The Effect Of Restraint Stress To Visceral Sensitivity In Rats

Part I Effects of Acute and Chronic Restraint Stress on VisceralSensitivity and Neuroendocrine Response in RatsAims: The aim of this study was to investigate the short- and long-term effects of acute and chronic partial restraint stress (PRS) on visceral sensitivity to colorectal distention (CRD) and the neuroendocrine response in rats. Methods: The study was performed in two experiments. In the first experiment, male Sprague-Dawley rats were studied in three groups including rats without PRS, with acute PRS (A-PRS) for 2 hours, and with chronic PRS (C-PRS) for 2 hours a day in 3 consecutive days. The abdominal withdrawal reflex (AWR) score to CRD was assessed before stress, at the end of A-PRS or C-PRS, and 7 days after the first stress. In the second experiment, the plasma levels of corticosterone (CORT) and adrenocorticotropic hormones (ACTH) at different time points were detected using radioimmunoassay method. Results: (1) The AWR scores of the rats with A-PRS or C-PRS at 20 and 40mmHg immediately after stress significantly higher than those before stress (P<0.05) and seven days after the first stress (P<0.05). (2) In comparison of those without PRS, the plasma levels of CORT and ACTH in rats with A-PRS after stress showed a significant elevation ((25.35±6.03)ng/ml vs. (7.24±2.97)ng/ml, P<0.05, and (312.47±50.76)pg/ml vs. (97.00±23.33)pg/ml, P<0.05). However, the concentrations of CORT and ACTH 7 days after A-PRS ((11.81±5.03)ng/ml and (113.73±24.58)pg/ml, respectively) returned to the baseline value. (3) The plasma levels of cortisol and ACTH with C-PRS immediately after the last stress were (20.84±2.19)ng/ml and (200.41±78.10)pg/ml, significantly higher than those without PRS (P<0.05), and the concentration of these hormones 7 days after C-PRS remained elevated ((19.95±5.31)ng/ml and (162.51±47.08)pg/ml, P>0.05 vs. immediately after C-PRS). Conclusions: Both acute and chronic PRS induce visceral hypersensitivity, but their effects are transient. Acute PRS elevates transiently the plasma levels of cortisol and ACTH, whereas chronic PRS has a long-term effect. The alterations in these neuroendorine hormones may partially attribute to the mechanisms of PRS-induced visceral hypersensitivity.Part II Colonic Serotonergic signaling molecule and receptors' mRNA Alteration in Rats with Acute or Chronic Restraint StressBackground & Aims: Serotonin (5-HT) is a critical signaling molecule in the gut and plays an important role in initiating peristaltic, secretory, and nociceptive reflexes. Stressful factors could induce gut motility and sensation dysfunction. The aim of this study was to investigate the effects of acute and chronic partial restraint stress (PRS) on 5-HT synthesize enzyme, 5-HT transporter and 5-HT receptors messenger RNA (mRNA) in colon tissues of rats. Methods: 35 male Sprague-Dawley rats were divided evenly into five groups including control without PRS, acute PRS for 2h, acute PRS with 7-day recovery, chronic PRS for 2h a day in 3 consecutive days, chronic PRS with 7-day recovery. Typtophan hydroxylase (TpH), 5-HT transporter, and 5-HT1A and 5-HT4 receptors mRNA in colon tissues were detected by using reverse transcription-polymerase chain reaction (RT-PCR) method. The mast cells in colon tissues were observed by using immunohistochemistry staining. Results: (1) Compared with the rats without PRS, the TpH and 5-HT transporter mRNA were significantly reduced in the rats with chronic PRS (P<0.05) and chronic PRS with 7-day recovery (P<0.05). (2) For the TpH and 5-HT transporter mRNA expressions, there were no significant differences among the rats with acute PRS or acute PRS with 7-day recovery or the rats without PRS (P>0.05). (3) In comparison with the rats without PRS, the 5-HT1A and 5-HT4 receptors mRNA were significantly higher in the rats with acute and chronic PRS (P<0.05). In the rats of 7 days after the acute or chronic PRS, the 5-HT1A and 5-HT4 receptor mRNA expressions were still higher than the rats without PRS (P<0.05). Conclusions: These results show that chronic PRS inhibits serotonergic signaling, whereas the acute PRS does not affect serotonergic signaling in colon tissues. Both acute and chronic PRS increase 5-HT receptors expression. These findings suggest that different changes of 5-HT signaling molecules and receptors may underlie the altered gut motility and sensation under acute or chronic stress conditions. Part III Effects of Tegaserod on Stress-induced Visceral Hypersensitivity and c-fos expression on spinal cord in RatsAims: To investigate the effects of tegaserod on partial restraint stress (PRS) -induced visceral hypersensitivity and c-fos expression on spinal cords in rats. Methods: The study was performed in two experiments. In the first experiment, male Sprague-Dawley rats were studied in control group, PRS with tegaserod injection groups, PRS with vehicle injection groups, and saline injection group. The abdominal withdrawal reflex (AWR) score to CRD was assessed. In the second experiment, using immunohistochemistry method to study the c-fos expression in T13-L1 and L6-S1 spinal segments following repeated CRD in different groups. Results: (1) Stress groups with vehicle or saline injection showed significant higher AWR scores than rats without stress (P<0.05). (2) Compared with vehicle or saline treatment group, tegaserod could significantly decrease the AWR scores dose dependently at all pressures, with a maximal reduction at 1.2mg/kg. (3) Following stress, CRD could induce c-fos protein express across both spinal segments T13-L1 and L6-S1, which is significantly higher than control rats (P<0.05). (4) After administration of tegaserod in the stress rats, c-fos expression decreased significantly compared with vehicle or saline group. Conclusion: Tegasrod could dose-dependently decrease stress-induced visceral hypersensitivity and c-fos expression on thorax-lumbar or lumbar-sacral segment spinal cords.