Takanori Esaki

Dichloroacetate effects on glucose and lactate oxidation by neurons and astroglia in vitro and on glucose utilization by brain in vivo

Neuronal cultures in vitro readily oxidized both D-[14C]glucose and l-[14C]lactate to 14CO2, whereas astroglial cultures oxidized both substrates sparingly and metabolized glucose predominantly to lactate and released it into the medium. [14C]Glucose oxidation to 14CO2 varied inversely with unlabeled lactate concentration in the medium, particularly in neurons, and increased progressively with decreasing lactate concentration. Adding unlabeled glucose to the medium inhibited [14C]lactate oxidation to 14CO2 only in astroglia but not in neurons, indicating a kinetic preference in neurons for oxidation of extracellular lactate over intracellular pyruvate/lactate produced by glycolysis. Protein kinase-catalyzed phosphorylation inactivates pyruvate dehydrogenase (PDH), which regulates pyruvate entry into the tricarboxylic acid cycle. Dichloroacetate inhibits this kinase, thus enhancing PDH activity. In vitro dichloroacetate stimulated glucose and lactate oxidation to CO2 and reduced lactate release mainly in astroglia, indicating that limitations in glucose and lactate oxidation by astroglia may be due to a greater balance of PDH toward the inactive form. To assess the significance of astroglial export of lactate to neurons in vivo, we attempted to diminish this traffic in rats by administering dichloroacetate (50 mg/kg) intravenously to stimulate astroglial lactate oxidation and then examined the effects on baseline and functionally activated local cerebral glucose utilization (lCMRglc). Dichloroacetate raised baseline lCMRglc throughout the brain and decreased the percent increases in lCMRglc evoked by functional activation. These studies provide evidence in support of the compartmentalization of glucose metabolism between astroglia and neurons but indicate that the compartmentalization may be neither complete nor entirely obligatory.

Local and global cerebral blood flow and glucose utilization in the α-galactosidase A knockout mouse model of Fabry disease

Fabry disease is an X‐linked lysosomal disorder characterized by deficient α‐galactosidase A activity and intracellular accumulations of glycosphingolipids, mainly globotriaosylceramide (Gb3). Clinically, patients occasionally present CNS dysfunction. To examine the pathophysiology underlying brain dysfunction, we examined glucose utilization (CMRglc) and cerebral blood flow (CBF) globally and locally in 18 brain structures in the α‐galactosidase A gene knockout mouse. Global CMRglc was statistically significantly reduced by 22% in Fabry mice (p < 0.01). All 18 structures showed decreases in local CMRglc ranging from 14% to 33%. The decreases in all structures of the diencephalon, caudate‐putamen, brain stem, and cerebellar cortex were statistically significant (p < 0.05). Global cerebral blood flow (CBF) and local CBF measured in the same 18 structures were lower in Fabry mice than in control mice, but none statistically significantly. Histological examination of brain revealed no cerebral infarcts but abundant Gb3 deposits in the walls of the cerebral vessels with neuronal deposits localized to the medulla oblongata. These results indicate an impairment in cerebral energy metabolism in the Fabry mice, but one not necessarily due to circulatory insufficiency.

Use of [18F]fluorodeoxyglucose and the ATLAS small animal PET scanner to examine cerebral functional activation by whisker stimulation in unanesthetized rats.

PurposeStroking the whiskers of a rat is known to increase cerebral blood flow and glucose utilization in the somatosensory cortex. We sought to determine whether this activation could be detected with small animal PET and 2-[18F]fluoro-2-deoxyglucose ([18F]FDG). MethodsAwake rats were coinjected with [18F]FDG and [14C]deoxyglucose ([14C]DG), and during the uptake of the tracers, five, 10, or 15 whiskers on one side of the face were continuously stimulated. At the end of uptake, the animal was killed and imaged with the Advanced Technology Laboratory Animal Scanner small animal PET scanner. Carbon-14 autoradiography was then performed on brain sections obtained from each animal, and increases in tracer uptake in the somatosensory cortex were compared with those determined with PET. ResultsBoth methods showed increases in [18F]FDG and [14C]DG uptake in the somatosensory cortex in response to the stimulation of as few as five whiskers. However, the magnitude of activation determined from the PET images was less than that from autoradiography due to the lower spatial resolution of the PET scanner. ConclusionAdvanced Technology Laboratory Animal Scanner small animal PET imaging with [18F]FDG can be used to assess neuronal functional activity in vivo.

Blockade of KATP channels with glibenclamide does not alter functional activation of cerebral blood flow in the unanesthetized rat

Possible involvement of ATP-sensitive K(+) (K(ATP)) channels in the cerebral blood flow (CBF) response to neuronal functional activation was investigated in unanesthetized rats. Glibenclamide (1, 2, or 10 micromol/l), a specific inhibitor of K(ATP) channels, was infused intracisternally continuously for 30 min prior to and during the 1-min period of measurement of CBF. Unilateral functional activation was maintained throughout the measurement of CBF by continuous stroking of the vibrissae on the left side of the face. Local CBF was determined bilaterally by the quantitative autoradiographic [14C]iodoantipyrine method in four structures of the whisker-to-barrel cortex pathway and in 18 structures unrelated to the pathway. Glibenclamide tended to lower baseline CBF in almost all regions examined, statistically significantly (P<0.05) in the cerebellar lobules with all doses, in the cerebellar cortex with 10 micromol/l, in the pontine nuclei with 2 and 10 micromol/l, and in the spinal trigeminal nucleus of the unstimulated side with all doses. Vibrissal stimulation increased CBF unilaterally in all the stations of the pathway, but the percent increases were not statistically significantly affected by the glibenclamide treatment, except in the spinal trigeminal nucleus where it was reduced statistically significantly (P<0.05) only by 2 micromol/l glibenclamide. These results indicate that K(ATP) channels may play a role in the tonic regulation of baseline CBF in some regions but provide no support for their role in the increases in CBF evoked by functional activation.