| Background and ObjectiveInterstitial cells of Cajal (ICC) are widely distributed throughout the gastrointestinal tract, which are believed to have a crucial role in gastrointestinal tissues by generating and propagating electrical slow waves to gastrointestinal muscles and/or mediating signals from the enteric nervous system. Recent studies have indicated that the abnormal distribution, the loss or decrease of ICC and the changes of their ultrastructure might play an important role in several disorders of human gastrointestinal motility.Ulcerative colitis (UC) is an idiopathic colitis, and its pathological changes mainly located in mucous layer and submucous layer. So far, the causes and mechanisms of UC are still unknown. It is generally considered that the pathogenesis of UC have close relationship with the disorder of immune function, hypersensitivity, heredity and idiopathic infection. Recent studies have indicated that the loss or decrease of ICC and the changes of their ultrastructure might influence the neurotransmission and the function of smooth mucle cell (SMC), and resulted in the dysfunction of human gastrointestinal motility. The incidence of UC in our country has been ascending in recent years, so it is important to establish an ideal colitis model for investigation of the pathogenesis and drug treatment effect of UC. Many studies indicated that the UC model of BALB/c mice induced by feeding dextran sulfate sodium (DSS) can be easily induced and readily applied in various studies of UC, and the symptoms observed in the mice and histopathological changes were similar to those of UC patients. But until now, there are no correlative reports about the distribution and the ultrastructural changes of ICC in colon or rectum in BALB/c mice with UC.In this study, we designed to establish the acute and chronic UC model in BALB/c mice by feeding 5% DSS, observe the distribution and ultrastructure of ICC in distal colon and compare with the changes of ICC in UC patients, explore the correlation between the pathogenesis of UC and the changes of the distribution and ultrastructure of ICC, compare the histopathological changes between the UC model in BALB/c mice and UC patients extensively, provide more theoretical argument for the UC model in BALB/c mice in studying the pathogenesis and drug treatment effect of UC.MethodsPart one: Establishment and identification of the acute and chronic UC model in BALB/c mice. To establish UC mice model according to the method of Cooper's: Thirty BALB/c mice were randomly divided into three groups. The experimental groups were fed with 5% DSS solution for 7 days and 5% DSS solution for 7 days followed by distilled water for 14 days to induce acute and chronic UC, respectively. The control group were fed with distilled water only. In all animals, daily weight, daily stool consistency and occult blood were observed, and the macroscopic and histopathological changes of the colon were also evaluated.Part two: Study of the distribution of ICC in distal colon of the UC model in BALB/c mice. We have studied the distribution of ICC in distal colon of three groups respectively by immunofluorescence (IF) using c-kit antibodies. Meanwhile, we have detected the fluorescence intensity by using OLYMPUS FV1000 laser confocal scanning microscope (LCSM).Part three: Study of the ultrastructural changes of ICC in distal colon of the UC model in BALB/c mice. We have studied the ultrastructrual featrures of ICC in distal colon of three groups respectively by using JEM-2000EX transmission electron microscope (TEM).Results1. We have induced the acute and chronic UC model in BALB/c mice successfully, which were identified by histopathological examination.2. IF and LCSM results:⑴In the control group, ICC were mainly distributed in submucosal plexus (IC-SM) and myenteric plexus (IC-MY) of the distal colon, and also distributed in circular muscle layer and longitudinal muscle layer (IC-IM). IC-MY were distributed continuously between the circular and longitudinal muscle layers and formed a network;⑵Compared with the control group and the chronic UC group, ICC were decreased obviously in the distal colon of the acute group (P<0.001). The IC-MY network were disappeared, and the configuration of the residual ICC were abnormal.⑶In the chronic group, ICC were reduced than those of the control group(P<0.05), but were more than those of the acute group(P<0.001). Their configuration were close to normal, but the IC-MY did not form a normal network.3. TEM results:⑴In the control group, ICC were characterized by long process, large oval nuclei and scant perinuclear cytoplasm. The cytoplasm contained numerous mitochondria, aboundant smooth and rough endoplasmic reticulum. ICC in the circular muscle layer and longitudinal muscle layer of BALB/c mice colon formed synaptic-like contacts.⑵In the acute UC group, the volume of ICC was increased, the mitochondria were swollen and their density were lower. The numbers of lysosomes were increased and often showed multiple secondary lysosomes. Large confluent lipid bodies were often found in cytoplasm. Macrophages were frequently appeared around submucosal plexus ICC (IC-SM).⑶In the chronic UC group, the configuration of ICC was normal, the mitochondria were normal or swollen mildly. The numbers of lysosomes were increased and mainly showed primary lysosomes. Macrophages were obviously decreased around IC-SM.Conclusions1. Decreased expression and changes of the ultrastructure of ICC in distal colon in BALB/c mice with UC might play an important role in the gastrointestinal dysfunction associated with UC.2. The symptoms observed in the mice and histopathological examination in distal colon were similar to those of UC patients, and the changes of the distribution and ultrastructure of ICC in distal colon in BALB/c mice with UC were also similar to those of UC patients. We concluded that the acute and chronic mice colitis induced by feeding DSS is an ideal model of UC, which might be served for investigation of the pathogenesis and drug treatment effect of UC.
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