Comparison Of Two Models Of Chronic Visceral Hypersensitivity And The Effect Of Stress On Chronic Visceral Hypersensitivity

Objective1. To compare two models of chronic visceral pain and explore the evaluation of chronic viscearal hypersensitivity.2. To explore the effect of stress on model rats and the involved mechanism.Method1. SD neonatal rats were randomly divided into the colon irritation(CI) group, maternal separation(MS) group and control group. CI rats were treated wih colorectal irritation once daily from postnatal day the 8th to 15th.Rats in the MS group were exposed to a 180-min period of daily maternal separation from postnatal day the 2th to 21th.Control rats were not handled in the above ways. When rats were adult, visceral hypersensitivity was evaluated by the scores of abdonmial withdrawal reflex(AWR), pain threshold and electromyographic(EMG) of external oblique of abdomen2. According to the factorial design, rats were divided into four groups. Group A , neonatal CI and adult with water avoidance (WA); Group B , neonatal CI and adult without WA; Group C, neonatal normal and adult with WA; Group D , neonatal normal and adult without WA. When rats were adult, visceral hypersensitivity was evaluated by the scores of abdonmial withdrawal reflex(AWR), pain threshold and electromyographic(EMG) of external oblique of abdomen.3. The semi-quantity analysis of staining density of SP in L6-S2 spinal cord were made by immunohisrochemical staining and computer image analyzing system.Result1.â‘ The AWR scores of rats in CI group were significantly higher than those in control while the CRD pressure was 20~60mmHg. The AWR scores of rats in MS group were significantly higher than those in control while CRD pressures were between 20~80mmHg. There was no significant difference in AWR scores of rats between CI and MS groups.â‘¡Both pain thresholds of CI and MS rats were significantly lower than those of controls. However, there was no significant difference in pain thresholds between CI and MS rats.â‘¢The responses of EMG to 20~40mmHg CRD in CI rats were significantly higher than those in controls . The responses of EMG to 20~60mmHg CRD in MS rats were significantly higher than those in controls . There was no significant difference in amplitude of EMG between CI and MS rats.2.â‘ The AWR scores of rats in Group A were significantly higher than those in group B while CRD pressures were between 20~60mmHg. There was no significant difference in AWR scores of rats between group C and D.â‘¡The pain thresholdsof rats in group A were was significantly higher than those in group B. There was no significant difference in pain thresholds of rats between group C and D.â‘¢The responses of EMG to 20~40mmHg CRD in group A rats were significantly higher than those in group B . There was no significant difference in responses of EMG between group C and D rats.3. The staining density of SP in group A rats was significantly lower than that in group B. There was no significant difference in staining density of SP between group C and D rats. The staining density of SP in group B rats was significantly lower than that in group D.Conclusion1. The persistent stimulation of CI and MS in neonatals both resulted in adult chronic visceral hypersensitivity.2. Stress can exaggerate visceral hypersensitivity in CI rats.3. SP in L6-S2 spinal cord was involved with the visceral hypersensitivity of CI rats before and after stress.