13C spectrum of representative extract of intact rat brain infused with [2,4,6,8-13C4]octanoate for 105 min. Glutamate (E) and glutamine (Q) regions of carbons 1–5 (C1–C5) and GABA (Gb) C2–C4 are shown. Multiplets are depicted as follows: singlet (S), doublet (D), and triplet (T). Doublets resulting from carbon–carbon coupling of adjacent carbons are noted [e.g., C3 and C4 (D34) in C4 region].Inset,Full13C spectrum; regions of E, Q, Gb, and lactate (La) carbon resonances are indicated. PPM, Parts per million.