TIME-COURSE OF NOS EXPRESSION AND NEURONAL DEATH IN CLARKES NUCLEUS FOLLOWING TRAUMATIC INJURY IN ADULT-RAT SPINAL-CORD

The objective of this study was to investigate the influence of the le ngth of the remaining axons on neuronal survival following axonal inju ry in the adult rat spinal cord. The relationship between the expressi on of nitric oxide synthase (NOS) and neuronal death was also studied. The time course of NOS expression and neuronal loss was observed in C larke's nucleus at segment Lf following hemisection of the cord at eit her segment C3, T1, or T11. NOS-positive neurons were first observed 3 days after injury, rising significantly after 5 days, and reaching a maximum by 10-20 days post-injury. During the same period the number o f neurons surviving in the nucleus decreased. The decrease began at 3 days, rapidly decreased after 5 days, and reached a minimum by 40 days post-injury. Among the three lesioned groups, the highest percentage of NOS expression and neuronal loss was observed in the group with les ions at T 11, while the lowest percentage was in the group with lesion s at C3. Although the time course of neuronal loss varied following le sion at different spinal levels, in all cases the majority of neurons in Clarke's nucleus had degenerated by 40 days after axotomy. (C) 1998 Published by Elsevier Science Ireland Ltd.