PubMed Health⌕ Search

Biomedical subjects

P J Magistretti

Publications and source records attributed to P J Magistretti.

At least 19 recordsLinked to original sources
PubMed2006

Glucose and lactate are equally effective in energizing activity-dependent synaptic vesicle turnover in purified cortical neurons.

This study examines the role of glucose and lactate as energy substrates to sustain synaptic vesicle cycling. Synaptic vesicle turnover was assessed in a quantitative manner by fluorescence microscopy in primary cultures of mouse cortical neurons. An electrode-equipped perfusion chamber was used to stimulate cells both by electrical field and potassium depolarization during image acquisition. An image analysis procedure was elaborated to select in an unbiased manner synaptic boutons loaded with the fluorescent dye N-(3-triethylammoniumpropyl)-4-(4-(dibutylamino)styryl)pyridinium dibromide (FM1-43). Whereas a minority of the sites fully released their dye content following electrical stimulation, others needed subsequent K(+) depolarization to achieve full release. This functional heterogeneity was not significantly altered by the nature of metabolic substrates. Repetitive stimulation sequences of FM1-43 uptake and release were then performed in the absence of any metabolic substrate and showed that the number of active sites dramatically decreased after the first cycle of loading/unloading. The presence of 1 mM glucose or lactate was sufficient to sustain synaptic vesicle cycling under these conditions. Moreover, both substrates were equivalent for recovery of function after a phase of decreased metabolic substrate availability. Thus, lactate appears to be equivalent to glucose for sustaining synaptic vesicle turnover in cultured cortical neurons during activity.

Animals↗
PubMed2004

Relationship between L-glutamate-regulated intracellular Na+ dynamics and ATP hydrolysis in astrocytes.

Glutamate uptake into astrocytes and the resulting increase in intracellular Na+ (Na+(i)) have been identified as a key signal coupling excitatory neuronal activity to increased glucose utilization. Arguments based mostly on mathematical modeling led to the conclusion that physiological concentrations of glutamate more than double astrocytic Na+/K+-ATPase activity, which should proportionally increase its ATP hydrolysis rate. This hypothesis was tested in the present study by fluorescence monitoring of free Mg2+ (Mg2+(i)), a parameter that inversely correlates with ATP levels. Glutamate application measurably increased Mg2+(i) (i.e. decreased ATP), which was reversible after glutamate washout. Na+(i) and ATP changes were then directly compared by simultaneous Na+(i) and Mg2+ imaging. Glutamate increased both parameters with different rates and blocking the Na+/K+-ATPase during the glutamate-evoked Na+(i) response, resulted in a drop of Mg2+(i) levels (i.e. increased ATP). Taken together, this study demonstrates the tight correlation between glutamate transport, Na+ homeostasis and ATP levels in astrocytes.

Adenosine Triphosphate↗
PubMed2004

Early acquisition of typical metabolic features upon differentiation of mouse neural stem cells into astrocytes.

Specific metabolic features, such as glutamate reuptake, have been associated with normal functions of mature astrocytes. In this study, we examined whether these characteristics are acquired together with classical phenotypic markers of differentiated astrocytes. Differentiation of E14 mouse neurospheres into astrocytes was induced by the addition of fetal bovine serum (FBS). Degree of differentiation was assessed by reverse transcription-polymerase chain reaction (RT-PCR) and immunofluorescence for both GFAP and nestin. Neural stem cells expressed nestin but not GFAP, while differentiated astrocytes were immunopositive for GFAP but displayed low levels of nestin expression. A strong increase in the expression of the glutamate transporter GLAST and the monocarboxylate transporter MCT1 accompanied phenotypic changes. In addition, active glutamate transport appeared in differentiated astrocytes, as well as their capacity to increase aerobic glycolysis in response to glutamate. Leukemia inhibitory factor (LIF) and ciliary neurotrophic factor, but not interleukin-6, triggered the expression of phenotypic and morphological characteristics of astrocytes. In addition, exposure to LIF led to the appearance of metabolic features typically associated with astrocytes. Altogether, our results show that acquisition of some specific metabolic features by astrocytes occurs early in their differentiation process and that LIF represents a candidate signal to induce their expression.

Animals↗
PubMed2004

Distribution of Aquaporin 9 in the adult rat brain: preferential expression in catecholaminergic neurons and in glial cells.

