| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
1Department of Pharmacology, German Institute of Human Nutrition Potsdam-Rehbruecke, Nuthetal; 2Research Group Neurogenetics, Leibniz-Institute for Neurobiology, Magdeburg; 3Department of Pharmacology and Toxicology, Pharmaceutical Institute of the University of Tübingen; 4Department of Internal Medicine, Division of Endocrinology, Nephrology, Vascular Disease and Clinical Chemistry, University of Tübingen, Tubingen; 5Max Planck Institute for Molecular Genetics, Berlin-Dahlem, Germany; and 6Centre for Genomic Regulation, Barcelona, Spain
Submitted 5 June 2008 ; accepted in final form 2 September 2008
 |
ABSTRACT |
|---|
 TOP ABSTRACT MATERIALS AND METHODSRESULTSDISCUSSIONGRANTSREFERENCES |
|---|
glucose transporter 3; knockout; glucose sensing; food in take; neurons and astrocytes
GLUT3 has been detected by immunohistochemistry and in situ hybridization in pre- and postsynaptic membranes of most brain areas, including hippocampus, cortex, thalamus, hypothalamus, striatum, hypophisis cerebri, corpus amygdaloideum, truncus encephali, cerebellum, and medulla spinalis (5, 16, 24, 32, 33, 38, 41). Some of these regions are involved in learning and memory (4, 35) as well as behavioral traits such as anxiety (10), hyperactivity (3), and exploration (19). In addition, since GLUT3 is also expressed in hypothalamic nuclei, the transporter could be involved in the hypothalamic sensing of glucose and in the regulation of feeding behavior. Other GLUT isotypes, such as GLUT1, -2, -4 and -8 are, if at all, only weakly expressed in hypothalamic cells (2, 25).
The consequences of a reduced transport of glucose across the blood-brain barrier have been intensively studied previously. Heterozygous mutations or hemizygosity of the SLC2A1 (GLUT1) gene in humans causes the GLUT1 deficiency syndrome (GLUT1DS), characterized by infantile seizures, developmental delay, acquired microcephaly, and hypoglycorrhachia (6, 11, 50). Mice with GLUT1 haploinsufficiency exhibit impaired motor activity and coordination, microencephaly, and frequent seizures (51). Thus, on the basis of the assumption that GLUT3 is the predominant carrier of energy substrate into neurons, we anticipated that Slc2a3+/– mice would show a similar syndrome.
Homozygous inactivation of Slc2a3 results in lethality of early postimplanted embryos (14) by apoptosis of ectodermal cells at day 6.5 (Schmidt S, Richter M, Gawlik V, Augustin R, Hommel A, Walther DJ, Montag D, Joost HF, Schürmann A, unpublished observations). More recently, Ganguly and Devaskar (15) reported a moderate, late-onsetting adiposity of male Slc2a3+/– mice, which was associated with a decline in basal metabolic rate and insulin sensitivity. In the present study, we investigated the role of GLUT3 in neuronal function and report a detailed characterization of Slc2a3+/– mice with regard to EEG activity, behavioral parameters, and feeding behavior.
|
MATERIALS AND METHODS |
|---|
|
TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONGRANTSREFERENCES |
|---|
To generate a Slc2a3 knockout mouse, we used the gene trap embryonic stem (ES) cell clone XG611 (Bay Genomics, San Francisco, CA) (48) as previously described (44). After testing the ES cell clone for a single integration event of the gene trap vector in the Slc2a3 gene, ES cells were injected into 129/Ola blastocysts and transferred into pseudopregnant (day 2.5) female mice. Chimerae were mated with C57BL/6J mice. F1 progeny carrying the transgene were backcrossed seven times onto the C57BL/6 background and subsequently intercrossed for characterization of heterozygous animals. Mice were genotyped by PCR with a combination of three primers (forward primer 1: 5'-CCCTGCATTCACCGTTCC-3'; forward primer 2: 5'-GGCATCAGAGCAGATTGTACT-3'; reverse primer: 5'-GATGACTCCAGTGTTGTAGC-3'). The animals were housed in air-conditioned rooms (temperature 20 ± 2°C, relative moisture 50–60%) under a 12:12-h light-dark cycle. They were kept in accordance with the NIH guidelines for the care and use of laboratory animals, and all experiments were approved by the ethics committee of the Ministry of Agriculture, Nutrition and Forestry (State of Brandenburg, Germany).
