Targeted Imaging of Lung Cancer with Hyperpolarized 129Xe MRI Using Surface-Modified Iron Oxide Nanoparticles as Molecular Contrast Agents.

Hyperpolarized 129Xe (HP 129Xe) MRI enables functional imaging of various lung diseases but has been scarcely applied to lung cancer imaging. The aim of this study is to investigate the feasibility of targeted imaging of lung cancer with HP 129Xe MRI using surface-modified iron oxide nanoparticles (IONPs) as molecular targeting contrast agents. A mouse model of lung cancer (LC) was induced in nine mice by intra-peritoneal injection of urethane. Three months after the urethane administration, the mice underwent lung imaging with HP 129Xe MRI at baseline (0 h). Subsequently, the LC group was divided into two sub-groups: mice administered with polyethylene glycol-coated IONPs (PEG-IONPs, n = 4) and folate-conjugated dextran-coated IONPs (FA@Dex-IONPs, n = 5). The mice were imaged at 3, 6, and 24 h after the intravenous injection of IONPs. FA@Dex-IONPs mice showed a 25% reduction in average signal intensity at cancer sites at 3 h post injection, and a 24% reduction at 24 h post injection. On the other hand, in PEG-IONPs mice, while a signal reduction of approximately 28% was observed at cancer sites at 3 to 6 h post injection, the signal intensity was unchanged from that of the baseline at 24 h. Proton MRI of LC mice (n = 3) was able to detect cancer five months after urethane administration, i.e., later than HP 129Xe MRI (3 months). Furthermore, a significant decrease in averaged 1H T2 values at cancer sites was observed at only 6 h post injection of FA@Dex-IONPs (p < 0.05). As such, the targeted delivery of IONPs to cancer tissue was successfully imaged with HP 129Xe MRI, and their surface modification with folate likely has a high affinity with LC, which causes overexpression of folate receptors.

Ex vivo imaging and analysis of ROS generation correlated with microglial activation in rat model with acute neuroinflammation induced by intrastriatal injection of LPS.

Neuroinflammation and oxidative stress are hallmarks of neurodegenerative diseases. Microglia, the major important regulators of neuroinflammation, are activated in response to excessive generation of reactive oxygen species (ROS) from damaged cells and resulting in elevated and sustained damages. However, the relationship between microglia and ROS-regulatory system in the early stages of neuroinflammation prior to the appearance of neuronal damages have not been elucidated in detail. In this study, we analyzed the time-dependent changes in ROS generation during acute neuroinflammation in rats that were given an intrastriatal injection of lipopolysaccharide (LPS). We evaluated the effects of minocycline, an anti-inflammatory antibiotic, and N,N'-dimethylthiourea (DMTU), a radical scavenger, to understand the correlation between activated microglia and ROS generation. Ex vivo fluorescence imaging using dihydroethidium (DHE) clearly demonstrated an increased ROS level in the infused side of striatum in the rats treated with LPS. The level of ROS was changed in time-dependent manner, and the highest level of ROS was observed on day 3 after the infusion of LPS. Immunohistochemical studies revealed that time-dependent changes in ROS generation were well correlated to the presence of activated microglia. The inhibition of microglial activation by minocycline remarkably reduced ROS levels in the LPS-injected striatum, which indicated that the increased ROS generation caused by LPS was induced by activated microglia. DMTU decreased ROS generation and resulted in remarkable inhibitory effect on microglial activation. This study demonstrated that ROS generation during acute neuroinflammation induced by LPS was considerably associated with microglial activation, in an intact rat brain. The results provides a basis for understanding the interaction of ROS-regulatory system and activated microglia during neuroinflammation underlying neurodegenerative diseases.

Evaluation of intracellular processes in quinolinic acid-induced brain damage by imaging reactive oxygen species generation and mitochondrial complex I activity.

