RESUMO
AIM: Spinal cord transection interrupts supraspinal input and leads to the development of prominent spasticity. In this study, we investigated the effect of rat spinal cord transection performed at low thoracic level on changes in (i) neuronal nitric oxide synthase immunoreactivity (nNOS-IR), and (ii) the level of neuronal nitric oxide synthase (nNOS) protein in the neuronal circuitry that underlies tail-flick reflex. METHODS: nNOS-IR was detected by immunohistochemistry and the level of nNOS protein was determined by the Western blot analysis. The tail-flick reflex was tested by a noxious thermal stimulus delivered to the tail of experimental animals. After surgery, experimental animals survived for 7 days. RESULTS: A significant increase in the level of nNOS protein was found 1 week after thoracic transection in the L2-L6 segments. Immunohistochemical analysis discovered that this increase may be a result of (1) a high nNOS-IR in a large number of axons, located predominantly in the dorsal columns (DCs) of lower lumbosacral segments, and (2) a slight increase of density in nNOS-IR in motoneurons. On the other hand the number of nNOS-IR neurons in the superficial dorsal horn and in area surrounded the central canal (CC) was greatly reduced. The tail-flick response was immediate in animals after spinal transection, while control rats responded to thermal stimulus with a slight delay. However, the tail-flick latency in experimental animals was significantly higher than in control. CONCLUSION: These data indicate that transection of the spinal cord significantly influences nNOS-IR in neuronal circuitry that underlies the tail-flick reflex activity.
