c-Fos Protein and NADPH-Diaphorase Detection in Rat Midbrain and Spinal Cord After Contusion Injury

Spinal cord injury appears to involve neuroplastic remodeling or cell death that is the result of intense neuronal cells response to lesion. The damage may occur near the site of lesion, as well as in proximal brain areas. Thus, neurons located in brain centers and functionally connected to the damaged areas may present constitutive changes after spinal cord damage. Experimental studies and clinical observations show that spinal cord trauma may be amplified by secondary neuronal damage. However, little is known about the molecular mechanism that initiates and maintains this neuronal reaction. We have started an investigation of neural changes induced by acute spinal cord injury. We assessed the degree of functional neurologic impairment that follows spinal cord injury by behavioral tests and histological methods. In lesioned areas and throughout the central nervous system expression of the transcription factor protein c-Fos was investigated by immunocytochemistry. The localization of c-Fos may indicate, in addition to neuronal activation spatial and temporal patterns related to the type of stimulus and to the long-term variation in neuronal physiology. In parallel to identify spinal neurons that synthesize Nitric Oxide cells and fibers histochemically stained for NADPH diaphorase (a nitric oxide synthase) were studied. Fos expression was detected in NADPH-diaphorase positive cells at intermedio lateral column central canal dorsal horn including nucleus trigeminalis caudalis two hours after contusion by weight drop. It was found that NADPH-diaphorase is induced in spinal motoneurons neurons that are normally NADPH-diaphorase negative; however no Fos protein expression was detected in these cells. The results suggest that central nervous system areas close or proximal to the lesion site are activated after contusion by weight drop. In addition they show that Fos protein expression and changes on NADPH-diaphorase activity after spinal cord contusion are not necessarily dependent on each other.