PURPOSE: Our study aimed to elucidate the intracellular processes associated with quinolinic acid (QA)-induced brain injury by acquiring semiquantitative fluorescent images of reactive oxygen species (ROS) generation and positron emission tomography (PET) images of mitochondrial complex I (MC-I) activity. METHODS: Ex vivo fluorescent imaging with dihydroethidium (DHE) and PET scans with 18F-BCPP-EF were conducted at 3 h and 24 h after QA injection into the rat striatum. Immunohistochemical studies were performed 24 h after QA injection into the rat brain using monoclonal antibodies against neuronal nuclei (NeuN) and CD11b. RESULTS: A strong DHE-derived fluorescent signal was detected in a focal area within the QA-injected striatum 3 h after QA injection, and increased fluorescent signal spread throughout the striatum and parts of the cerebral cortex after 24 h. By contrast, 18F-BCPP-EF uptake in the QA-injected rat brain was unchanged after 3 h and markedly decreased after 24 h, not only in the striatum but also in the cerebral hemisphere. The fluorescent signal in the striatum 24 h after QA injection colocalised with microglial marker expression. CONCLUSIONS: We successfully obtained functional images of focal ROS generation during the early period of excitotoxic injury, and microglial ROS generation and mitochondrial dysfunction were observed during the progression of the inflammatory response. Both ex vivo DHE imaging and in vivo 18F-BCPP-EF-PET were sufficiently sensitive to detect the respective processes of QA-induced brain damage. Our study contributes to the functional imaging of multiple events during the pathological process.

A Simple Ex Vivo Semiquantitative Fluorescent Imaging Utilizing Planar Laser Scanner: Detection of Reactive Oxygen Species Generation in Mouse Brain and Kidney.

OBJECTIVE: Oxidative stress plays an important role in the onset of many neuronal and peripheral disorders. We examined the feasibility of obtaining semiquantitative fluorescent images of reactive oxygen species (ROS) generation in mouse brain and kidney utilizing a planar laser scanner and dihydroethidium (DHE). METHODS: To investigate ROS generation in brain, sodium nitroprusside was injected into the striatum. Dihydroethidium was injected into the tail vein. After DHE injection, tissue slices were analyzed utilizing a planar laser scanner. For kidney study, cis-diamminedichloroplatinum [II] (cisplatin) was intraperitoneally administrated into mice. RESULTS: Clear and semiquantitative fluorescent images of ROS generation in the mouse brain and kidney were obtained. Furthermore, the fluorescence intensity was stable and not affected by fading. Sodium nitroprusside induced approximately 6 times the fluorescence accumulation in the brain. Cisplatin caused renal injury in all mice, and in comparison with control mice, more than 10 times fluorescence accumulation was observed in the renal medulla with tubular necrosis and vacuolization. CONCLUSIONS: We successfully obtained ex vivo semiquantitative fluorescent images of ROS generation utilizing a planar laser scanner and DHE. This simple method is useful for ROS detection in several ROS-related animal models and would be applicable to a variety of biochemical processes.

Kinetic study of benzyl [1-14C]acetate as a potential probe for astrocytic energy metabolism in the rat brain: Comparison with benzyl [2-14C]acetate.

Brain uptake of [(14)C]acetate has been reported to be a useful marker of astrocytic energy metabolism. In addition to uptake values, the rate of radiolabeled acetate washout from the brain appears to reflect CO2 exhaustion and oxygen consumption in astrocytes. We measured the time-radioactivity curves of benzyl [1-(14)C]acetate ([1-(14)C]BA), a lipophilic probe of [1-(14)C]acetate, and compared it with that of benzyl [2-(14)C]acetate ([2-(14)C]BA) in rat brains. The highest brain uptake was observed immediately after injecting either [1-(14)C]BA or [2-(14)C]BA, and both subsequently disappeared from the brain in a single-exponential manner. Estimated [1-(14)C]BA washout rates in the cerebral cortex and cerebellum were higher than those of [2-(14)C]BA. These results suggested that [1-(14)C]BA could be a useful probe for estimating the astrocytic oxidative metabolism. The [1-(14)C]BA washout rate in the cerebral cortex of immature rats was lower than that of mature rats. An autoradiographic study showed that the washout rates of [1-(14)C]BA from the rat brains of a lithium-pilocarpine-induced status epilepticus model were not significantly different from the values in control rat brains except for the medial septal nucleus. These results implied that the enhancement of amino acid turnover rate rather than astrocytic oxidative metabolism was increased in status epilepticus.