Aquaporin 9 (AQP9) is a recently cloned water channel that is permeable to monocarboxylate, glycerol and urea. In rat, AQP9 has been found in testis and liver as well as in brain where its expression has been initially shown in glial cells in forebrain. However, the expression of AQP9 has not been investigated in the brainstem. The purpose of this study is to describe the distribution of AQP9-immunoreactive cells throughout the adult rat brain using reverse transcriptase-polymerase chain reaction (RT-PCR), Western blot and immunohistochemistry. We performed immunolabeling on brain from animals perfused with fixative and we show that AQP9 is expressed (i) in astrocytes in the glia limitans, in the white matter and in glial cells of the cerebellum, (ii) in the endothelial cells of pial vessels, and (iii) in specific groups of neurons. The neuronal AQP9 expression was almost exclusively observed in catecholaminergic cells including the adrenergic, noradrenergic and dopaminergic groups, but not in other monoaminergic neurons such as serotonergic or histaminergic cells. A slight labeling was also observed in non-catecholaminergic neurons localized in the paraventricular nucleus of the hypothalamus. These results indicate that AQP9 has a unique brain distribution with a preferential localization in catecholaminergic nuclei known to be involved in many cerebral functions. While the presence of AQP9 in glia limitans and in endothelial cells of the pial vessels could be related to water transport through the blood-brain barrier, its expression in neuronal cells, not directly involved in the osmoregulation, suggests that brain AQP9 could also be used as a metabolite channel since lactate and glycerol can be energy substrates for neurons.

Animals↗
PubMed2003

Aquaporin 1 and aquaporin 4 expression in human brain after subarachnoid hemorrhage and in peritumoral tissue.

Aquaporins (AQPs) are a protein family of water channels which facilitate the water flux through the plasmatic membranes. The expression of AQPs has been described in rat brain by several studies. Despite recent reports that have shown an over-expression of AQP1 and 4 in human tumoral cells, little is known about AQP expression in human brain. The purpose of this study was to investigate the expression of AQP1 and AQP4 in human brain after subarachnoid hemorrhage (SAH) and in peritumoral tissue by western blot and immunohistochemistry. The results showed a marked increase of the expression of AQP1 and AQP4. This over-expression occurred on the astrocytic processes and polarization on astrocytic end-feet was lost. No expression was observed on neuronal cells. This study is the first demonstration of the induction of AQP1 and AQP4 on reactive astrocytes in an acute brain injury, such as SAH. These results reinforce the hypothesis that AQPs may be involved in the dynamics of brain edema formation or resolution. Further studies are needed to understand their functional role.

Aquaporin 1↗
PubMed2003

Patterns of calcium-binding proteins in human inferior colliculus: identification of subdivisions and evidence for putative parallel systems.

The subdivisions of human inferior colliculus are currently based on Golgi and Nissl-stained preparations. We have investigated the distribution of calcium-binding protein immunoreactivity in the human inferior colliculus and found complementary or mutually exclusive localisations of parvalbumin versus calbindin D-28k and calretinin staining. The central nucleus of the inferior colliculus but not the surrounding regions contained parvalbumin-positive neuronal somata and fibres. Calbindin-positive neurons and fibres were concentrated in the dorsal aspect of the central nucleus and in structures surrounding it: the dorsal cortex, the lateral lemniscus, the ventrolateral nucleus, and the intercollicular region. In the dorsal cortex, labelling of calbindin and calretinin revealed four distinct layers.Thus, calcium-binding protein reactivity reveals in the human inferior colliculus distinct neuronal populations that are anatomically segregated. The different calcium-binding protein-defined subdivisions may belong to parallel auditory pathways that were previously demonstrated in non-human primates, and they may constitute a first indication of parallel processing in human subcortical auditory structures.

Adult↗
PubMed2002

Evidence for a susceptibility gene for anorexia nervosa on chromosome 1.

Eating disorders, such as anorexia nervosa (AN), have a significant genetic component. In the current study, a genomewide linkage analysis of 192 families with at least one affected relative pair with AN and related eating disorders, including bulimia nervosa, was performed, resulting in only modest evidence for linkage, with the highest nonparametric linkage (NPL) score, 1.80, at marker D4S2367 on chromosome 4. Since the reduction of sample heterogeneity would increase power to detect linkage, we performed linkage analysis in a subset (n=37) of families in which at least two affected relatives had diagnoses of restricting AN, a clinically defined subtype of AN characterized by severe limitation of food intake without the presence of binge-eating or purging behavior. When we limited the linkage analysis to this clinically more homogeneous subgroup, the highest multipoint NPL score observed was 3.03, at marker D1S3721 on chromosome 1p. The genotyping of additional markers in this region led to a peak multipoint NPL score of 3.45, thereby providing suggestive evidence for the presence of an AN-susceptibility locus on chromosome 1p.