Western Blot Analysis
Total membranes were prepared as described previously (1). Samples of 10 µg protein/lane were separated by SDS-PAGE and transferred onto nitrocellulose membranes. The membranes were incubated with primary antibodies [1:4,000 goat anti-GLUT3 (M20), Santa Cruz Biotechnology, San Diego, CA; 1:20,000 mouse anti 
-tubulin, clone B-5-12, Sigma-Aldrich, St. Louis, MO; 1:200 rabbit polyclonal anti-monocarboxylate transporter 4 (MCT4; H-90) antiserum, Santa Cruz Biotechnology], washed, incubated again with peroxidase-labeled secondary antibodies (peroxidase-conjugated rabbit and mouse anti-goat IgG, Jackson ImmunoResearch Laboratories, San Diego, CA; peroxidase-conjugated rabbit anti-mouse IgG, Dianova, Hamburg, Germany) and developed by ECL (Amersham Biosciences, Buckinghamshire, UK).
Quantitative Real-Time PCR
Quantitative real-time PCR analysis was performed with the Applied Biosystems 7300 Real-Time PCR System. The PCR mix (25 µl) was composed of TaqMan Universal PCRMaster Mix, NoAmpEraseUNG, and a cDNA corresponding to 25 ng RNA used for cDNA synthesis (each sample in triplicate), and a TaqMan gene expression assay. The TaqMan gene expression assay (Mm00441483_m1) was used to detect the GLUT3 mRNA expression. For the determination of expression of other mRNAs, the following TaqMan gene expression assays were used: GLUT1 (Mm00441473_m1), GLUT2 (Mm00503040_m1); GLUT4 (Mm00436615_m1); GLUT5 (Mm00600311_m1), GLUT8 (Mm00444634_m1), MCT1 (Slc16a1: Mm00436566_m1), MCT2 (Slc16a7: Mm00441442_m1), MCT4 (Slc16a3: Mm00446102_m1), brain-specific glycogen phosphorylase (Pygb: Mm00464080_m1), muscle-specific glycogen phosphorylase (Pygm: Mm00478582_ m1), glycogen synthase 1 (Gys1: Mm00472712_m1), and glycogen synthase 2 (Gys2: Mm00523953_m1). Data were normalized according to Livak and Schmittgen (28), and a β-actin expression assay (Mm00607939_s1; Applied Biosystems) was used as endogenous control.
Electroencephalography Analysis
At least 1 wk before experimentation, litter-matched wild-type and Slc2a3+/– male mice received an implantable telemetry electroencephalography (EEG) transmitter as described (17). At the time of surgery, wild-type mice (n = 9) were 31.0 ± 2.7 wk, Slc2a3+/– (n = 10) were 31.0 ± 2.8 wk old with body weight of 29.6 ± 0.6 g (Slc2a3+/+) and 29.2 ± 1.0 g (Slc2a3+/–), respectively. Briefly, animals were anesthetized with isoflurane (5% induction, 1.5% maintenance) and placed in a stereotaxic head holder. The body of the telemetry transmitter [PhysioTel transmitter TA10EA-F20; Data Sciences International (DSI), Lexington, MA] was implanted subcutaneously, and two EEG lead wires were connected to screws placed epidurally 1 mm anterior to lambda and 1 mm left of the sutura sagittalis for the recording electrode and 1 mm anterior to Bregma and 1 mm right of the sutura coronaria for the reference electrode. Electrodes and screws were then fixed in place with dental acrylic cement, and the scalp was sutured closely around the resulting wound with nonabsorbable 5-0 suture material (Ethilon polyamide, Ethicon, Germany). Proper screw placement was confirmed histologicaly post mortem. Mice were allowed 1 wk of postsurgical recovery before the start of EEG recordings for further analysis. All procedures were conducted in accordance with the local governmental commission for animal research.
