Fig. 5. Nitric oxide synthase activity in the diencephalon of the epaulette shark in response to hypoxic exposure. The level of nitric oxide synthase (NOS) staining is uniformly low over the entire brain in control animals (A). After hypoxia (B), a striking NOS staining makes the vasculature clearly visible, showing that the endothelial cells have increased their NOS activity. See Renshaw and Dyson (1999) for experimental details.