Biomedical subjects

Angélique Bordey

Publications and source records attributed to Angélique Bordey.

8 recordsLinked to original sources

PubMed2006

Adult neurogenesis: basic concepts of signaling.

Findings over the past decades demonstrating persistent neurogenesis in the adult brain have challenged the view of a fixed circuitry in normally functioning brain and raised hopes for self-renewal following brain injury. In addition to providing insights for repair, studying adult neurogenesis may improve our understanding of embryonic development assuming that fundamental mechanisms are similar. It is argued here, using examples of cell:cell communication, that parallels can be drawn between adult and embryonic neurogenesis. Paradoxically, cell:cell communication in neurogenic regions resembles that in a mature neuroglial network. This suggests that differences in the integrative properties of cells and the extracellular matrix molecules may constitute a neurogenic environment or "niche". While reasons for persistent adult neurogenesis in humans remains obscure, recent findings regarding the environmental and activity-driven control of neurogenesis reinforce the original concept of a role for neurogenesis in motor memory formation and refinement of information processing.

Aging↗

PubMed2006

GFAP-expressing cells in the postnatal subventricular zone display a unique glial phenotype intermediate between radial glia and astrocytes.

Neural stem cells in the adult subventricular zone (SVZ) derive from radial glia and express the astroglial marker glial fibrillary acidic protein (GFAP). Thus, they have been termed astrocytes. However, it remains unknown whether these GFAP-expressing cells express the functional features common to astrocytes. Using immunostaining and patch clamp recordings in acute slices from transgenic mice expressing green fluorescent protein (GFP) driven by the promoter of human GFAP, we show that GFAP-expressing cells in the postnatal SVZ display typical glial properties shared by astrocytes and prenatal radial glia such as lack of action potentials, hyperpolarized resting potentials, gap junction coupling, connexin 43 expression, hemichannels, a passive current profile, and functional glutamate transporters. GFAP-expressing cells express both GLAST and GLT-1 glutamate transporters but lack AMPA-type glutamate receptors as reported for dye-coupled astrocytes. However, they lack 100 microM Ba2+-sensitive inwardly rectifying K+ (K(IR)) currents expressed by astrocytes, but display delayed rectifying K+ currents and 1 mM Ba2+-sensitive K+ currents. These currents contribute to K+ transport at rest and maintain hyperpolarized resting potentials. GFAP-expressing cells stained positive for both K(IR)2.1 and K(IR)4.1 channels, two major K(IR) channels in astrocytes. Ependymal cells, which also derive from radial glia and express GFAP, display typical glial properties and K(IR) currents consistent with their postmitotic nature. Our results suggest that GFAP-expressing cells in concert with ependymal cells can perform typical astrocytic functions such as K+ and glutamate buffering in the postnatal SVZ but display a unique set of functional characteristics intermediate between astrocytes and radial glia.

Amino Acid Transport System X-AG↗

PubMed2005

Nonsynaptic GABA signaling in postnatal subventricular zone controls proliferation of GFAP-expressing progenitors.

In the postnatal subventricular zone (SVZ), local cues or signaling molecules released from neuroblasts limit the proliferation of glial fibrillary acidic protein (GFAP)-expressing progenitors thought to be stem cells. However, signals between SVZ cells have not been identified. We show that depolarization of neuroblasts induces nonsynaptic SNARE-independent GABA(A) receptor currents in GFAP-expressing cells, the time course of which depends on GABA uptake in acute mouse slices. We found that GABA(A) receptors are tonically activated in GFAP-expressing cells, consistent with the presence of spontaneous depolarizations in neuroblasts that are sufficient to induce GABA release. These data demonstrate the existence of nonsynaptic GABAergic signaling between neuroblasts and GFAP-expressing cells. Furthermore, we show that GABA(A) receptor activation in GFAP-expressing cells limits their progression through the cell cycle. Thus, as GFAP-expressing cells generate neuroblasts, GABA released from neuroblasts provides a feedback mechanism to control the proliferation of GFAP-expressing progenitors by activating GABA(A) receptors.

Animals↗

PubMed2005

Assays for measuring extracellular GABA levels and cell migration rate in acute slices.

