| Objective: To observe the changes of the HCN2 channel in the hippocampus of visceral hypersensitivity SD rats and to investigate the role of HCN2 protein in chronic visceral pain, and to provide a theoretical basis for the treatment of chronic visceral pain in children.Methods: 44 neonatal SD rats were randomly divided into 4 groups which according to whether or not received colorectal irritation(CI) in the neonatal period and colorectal distension(CRD) in the young period. Group CI+CRD:imposed on CI at neonatal period and imposed on colorectal distension(CRD) at 42 days age; Group CI:imposed on CI at neonatal period and not imposed on CRD at 42 days age; Group CRD:not imposed on CI at neonatal period and imposed on CRD at 42 days age; control: not imposed on CI at neonatal period and not imposed on CRD at 42 days age. Group CI+CRD and Group CI were treated with colorectal irritation once a day during 7consecutive days from the 8m day after birth, Group CRD and control were just seperated from mother, but not imposed on CI. Abdominal withdrawal reflex(AWR score) and pain threshold were used to evaluate the visceral pain sensitivity of CI+CRD group, CRD group rats at the age of 42 days. Morris water maze test(navigation test and spatial probe test) were used to test the spatial memory ability of the rats of CI group and control group rats at the 45 days age.After the end of the experiment, the four groups of rats were sacrificed.The hippocampus of rats were selected and the HCN2 in the hippocampus were detected by immunohistochemistry and western blot. SPSS 17.0software package were used in all statistical analysis, α=0.05 for the significance of the test standards.Result: With the CRD pressure,the AWR score of the CI+CRD group and the CRD group increased too;when the CRD pressure was 40 mm Hg and 60 mm Hg,the AWR scores of the CI+CRD group was higher than the CRD group(P < 0.05); the pain threshold of the CI+CRD group and the CRD group were respectively(18.18±2.52)mm Hg,(37.42±5.13)mm Hg, the difference between the two groups had statistical significance(P < 0.05);in the place navigation experiment, the escape latency of CI group and control group at the same time was no statistically significant;in spatial probe,the number of the rats cross the location previously containing the platform,the ratio of the time rats spent in the quadrant previously containing the platform to all time and the ratio of the distances rats spent in the quadrant previously containing the platform to all distances in these two group were no statistically significant(P>0.05); the result of the immunohistochemistry, the percentage of HCN2 positive cells in hippocampal CA1 area in CI+CRD group, CI group, CRD group and control group were 33.38%, 24.25%,13.06%, 7.94%; the difference of the percentage of HCN2 positive cells in hippocampal CA1 area between the CI group and control group, CI+CRD group and control group,CRD group and control group, CI+CRD group and CRD group, CI group and CRD group had statistical significance(P<0.05); the differences between the CI+CRD group and CI group was without statistical significance(P = 0.156);the result of western bloting,the expression of HCN2 protein in the hippocampus: CI+CRD group>CI group>CRD group>control group; there was significant difference between CI+CRD group and control group, CI group and control group(P<0.05), the difference between CRD and control group was without statistical significance(P>0.05).Conclusion: The neonatal CI could establish visceral pain hypersensitive mode and couldn’t damage spatial memory of the model rats;HCN2 channel in the hippocampus of model rat was high expression,it has nothing to do with the impairment of spatial memory;the high expression of HCN2 in the hippocampus may be involved in high visceral hypersensitivity in young rats induce by CI. |
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