ABSTRACT
Objective To investigate the effects of dorsal hippocampal lesions (DH) or fimbria-fornix transection (FF) on the learning and memory of conditioned fear and the heart rate and blood pressure in rats.Methods Nineteen male adult Wistar rats were used in this experiment.They were implanted telemetry sensors in their abdominal aortas.Two week later,six of the rats were subjected to permanent NMDA-induced neurotoxic lesions to the dorsal hippocampus (DH) and seven for the fimbria-fornix transection (FF)through stereotactic brain surgery,the left six were treated with saline as the control (Sham).All rats were subjected to a conditioned fear experiment.Meanwhile,changes in heart rate and blood pressure were measured.Results There was no significant difference in heart rate and blood pressure among the rats with the hippocampal operation or fimbria-fornix transection.In the acquisition of conditioned fear,there were significant difference in freezing time among the three group in both inter-trial-interval (ITI) and conditioned stimulus (CS) process (all P＜0.05).The freezing time of the FF group showed significantly lower than that of the Sham group (P＜0.05).There was no significant difference in heart rate and blood pressure among the three group(P＞0.05).In the test of conditioned contextual fear memory,the freezing time percentage in the FF group ((0.31±0.16) ％) significantly lower than that in the Sham group ((2.78± 1.23) ％) (P＜0.05)at the first 3 min of the test.There was a significant difference in heart rate among the three group.The heart rate of FF group ((436.42± 10.16) times/min) was significantly lower than that of the Sham group ((472.48±4.43) times/min,P＜0.01) and the DH group ((469.94 ±7.36)times/min,P＜0.01).In the test of conditioned tone fear memory.The freezing time percentage in FF group ((18.78±6.29) ％) was significantly lower than that in the Sham ((51.77±9.33)％,P＜0.01) and DH group ((59.19±8.13)％,P＜0.01),but the freezing time percentage between the later two groups had no difference (P=0.52).The synchronous telemetry measurement showed there was no significant difference both in the heart rate and the blood pressure among the groups (all P＞0.05) during the conditioned tone test.Conclusion The dorsal hippocampal lesions and fimbria-fornix transection in rats can significantly reduce the learning and memory ability in conditioned fear and scene fear in rats,and the effect of fimbria-fornix transection is more obvious.The decrease in,fear memory is not synchronously reflected in heart rate and blood pressure in rats.