Improvement of brain uptake for in vivo PET imaging of astrocytic oxidative metabolism using benzyl [1-(11)C]acetate.

Brain uptake of acetate is insufficient for obtaining a quantitative image of astrocytic oxidative metabolism. To improve the brain uptake of [1-(11)C]acetate, we synthesized benzyl [1-(11)C]acetate ([1-(11)C]BA) and conducted a positron emission tomography (PET) study assessing astrocytic oxidative metabolism. The brain uptake of [1-(11)C]BA was markedly higher compared with [1-(11)C]acetate, and disappeared with a half-life of 20 min in all regions studied. The brain uptake of [1-(11)C]BA was significantly decreased by fluorocitrate. The results indicate that [1-(11)C]BA could be a useful PET probe for assessing astrocytic oxidative metabolism.

Microdialysis with radiometric monitoring of L-[ß-11C]DOPA to assess dopaminergic metabolism: effect of inhibitors of L-amino acid decarboxylase, monoamine oxidase, and catechol-O-methyltransferase on rat striatal dialysate.

The catecholamine, dopamine (DA), is synthesized from 3,4-dihydroxy-L-phenylalanine (L-DOPA) by aromatic L-amino acid decarboxylase (AADC). Dopamine metabolism is regulated by monoamine oxidase (MAO) and catechol-O-methyltransferase (COMT). To measure dopaminergic metabolism, we used microdialysis with radiometric detection to monitor L-[ß-(11)C]DOPA metabolites in the extracellular space of the rat striatum. We also evaluated the effects of AADC, MAO, and COMT inhibitors on metabolite profiles. The major early species measured after administration of L-[ß-(11)C]DOPA were [(11)C]3,4-dihydroxyphenylacetic acid ([(11)C]DOPAC) and [(11)C]homovanillic acid ([(11)C]HVA) in a 1:1 ratio, which shifted toward [(11)C]HVA with time. An AADC inhibitor increased the uptake of L-[ß-(11)C]DOPA and L-3-O-methyl-[(11)C]DOPA and delayed the accumulation of [(11)C]DOPAC and [(11)C]HVA. The MAO and COMT inhibitors increased the production of [(11)C]3-methoxytyramine and [(11)C]DOPAC, respectively. These results reflect the L-DOPA metabolic pathway, suggesting that this method may be useful for assessing dopaminergic metabolism.

In vivo imaging and quantitative analysis of TSPO in rat peripheral tissues using small-animal PET with [18F]FEDAC.

INTRODUCTION: The translocator protein (18 kDa) (TSPO) is widely expressed in peripheral tissues, including the heart, lung, and kidney. Our laboratory developed N-benzyl-N-methyl-2-[7,8-dihydro-7-(2-[(18)F]fluoroethyl)-8-oxo-2-phenyl-9H-purin-9-yl]acetamide ([(18)F]FEDAC) as a TSPO positron emission tomography (PET) ligand. Here, using small-animal PET with [(18)F]FEDAC, we performed TSPO imaging and quantitative analysis of TSPO binding in rat peripheral tissues. METHODS: The in vivo distribution and kinetics of [(18)F]FEDAC were measured in rat peripheral tissues (heart, lung and kidney). Using the in vivo pseudo-equilibrium method, TSPO binding parameters [TSPO density (B(max)), dissociation constant (K(D))] and receptor occupancy were estimated in these peripheral tissues. RESULTS: [(18)F]FEDAC was highly distributed in the lung, heart and kidney, and these TSPO-enriched tissues could be clearly visualized. The kinetics of this radioligand in these tissues was rapid, which is suitable for the determination of in vivo TSPO binding parameters and receptor occupancy. The B(max) value of TSPO in the heart, lung, and kidney was 393, 141, and 158 pmol/ml, respectively. The K(D) value of the radioligand in the heart, lung, and kidney was 119, 36 and 123 nM, respectively. By pretreatment with 5 mg/kg Ro 5-4864 (a TSPO ligand), about 90% of binding sites for TSPO in the heart and lung were occupied. In the kidney, the binding sites were completely occupied by 5 mg/kg Ro 5-4864. CONCLUSIONS: [(18)F]FEDAC is a suitable PET ligand for TSPO imaging and quantitative analysis of TSPO binding in rat peripheral tissues. The utilization of [(18)F]FEDAC-PET and the pseudo-equilibrium method can contribute to the study of the TSPO function and evaluate the in vivo binding parameters and receptor occupancy of TSPO therapeutic compounds.