Adult↗
PubMed2002

Similar perisynaptic glial localization for the Na+,K+-ATPase alpha 2 subunit and the glutamate transporters GLAST and GLT-1 in the rat somatosensory cortex.

Several isoenzymes of the Na(+),K(+)-ATPase are expressed in brain but their specific roles are poorly understood. Recently, it was suggested that an isoenzyme of the Na(+),K(+)-ATPase containing the alpha(2) subunit, together with the glutamate transporters GLAST and GLT-1, participate in a coupling mechanism between neuronal activity and energy metabolism taking place in astrocytes. To substantiate this hypothesis, we compared the distribution of alpha(2), GLAST and/or GLT-1 in the rat cerebral cortex using double immunofluorescence and confocal microscopy, and immunocytochemistry at the electron microscopic level. We also investigated the relationship between alpha(2), GLAST or GLT-1 and asymmetrical synaptic junctions (largely glutamatergic) and GABAergic nerve terminals. Results show that the alpha(2) subunit has an exclusive astroglial localization, and that it is almost completely co-distributed with GLAST and GLT-1 when evaluated by confocal microscopy. This similar distribution was confirmed at the ultrastructural level, which further showed that the vast majority of the alpha(2) staining (73% of all labelled elements), like that of GLAST and GLT-1, was located in glial leaflets surrounding dendritic spines and the dendritic and/or axonal elements of asymmetrical (glutamatergic) axo-dendritic synapses. Synapses ensheathed by alpha(2), GLAST or GLT-1 virtually never included (<or=2%) GABAergic nerve terminals or synaptic junctions. However, a subset of GABAergic nerve terminals (10-14%) were directly apposed to asymmetrical axo-dendritic junctions surrounded by alpha(2), GLAST or GLT-1. Altogether these results demonstrate that alpha(2), GLAST and GLT-1 have comparable perisynaptic distribution within cortical astrocytes most likely associated with glutamatergic synapses.

Amino Acid Transport System X-AG↗
PubMed2001

Effects of glial glutamate transporter inhibitors on intracellular Na+ in mouse astrocytes.

The effects of inhibitors of the glial Na+/glutamate co-transporter on the intracellular Na+ concentration ([Na+](i)) were investigated in mouse cortical astrocytes. [Na+](i) was monitored by fluorescence microscopy on single astrocytes using the Na+-sensitive probe sodium-binding benzofuran isophtalate. Application of the competitive inhibitors threo-beta-hydroxyaspartate (THA) and trans-pyrrolidine-2,4-dicarboxylic acid (t-PDC) resulted in robust and reversible increases in [Na+](i) that were comparable in shape to the response to glutamate but about twice lower in amplitude. As previously observed with glutamate, the amplitude of the [Na+](i) response to these compounds was concentration-dependent with EC(50) values of 11.1 microM (THA) and 7.6 microM (t-PDC), as was the initial rate of [Na+](i) rise (EC(50) values of 14.8 microM for THA and 11.5 microM for t-PDC). Both compounds diminished the response to subsequent glutamate applications, possibly because of an inhibitory effect of the intracellularly-accumulated compounds. In comparison, the newly-developed compound threo-beta-benzyloxyaspartate (TBOA) alone did not cause any significant alteration of [Na+](i) up to a concentration of 500 microM . TBOA inhibited the [Na+](i) response evoked by 200 microM glutamate in a concentration-dependent manner with IC(50) values of 114 and 63 microM, as measured on the amplitude and the initial rate, respectively. The maximum inhibition of glutamate-evoked [Na+](i) increase by TBOA was approximately 70%. The residual response persisted in the presence of a non-NMDA receptor antagonist or the inhibitor of the GLT-1 glutamate transporters, dihydrokainate (DHK). In view of the complete reversibility of its effects, TBOA represents a very useful pharmacological tool for studies of glutamate transporters.

ATP-Binding Cassette Transporters↗
PubMed2001

Brain energy metabolism in Alzheimer's disease: 99mTc-HMPAO SPECT imaging during verbal fluency and role of astrocytes in the cellular mechanism of 99mTc-HMPAO retention.

