The Role Of Synaptic Plasticity On The Visceral Hypersensitivity And Its Possible Mechanisms

PartⅠThe Role of Synaptic Plasticity on the Rats with Visceral Hypersensitivity induced by Acute Restraint StressObjective To investigate the role of synaptic plasticity on the formation of visceral hypersensitivity on rats induced by acute restraint stress.Methods Twenty male Sprague-Dawley rats were randomly divided into control group and visceral hypersensitivity group. Visceral hypersensitivity was made by acute partial restraint stress (APRS) for 1h. All rats were received colorectal distension (CRD), and electromyography (EMG) was recorded at the same time. The areas under curve (AUCs) of EMG in 20s were calculated to evaluate the visceral sensitivity. The synaptic ultrstructure was observed with transmission electron microscope (TEM). RT-PCR and Western-blot were employed to detect the mRNA and protein expression of Synaptophysin and PSD-95.Results (1) The AUCs of EMG in the two groups showed significantly positive correlation with CRD pressure. The Correlation coefficients and P value of APRS and control group were 0.740, 0.000; 0.777, 0.000 respectively. Under the pressure of 40mmHg,60mmHg, The AUCs in APRS group were significantly increased than that of control group(P=0.003,0.049). (2) The synaptic ultrastructure showed that more synaptic vesicles were accumulated in the presynaptical terminal in visceral hypersensitivity group. And post synaptic density was also increased. (3) In the proximal and distant colon, the expression of Synaptophysin mRNA and protein was significantly higher in visceral hypersensitivity group than that of control group (P=0.035,0.047;0.033,0.0450). (4) The expression of PSD-95 mRNA and protein were also significantly increased in APRS group than that of control group in the proximal and distant colon (P=0.042,0.034;0.029,0.048). In the ilececum, IOD of PSD-95 protein of APRS group was also higher than that of control (P=0.045).Conclusion The synaptic plasticity has an important role in the formation of high visceral hypersensitivity on rats induced by acute restraint stress.PartⅡThe Role of Synaptic Plasticity on the Rats with Visceral Hypersensitivity Induced by Transient Intestinal InfectionObjective Synaptic plasticity plays an important role in affecting the intensity of visceral reflex. It may also be involved in the development of visceral hypersensitivity. The aim of this study was to investigate the role of synaptic plasticity on visceral hypersensitivity of rats infected by Trichinella Spiralis.Methods Thirty male Sprague-Dawley rats were randomly divided into control, acute and chronic infection group,and were investigated at 1 week after adaptive feeding, 2 week and 8 week post-infection(PI) by orally administering 1ml of PBS with 8000 Trichinella Spiralis larvae. Visceral sensitivity was evaluated by electromyography (EMG) recording during the colorectal distension. Intestinal inflammation was observed by HE staining. The synaptic ultrastructure, such as postsynaptic density (PSD) length, synaptic cleft and the number of synaptic vesicles, were examined by transmission electron microscopy (TEM). The expression of protein associated with synaptic plasticity, including postsynaptic density-95 (PSD-95), Synaptophysin, calbindin-D28K and glial cell line-derived neurotrophic factor (GDNF) were analyzed by Western-blot.Results (1)Visceral hypersensitivity was noted in the chronic infection group, although the inflammation was nearly eliminated (P<0.05). Severe inflammation and down-regulation of visceral sensitivity were observed in acute infection group (P<0.05). (2) There were much more synaptic vesicles and longer PSD in chronic infection group than those in control group (P<0.05 respectively); However, in comparison with control rats, disappearance of mitochondria cristae in the synapses, decrease of synaptic vesicles and the length of PSD were observed in acute infection group. There was no significant difference in width of synaptic cleft among the three groups. (3) Compared with control, the expression of proteins associated synaptic plasticity was significantly up-regulated during chronic infection phase (P<0.05), and down-regulated during acute infection phase.Conclusion Synaptic plasticity was observed in SD rats infected by Trichinella Spiralis and was associated with the visceral sensitivity, which suggested it may play an important role in the formation of visceral hypersensitivity.PartⅢThe Role of NMDA-R1 on the Rats with Visceral Hypersensitivity Induced by Transient Intestinal InfectionObjective To investigate the role of NMDA-R1 of the postsynaptic terminal on the formation of visceral hypersensitivity on rats induced by transient intestinal infection.Methods Forty male Sprague-Dawley rats were randomly divided into normal control, visceral hypersensitivity, saline and MK-801 group. The rats in visceral hypersensitivity, saline and MK-801 group were infected by administering 1.0ml of PBS containing 8000 T. spiralis larvae by gavage. Electromyography (EMG) was recorded for the four groups at 1 week after adaptive feeding for normal control and 8 week postinfection for visceral hypersensitivity, saline and MK-801 group. The areas under curve (AUC) of EMG in 20s were calculated to evaluate the visceral sensitivity. RT-PCR and Western-blot were respectively employed to detect mRNA and protein expression of NMDA-R1.Results (1) There is significant difference in AUCs of normal control, visceral hypersensitivity, saline and MK-801 group(P < 0.05). The coefficient of multiple correlation and P value of the four groups were 0.823, 0.000; 0.618,0.004; 0.913, 0.000; 0.889, 0.000 respectively. Under every CRD pressure, the AUC of MK-801 group was significantly inferior to that of visceral hypersensitivity group(P=0.015,0.000,0.000, 0.013 respectively). The AUC of MK-801 group was also less than that of normal control. Only at 80mmHg, there is significant difference between normal control and MK-801 group (P=0.029). No significant difference was found between visceral hypersensitivity and saline group (P>0.05).(2) In normal control, visceral hypersensitivity, saline and MK-801group, the IODs of NMDA-R1mRNA were 1.27±0.12,1.64±0.35,1.67±0.31,1.30±0.13 respectively. In visceral hypersensitivity and saline group, the expression of NMDA-R1 mRNA was significantly increased than normal control(P=0.034,0.023 respectively). The IOD of NMDA-R1 was significantly down-regulated in MK-801 group than visceral hypersensitivity and saline group(P=0.047,0.032). No significant difference was found between visceral hypersensitivity and saline group (P=0.873)(3) In normal control, visceral hypersensitivity, saline and MK-801 group, the IODs of NMDA-R1 protein were 0.998±0.14,2.2312±0.45,2.104±0.22,1.238±0.21 respectively. The expression of NMDA-R1 of MK-801 group was significantly decreased than visceral hypersensitivity and saline group(P=0.025,0.046). The expression of NMDA-R1 was significantly increased in visceral hypersensitivity and saline group than that of normal control(P=0.007 , 0.014). No significant difference was found between visceral hypersensitivity and saline group (P=0.558).Conclusion The increased expression of NMDA-R1 plays an important role in the formation of visceral hypersensitivity. To inhibit the expression of NMDA-R1 can relieve the visceral hypersensitivity in rats induced by transient intestinal infection.