Figure 3.

The brain oxidizes lactate in an activity-dependent manner. A, Schematic of the biochemical pathways involved in the degradation of 1-[¹¹C]l-lactate (¹¹C-Lac) and the proposed interpretation of the rate constants K₁ and k₂ describing the kinetics of the radiotracer (for details, see Results). Briefly, K₁ represents delivery of 1-[¹¹C]l-lactate (orange arrow), and k₂ reflects kinetically the loss of radiolabel after conversion of lactate to pyruvate and of pyruvate to acetyl-coenzyme A (purple arrows). During activation (B; S; n = 5), delivery (K₁) and washout (k₂) increased, whereas during MCT blockade (C; CIN; n = 5), the transfer of 1-[¹¹C]l-lactate slowed down in both directions (Pyr, pyruvate; Ac CoA, acetyl coenzyme A; TCA cycle, tricarboxylic acid cycle). *p < 0.05, n.s., not significant.