Involvement of glial endothelin/nitric oxide in delayed neuronal death of rat hippocampus after transient forebrain ischemia

1. We examined time- and cell-type-dependent changes in endothelin (ET)-1-l ike immunoreactivity, ET receptors binding and nitric oxide (NO) synthase ( NOS) activity in CA1 subfields of the hippocampus of stroke-prone spontaneo usly hypertensive rats subjected to a 10-min bilateral carotid occlusion an d reperfusion. 2. Microglia aggregated in accord with neuronal death and expressed a high density of ETB receptors and an intense NOS activity in the damaged CA1 pyr amidal cell layer, 7 days after the induced transient forebrain ischemia. T he increased NOS activity and ETB receptor in microglia disappeared 28 days after this transient ischemia. 3. In contrast to microglia, astrocytes presented a moderate level of ET-1- like immunoreactivity, ETB receptors, and NOS activity in all areas of the damaged CA1 subfields, 7 days after the ischemia. These events were further enhanced 28 days after the ischemia. 4. In light of these findings, the possibility that the microglial and the astrocytic ETB/ NO system largely contributes to development of the neurona l death and to reconstitution of the damaged neuronal tissue, respectively, in the hippocampus subjected to a transient forebrain ischemia would have to be considered.