Genetics in the epilepsies

Abnormalities in the levels of extracellular and tissue amino acids in the brain of the seizure-susceptible rat

Basal and high potassium-stimulated release of endogenous amino acids was measured using brain dialysis in the hippocampus of urethane-anesthetized seizure-resistant (SR) and seizure-susceptible (SS) rats. Moreover, the tissue level of amino acids was determined in the hippocampus, sensorimotor cortex, cerebellum and corpus striatum. The basal extracellular concentration of amino acids did not differ between SR and SS rats. However, aspartate release was higher, and taurine and phosphoethanolamine release was lower in SS rats during stimulation with 100 mM K+. Several strain differences were observed with regard to regional tissue levels of amino acids. Aspartate was significantly elevated in the hippocampus, cortex and cerebellum of SS animals, and the catecholamine precursor tyrosine was diminished in all regions examined. Other disparities included a depressed gamma-aminobutyrate concentration in the hippocampus and cortex, slightly increased levels of phosphoethanolamine in the cerebellum and minor decreases in striatal and cortical taurine. Glutamate, glutamine, serine and alanine concentrations were not significantly altered in any brain area of the SS rat. The results confirm and extend previous findings on abnormalities in aspartate, taurine and phosphoethanolamine regulation in this model. In addition, decreased availability of tyrosine may provide a partial explanation for the well-documented deficiency in cerebral norepinephrine in the SS strain.