INDUCTION OF MICROGLIAL REACTION AND EXPRESSION OF NITRIC-OXIDE SYNTHASE-I IN THE NUCLEUS DORSALIS AND RED NUCLEUS FOLLOWING LOWER THORACICSPINAL-CORD HEMISECTION

In the present study, immunohistochemical stainings for OX-6, OX-42, n itric oxide synthase I and II as well as nitrotyrosine were used to in vestigate possible correlation among microglial reactivity, nitric oxi de synthase upregulation, peroxynitrite involvement and neuronal death in the nucleus dorsalis and red nucleus following lower thoracic spin al cord hemisection. Significant neuronal loss was found in the ipsila teral nucleus dorsalis and contralateral red nucleus after cord hemise ction. A distinctive microglial reaction for OX-42 could be observed f rom one to four weeks post axotomy in the ipsilateral nucleus dorsalis ; by contrast, it was observed on both sides of the red nucleus from o ne to three weeks following cord hemisection. The activated microglial cells showed some degree of hypertrophy. From the microglial immunore activity as well as their appearance, it was speculated that microglia l activation might be beneficial or protective to the axotomized neuro ns. In normal and sham-operated rats, neurons of the nucleus dorsalis were not nitric oxide synthase I reactive. Three weeks after cord hemi section, neurons in the ipsilateral nucleus dorsalis below the lesion showed strong immunoreactivity. Neurons in the red nucleus that normal ly displayed weak nitric oxide synthase I immunoreactivity showed an i ncrease on both sides of the nucleus. These results suggested that nit ric oxide synthase I expression in the nucleus dorsalis following axot omy was synthesized de novo and might act as a neurotoxic agent. Howev er, the bilateral increase in expression of nitric oxide synthase I in the red nucleus after lower thoracic cord hemisection was due to up-r egulation of the constitutive enzyme and might have some neuroprotecti ve function. Our results also suggested that peroxynitrite played no o r little role in the neurodegeneration in the nucleus dorsalis and red nucleus following axotomy. (C) 1998 Elsevier Science B.V. All rights reserved.