EEG telemetry signals were recorded continuously for 14 days processed by a Data Sciences analog converter (Data Exchange Matrix, DSI) and stored digitally using the Dataquest A.R.T. 3.1 software (DSI). EEG activity was sampled at 250 Hz with a filter cut-off of 40 Hz. A video monitoring system was used to record referential EEGs and simultaneous video images showing the behavior of the mouse. Data analysis for EEG measurements was performed as previously described (17). Data are expressed as means ± SE. Differences between groups were analyzed by two-tailed unpaired Student's t-test, P < 0.05 was considered to be statistically significant.
Behavioral Screening
For the behavioral analysis, Slc2a3+/– males and age-matched littermate wild-type males were used. During the light phase, mice were subjected to a series of behavioral tests (35, 36) by an experimenter not aware of the genotype. First, general parameters indicative of the health and neurological state were addressed following the neurobehavioral examination described by Whishaw et al. (53) and the tests of the primary screen of the SHIRPA protocol except startle response (42). Then, the following behavioral parameters were determined in sequential order.
Grip strength. Strength was measured with a high-precision force sensor to evaluate neuromuscular functioning (TSE Systems, Bad Homburg, Germany).
Rotarod performance. Animals received two training sessions (3-h interval) on a rotarod apparatus (TSE) with increasing speed from 4 to 40 rpm for 5 min. After 4 days, mice were tested at 16, 24, 32, and 40 rpm constant speed. The latency to fall off the rod was measured.
Open field. Exploration was assessed by placing mice in the middle of a 50 x 50 cm arena (for 15 min). Using the VideoMot 2 system (TSE) and Wintrack software (54), tracks were analyzed for path length, visits, and relative time spent in the central area (infield, 30 x 30 cm), in the area close to the walls (outfield, 10 x 10 cm) and in the corners, walking speed, latency to move, time moving or resting, and number of stops and rests.
Elevated plus maze. Mice were placed in the center of an elevated plus maze (6.5 x 45 cm arms, 75 cm above floor level, 22 cm high, nontransparent side walls). Their behavior during 5 min was recorded on videotape, and the number of entries into the central part and the closed or open arms was counted, and the time spent in these compartments was determined using the VideoMot 2 system (TSE).
Light-dark avoidance. Anxiety-related behavior was tested by placing mice in a brightly lit compartment (250 lux, 25 x 25 cm) adjacent to a dark compartment (12.5 x 25 cm). The number of transitions between the compartments and the time spent within each were analyzed during 10 min. As a test for long-term memory, animals were placed in the light-dark avoidance box on the last day of testing again. The latency to enter the dark compartment was measured and compared with the latency at the first time in the box.
Morris water maze. Spatial learning was assessed in the hidden platform version of the Morris task. Mice were allowed to swim until they found the platform or until 120 s had elapsed. The animals received 6 trails per day during 5 consecutive days with the platform positioned in the southeast quadrant during the first 3 days (total of 18 trials, acquisition phase), and in the opposite quadrant for the last 2 days (total of 12 trials, reversal phase). Trials 19 and 20 were defined as probe trials to analyze the precision of spatial learning. Trials were analyzed using the VideoMot 2 system and Wintrack software (54).
Two-way active avoidance learning. A two-chambered shuttle box (TSE) was used to assess associative learning. During the conditioning stimulus (CS; 10 s light), the animals had to move to the dark side of the shuttle box to avoid an electrical footshock [unconditioned stimulus (US), 5 s, 0.5 mA pulsed] delivered after the CS. The mice were tested during 5 consecutive days with 80 trials per day, and 5- to 15-s intertrial intervals varied stochastically. Compartment changes during presentation of the CS were counted as conditioned (correct) avoidance reactions and compared between groups.
