EFFECTS OF BRAIN ISCHEMIA ON INTERMEDIATE FILAMENTS OF RAT HIPPOCAMPUS

Neurofilaments subunits (NF-H, NF-M, NF-L) and glial fibrillary acidic protein (GFAP) were investigated in the hippocampus of rats after dis tinct periods of reperfusion (1 to 15 days) following 20 min of transi ent global forebrain ischemia in the rat. In vitro [Ca-14]leucine inco rporation was not altered until 48 h after the ischemic insult, howeve r concentration of intermediate filament subunits significantly decrea sed in this period. Three days after the insult, leucine incorporation significantly increased while the concentration NF-H, NF-M, and NF-L were still diminished after 15 days of reperfusion. In vitro incorpora tion of P-32 into NF-M and NF-L suffered immediately after ischemia, b ut returned to control values after two days of reperfusion. GFAP leve ls decreased immediately after ischemia but quickly recovered and sign ificantly peaked from 7 to 10 days after the insult. These results sug gest that transient ischemia followed by reperfusion causes proteolysi s of intermediate filaments in the hippocampus, and that proteolysis c ould be facilitated by diminished phosphorylation levels of NF-M and N F-L.