The central hypothesis of the study which has been carried out as part of the NRP38 program, is that perturbations of brain energy metabolism are critically involved in the neurodegeneration occurring in Alzheimer's disease (AD) and that they may correlate with early cognitive dysfunctioning. In the present multidisciplinary study we set out to monitor brain energy metabolism using FDG-PET and HMPAO-SPECT imaging in a cohort of individuals over 65 years of age, drawn from the general population. HMPAO-SPECT imaging, which is a simpler and more widely accessible imaging procedure than FDG-PET, was performed under basal conditions and during the performance of a cognitive task (verbal fluency test). Three groups were studied. Two groups (groups I and II) included individuals age 65 or more, with no cognitive impairment and carrying an APOE4 positive or APOE4 negative phenotype, respectively; a third group (group III) included patients with clinical signs of AD. Each subject entering the study underwent an FDG-PET, an HMPAO-SPECT and an extensive battery of neuropsychological tests which assess various aspects of cognitive functioning, with a strong emphasis on working memory, divided attention and executive functions. A total of 101 participants were submitted to brain imaging and neuropsychological testing. Among these, 60 participants received the same set of imaging and neuropsychological tasks 24-36 months after the first set (phase II). In this article, we present a preliminary analysis performed on ten subjects from groups I and II and nine subjects from group III: activation (verbal fluency task) induced a specific pattern of increase in HMPAO retention (including BA 9/10, BA 18 bilaterally and right BA 17). In contrast to controls, in nine AD subjects no significant differences in HMPAO retention were observed when comparing activation and basal conditions. The cellular and molecular mechanisms that underlie the retention of HMPAO, the tracer used for single photon emission computed tomography (SPECT) imaging, has been studied in vitro in purified preparations of neurons and astrocytes with the aim of investigating the contribution of different cell types to hexamethyl-propyleneamineoxime labeled with technetium-99m (99mTc-HMPAO) retention in vitro. Results show that 99mTc-HMPAO retention predominates in astrocytes over neurons by a factor of approximately 2.5. Diethyl maleate, ethacrynic acid and buthionine sulfoximine, three agents which significantly reduce glutathione levels, also decreased 99mTc-HMPAO retention in both astrocytes and in neurons. Decrease did not always correlate with glutathione levels however, thus suggesting that other factors could be involved. The data presented indicate that astrocytes might constitute a prominent site of 99mTc-HMPAO retention and most likely contribute significantly to the SPECT signal. In addition, they also suggest that specific alterations in glial cell metabolism could explain flow-independent changes in 99mTc-HMPAO retention in the brain as observed by SPECT in certain pathologies (including Alzheimer's disease). In particular, these observations suggest a key role of astrocytes in the signal detected with the imaging procedure, which is altered in the Alzheimer's cohort subjected to the verbal fluency activation task.

Aged↗
PubMed2001

Astrocytes as a predominant cellular site of (99m)Tc-HMPAO retention.

Technetium-99m-d,l-hexamethylpropylene amine oxime ((99m)Tc-HMPAO) retention in the brain monitored by single photon emission computed tomography (SPECT) is currently used as a marker of cerebral blood flow. The purported mechanism by which (99m)Tc-HMPAO accumulates in the brain is through its intracellular conversion from a lipophilic form to more hydrophilic derivatives within the brain parenchyma. The issue of the contribution of different cell types on (99m)Tc-HMPAO retention was investigated in vitro by studying the accumulation of (99m)Tc-HMPAO in primary cultures of mouse cortical astrocytes and neurons. Results show that (99m)Tc-HMPAO retention predominates in astrocytes over neurons by a factor of approximately 2.5 (0.26 +/- 0.05 vs. 0.095 +/- 0.042 fmol/mg protein after 120 minutes, respectively). Diethyl maleate (60 micromol/L), ethacrynic acid (1 mmol/L) and buthionine sulfoximine (1 mmol/L), 3 agents which significantly reduced glutathione levels also decreased (99m)Tc-HMPAO retention in both astrocytes (29%, 3%, and 46% of control, respectively) and neurons (69%, 11% and 63% of control). Decrease did not always correlate with glutathione levels, however, which suggests that other factors could be involved. The possibility that cell energy status determines (99m)Tc-HMPAO retention was also assessed. Agents that activate (glutamate, azide) or inhibit (cytochalasin B) glucose utilization in astrocytes, as measured by the (3)H-2-deoxyglucose method, were without effect on (99m)Tc-HMPAO retention. In conclusion, the data presented indicate that astrocytes may constitute a prominent site of (99m)Tc-HMPAO retention and most likely contribute significantly to the SPECT signal. In addition, the data also suggest that specific alterations in glial cell metabolism could explain flow-independent changes in (99m)Tc-HMPAO retention in the brain as observed by SPECT in some pathologies.