Acoustic startle response and prepulse inhibition (PPI). A startle stimulus (50 ms, 120 dB) was delivered to the mice in a startle box system (TSE) with or without preceeding prepulse stimulus (30 ms, 100 ms before the startle stimulus) at eight different intensities (73–94 dB, 3-dB increments) on a 70-dB white noise background. After habituation to the box (3 min), two startle trials were followed in pseudo-random order by 10 startle trials and 5 trials at each of the prepulse intensities with stochastically varied intertrial intervals (5–30 s). The maximal startle amplitude was measured by a sensor platform.
Statistical analysis of behavioral data. Behavioral data were analyzed using one-way analysis of variance (1-way ANOVA with genotype as factor) and post hoc with Scheffé's test (Statview Program; SAS Institute, Cary, NC). In addition, for the rotarod, open-field, water maze, two-way active avoidance, and startle/PPI experiments, statistical analysis was performed using repeated-measures ANOVA (with between-subject factor genotype and within-subject factor session). A P value <0.05 was considered significant.
Analysis of Body Composition
Body composition (fat and lean mass) was measured by NMR with a Bruker Minispec instrument (Echo Medical Systems, Houston, TX). Conscious mice were placed in the applied static magnetic field for 0.9 min.
Analysis of Serum Parameters
Blood glucose levels and plasma insulin were analyzed as previously described (8).
Rectal Body Temperature
Rectal body temperature in wild-type and Slc2a3+/– mice was measured with a signal conditioner (ML312 T-type Pod) in combination with a rectal probe for mice (MLT1404; AD Instruments, Spechbach, Germany) when mice were resting. Analysis of the data was performed with the program Chart version 3.4.8.
Locomotor and Running Wheel Activity
Locomotor activity was monitored with an infrared detector (InfraMot-Activity System; TSE, Bad Homburg, Germany) as described previously (21). The voluntary activity was recorded with an automated running wheel system (TSE) as described previously (21). Slc2a3+/+ and Slc2a3+/– mice at the age of 8 wk were adapted for 3 days to type III Macrolon cages or to the running wheels, and data were then collected for 3 days. The animals had free access to the running wheels as well as to food and water. The system recorded each quarter revolution of the wheel, and data were expressed as total number of revolutions per 10 min.
Feeding Behavior
Food intake was recorded with an automated drinking and feeding monitor system (TSE) consisting of Macrolon type III cages equipped with baskets connected to weight sensors. The baskets contained high-fat diet pellets and were freely accessible to the mice. Mice were habituated to the test cages for 4 days before trials, and the measurement period lasted 24 h after a 16-h fasting period. Recorded data were analyzed as food intake per body mass.
ICV Application of 2-Deoxyglucose and D-Glucose
Eighteen- to 22-wk-old Slc2a3+/+ and Slc2a3+/– mice were anesthetized by intraperitoneal injection of ketamine (Albrecht, Aulendorf, Germany)/Rompun (Bayer, Leverkusen, Germany) mixture (1 + 3; 1.5 µl/g body wt). A modified 27-gauge cannula (Braun, Melsungen, Germany) was stereotaxicaly implanted (Ultra Precise Small Animal Stereotaxic Instrument model 963; David Kopf Instruments, Tujunga, CA) into the left lateral cerebral ventricle (positions to Bregma: 0.3 mm posterior, 1 mm lateral, 3 mm ventral). Mice were handled and weighed daily during a 1-wk postsurgical recovery period, and only healthy animals that showed progressive weight gain were used in subsequent experiments. The correct placement of the cannulae was verified by an angiotensin II-stimulated drinking test (50 ng/2 µl; Bachem Biochemica, Heidelberg, germany) prior to each experiment. Only mice with correct implantation were used in the experiments. Pyrogen-free saline (Sigma-Aldrich, Steinheim, Germany) or 400 µg of 2-deoxyglucose or 200 µg or D-glucose in a total volume of 4 µl was injected with a 10-µl Hamilton syringe connected via a polyethylene catheter to the implanted cannula. Feeding behavior was analyzed over a 3-h period.
