UC is a chronic idiopathic inflammatory disease of the colon with unclear pathogenesis. Clinical epidemiology has found that most UC patients are chronic inflammatory bowel disease and are prone to mental abnormalities, usually manifested as depression, anxiety and other symptoms [22]. It shows that mental factors affect the pathogenesis of UC to a certain extent. According to the 2019 American College of Gastroenterology (ACG) guidelines for adult UC and the 2021 European Crohn's and Colitis Organization (ECCO) guidelines, the commonly used drugs for the treatment of UC are 5-aminosalicylic acid and corticosteroids, immunosuppressive modulators, TNF drugs and monoclonal antibody drugs[26, 27]. These drugs mainly reduce the symptoms of UC patients by improving inflammation. It is difficult to completely cure UC, and these drugs have the disadvantages of inducing hepatitis, causing a serious infection, increasing the risk of lymphoma cancer, and being expensive[28, 29]. In laboratory UC drug research, the DSS-induced UC model has a short modeling time and a simple method and is widely used by researchers. Although clinicians have begun to use some antipsychotic drugs to adjuvant UC and achieved certain effects, few researchers have paid attention to its treatment mechanism[30–32]. Therefore, we guessed whether the mice in the DSS-induced UC model had behavioral abnormalities, and hoped to improve the behavioral abnormalities to achieve the purpose of treating UC.
We established acute and chronic UC models by DSS. The general condition, body weight, fecal state and other indicators of the mice were recorded during modeling, and whether the modeling was successful was judged by the changes in body weight, DAI score, colon length and colon HE staining results. The behavior of mice was detected by open field experiment, the tail suspension experiment, sucrose preference test and the levels of HE in the hippocampus were used to reflect whether the mice had mental disorders. The open-field experiment is usually used to measure the motor function and emotion of rodents. It has the characteristics of simple operation and good feasibility. It can evaluate the different behavioral changes of mice by recording the number of running times, the times of standing up, and the times of grooming. The number of runs and the number of uprights in the open field experiment reflected the rodent's exploratory behavior in novel environments[33]. Studies have shown that fatigued or depressed rats have reduced voluntary movements, prefer to move around the edge of the box, and have less total travel distance. The tail suspension experiment is to induce depression and despair behavior by being unable to overcome the abnormal body position. It belongs to the "dry" behavioral despair model. Usually, immobility state latency and the immobility state duration percentage are used to evaluate the immobility state of the animal[34, 35].
By analyzing the body weight, DAI score, colon length and colon HE staining results of the mice, the mice in the 3% DSS model group and the 1.5% DSS model group had weight loss compared with the mice in the Control group and the Control2 group, blood in the stool, increased DAI score and shortened colon length. Colon HE staining showed that the colon tissue of the mice in the model group had crypt destruction, gland disorder, and inflammatory cell infiltration. The above results demonstrate that the modeling of acute UC model with 3% DSS and the chronic UC model with 1.5% DSS was successful. Through the analysis of the open field test, tail suspension test, forced swimming test, sugar water preference test and hippocampal HE staining results of mice, compared with the Control group, the mice in the 3% DSS model group had the number of running spaces, the number of time points in the open field test, and The number of hairs and the number of standing were reduced; in the tail suspension experiment, the resting time of the two groups of mice was not much different; in the sucrose preference test, the pure water drinking amount of the 3% DSS model group was slightly reduced while the sucrose water drinking The amount is greatly reduced. From the perspective of mouse behavioral indicators, the acute UC model induced by 3% DSS has a certain effect on the mental state of mice. However, through the analysis of the results of hippocampal HE staining, the hippocampal DG, CA1 and CA3 regions of the mice in the 3% DSS model group were not significantly different from those in the Control group, and the cells did not appear to be significantly reduced and pyknosis. Based on the analysis of various data and results, the acute UC model induced by 3% DSS has a certain effect on the behavior of mice, but it may be affected by UC symptoms rather than by mental factors. Compared with the Control2 group, the mice in the 1.5% DSS model group had reduced running times and standing times in the open field test, and the number of grooming was not much different; in the tail suspension experiment, the resting time of the mice in the 1.5% DSS model group was significantly reduced compared to the mice in the Control2 group; in the sugar water preference test, the difference between the two groups of mice was not significant. The results of hippocampal HE staining showed that the staining in the hippocampal DG area of the mice in the 1.5% DSS model group was significantly deepened, the distribution of cells in the CA3 area was looser, and there was obvious reduction and pyknosis., there was no significant difference in the CA1 area. This indicated that the chronic UC model induced by 1.5% DSS had a certain effect on the nerve center of mice. Based on the analysis of various data results, the chronic UC model induced by 1.5% DSS may affect the behavior of mice through mental factors.
Therefore, we believe that the DSS-induced chronic UC model is an ideal model rather than an acute model when studying the relationship between psychiatric factors and the onset of UC. At the same time, the use of DSS-induced acute UC models to evaluate the efficacy of anti-UC drugs is insufficient, and more studies using chronic UC models should be considered. This is similar to the clinical course for UC patients.