The postnatal subventricular zone (SVZ) contains the largest pool of dividing and migrating neural precursors in the adult rodent brain. Neuronal precursors migrate throughout the SVZ and along the rostral migratory stream (RMS) towards the olfactory bulb where they differentiate into interneurons. To facilitate the investigation of cell migration in the SVZ and RMS, an inexpensive migration assay was developed for use in acute brain slices. Acute sagittal slices were kept at 37 degrees C in 5% O2/95% CO2-saturated solution and migrating cells in the SVZ and RMS were visualized using an upright infrared-differential interference contrast microscope. Time-lapse movies were acquired to identify the direction and measure the speed of cell migration. The neurotransmitter GABA and inhibitors of GABA receptors or transporters can be bath applied to determine the function of endogenous GABA on the direction and speed of cell migration. In parallel, the levels of endogenous GABA released from acute SVZ or RMS explants were measured with mass spectrometry. Additional techniques such as electrophysiology and immunohistochemistry confirmed the identity of cells as neuronal precursors and characterized the expression of GABA receptors and transporters. This report describes how modulations in the direction and speed of neuronal precursor migration can be accurately monitored and how changes in local GABA levels can be measured. The described techniques can be used to identify the endogenous factors that regulate cell migration. Identifying such factors is essential for the future therapeutic use of SVZ cells to replace damaged or lost cells.

Animals↗

PubMed2004

GABA release and uptake regulate neuronal precursor migration in the postnatal subventricular zone.

In the postnatal subventricular zone (SVZ), astrocyte-like cells tightly encapsulate chains of migrating neuronal precursors, although an influence of the astrocyte-like cells on precursor migration has not yet been demonstrated. Cell migration was studied in acute sagittal brain slices to determine whether GABA signaling between astrocyte-like cells and neuronal precursors controls the speed of neuronal precursor migration in the anterior SVZ and rostral migratory stream of juvenile and adult mice. Application of GABA at 10 microm, a nondesensitizing concentration for GABA(A) receptors (GABA(A)Rs), reduced the rate (mean of approximately 50 microm/hr) of cell migration by 21% via GABA(A)R activation. Application of the GABA(A)R antagonist bicuculline enhanced the migration rate by 30%, suggesting that endogenous GABA tonically reduces the speed of cell migration via GABA(A)R activation. Using immunohistochemistry, we found that astrocyte-like cells express the high-affinity GABA transporter subtype GAT4 on processes ensheathing neuronal precursors that contain GABA. Inhibition of GABA uptake into astrocyte-like cells or enhancement of GABA release from neuronal precursors during high K(+) application further reduced the migration rate by increasing ambient GABA levels. GABA altered the migration speed by interfering with intracellular Ca(2+) signaling independently of cell depolarization, because high K(+) application did not alter the speed of cell migration in the presence of bicuculline. These data indicate that astrocyte-like cells create a microenvironment in which their uniquely positioned GABA transporters control the degree of GABA(A)R activation and the migration of neuronal precursors.

Animals↗

PubMed2004

Bergmann glial GlyT1 mediates glycine uptake and release in mouse cerebellar slices.

Glycine is an inhibitory neurotransmitter and is critical for NMDA receptor activation. These roles are dependent on extracellular glycine levels, which are regulated by Na(+)/Cl(-)-dependent glycine transporters (GlyTs) in neurones and glia. The glial GlyT subtype GlyT1 is well located to activate NMDA receptors. However, glial GlyTs have not been studied in an intact system thus far. Whole-cell patch-clamp recordings were obtained from Bergmann glia in mice cerebellar slices to determine whether these glia express functional GlyT1 that can mediate both glycine uptake and efflux. In the presence of a glycine receptor blocker, glycine and a substrate agonist for GlyT1, sarcosine, induced voltage-dependent inward currents that were abolished by removing external Na(+), identifying them as transport currents. Inhibitors of glycine transport through GlyT1 (sarcosine and (N-[3-(4'-fluorophenyl)-3-(4'-phenylphenoxy)propyl]sarcosine (NFPS)) reduced glycine currents by approximately 85%, consistent with positive immunostaining for GlyT1 in Bergmann glia while inhibitors of glycine transport through GlyT2 (4-benzyloxy-3,5-dimethoxy-N-[1-(dimethylaminocyclopently)methyl]benzamide (ORG 25543) and amoxapine) or through systems A and ASC did not affect glycine transport currents. Following internal glycine perfusion during the recording, outward currents progressively developed at -50 mV and external glycine-induced uptake currents were reduced. Using paired recordings of a Bergmann glial cell and a granule cell in the whole cell and outside-out modes, respectively, depolarizations of Bergmann glia to +20 mV induced a 73% increase in the open probability of glycine receptor channels in membrane patches of granule cells. This increase was prevented when NFPS was included in the bath solution. Overall, these results demonstrate for the first time that Bergmann glia express functional GlyT1 that can work in reverse at near-physiological ionic and internal glycine conditions in brain slices. These glial GlyTs can probably mediate glycine efflux under conditions of metabolic impairments like ischaemia.

