Left, physiological ammonia handling in the brain. Right, some of the proposed neurotoxic effects of excess brain ammonia. Glutamate (Glu), glutamine synthetase (GS), glutamine (Gln), adenosine triphosphate (ATP), sodium-coupled neutral amino acid transporters (SNAT1/2 and 5), glutamate transporter 1 (GLT1), glutaminase (Glnase), glutamate and γ-aminobutyric acid (GABA), glutamate receptor (GluR), GABA receptor (GABAR), cerebral blood flow (CBF), cerebral metabolic rate of oxygen (CMRO2), cerebral metabolic rate of glucose (CMRGlc), GABA reversal potential (EGABA), cytokines (CK).