Partial correlations among concentrations of each of the six metabolites, controlling for age (PCA).

Significant correlations are in bold. Note the correlations among glutamate, glutamine, and NAA, which provide convergent validity of our quantitation of glutamate separate from glutamine: glutamate and NAA are both synthesized in the mitochondria of neurons, whereas glutamine is synthesized in astrocytes. The pattern of cross-correlation is consistent with the compartmentalization of glutamate and glutamine in neurons and astrocytes, respectively.