Changes of the acoustic startle reflex in rats with radiation-induced hippocampal lesion

The main question of the study was: to what extent does a neonatal radiation-induced hippocampal lesion lead to emotional changes in adulthood? Acoustic startle response (ASR) was studied in two groups of adult rats. The rats from the first group (14 animals) were exposed to neonatal x-ray irradiation. Their ASR were compared with those from the 10 intact rats that formed a control group. The ASR was tested during two sessions with different illumination of the acoustic chamber. During the first session the rats were tested in the darkness while during the second test the acoustic chamber was illuminated with a 15 W bulb. Irradiation resulted in a significant reduction of granule cells of the hippocampus (about 55%). The lesion resulted in emotional and behavioral changes evidenced by modification of the ASR. The irradiated rats exhibited a significantly increased amplitude of the startle response. In contrast to the light condition, the darkness context caused a decline of the ASR amplitude in the control group and failed to elicit significant changes in the lesioned animals. The results support the hypothesis that hippocampal lesions disrupt motor inhibition.