Anticonvulsant effects of methyl ethyl ketone and diethyl ketone in several types of mouse seizure models.

The anticonvulsant effects of acetone have been reported in various animal models of epilepsy. We recently demonstrated that other ketone bodies, methyl ethyl ketone (MEK) and diethyl ketone (DEK), suppressed status epilepticus that was induced by lithium-pilocarpine in rat. In the present study, the anticonvulsant effects of MEK and DEK were evaluated by using four different types of mouse seizure models, which were induced by pentylenetetrazole, kainic acid, methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate (DMCM), and electroshock. The effects of clonazepam, a typical anticonvulsant, and acetone were also evaluated and compared with MEK and DEK. In this study, MEK (5 and 10 mmol/kg, i.p.) and DEK (2.5 and 5 mmol/kg, i.p.) produced anticonvulsant activity against all types of seizure models. Furthermore, MEK and DEK showed almost the same potencies against four different seizure models used, while clonazepam showed significant higher ED(50) values against kainic acid-induced and electroshock-induced seizure models as compared with the pentylenetetrazole- or DMCM-induced seizure model. In each study, the highest doses of clonazepam (1 or 3mg/kg) did not show clear anticonvulsant effects against the kainic acid- or electroshock-induced seizures. In conclusion, MEK and DEK showed broad-spectra anticonvulsant effects in both chemically- and electroshock-induced experimental seizure models.

PK11195 might selectively suppress the quinolinic acid-induced enhancement of anaerobic glycolysis in glial cells.

PK11195 was previously reported to attenuate the quinolinic acid (QUIN)-induced enhancement of glucose metabolism in rat brain. In the present study, the effect of PK11195 or anesthesia on [(14)C]2-deoxyglucose ([(14)C]DG) uptake was investigated in order to determine whether the QUIN-induced enhancement of glucose metabolism occurred in glial cells or neurons. We confirmed that the microinjection of QUIN caused a significant enhancement of [(14)C]DG uptake at 2h after the infusion, while the co-injection of PK11195 and QUIN almost completely suppressed this enhancement of [(14)C]DG uptake. No effect of chloral hydrate anesthesia on the QUIN-induced enhancement of [(14)C]DG uptake was observed. In contrast to rats treated with QUIN, PK11195 did not affect the enhancement of [(14)C]DG uptake induced by fluorocitrate (FC); however, chloral hydrate anesthesia completely suppressed the FC-induced increase in [(14)C]DG uptake. These results indicated that the enhancement of glucose metabolism induced by QUIN mainly occurred in glial cells, and the neuroprotective effect of PK11195 in rats injected with QUIN might be related to the suppression of anaerobic glycolysis in glial cells.

Remarkable selectivity of the in vivo binding of [3H]Ro15-4513 to α5 subtype of benzodiazepine receptor in the living mouse brain.

To evaluate the binding characteristics of [(3)H]Ro15-4513 with the central benzodiazepine (BZ) receptor, inhibition experiments of [(3)H]Ro15-1788 and [(3)H]Ro15-4513 were performed both in vitro and in vivo, using two BZ ligands, flunitrazepam (FNP), and ethyl-ß-carboline-3-carboxylate (ß-CCE). FNP inhibited the binding of [(3)H]Ro15-1788 and [(3)H]Ro15-4513 in a dose-dependent manner in the mouse cerebral cortex, hippocampus, and cerebellum, both in vitro and in vivo. ß-CCE also inhibited the binding of [(3)H]Ro15-1788 and [(3)H]Ro15-4513 in all the aforementioned brain regions in vitro. However, in vivo, ß-CCE inhibited the binding of [(3)H]Ro15-4513 in the cerebral cortex and cerebellum, but not in the hippocampus, even at an injected dose of up to 1mg/kg. In contrast, more than 50% of the in vivo binding of [(3)H]Ro15-1788 was inhibited by 1 mg/kg of ß-CCE in all regions. The time-activity curve of [(3)H]Ro15-4513 in the hippocampus also showed no alteration of the peak uptake between the control group and 0.3 mg/kg of ß-CCE coinjected group. These results indicated that the binding characteristics of [(3)H]Ro15-4513 with the BZ receptor differed markedly between the in vitro and in vivo condition, and the selectivity of [(3)H]Ro15-4513 binding to α5 subtype of BZ receptor in the mouse brain seemed to be remarkable under the in vivo condition.