Test of Food Preference
To compare the food preference of Slc2a3+/+ and Slc2a3+/– mice, 3-wk-old mice were housed singly and had access to two different diets, a carbohydrate-protein and a fat-protein diet, for 34 days. Food intake was recorded every second day. The carbohydrate-protein diet contained 45.3% (wt/wt) starch, 22.7% sucrose, 20% casein, 5% microcellulose, 5% mineral mix (Altromin, Lage, Germany), and 2% vitamin mix (Altromin). The fat-protein dietcontained 33.5% lard, 33.5% coconut oil, 0.5% safflower oil, 0.5% linseed oil, 20% casein, 5% microcellulose, 5% mineral mix, and 2% vitamine mix.
Isolation and Culture of Astrocytes
Brains from newborn Slc2a3+/+ and Slc2a3+/– mice were isolated and homogenized in DMEM-F12 medium (4.5 g/l glucose) supplemented with 10% fetal calf serum. The homogenate was filtered through an 80-µm nylon mesh, and the supernatant was incubated in 25-cm2 flasks (cells out of one brain per flask) until cells were confluent. Microglia and oligodendrocytes were removed by shaking at 100 rpm for 16 h, followed by a medium change. Two days later, Ara-C (20 nM final concentration) was added for 48 h, and astrocytes were seeded in six-well plates for the final experiments.
Determination of 2-Deoxyglucose Uptake and Lactate Production in Isolated Astrocytes
Astrocytes were serum and glucose deprived for 3 h in 2 ml of Krebs-Ringer-HEPES (KRH) buffer and incubated with a mixture of [3H]deoxyglucose (PerkinElmer, Wellesley, MA) and 400 nM unlabeled deoxyglucose and 0.1 mM D-glucose (Sigma Taufkirchen, Germany) for 5 min. Plates were washed with ice-cold KRH buffer, and cells were lysed using 1% Triton. Radioactivity was determined by liquid scintillation counting (18). Lactate concentration in the medium was measured 2 days after seeding with the Avia 1650 Clin Chem Analyzer (Siemens Healthcare Diagnostics, Fernwald, Germany) and normalized to the protein concentration as determined by Bradford assay.
|
RESULTS |
|---|
|
TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONGRANTSREFERENCES |
|---|
Slc2a3+/– mice were generated by mating of C57BL/6J-Slc2a3+/– mice (backcross N7), and were distinguished from wild-type littermates by PCR with a combination of three primers generating a 700-bp fragment for the knockout allele and a 500-bp fragment for the wild-type allele (Fig. 1). Slc2a3+/– mice were viable with normal growth and did not display apparent abnormalities. GLUT3 mRNA levels were decreased by 
50% in brain and testis of Slc2a3+/– males (Fig. 2A), corresponding to an 50% reduction of GLUT3 protein levels (Fig. 2B). No compensatory upregulation of GLUT1, GLUT2, GLUT4, or GLUT8 was observed by quantitative real-time PCR experiments in brain of Slc2a3+/– animals (Fig. 3A). Normalizing expression of different glucose transporters to GLUT1 demonstrated that GLUT3 is the most abundant mRNA in brain of Slc2a3+/+ males: expression of GLUT1 was 20% lower than that of GLUT3, expression of GLUT4 and GLUT8 was 10% of that of GLUT1, whereas GLUT2 expression was almost undetectable (Fig. 3A). Similarly, quantitative real-time PCR experiments indicated that GLUT3 is the most abundant glucose transporter isoform in testis and that no other glucose transporters were upregulated in compensation for the disruption of Slc2a3 (Fig. 3B).
