Effect Of Neonatal Colorectal Irritation On Visceral Pain Sensitivity In The Developmental Rats And C-fos Expression In Spinal Dorsal Horn

Effect of Neonatal Colorectal Irritation on Visceral Sensitivity in the Developmental Rats and c-fos Expression in Spinal Dorsal HornObjective: To explore the effect of detrimental colorectal irritation (CI) stimulation in neonatal period on developmental rats' visceral pain sensitivity by the method of behavior and electrophysiology research, establish the model of visceral hyperalgesia in developmental rats. Observeing the c-fos expression of lumbosacral spinal dorsal horn in visceral sensitivity rats to investigate the mechanism of highly visceral pain sensitivity.Method: [1]32 SD neonatal rats were randomly divided into the experimental group and control group with each 16. Rats in the experimental group were treated with colorectal irritation once a day during 7 consecutive days from the 8th day after birth, the control rats were not except handled in the same way. Conventionally breeding to the young period (6-week age), the following study was implemented:â‘ By the method of Abdonminal Withdrawal Reflex (AWR) and Pain Thresholds to test its pain sensitivity of intestinal tract under colorectal distension irritation;â‘¡The histopatholigical analysis on descending colon;â‘¢By the method of electrophysiological on external oblique to appraise its pain sensitivity of intestinal tract under colorectal distension irritation. [2]According to the factorial design, 32 SD rats were divided into four groups with each 8, Group A was model group and imposed on CRD at 6-week age, yet Group B were not imposed on CRD as the model group. Group Cwas imposed on CRD at 6-week age while Group D without treatment both as the control groups. When they 6 weeks old, after the rats of Group A and C were imposed on CRD for 2 hours while rats of Group B and D not imposed on CRD were sampled the spinal cord from L₆ to S₂, the semi-quantity analysis of staining density and the cell number of Fos-Like Immunoreactivity (FLI) of spinal cord were made through immunohisrochemical coloration and computer image analyzing system. SPSS 11.0 software for Windows was used in all statistical tests,α=0.05 was considered significant.Result: [1]The AWR score was increased with the rise of the CRD pressure in young rats; Accepting neonatal CI and gender had effect on the AWR scores (F was 45.19, 7.44 respectively, p＜0.05), The AWR scores of female rats were obviously higher than those of males, and the AWR scores of experimental group were obviously higher than those of control group too, there was interaction between CI and gender on affecting the AWR scores (F=4.66, p=0.040); When the CRD pressure were 20 and 40 mmHg, the AWR scores were higher in the experimental group than the control signigficantly, but under 60 and 80 mmHg CRD pressure the difference was not significant between gruops. The Pain Thresholds of the model group and control group were 26.5±4.9mmHg,47.8±5.0mmHg respectively (F=149.753, p＜0.01). [2] With the CRD pressure increased, the external oblique spikes of electrical discharge increased too; Accepting neonatal CI and gender had effects on the spikes (F was 7.09,5.95 respectively, p＜0.05), the spikes of female rats were obviously higher than those of males, and the spikes in experimental group were higher than control, under 30, 45mmHg CRD pressure, the spikes in experimental groups were found significantly higher than those of the control groups. With 60, 75mmHg CRD pressure, the differences were no statistical significance. No significant differences in weight between the two groups and no obvious histopatholigical changes were observed in both groups of rats in the gross and under microscope of descending colon. [3]Rats imposed on CI at the neonatal period and CRD at 6-week age both can make the number of FLI increase and staining density of FLI significantly decrease in lumbosacral spinal dorsal horn, the differences had statistical significance. There was interaction between CI and CRD on affecting the staining density of FLI.Conclusion: The persistent stimulation of CI in neonatal phase resulted in low pain threshold and chronic high visceral pain sensitivity, histological change was not found in colorectal tissue, thus it may be the model of visceral hyperalgesia. Comparing with the behavior research, electrophysiological appraisal was a quantitative test, it can reflect the pain sensitivity of visceral objectively, especially for the young rat model. Continuous CI on the neonatal rat may cause rat's central sensitization of spinal. Imposing on detrimental CRD may significantly cause the high expression of Fos in spinal cord, emerge a chronic high visceral sensitivity.