Remarkable increase in 14C-acetate uptake in an epilepsy model rat brain induced by lithium-pilocarpine.

The present study demonstrates changes in rat brain glial metabolism during the acute phase of epilepsy. Status epilepticus (SE) was induced using the lithium-pilocarpine model. Glial metabolism was measured with (14)C-acetate. Local cerebral blood flow and glucose metabolism were also measured using (14)C-N-isopropyl-p-iodoamphetamine (IMP) and (14)C-2-deoxyglucose (2DG), respectively. At the initiation of the seizure, (14)C-acetate uptake did not change significantly. However, a marked increase was observed 2 h after the pilocarpine injection in all brain regions studied. The increase of brain uptake was transient, and the maximum enhancement was seen at 2 h after the pilocarpine injection. The increase of (14)C-acetate uptake was almost to the same degree in all regions, whereas (14)C-IMP and (14)C-2DG uptakes showed a heterogeneous increase. In the case of (14)C-IMP, the highest increase was observed in the thalamus (280%), and a moderate increase (120 to 150%) was seen in the orbital cortex, cingulate cortex and pyriform cortex. (14)C-2DG uptake increased by 130 to 240% in most regions of the brain, however, an increase of only 40 and 20% was observed in the cerebellum and pons-medulla, respectively. These results demonstrated that glial energy metabolism was markedly enhanced during a prolonged seizure. To our knowledge, this study is the first observation showing large and widespread glial metabolic increases in the rat brain during status epilepticus.

Glucose utilization in the brain during acute seizure is a useful biomarker for the evaluation of anticonvulsants: effect of methyl ethyl ketone in lithium-pilocarpine status epilepticus rats.

Enhancement of glucose utilization in the brain has been well known during acute seizure in various kinds of animal model of epilepsy. This enhancement of glucose utilization might be related to neural damage in these animal models. Recently, we found that methyl ethyl ketone (MEK) had both anticonvulsive and neuroprotective effects in lithium-pilocapine (Li-pilo) status epilepticus (SE) rat. In this article, we measured the uptake of [(14)C]2-deoxyglucose ([(14)C]DG) in the Li-pilo SE and Li-pilo SE with MEK rat brain in order to assess whether the glucose utilization was a useful biomarker for the detection of efficacy of anticonvulsive compounds. Significant increase of [(14)C]DG uptake (45 min after the injection) in the cerebral cortex, hippocampus, amygdala and thalamus during acute seizure induced by Li-pilo were observed. On the other hand, the initial uptake of [(14)C]DG (1 min after the injection) in the Li-pilo SE rats was not different from the control rats. Therefore, the enhancement of glucose metabolism during acute seizure was due to the facilitation of the rate of phosphorylation process of [(14)C]DG in the brain. Pretreatment with MEK (8 mmol/kg) completely abolished the enhancement of glucose utilization in the Li-pilo SE rats. The present results indicated that glucose utilization in the brain during acute seizure might be a useful biomarker for the evaluation of efficacy of anticonvulsive compounds.

Lactate is an alternative energy fuel to glucose in neurons under anesthesia.

The uptake of [14C]lactate was measured in the brains of mice anesthetized with pentobarbital or chloral hydrate. The results showed significant increase of the [14C]lactate uptake in the brain under both anesthesia. Despite energy metabolism in the brain being suppressed by both pentobarbital and chloral hydrate, the [14C]lactate uptake was unexpectedly increased under anesthesia. [14C]Lactate uptake in rat brain injured by infusion of quinolic acid was significantly decreased, and the reduction of [14C]lactate uptake was parallel to neural cell death, suggesting that exogenous lactate might be selectively taken up by neuron. These results indicated that lactate rather than glucose might serve as an energy substrate for neuron in intact brain under anesthesia.