Amino Acid Transport Systems, Neutral↗

PubMed2004

Glial glutamate transporters limit spillover activation of presynaptic NMDA receptors and influence synaptic inhibition of Purkinje neurons.

Glutamate transporters limit cross talk between excitatory synapses by removing synaptically released glutamate. However, the role of glutamate transporters in limiting the action of synaptically released glutamate at inhibitory synapses remains unknown. Single and paired whole-cell patch-clamp recordings were obtained from Purkinje neurons and Bergmann glia in mouse cerebellar slices to determine the function of neuronal and glial glutamate transporters at GABAergic synapses onto Purkinje neurons. NMDA and inhibition of glutamate transporters with DL-threo-beta-benzyloxyaspartic acid (TBOA) increased the frequency of miniature IPSCs (mIPSCs) by enhancing presynaptic NMDA receptor (NMDAR) activation, whereas inhibition of cystine-glutamate antiporters had no effect on mIPSCs. Selective inhibition of glutamate transporters in an individual Bergmann glial cell enhanced mIPSC frequency recorded in an adjacent Purkinje neuron significantly more than did postsynaptic transporter inhibition. TBOA did not change the frequency of spontaneous IPSCs (sIPSCs) but decreased their amplitude, as well as that of evoked IPSCs (eIPSCs), and enhanced the paired-pulse ratio. The action of NMDAR activation on eIPSCs but not that on mIPSCs was prevented by 100 microm ryanodine. Repetitive stimulations of climbing fibers resulted in a NMDAR-dependent reduction of sIPSC amplitude, and this effect was enhanced by TBOA even when postsynaptic glutamate transporters were blocked. These data indicate that glial glutamate transporters limit glutamate spillover from excitatory to inhibitory synapses and strongly influence synaptic inhibition of Purkinje neurons by controlling NMDAR activation on GABAergic terminals.

Action Potentials↗

PubMed2003

Modulation of glutamatergic transmission by bergmann glial cells in rat cerebellum in situ.

We obtained patch-clamp recordings from neuron-glial cell pairs in cerebellar brain slices to examine the contribution of glutamate (Glu) uptake by Bergmann glial cells to shaping excitatory postsynaptic currents (EPSCs) at the parallel fiber to Purkinje cell synapse. We show that electrical stimulation of parallel fibers not only activates EPSCs in Purkinje cells but also activates inward currents in antigenically identified Bergmann glial cells that invest Purkinje cell synapse with their processes. The inward current is partially due to 6-cyano-7-nitroquinoxalene-2,3-dione (CNQX)- and 2-amino-5-phosphonopentanoic acid (AP5)-sensitive ionotropic Glu receptors, but >/=70% of the current was mediated by D,L-threo-beta-hydroxyaspartate (THA)-sensitive Glu transporters. Glu inward currents were completely and reversibly inhibited by depolarization of Bergmann glial cells to positive membrane potentials allowing biophysical inhibition of Glu uptake into a single glial cell. Inhibition of Glu transport into Bergmann glial cells by voltage-clamping the cell to depolarized potentials caused a reversible increase in spontaneous EPSC frequency in the Purkinje cell. This increase could also be achieved by pharmacological inhibition of Glu transport with the Glu transport inhibitor THA, suggesting that inhibition of Glu uptake into Bergmann glial cells is responsible for the modulation of postsynaptic EPSCs. THA modulation of spontaneous EPSCs could only be observed in the absence of TTX, suggesting primarily a presynaptic effect. Taken together these data suggest that glial Glu uptake can profoundly affect excitatory transmission in the cerebellum, most likely by regulating presynaptic glutamate release.

6-Cyano-7-nitroquinoxaline-2,3-dione↗