB stimuli. (E) Startle response was not altered by X-irradiation or the combination of X-irradiation and FSS. Mice were placed in the conditioning chamber for 1 min and then presented with tones (1000 Hz and 3000 Hz, 3 sec in length) of increasing sound intensity. The interval between tones was 10 sec. The sound level required to elicit an orienting reflex was determined. (F) Corticosterone was increased significantly in 10 Gy plus FSS group. All data were expressed as mean ± S.E.M, n = 6–10.