|
|
|
The electrographic features of the GLUT3 heterozygous disruption were examined by EEG recordings of freely moving mice, performed continuously 24 h a day for 14 days with simultaneous infrared video monitoring to monitor behavior. The long-term EEG recordings also allowed us to examine whether the heterozygous disruption of GLUT3 (Slc2a3+/–) caused epileptic seizures under basal conditions. Visual inspection and automated analysis of the EEG recordings revealed no paroxysmal EEG activity (e.g., single spikes and low-frequency high-amplitude sharp waves) or epileptic seizures in Slc2a3+/– mice. To quantify differences in cortical rhythmic activity, we determined the power spectra of the EEG for 12-h daylight and 12-h darkness periods. Figure 4 depicts the baseline EEG power for the different frequency bands computed in consecutive 2-s epochs for a 24-h time course over a 14-day interval. The data showed an increase of cerebrocortical activity in Slc2a3+/– mice (n = 10) compared with the corresponding wild-type controls (n = 9). Absolute EEG power densities measured by delta (0.5–4 Hz), theta (4–8 Hz), alpha (8–12 Hz), beta (12–30 Hz) and gamma (30–100 Hz) frequency bands were slightly but significantly enhanced in the basal state in Slc2a3+/– mice.
|
Assessment of the general state, gross sensory functions, reflexes, and motor abilities based on grip strength and rotarod tests (Table 1) did not reveal significant differences between adult wild-type and Slc2a3+/– littermates. Slc2a3+/– males placed for 15 min in the open field (50 x 50 cm) spent approximately the same time in the central area of the maze during the entire test time compared with control animals (Table 1). In addition, no change in time spent in the outfield or corner was observed (Table 1). In the shuttle box paradigm, Slc2a3+/– mice learned the active-avoidance task. No significant alterations in the number of conditioned avoidance reactions were detected on all test days (Table 1).
|
|
Body Weight Development and Feeding Behavior of Slc2a3+/– Mice
Figure 6, A and B, illustrates the body weight development in heterozygous male mice fed the standard diet (SD; containing 15% of total calories from fat) and the high-fat diet (HFD; containing 60% of total calories from fat). Until the age of 12 wk, both genotypes showed a progressive body weight gain with no differences in body weight or body fat content (Supplementary Fig. 1) on both SD (Fig. 6A) and a HFD (Fig. 6B). In addition, no differences in plasma glucose or insulin levels were observed (Fig. 6, C and D, and Supplementary Fig. 2). Furthermore, no differences in triglyceride, free fatty acid, and cholesterol concentrations were observed between wild-type and Slc2a3+/– mice (Table 2).
|
|
|
|
|
|
DISCUSSION |
|---|
|
TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONGRANTSREFERENCES |
|---|
The moderate phenotype of Slc2a3+/– mice is in striking contrast to that of the heterozygous disruption of the blood-brain barrier glucose transporter GLUT1 in Slc2a1+/– mice. In these mice, reduction of GLUT1 expression by 33% produced microencephaly, impaired motor activity, cerebral ataxia, and multiple spontaneous cortical seizures as detected by EEG (51). Therefore, the phenotype of Slc2a1+/– mice closely resembled human GLUT1 deficiency syndrome (GLUT1DS, OMIM 606777
[OMIM]
), which is an autosomal-dominant disorder characterized by infantile seizures, developmental delay, acquired microcephaly, ataxia, and spasticity (6, 11, 23, 50).
This striking difference in the phenotypes of Slc2a3+/– and Slc2a1+/– mice may indicate that the glucose transport capacity of GLUT3 in neurons is redundant and that the intracellular glucose metabolism is normal even when 50% of GLUT3 protein is lost. Indeed, glucose transport activity in isolated astrocytes of Slc2a3+/– was not different from that of Slc2a3+/+ mice (Fig. 9C), consistent with the conclusion that a single allele of Slc2a3 is sufficient to maintain substrate supply in the brain.
