A New Rat Model of Thalamic Pain Produced by Administration of Cobra Venom to the Unilateral Ventral Posterolateral Nucleus

Background: Thalamic pain is a neuropathic pain syndrome that occurs as a result of thalamic damage. It is difficult to develop therapeutic interventions for thalamic pain because its mechanism is unclear. To better understand the pathophysiological basis of thalamic pain, we developed and characterized a new rat model of thalamic pain using a technique of microinjecting cobra venom into the ventral posterolateral nucleus (VPL) of the thalamus. Objectives: This study will establish a new thalamic pain rat model produced by administration of cobra venom to the unilateral ventral posterolateral nucleus. Study Design: This study used an experimental design in rats. Setting: The research took place in the laboratory at the Aviation General Hospital of China Medical University and Beijing Institute of Translational Medicine. Methods: Male Sprague-Dawley rats were subjected to the administration of cobra venom or saline into the left VPL. The development of mechanical hyperalgesia and changes in pain-related behaviors and motor function were measured after intrathalamic cobra venom microinjection using the von Frey test, video recording, and cylinder test, respectively. On postoperative days 7 to 35, both electroacupuncture and pregabalin (PGB) were administered to verify that the model reproduced the findings in humans. Moreover, the organizational and structural alterations of the thalamus were examined via transmission electron microscopy (TEM). Results: The threshold for mechanical stimuli in the left facial skin was significantly decreased on day 3 after thalamic pain modeling as compared with pre-venom treatment. Furthermore, the ultrastructural alterations of neurons such as indented neuronal nuclei, damaged mitochondria and endoplasmic reticulum, and dissolved surrounding tissues were observed under TEM. Moreover, electroacupuncture treatment ameliorated mechanical hyperalgesia, pain-like behaviors, and motor dysfunction, as well as restore normal structures of neurons in the thalamic pain rat model. However, no such beneficial effects were noted when PGB was administered. Limitations: The pathophysiological features were different from the present model and the patients in clinical practice (in most cases strokes, either ischemic or hemorrhagic). Conclusion: The cobra venom model may provide a reasonable model for investigating the mechanism of thalamic pain and for testing therapies targeting recovery and pain after thalamic lesions.