Fluorometric Determination of Glucose Utilization in Neurons in Vitro and in Vivo

Abstract

Summary:Glucose is the major energy source the adult brain utilizes under physiologic conditions. Recent findings, however, have suggested that neurons obtain most of their energy from the oxidation of extracellular lactate derived from astroglial metabolism of glucose transported into the brain from the blood. In the present studies we have used 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxy-D-glucose (2-NBDG), a fluorescent analogue of 2-deoxyglucose, which is often used to trace glucose utilization in neural tissues, to examine glucose metabolism in neurons in vitro and in vivo. Cultured neurons and astroglia were incubated with 2-NBDG for up to 15 minutes, and nonmetabolized 2-NBDG was washed out. We found that fluorescence intensity increased linearly with incubation time in both neurons and astroglia, indicating that both types of brain cells could utilize glucose as their energy source in vitro. To determine if the same were true in vivo, Sprague-Dawley rats were injected intravenously with a pulse bolus of 2-NBDG and decapitated 45 minutes later. Examination of brain sections demonstrated that phosphorylated 2-NBDG accumulated in hippocampal neurons and cerebellar Purkinje cells, indicating that neurons can utilize glucose in vivo as energy source.

GLP-2 potentiates L-type Ca2+ channel activity associated with stimulated glucose uptake in hippocampal neurons

“…Neurons could directly take up and utilize glucose as energy sources in vitro (Fig. 5a), which is in agreement with recent reports (31,52). Furthermore, we detected the protein expression of the facilitative glucose transporter (GLUT3) mainly responsible for neuronal glucose uptake, which may play a key role in synaptic energy supply and neurotransmitter synthesis (19).…”

“…To determine whether hippocampal neurons directly take up glucose, we first used 6-NBDG as a fluorescent, nonhydrolyzable glucose analog to trace glucose uptake and transport (31,64). Neurons could directly take up and utilize glucose as energy sources in vitro (Fig.…”

Direct evidence for activity-dependent glucose phosphorylation in neurons with implications for the astrocyte-to-neuron lactate shuttle

“…The finding of high resting neuronal FDG phosphorylation in adult rats is consistent with in vivo findings from high-resolution 2-DG autoradiography (42), reporting approximately equal amounts of glucose utilization by neurons and astrocytes. In addition, an in vivo study using the fluorescent glucose analog, 2-deoxy-N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)-aminoglucose (2-NBDG), which is phosphorylated by hexokinase to 2-NBDP 6P (43), also found uptake/metabolism in both neurons (hippocampal pyramidal and cerebellar Purkinje cells) and astroglia of adult rats. The in vivo findings, however, are at odds with two recent in vitro studies using 2-NBDG in immature (P10 to P21) cerebellar (44) and hippocampal (45) brain slices, which found less uptake in neurons than in astrocytes, inferring support for the ANLS mechanism.…”

Oxidative Metabolism in Cultured Rat Astroglia: Effects of Reducing the Glucose Concentration in the Culture Medium and of D-Aspartate or Potassium Stimulation

“…In addition, the contribution of lactate transport through gap junctions between astroglia remains to be resolved (Dienel and Cruz, 2003). However, neurons do indeed use glucose in vivo and in vitro (Itoh et al, 2004 …”