Unilateral Vestibulopathy Mimicking Inner Ear Ischemia Modeling Using Photothrombosis and Behavioral Assessment Using EthoVision

Abstract

Objectives: Inner ear ischemic animal models using photochemical reactions have been devised in various ways. Localized vascular ischemia occurs with 532-nm laser irradiation after systemic rose bengal injection, a known photothrombotic mechanism. The aim of this study is to evaluate a photothrombosis-induced vestibulopathy mimicking behavioral changes in the inner ear ischemia model.Methods: Seven-week-old male Spraque-Dawley rats were used. Animals were divided into three groups: control group (n=6), sham laser group (n=9), and laser group (n=9). To induce the photothrombosis, animals were injected with rose bengal into the femoral vein and then were irradiated with a 532-nm laser (175 mW for 900 seconds) via transtympanic membrane. To investigate the vestibulopathy after photothrombosis, the behavior tests (tail lift reflex test, air righting reflex test, rotarod test) were performed on the 1st, 3rd, and 7th days after surgery. Additionally, an open field test was conducted and analyzed using EthoVision XT (Noldus).Results: The laser group exhibited significant behavioral change to mimic vestibulopathy in all assessments. Inducing photothrombosis with rose bengal caused severe gait instability, which precluded rotarod testing. In the tail lift reflex test, the laser group displayed vestibular dysfunction with a lower angle formation compared to the control rats. During the open field test, the laser group exhibited reduced mobility, a condition that persisted in the laser groups for 7 days.Conclusions: Noninvasive laser irradiation using rose bengal and a 532-nm laser induces photothrombosis in the inner ear of animals, leading to the development of vestibulopathy mimicking imbalanced behavior.