REGION-SELECTIVE GLUTAMINE-SYNTHETASE EXPRESSION IN THE RAT CENTRAL-NERVOUS-SYSTEM FOLLOWING PORTACAVAL ANASTOMOSIS

Glutamine synthetase (GS) content was investigated using immunohistoch emical methods in the hippocampus, cerebellum and spinal cord of rats after long-term portocaval anastomosis (PCA). Six months after surgery , GS content was increased in several areas of each region, and decrea sed in others, compared with controls. In the hippocampus, the CA1-CA3 pyramidal subfields and the dentate molecular layer had a high level of GS expression; PCA reduced GS content in othe hippocampal regions, such as the dentate hilus. In the cerebellum, PCA significantly increa sed GS immunoreactivity in the Bergmann glial processes of the molecul ar layer and decreased GS immunoreactivity in astrocytes of the granul e cell layer. In the spinal cord, GS immunoreactivity increased in the dorsal horn and decreased in the ventral horn. Blood vessels located in zones with GS-immunopositive perineuronal astrocytes in PCA-exposed brains were surrounded by strongly GS-immunostained perivascular prof esses. These results suggest that PCA exposure had a differential effe ct on GS expression in different regions of the central nervous system . The increased immunoreactivity of GS-positive cells in PCA-exposed b rains correlates with glutamatergic areas, which may contribute to pro tecting neurons against extracellular glutamate and/or ammonia excess.