Methyl ethyl ketone blocks status epilepticus induced by lithium-pilocarpine in rats.

BACKGROUND AND PURPOSE: A ketogenic diet has been used successfully to treat patients with intractable epilepsy, although the mechanism is unknown. Acetone has been shown to have an anticonvulsive effect in various animal models. The main purpose of this study was to determine whether other ketones, 2-butanone (methyl ethyl ketone: MEK) and 3-pentanone (diethyl ketone: DEK), also show anticonvulsive effects in lithium-pilocarpine (Li-pilocarpine)-induced status epilepticus (SE) in rats. EXPERIMENTAL APPROACH: Anticonvulsive effects of MEK and DEK in Li-pilocarpine SE rats were measured by behavioural scoring. Anti-seizure effects of MEK were also evaluated using electroencephalography (EEG). Neuroprotective effect of MEK was investigated by haematoxylin and eosin staining 4 weeks after the treatment with pilocarpine. KEY RESULTS: Acetone, MEK and DEK showed anticonvulsant effects in Li-pilocarpine-induced SE rats. Treatment with MEK twice (8 mmol.kg(-1) and 5 mmol.kg(-1)) almost completely blocked spontaneous recurrent cortical seizure EEG up to 4 weeks after the administration of pilocarpine. MEK also showed strong neuroprotective effects in Li-pilocarpine-treated rats 4 weeks following the administration of pilocarpine. Significant neural cell death occurred in the hippocampus of Li-pilocarpine SE rats, especially in the CA1 and CA3 subfields. In contrast, normal histological characteristics were observed in these regions in the MEK-pretreated rats. CONCLUSIONS AND IMPLICATIONS: Both MEK and DEK showed strong anticonvulsive effects in Li-pilocarpine-induced SE rats. They also inhibited continuous recurrent seizure and neural damage in hippocampal region for 4 weeks after the treatment with pilocarpine. These findings appear to be of value in the investigation of epilepsy.

Inhibitory effect of methyl ethyl ketone upon the enhancement of cerebral blood flow during status epilepticus induced by lithium-pilocarpine.

Significant increases in local cerebral blood flow during lithium-pilocarpine (Li-P) induced seizure have been reported. We recently found that both acetone and methyl ethyl ketone (MEK) showed anticonvulsive effects in status epilepticus induced by Li-P in rats. In this study, we examined whether MEK also suppressed the enhancement of local cerebral blood flow induced by Li-P with a simplified autoradiographic method using [(14)C]-para-iodo-N-isopropyl amphetamine ([(14)C]-IMP). Significant increases in local cerebral blood flow in the thalamus, hypothalamus, hippocampus and cerebellum were observed in Li-P induced status epilepticus rats. Pretreatment with MEK (8 mmol/kg) completely suppressed the enhancement of local cerebral blood flow to or below the control level in all regions.

In vivo monitoring of extracellular 13N-glutamine derived from blood-borne 13N-ammonia in rat striatum using microdialysis with radio-LC method.

Glutamine synthetase (GS) is selectively localized in astrocytes and has important roles in the central nervous system (CNS). Cerebral extracellular excess ammonia and glutamate are taken up by astrocytes and converted to glutamine via GS to protect the CNS against neurotoxicity. In this study, we monitored cerebral extracellular 13N-glutamine derived from 13N-ammonia as a potential marker for astroglial metabolism using in vivo microdialysis combined with ultra performance liquid chromatography-radiometric detection. This method allowed rapid and highly sensitive radiometric analysis of 13N-ammonia and its metabolite, 13N-glutamine, in striatal extracellular fluid with good time resolution. Inhibition of GS with methionine sulfoximine resulted in a decrease of extracellular 13N-glutamine accompanied by an increase of 13N-ammonia as compared with control. Fluorocitrate, a selective inhibitor of glial metabolism, also decreased 13N-glutamine production and increased unmetabolized 13N-ammonia. In contrast, 13N-glutamine was increased with 5 mmol/kg of ammonium acetate without significant changes in 13N-ammonia as compared with control. These results suggest that the concentration of extracellular 13N-glutamine strongly reflects the biological changes in the metabolic activity of astroglial cells.

