TEMPORAL PROFILES OF THE IN-VITRO PHOSPHORYLATION RATE AND IMMUNOCONTENT OF GLIAL FIBRILLARY ACIDIC PROTEIN (GFAP) AFTER KAINIC ACID-INDUCED LESIONS IN AREA CA1 OF THE RAT HIPPOCAMPUS - DEMONSTRATION OF A NOVEL PHOSPHOPROTEIN ASSOCIATED WITH GLIOSIS

The in vitro phosphorylation rate and immunocontent of glial fibrillar y acidic protein was studied in slices of area CA1 of the rat hippocam pus after stereotaxic injection of 1 nmol of kainic acid. For controls the contralateral hippocampus was injected with saline. Hippocampal t issue was incubated with [P-32]phosphate and analysed by two-dimension al electrophoresis for phosphorylation rate and by immunoblotting for immunocontent. Both these parameters decreased during the first 4 days after injection and then started to increase at 10 days and continued to increase until at least 84 days. Except for a small excess of phos phorylation rate at 28 days, the relationship between immunocontent an d in vitro phosphorylation rate of glial fibrillary acidic protein rem ained constant, indicating that the reactive gliosis was not associate d with hypo-or a major hyperphosphorylation of this protein. Histology showed a pronounced loss of CA1 pyramidal cells 1 day after injection . At 28 days after injection the pyramidal cells had disappeared and o nly a few abnormal neurones were present. In contrast, immunocytochemi stry after 28 days showed a marked increase in astrocytes reacting pos itive to the antibody in the strata radiatum and lacunosum moleculare. Besides glial fibrillary acidic protein the expression of several oth er proteins was upregulated as a result of the injection of kainic aci d. These included phosphovimentin and an unknown phosphoprotein design ated pp25 which co-migrated on 2-D gels with a prominent phosphoprotei n expressed in primary cultures of astrocytes. Pp25 was expressed in l esioned tissue more frequently than phosphovimentin and with a time co urse that started earlier. Of particular interest was the expression o f pp25 in the contralateral saline-injected hippocampus 1 day after in jection of kainic acid. It is possible that pp25 will prove to be a se nsitive marker of gliosis. (C) 1997 Elsevier Science B.V.