Impaired hippocampal glucoregulation in the cannabinoid CB1 receptor knockout mice as revealed by an optimized in vitro experimental approach

Abstract: Several techniques exist to study the rate of glucose uptake and metabolism in the brain but most of them are not sufficiently robust to permit extensive pharmacological analysis. Here we optimized an in vitro measurement of the simultaneous accumulation of the metabolizable and non-metabolizable 3H and 14C d-glucose analogues; permitting convenient large-scale studies on glucose uptake and metabolism in brain slices. Next, we performed an extensive pharmacological characterization on the putative glucoregulator role of the endocannabinoid system in the hippocampal slices of the rat, and the wild-type and the CB1 cannabinoid receptor (CB1R) knockout mice. We observed that 3H-3-O-methylglucose is a poor substrate to measure glucose uptake in the hippocampus. 3H-2-deoxyglucose is a better substrate but its uptake is still lower than that of 14C-U-d-glucose, from which the slices constantly metabolize and dissipate 14C atoms. Thus, uptake and the metabolism values are not to be used as standalones but as differences between a control and a treatment. The CB1R knockout mice exhibited ∼10% less glucose uptake and glucose carbon atom dissipation in comparison with the wild-type mice. This may represent congenital defects as acute treatments of the rat and mouse slices with cannabinoid agonists, antagonists and inhibitors of endocannabinoid uptake/metabolism failed to induce robust changes in either the uptake or the metabolism of glucose. In summary, we report here an optimized technique ideal to complement other metabolic approaches of high spatiotemporal resolution. This technique allowed us concluding that CB1Rs are at least indirectly involved in hippocampal glucoregulation. [Copyright &y& Elsevier]