c-Fos expression in spinal trigeminal tract neurons of rats induced by intrapericardiac injection of algogenic chemicals

AIM: To identify the correlation between intrapericardial injection of allogeneic chemicals and activation of the rat spinal trigeminal tract (STT) neurons.METHODS: Adult male Wistar rats were anesthetized with urethane and divided into 3 groups: inflammatory exudate solution (IES) group, receiving intrapericardial infusion of IES; negative control (saline) group, receiving intrapericardial infusion of saline; and sham group, undergoing the same surgical procedure without intrapericardial infusion. The expression of c-Fos in the neurons of the cervical spinal cord and brain stem, particularly in the region of the trigeminal sensory nuclear complex, including the principal sensory trigeminal nucleus (Pr5VL), subnucleus oralis (Sp5O), subnucleus interpolaris (Sp5I) and subnucleus caudalis (Sp5C), was analyzed by immunohistochemistry as an index of neuronal activation. RESULTS: Compared with saline group and sham group, the number of c-Fos-positive neurons in IES group increased significantly (P＜0.05). c-Fos-positive neurons were mainly found in the dorsal horns of laminae I-V at C2, as well as at the rostral edge of the Pr5VL, Sp5O, Sp5I, and Sp5C. The number of c-Fos-positive neurons gradually increased from bregma to interaural line at the pyramidal decussation. Interestingly, fewer c-Fos-positive neurons were observed on the right side than that on the left (P＜0.05).CONCLUSION: Intrapericardial injection of algogenic chemicals activates STT neurons, possibly underlying the phenomenon whereby cardiac ischemia causes craniofacial pain.