DYNORPHIN MESSENGER-RNA EXPRESSION IN DORSAL HORN NEURONS AFTER TRAUMATIC SPINAL-CORD INJURY - TEMPORAL AND SPATIAL-ANALYSIS USING IN-SITU HYBRIDIZATION

Dynorphin, an endogenous opioid, may contribute to secondary nervous t issue damage following spinal cord injury. The temporal and spatial di stribution of preprodynorphin (PPD) mRNA expression in the injured rat spinal cord was examined by in situ hybridization. Rats were subjecte d to traumatic spinal cord injury at the T13 spinal segment using the weight-drop method. Motor function of these rats was evaluated by thei r ability to maintain their position on an inclined plane, Two double- labeling experiments revealed that increased PPD mRNA and dynorphin pe ptide expression were found exclusively in dorsal horn neurons. Neuron s exhibiting an increase in the level of PPD mRNA were concentrated in the superficial laminae and the neck of dorsal horn within several sp inal segments from the epicenter of the injury at 24 and 48 h after in jury. A number of neurons showing increased PPD mRNA were found in gra y matter adjacent to the injury areas. Segments caudal to the injury s ite exhibited a long-lasting elevation of PPD mRNA in neurons, compare d to the rostral segments. The number of neurons expressing PPD mRNA i n each rat was significantly positively correlated with its motor dysf unction, These findings suggest that increased expression of dynorphin mRNA and peptide in dorsal horn neurons occurs after traumatic spinal cord injury. This also supports the hypothesis that the dynorphin has a pathological role in secondary tissue damage and neurological dysfu nction after spinal cord injury.