in brain (cerebellum and stratum), ammonia over activates the excitation N-methyl-D-aspartate (NMDA) receptors at its glycine site, resulting in accumulation of cyclic guanosine monophosphate (cyclic GMP). NH4 in the brain directs glutamate dehydrogenase to convert ketoglutarate and NH4 to glutamate, depressing the citric acid cycle by lowering the level of ketoglutarate and subsequently oxaloacetate (Figure 10-1). Depression of aerobic oxidatin causes cell damage and cell death. If hyperammonemia is suspected, the plasm level of ammonia must be tested