Uncoupling of flow and metabolism by chloral hydrate: a rat in-vivo autoradiographic study.

General anesthesia is commonly used in experiments; however, its effects on cerebral circulation remain unknown. We measured cerebral blood flow using N-isopropyl[methyl 1,3-14C] p-iodoamphetamine (14C-IMP) and glucose utilization using 2-[1-14C] deoxy-D-glucose during general anesthesia with pentobarbital and chloral hydrate as well as conscious controls using rats and in-vivo autoradiography. Although a substantial reduction in 14C-IMP uptake was seen in the pentobarbital group, there was a significant increase in the chloral hydrate group. The ratio of cerebral blood flow against cerebral glucose utilization was 0.58 over all regions in the pentobarbital group, similar to the value for the controls, whereas this value was significantly high (over 1.5) in the chloral hydrate group. This decoupling effect should be considered when extrapolating experimental study data to normal physiology.

De-coupling of blood flow and metabolism in the rat brain induced by glutamate.

OBJECTIVE: Glutamate plays an essential role in neuronal cell death in many neurological disorders. In this study, we examined both glucose metabolism and cerebral blood flow in the same rat following infusion of glutamate or ibotenic acid using the dual-tracer technique. The effects of MK-801, an NMDA receptor antagonist, and NBQX, an AMPA-kainate receptor antagonist, on the changes in the glucose metabolism and cerebral blood flow induced by glutamate were also examined. METHODS: The rats were microinjected with glutamate (1 micromol/microl, 2 microl) or ibotenic acid (10 microg/microl, 1 microl) into the right striatum, and dual-tracer autoradiograms of [(18)F]FDG and [(14)C]IMP were obtained. MK-801 and NBQX were injected intravenously about 45 and 30 min, respectively, after the infusion of glutamate. RESULTS: De-coupling of blood flow and metabolism was noted in the glutamate-infused hemisphere (as assessed by no alteration of [(18)F]FDG uptake and significant decrease of [(14)C]IMP uptake). Pretreatments with MK-801, NBQX, or combined use of MK-801 and NBQX did not affect the de-coupling of the blood flow and metabolism induced by glutamate. A histochemical study revealed that about 20% neuronal cell death had occurred in the striatum at 105 min after the infusion of glutamate. In addition, a significant increase of the [(18)F]FDG uptake and decrease of [(14)C]IMP uptake were also seen in the rat brain infused with ibotenic acid. CONCLUSION: These results indicate that glutamate and ibotenic acid caused a significant de-coupling of blood flow and glucose metabolism in the intact rat brain during the early phase of neurodegeneration. It is necessary to evaluate the relation between metabotropic glutamate receptors and de-coupling of blood flow and metabolism.

Role of NMDA receptor upon [14C]acetate uptake into intact rat brain.

OBJECTIVE: To clarify the role of N-methyl-D: -aspartate (NMDA) receptors upon [(14)C]acetate uptake in the rodent central nervous system (CNS), ibotenic acid (IBO) was infused into the right striatum of the rat brain. METHODS: Autoradiograms of [(14)C]acetate uptake in the brain for 2 h following the infusion of IBO (10 microg/microl) were obtained in both non-treated and MK-801 (1 mg/kg, i.v.) pretreated rats. The effect of MK-801 on [(14)C]acetate uptake in the normal rat brain was also studied. RESULTS: Infusion of IBO significantly decreased [(14)C]acetate uptake in the infused side of the striatum. The expression of monocarboxylate transporter-1 was not altered, suggesting that the activity of tricarboxylic acid (TCA) cycle in glial cells might be depressed. Pretreatment with MK-801 completely blocked the decreasing effect of IBO on [(14)C]acetate uptake. MK-801 also increased [(14)C]acetate uptake in the whole brain of normal rats. CONCLUSIONS: These results indicate the important roles of NMDA receptors on [(14)C]acetate uptake in the intact rat brain.