| Objective: To investigate the effects of acrylamide(ACR) at lower doses on cognitive functions such as learning and memory in rats and its possible mechanism, to provide new ideas and clues for the prevention of ACR poisoning.Methods: Forty healthy adult SPF male SD rats were randomly divided into four groups with ten rats in each group, including one control group and three ACR groups. The rats of the control group were administrated with normal saline by gavage, while the ACR groups were respectively administrated with ACR at doses of 5mg/kg, 10mg/kg and 15mg/kg once daily for 28 days. The behavior and the gait scores of rats were observed and the body weights were measured daily. The food intake was measured every 3 days and the hindlimb support indexes were tested every 7 days. The Morris water maze test was performed for 5 days. Twenty-four hours after the Morris water maze test, 7 rats were sacrificed in each group and the blood, heart, liver, spleen, lung, kidney, brain and testis were collected, and the hippocampus, cortex and striatum. were separated. The tissues of the other 3 rats in each group were fixed with 4% formaldehyde through heart perfusion, and then the brain, liver, kidney and testis were separated to make paraffin sections. Observe the pathological changes of liver, kidney and testis by HE staining, and the hippocampus, cerebral cortex, striatum and cerebellum by Nissl staining. Then the changes of indexes for liver and kidney function in the serum and the contents of ACh, the activity of ACh E and Ch AT in the hippocampus were detected. The distribution and expression of BDNF in hippocampus, cerebral cortex and striatum was also detected by immunohistochemistry and Western Blot.Results:(1) General toxicity: The body weight of the rats in the 15mg/kg ACR group was significantly lower than that of the control group on the day 28(P < 0.05). The body weight increase and food utilization rate of the rats in the 15mg/kg ACR group were significantly lower than that of the control group in the late exposure period(P < 0.05). The liver and kidney organ coefficients in the 15mg/kg ACR group increased when compared with the control group(P < 0.05). There was no difference in the contents of ALT, AST, ALT/AST, BUN and Cr in the serum between the ACR groups and the control group(P > 0.05). Histopathology results showed that there were no significant pathological changes in the liver, kidney and testis in the ACR groups.(2) Neurotoxicity: 1 Changes in motor function: The gait score of the rats in the 15mg/kg ACR group was higher than that of the control group on the day 26~28(P < 0.05), and the hindlimb support indexes of the rats in the 15mg/kg ACR group were higher than that of the control group on the day 7, day 14, day 21 and day 28(P < 0.05). 2 Histopathology of different brain regions: Compared with the control group, the number of the neurons decreased along with light staining and wider cell spacing in the CA1 area of the hippocampus, and the neurons in CA3 area arranged in disorder, along with wider cell spacing, decreased Nissl bodies and dissolved nucleolus partly in the 15mg/kg ACR group. Meanwhile, the number of the neurons decreased in the cerebral cortex with disordered granulosa cells and wider cell spacing, and the Nissl bodies in pyramidal cell layer decreased along with partly dissolved nucleolus in the 15mg/kg ACR group when compared with the control group. Whereas, no pathological changes could be seen in the striatum and cerebellum of the rats in the 15mg/kg ACR group. 3 Cognitive dysfunction: In the space navigation trial of the Morris water maze, the escape latency and cumulative swimming distance of the rats in the 15mg/kg ACR group were significantly higher than that of the control group on day 3 and day 4(P < 0.05), while the swimming velocity without significant change(P > 0.05). In the spatial probe trial, both the times of crossing the platform and the ratio of the time of the target quadrant to the total time were significantly less than that of the control group(P < 0.05). ○4 Research on mechanisms: The content of ACh and activity of ACh E and Ch AT in the ACR groups were not different from those in the control group(P > 0.05). There was no difference in the distribution and protein expression of the BDNF in hippocampus, cerebral cortex and striatum between the ACR groups and the control group(P > 0.05).Conclusion: After 28 days of subacute exposure of 5~15mg/kg ACR in rats by gavage, there were no changes observed on the biochemical function and tissue pathology of liver, kidney and testis. The rats in 15mg/kg ACR group showed abnormal gait and lower muscle tension on hindlimb, but no significant neuronal pathological damage was found in the cerebellum and striatum. Morris water maze test showed that the 15mg/kg ACR could impair learning and memory function of the rats, and neuronal pathological damage was found in the hippocampus and cerebral cortex, which could provide the histopathological basis for the cognitive dysfunction. The content of ACh, activity of ACh E and Ch AT, distribution and protein expression of BDNF exhibited no significantly changes in this exposure model, which indicates that the mechanism of the effect of ACR on cognitive function may not be related to the ACh and BDNF, and it needs further research. |
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