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 radiatio n-induced hippocampal lesion lead to emotional changes in adulthood? Acoust ic 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 ii-radiat ion. 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 ill umination of the acoustic chamber. During the first session the rats were t ested in the darkness while during the second test the acoustic chamber was illuminated with a 15 W bulb. Irradiation resulted in a significant reduct ion 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 start le response. In contrast to the light condition, the darkness context cause d a decline of the ASR amplitude in the control group and failed to elicit significant changes in the lesioned animals. The results support the hypoth esis that hippocampal lesions disrupt motor inhibition.