Abstract: BACKGROUND: The establishment of animal models is one of the important methods to study swallowing disorders after stroke. Suture-occluded method is the most commonly classic model of ischemic stroke. Recent studies have shown that the chemical destruction of the nucleus ambiguus can also cause swallowing disorders in rats. However, its modeling success rate, clinical similarity, and controllability remain uncertain.
OBJECTIVE: To observe the changes in swallowing function in the rat model established by two different modeling methods, namely, suture-occluded method and chemical destruction method, and to investigate the clinical and pathological characteristics of swallowing disorders similar to those in humans. 
METHODS: Forty Sprague-Dawley rats were randomly divided into three groups: normal group (n=10), suture-occluded group (n=15), and chemical destruction group (n=15). The left-sided ischemic stroke models were prepared using the suture-occluded method through reperfusion after 90 minutes of transient cerebral ischemia in the suture-occluded group, while rat models of swallowing disorders were established through the chemical destruction of the nucleus ambiguus by gooseberry muscarinic acid in the chemical destruction group. Survival numbers per week, body mass, and 24-hour food and water intake in each group were recorded. The rats were examined on days 2, 7, 14, and 30 after modeling using a biosignal collector and a tension transducer to detect the swallowing initiation response time and the number of swallows. Hematoxylin-eosin staining was used to observe the pathomorphological changes of the nucleus ambiguus of the medulla oblongata swallowing center. ELISA method was used to detect the levels of serum interleukin-6, interleukin-1β and tumor necrosis factor-α.
RESULTS AND CONCLUSION: The mortality rate in the suture-occluded group was significantly lower than that in the chemical destruction group on days 2 and 7 (P < 0.05), but there was no significant difference between the two groups at other observation time points (P > 0.05). The final mortality rate in the suture-occluded group was significantly lower than that in the chemical destruction group (40% vs.73%, P < 0.05). Compared with the normal group, body mass, 24-hour food and water intake, swallowing initiation response time, and the number of swallows were significantly worse in the chemical destruction group on day 7 (P < 0.05) but showed no significant changes in the suture-occluded group (P > 0.05). Compared with the normal group, the other two model groups showed a significant reduction in body mass, 24-hour food and water intake, and the number of swallows and significantly prolonged swallowing initiation response time (P < 0.05). There were significant differences in body mass, 24-hour food and water intake, swallow initiation response time, and the number of swallows between the suture-occluded group and the chemical destruction group on day 7 (P < 0.05), but no significant difference at other observation time points (P > 0.05). Rats in the two model groups showed obvious pathological changes in the medulla oblongata with a significant increase in inflammatory cells. However, there was no significant difference between the two groups (P > 0.05). To conclude, both the suture-occluded method and the chemical destruction method could cause swallowing disorders in rats. The mortality rate in the suture-occluded group was significantly lower than that in the chemical destruction group at all times after modeling. Therefore, the suture-occluded method with reperfusion following 90 minutes of transient ischemia is more replicative in terms of the final success rate.

Key words: swallowing function, chemical destruction, nucleus ambiguus, cerebral ischemia, animal model