[Autoradiography determination of the GABA(A) receptor density in the brain of rats with portacaval shunt].
Quantitative autoradiography was used to assess the densities of gamma-aminobutyric acid (GABAA) receptors in the brains of rats with a portacaval end-to-side shunt (PCA). The shunt alone induced only mild encephalopathy with ataxia and decreased locomotion. Aggravation of the encephalopathy was achieved by gavage feeding of packed erythrocytes or by induction of severe hyperammonemia by intraperitoneal injection of urease. Gavage feeding of erythrocytes led to severe encephalopathy in about 50% of the animals with PCA. The combination of PCA and urease treatment caused severe encephalopathy in every animal. The serum ammonia concentration increased 5 times normal by PCA alone, 20 times normal by gavage feeding of erythrocytes and more than 30 times normal by urease-treatment of the PCA-animals. For autoradiography, coronal slices were cut at the level of the hippocampal formation and through the cerebellum. Radioligand binding was measured using as a ligand 3H-muscimol, a specific GABAA receptor agonist. The specific binding of 3H-muscimol was assessed densitometrically in several microregions of cerebral cortex, hippocampus and cerebellar cortex. No significant differences were observed between the magnitude of ligand binding to specific microregions of brains from normal animals, animals with PCA without overt encephalopathy and animals with severe encephalopathy induced by a combination of PCA and gavage feeding of erythrocytes or urease treatment.