Neuronal expression of Fos and Jun protein in the rat medulla and spinal cord after anoxic and hypercapnic stimulations.

After inhalation of 100% N2 (anoxia) or 8% CO2 (hypercapnia), neurons that express Fos protein (FOS) and/or Jun protein (JUN) were immunohistochemically identified in the CNS of rats anesthetized with urethane and alpha-chloralose. JUN-labeled cells were characteristically found in the respiration-related motor nuclei of the medulla and spinal cord, and in the central chemoreceptive area of the ventral medullary surface on which hypercapnia was more effective than anoxia, whereas FOS-labeled cells were dominant in the respiration-related sensory nuclei of the medulla on which anoxia was more effective than hypercapnia. The results suggest that the peripheral chemoreceptor and the central chemoreceptive pathways in the medulla and spinal cord may be traced by a combination of FOS and JUN expression methods.