The possibility has to be considered that the reduction in GLUT3 protein is compensated for by a different transporter isotype. However, we failed to detect a compensatory upregulation of one of the other GLUTs known to be expressed in brain. A reduction in neuronal glucose transport could be compensated for by an alternative substrate such as lactate. Contrary to traditional belief, previous experimental evidence has suggested that most neurons in the brain do not need glucose as their sole source of energy but may utilize lactate (29, 30, 31). According to this scenario, astrocytes take up glucose via GLUT1, convert the sugar to lactate, and release the lactate via MCTs into the extracellular space (46), from which it is transported into neuronal cells. However, we did not observe an elevation in lactate production in astrocytes of Slc2a3+/– mice or an upregulation of MCT expression (Fig. 9, A and B). Another compensatory mechanism to maintain neuronal glucose metabolism in mice with a partial ablation of GLUT3 could occur via the upregulation of enzymes such as hexokinase. Thereby, the efficiency of energy production from a small amount of glucose supplied to the brain of Slc2a3+/– mice would be elevated, as was demonstrated in the muscle of Slc2a4+/– and Slc2a4–/– mice (12, 13).
The acoustic startle response and PPI are considered markers of schizophrenia-like alterations. Thus, the findings are consistent with a previous suggestion by McDermott and deSilvia (34) that deficits in neuronal glucose transporters might result in intracellular hypoglycemia of neurons and astrocytes and thereby produce symptoms of schizophrenia. However, other schizophrenia-related mouse traits, such as alterations in locomotor activity, learning, and memory, were not observed in Slc2a3+/– mice.
Glucose is also believed to be a signaling molecule in specialized hypothalamic neurons. Glucose-sensing neurons alter their membrane potential and firing rate as a function of the ambient glucose concentration and contribute to the regulation of hunger and satiety. Under hypoglycemic conditions, glucose-inhibited neurons are activated, whereas glucose-excited neurons are inactivated (22, 26, 46). Contrary to our expectation, heterozygous Slc2a3 mice did not show any changes in food intake or body weight development. Furthermore, icv application of 2-deoxyglucose increased food intake and application of D-glucose suppressed refeeding to the same extend in Slc2a3+/– mice as in wild-type littermates (Fig. 7D). Therefore, glucose sensing is fully normal when GLUT3 expression is reduced by 50%.
Recently, Ganguly and Devaskar (15) described late-onsetting adiposity in Slc2a3+/– males starting at the age of 9–11 months. Consistent with our results, no difference in body weight was observed at earlier time points. It is unlikely that the late-onsetting obesity is due to an altered hypothalamic glucose sensing; such a mechanism should produce differences in body weight at earlier time points. Rather, the authors speculate that limited fetal glucose supply in the Slc2a3+/– mice is responsible for a late-onsetting reduction in basal metabolic rate and obesity (15).
In summary, our data indicate that, in contrast to Slc2a1, a single allele of Slc2a3 is sufficient for maintenance of neuronal energy supply, motor abilities, learning and memory, and feeding behavior.
|
GRANTS |
|---|
|
TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONGRANTSREFERENCES |
|---|
|
ACKNOWLEDGMENTS |
|---|
|
FOOTNOTES |
|---|
The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
* S. Schmidt and M. Richter contributed equally to this work. 
|
REFERENCES |
|---|
|
TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONGRANTSREFERENCES |
|---|
CT) method. Methods 25: 402–440, 2001.[CrossRef][Web of Science][Medline]This article has been cited by other articles:
|
|
 |
|
  P. J Magistretti Role of glutamate in neuron-glia metabolic coupling Am. J. Clinical Nutrition, September 1, 2009; 90(3): 875S - 880S. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| Visit Other APS Journals Online |
