Altered reactivity to modulation of cerebral energy metabolism by tDCS in obese. A phosphorus spectroscopy and morphometric study

Aims: Obese have an overall lower brain energy level as normal weighted as shown by phosphorus spectroscopy and changes in brain morphology as shown in VBM. We tested whether tDCS induced transient neuronal energy depletion and the resulting effects on systemic glucose homeostasis and related neuroendocrine mediators differ in obese and normal subjects and whether the altered brain morphology can give us clues about the nature of the altered brain regulation in obese. Methods: In a crossover design (15 healthy males and 15 obese (BMI > 30)) we increased neuronal excitation by anodal tDCS versus sham and examined cerebral energy consumption with 31phosphorus MR spectroscopy. Systemic glucose uptake was determined by euglycemic hyperinsulinemic glucose clamp. Each subject obtained a 3D MRI scan for VBM and for correlation between the morphological and spectroscopy data. Results: We found that the energetic depletion and the resulting energy consumption caused by anodic tDCS, as quantified by 31phosphorus MR spectroscopy, which promotes systemic glucose tolerance in a standardized euglycemic-hyperinsulinemic glucose clamp procedure in normal subjects (1), is altered in the obese. The reactivity to tDCS is much weaker in the obese. VBM revealed a reduction of gray matter volume in fronto-temporal structures, anterior cingulum, putamen, insula and cerebellum, which was correlated with the BMI. Regression analysis revealed a main association in the right insula between gray matter values and ATP Conclusions: Our data demonstrate that the modulation of local neuronal processes and the influence on downstream metabolic systems caused by tDCS is dramatically altered in obese subjects. The insufficient energy regulation in the obese could be the reason for their overall lowered brain energy level and altered regulation of their global energy regulation. The key structure in this process could be the insula, which reduced volume is related to lower ATP levels.

Literatur: 1. Binkofski F, Loebig M, Jauch-Chara K, Bergmann S, Melchert UH, Scholand-Engler HG, Schweiger U, Pellerin L, Oltmanns KM. Brain energy consumption induced by electrical stimulation promotes systemic glucose uptake. Biol Psychiatry. 2011 Oct 1;70(7):690-5. Epub 2011 Jun 24.