Metabolic pathways affected by GDH KO in neurons. In the presence of GDH neurons metabolize glutamine by the truncated TCA cycle in the absence of glucose (a, control). GDH KO neurons metabolize glutamine, but are not able to use the truncated TCA cycle upon glucose deprivation as shown by deceased aspartate content (a, GDH KO). GDH KO neurons metabolize glucose and respire in the presence of glucose ± glutamine comparable to control neurons (b, without stimulation). However, upon stimulation (e.g. veratridine or FCCP), GDH KO neurons are not able to respond with an increased respiration (b, with stimulation).