UP-REGULATION OF NEURONAL NITRIC-OXIDE SYNTHASE AND MESSENGER-RNA, AND SELECTIVE SPARING OF NITRIC-OXIDE SYNTHASE-CONTAINING NEURONS AFTER FOCAL CEREBRAL-ISCHEMIA IN RAT

Nitric oxide synthase-containing neurons are presumed to be resistant to neurodegeneration and neurotoxicity, however this resistance has no t been demonstrated after focal cerebral ischemia. We therefore measur ed the temporal profile of neuronal nitric oxide synthase (NOS-I) mRNA and immunoreactivity and NADPH-diaphorase reactivity over a one week period after permanent middle cerebral artery (MCA) occlusion in 48 ma le Wistar rats and compared these data to ischemic cell damage as eval uated on hematoxylin and eosin (H&E) stained sections by light microsc opy. NOS-I mRNA increased as early as 15 min after MCA occlusion in th e ipsilateral striatum and maximal expression of NOS-I was found in th e ipsilateral cortex and striatum 1 h after MCA occlusion. The numbers of NOS-I-containing neurons in the ipsilateral cortex and striatum we re significantly greater (P < 0.05) than NOS-I-containing neurons in t he contralateral hemisphere at 2-48 h after the onset of ischemia. The number of NOS-I-containing neurons peaked at 4 h after MCA occlusion. Neurons exhibited shrinkage or were swollen at 1 to 4 h after MCA occ lusion. At 24-48 h after ischemia, neurons in the ischemic lesion appe ared to be eosinophilic or ghost like on H&E stained sections. However , some of these neurons retained morphological integrity on the NOS-I immunohistochemical sections. At 168 h after ischemia, all neurons wit hin the lesion appeared necrotic on H&E stained sections; however, sca ttered neurons expressed NOS-I and NADPH-diaphorase. The rapid upregul ation of NOS-I and mRNA in the ischemic lesion suggests that NOS-I is involved in focal cerebral ischemic injury; the expression of NOS-I by neurons that retain their morphological structure in the area of the infarct suggests that NOS-I-containing neurons are more resistant to t he ischemic insult. Our data also indicate a close association of NOS- I immunoreactivity and NADPH-diaphorase reactivity in ischemic brain.