Reactive astrocytes express NADPH diaphorase in vivo after transient ischemia.

In the hippocampus, ten minutes of transient global ischemia results in the death of CA1 pyramidal cells after a period of one to three days. The neurons in the CA1 region constitutively express NADPH-D (NADPH diaphorase activity). In contrast, astrocytes in the hippocampus do not normally express NADPH-D; but a population of reactive astrocytes (GFAP+ cells) begin to express of NADPH-D one day after transient global ischemia. NADPH-D is thought to be a histological marker for Nitric Oxide Synthase (NOS), the enzyme that is responsible for the synthesis of NO, a potent neurotoxin. We suggest that this increase in NADPH-D/NOS expression is an important element in the sequence of changes that occurs after ischemia, and that NO derived from reactive astrocytes or from neurons may play a causal role in neural cell death after ischemia in the hippocampus.