Neuropeptide Y and somatostatin immunoreactivity in the rat hippocampus after moderate hypoxia

Transient moderate hypoxia has been previously shown to exert a potent protective role to subsequently applied convulsant drugs. We now investigated neuropeptide Y and somatostatin immunoreactivities seven days after moderate hypoxia (9% O2 in N2 for two times 8 h) in the hippocampus of the rat. A slight reduction of somatostatin immunoreactive cells was observed in the hilus of the dorsal and ventral hippocampus. At the same time, the total number of neuropeptide Y immunoreactive neurons was increased in this area due to a pronounced increase in staining of presumable basket cells. There was also increased staining of neuropeptide Y positive fibers in the outer molecular layer. Our data suggest activation of neuropeptide Y containing interneurons after a moderate or a mild transient hypoxia. Activation of these inhibitory neurons may contribute to the protective effect of this treatment.