Behavioral and neurotransmitter changes in the urease-infused rat: a model of congenital hyperammonemia

Rats implanted with subcutaneous or intraperitoneal osmotic minipumps infusing 0.8-1.25 IU urease/kg/h develop sustained hyperammonemia (range 137-497 microM, controls 88 +/- 51 microM +/- SD) for 5-7 days. Glutamine levels are also significantly elevated in plasma (677 +/- 166 versus 428 +/- 122 microM) and cerebral cortex (13.2 +/- 9.8 versus 4.7 +/- 2.8 nmol/mg tissue). Neurobehavioral abnormalities include decreased food intake and increased stereotypic activity. Increased serotonin turnover was suggested by elevated levels of tryptophan and 5-hydroxyindoleacetic acid in cerebral cortex, brain stem, and cerebellum of urease-infused compared to sham-operated animals. There were no changes in norepinephrine or gamma aminobutyric acid, and there was no correlation between the degree of hyperammonemia or glutaminemia and brain levels of tryptophan or biogenic amines. Animals receiving a tryptophan-deficient diet had significantly lower levels of tryptophan and 5-hydroxyindoleacetic acid in brain regions compared to animals receiving a normal tryptophan intake, under both control and hyperammonemic conditions. Despite the prevention of increased serotonin flux in hyperammonemic animals receiving a tryptophan-deficient diet, food intake and weight declined and there was increased stereotypic behavior.