Animals↗
PubMed2001

Astrocyte-specific expression of aquaporin-9 in mouse brain is increased after transient focal cerebral ischemia.

Aquaporin-9 (AQP9) is a new member of the aquaporin family of water-selective channels mainly expressed in liver and testis, presenting the characteristic of also being permeable to various solutes, particularly lactate. Recent data have shown the presence of AQP9 on tanycytes in the rat brain. In the current study, the authors show the expression of AQP9 in astrocytes in the mouse brain and changes in its expression after cerebral ischemia. Indeed, in control mouse, the AQP9 immunolabeling is present on astrocytic processes bordering the subarachnoid space and ventricles. The labeling also is observed on astrocytes in the white matter, hippocampus, hypothalamus, and lateral septum. After focal transient ischemia, an increase of the immunolabeling is detected on astrocytes in periinfarct areas. This AQP9 distribution study in mouse brain suggests a role of AQP9 in water homeostasis in the central nervous system. Furthermore, the overexpression of AQP9 on astrocytes surrounding an ischemic lesion suggests that AQP9 may also play a role in the regulation of postischemia edema and, in view of its permeability to monocarboxylates, in the clearance of lactate from the ischemic focus.

Animals↗
PubMed2001

Insights into the mechanisms of ifosfamide encephalopathy: drug metabolites have agonistic effects on alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainate receptors and induce cellular acidification in mouse cortical neurons.

Therapeutic value of the alkylating agent ifosfamide has been limited by major side effects including encephalopathy. Although the underlying biochemical processes of the neurotoxic side effects are still unclear, they could be attributed to metabolites rather than to ifosfamide itself. In the present study, the effects of selected ifosfamide metabolites on indices of neuronal activity have been investigated, in particular for S-carboxymethylcysteine (SCMC) and thiodiglycolic acid (TDGA). Because of structural similarities of SCMC with glutamate, the Ca(2+)(i) response of single mouse cortical neurons to SCMC and TDGA was investigated. SCMC, but not TDGA, evoked a robust increase in Ca(2+)(i) concentration that could be abolished by the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), but only partly diminished by the N-methyl-D-aspartate receptor antagonist 10,11-dihydro-5-methyl-5H-dibenzo[a,d]cyclohepten-5,10-imine (MK=801). Cyclothiazide (CYZ), used to prevent AMPA/kainate receptor desensitization, potentiated the response to SCMC. Because activation of AMPA/kainate receptors is known to induce proton influx, the intracellular pH (pH(i)) response to SCMC was investigated. SCMC caused a concentration-dependent acidification that was amplified by CYZ. Since H(+)/monocarboxylate transporter (MCT) activity leads to similar cellular acidification, we tested its potential involvement in the pH(i) response. Application of the lactate transport inhibitor quercetin diminished the pH(i) response to SCMC and TDGA by 43 and 51%, respectively, indicating that these compounds may be substrates of MCTs. Taken together, this study indicates that hitherto apparently inert ifosfamide metabolites, in particular SCMC, activate AMPA/kainate receptors and induce cellular acidification. Both processes could provide the biochemical basis of the observed ifosfamide-associated encephalopathy.

Animals↗
PubMed2000

Pro-inflammatory cytokines induce the transcription factors C/EBPbeta and C/EBPdelta in astrocytes.

The transcription factors CCAAT/enhancer binding protein (C/EBP)-beta and -delta are key regulators for the expression of the acute phase genes in the liver, such as complement component C3 and antichymotrypsin. In the brain, these acute phase proteins are produced in response to pro-inflammatory cytokines by the reactive astrocytes, in particular those surrounding the amyloid plaques of Alzheimer's disease brains. Here we show that lipopolysaccharides (LPS), IL-1beta, and TNFalpha induce the expression of the c/ebpbeta and -delta genes in mouse primary astrocytes. This induction precedes the expression of the acute phase genes coding for the complement component C3 and the mouse homologue of antichymotrypsin. The induction of these two acute phase genes by LPS is blocked by cycloheximide, whereas this protein synthesis inhibitor does not affect the expression of the c/ebp genes. Altogether, our data support a role as immediate-early genes for c/ebpbeta and -delta, whose expression is induced by pro-inflammatory cytokines in mouse cortical astrocytes. In the liver, these transcription factors are known to play an important role in inflammation and energy metabolism regulation. Therefore, C/EBPbeta and -delta could be pivotal transcription factors involved in brain inflammation, in addition to their previously demonstrated role in brain glycogen metabolism regulation (Cardinaux and Magistretti. J Neurosci 16:919-929, 1996).

Animals↗