EFFECT OF REPEATED HYPERAMMONEMIA ON NA-DEPENDENT BINDING OF GLUTAMATE IN RAT CORTICAL AND HIPPOCAMPAL SYNAPTIC-MEMBRANES()

Na+-dependent binding of L-glutamate in cortical and hippocampal synap tic membranes from hyperammonemic rats was compared to corresponding d ata in the controls. In hippocampal membranes, repeated hyperammonemia resulted in a 13% and 18% decrease in binding in 20-day-old and 50-da y-old rats, respectively. The decrease was statistically significant ( P < 0.05) in the older animals and Scatchard analysis revealed a 19% r eduction in the number of binding sites without any changes in the aff inity. Within the hippocampal formation, the binding in the dentate gy rus was the most sensitive to hyperammonemia where a 21% decrease was found (P < 0.01), whilst the decline of binding in CA1 and CA3 areas o f the hippocampus proper was not significant. The results support the idea that excessive accumulation of extracellular glutamate during hyp erammonemia is a consequence not only of its increased release, but al so of the blocking of Na+-dependent binding of glutamate to specific u ptake sites.