Immunohistochemically demonstrated increase of prostaglandin F2-alpha in neurons after reoxygenation in anoxic rats

Immunohistochemical staining for prostaglandin F2-alpha (PG F2 alpha) was conducted to identify PG F2 alpha synthesizing or binding sites in anoxic rat brains. Anoxia was produced in 22 rats to lower the arterial oxygen tension (PaO2) to 21 +/- 4 mmHg by ventilation with a 95% nitrogen and 5% carbon dioxide gas mixture. In 8 animals anoxia was continued for 30 sec, and in 14 rats for 3 min. Prior to decapitation, 5 animals in the 30-sec anoxia group and 8 rats in the 3-min anoxia group were reoxygenated for 5 min, while the remaining 9 were not. Five-min reoxygenation returned the PaO2 to 106 +/- 7. Three non-reoxygenated and 3 reoxygenated rats, all pretreated with indomethacin, and 5 normal rats served as controls. The brains were snap-frozen. The cryosections were stained by the indirect immunofluorescence method. PG F2 alpha was noted mainly in pial vessels in all normal rats. All reoxygenated rats showed a positive reaction not only in blood vessels, but also in neurons, particularly hippocampal neurons and Purkinje cells. The staining of the above neurons was noted to be less in non-reoxygenated rats. The stronger staining was observed in rats reoxygenated after 3-min anoxia than 30-sec anoxia. The indomethacin-pretreated rats showed almost no increase in staining intensity. The above results indicate that reoxygenation after anoxia results in an increase of PG F2 alpha in neurons of both cerebrum and cerebellum.