Constitutive and inducible nitric oxide synthases after dynorphin-induced spinal cord injury

It has recently been demonstrated that selective inhibition of both neurona l constitutive and inducible nitric oxide synthases (ncNOS and iNOS) is neu roprotective in a model of dynorphin (Dyn) A(1-17)-induced spinal cord inju ry. In the present study, various methods including the conversion of H-3-L -arginine to H-3-citrulline, immunohistochemistry and in situ hybridization are employed to determine the temporal profiles of the enzymatic activitie s, immunoreactivities, and mRNA expression for both ncNOS and iNOS after in trathecal injection of a neurotoxic dose (20 nmol) of Dyn A(1-17). The expr ession of ncNOS immunoreactivity and mRNA increased as early as 30 min afte r injection and persisted for 1-4 h. At 24-48 h, the number of ncNOS positi ve cells remained elevated while most neurons died. The cNOS enzymatic acti vity in the ventral spinal cord also significantly increased at 30 min-48 h , but no significant changes in the dorsal spinal cord were observed. Howev er, iNOS mRNA expression increased later at 2 h, iNOS immunoreactivity and enzymatic activity increased later at 4 h and persisted for 24-48 h after i njection of 20 nmol Dyn A(1-17). These results indicate that both ncNOS and iNOS are associated with Dyn-induced spinal cord injury, with ncNOS predom inantly involved at an early stags and iNOS at a later stage: (C) 2000 Else vier Science B.V. All rights reserved.