Expression of neuronal and inducible nitric oxide synthase in neuronal and glial cells after transient occlusion of the middle cerebral artery

We presently investigated the time-course of neuronal nitric oxide synthase and inducible nitric oxide synthase expression and content in the rat striatum up to 6 days after ischemia induced by transient middle cerebral artery occlusion, a condition that potentially allows functional recovery, with the aim to identify the cell types expressing these two enzymes and to correlate neuronal nitric oxide synthase and inducible nitric oxide synthase changes in order to verify whether and how these changes are related to tissue damage, motor-sensory performances and survival. Before and after surgery, the animals underwent neurological evaluation. The results demonstrated that the rats with a score :12 at the neurological evaluation 24 h after ischemia showed a significant increase in neuronal nitric oxide synthase-immunoreactive neurones and absence of inducible nitric oxide synthase-immunoreactive cells and survived up to the sixth day; conversely, the rats with a score < 12 at the neurological evaluation 24 h after ischemia showed a progressive significant decrease in neuronal nitric oxide synthase-immunoreactive neurones and appearance of inducible nitric oxide synthase-immunoreactive cells and none of the rats survived up to the sixth day. Microglia cells were activated in both groups but only in the latter did these cells express inducible nitric oxide synthase. Measurement of the infarct area demonstrated that it occupied a similar territory in both groups of rats but in those with a score < 12 the edema was more extended. In conclusion, we demonstrated that a neurotoxic insult such as ischemia can induce neuronal nitric oxide synthase expression in the neurones and that when neuronal nitric oxide synthase-immunoreactive neurones increase in number, microglia activation is less extended, inducible nitric oxide synthase-immunoreactive cells are absent, tissue damage reduced and the rats survive longer. Conversely, when there is a significant decrease of neuronal nitric oxide synthase-immunoreactive neurones, microglia cells are intensely activated, inducible nitric oxide synthase-immunoreactive cells appear and the animal survival is shortened.