During cerebellar development, granule cells display well char- acterized changes in the expressi... more During cerebellar development, granule cells display well char- acterized changes in the expression of NMDA receptor (NMDAR) NR2 subunits, switching from NR2B to NR2A and NR2C in mature cells. Although various studies, including experiments on mutant mice with one or more NR2 subunit types deleted, sug- gest that NR2A, NR2B, and NR2C subunits contribute to synap- tic NMDARs, changes in
Activity-dependent change in the efficacy of transmission is a basic feature of many excitatory s... more Activity-dependent change in the efficacy of transmission is a basic feature of many excitatory synapses in the central nervous system. The best understood postsynaptic modification involves a change in responsiveness of AMPAR (alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor)-mediated currents following activation of NMDA (N-methyl-D-aspartate) receptors or Ca2+-permeable AMPARs. This process is thought to involve alteration in the number and phosphorylation state of postsynaptic AMPARs. Here we describe a new form of synaptic plasticity--a rapid and lasting change in the subunit composition and Ca2+ permeability of AMPARs at cerebellar stellate cell synapses following synaptic activity. AMPARs lacking the edited GluR2 subunit not only exhibit high Ca2+ permeability but also are blocked by intracellular polyamines. These properties have allowed us to follow directly the involvement of GluR2 subunits in synaptic transmission. Repetitive synaptic activation of Ca2+-permeable AMPARs causes a rapid reduction in Ca2+ permeability and a change in the amplitude of excitatory postsynaptic currents, owing to the incorporation of GluR2-containing AMPARs. Our experiments show that activity-induced Ca2+ influx through GluR2-lacking AMPARs controls the targeting of GluR2-containing AMPARs, implying the presence of a self-regulating mechanism.
The assumption that synaptic and extrasynaptic glutamate re- ceptors are similar underpins many s... more The assumption that synaptic and extrasynaptic glutamate re- ceptors are similar underpins many studies that have sought to relate the behavior of channels in excised patches to the mac- roscopic properties of the EPSC. We have examined this issue for NMDA receptors in cerebellar granule cells, the small size of which allows the opening of individual synaptic NMDA chan- nels
Many neurons express a multiplicity of GABAA receptor subunit isoforms. Despite having only a sin... more Many neurons express a multiplicity of GABAA receptor subunit isoforms. Despite having only a single source of inhibitory input, the cerebellar granule cell displays, at various stages of devel- opment, more than 10 different GABAA subunit types. This subunit diversity would be expected to result in significant receptor heterogeneity, yet the functional consequences of such heterogeneity remain poorly understood. Here
In many neurons, responses to individual quanta of transmitter exhibit large variations in amplit... more In many neurons, responses to individual quanta of transmitter exhibit large variations in amplitude. The origin of this variability, although central to our understanding of synaptic transmission and plasticity, remains controversial. To examine the relationship between quantal amplitude and postsynaptic receptor number, we adopted a novel approach, combining patch-clamp recording of synaptic currents with quantitative immunogold localization of synaptic receptors.
High-frequency synaptic stimulation is thought to cause a rapid and lasting change in the express... more High-frequency synaptic stimulation is thought to cause a rapid and lasting change in the expression of GluR2 subunit- containing AMPA receptors (AMPARs) at synapses in cere- bellar stellate cells. We examined whether spontaneous synaptic activity affects the expression of GluR2-containing synaptic AMPARs and whether the change in AMPAR sub- types alters their Ca 2 permeability and kinetic properties. We used
Many neurons receive a continuous, or `tonic', synaptic input, which increases their membrane... more Many neurons receive a continuous, or `tonic', synaptic input, which increases their membrane conductance, and so modifies the spatial and temporal integration of excitatory signals. In cerebellar granule cells, although the frequency of inhibitory synaptic currents is relatively low, the spillover of synaptically released GABA (gamma-aminobutyric acid) gives rise to a persistent conductance mediated by the GABA A receptor that
We have identified an excitatory synapse in cerebellar molec- ular layer interneurons at which th... more We have identified an excitatory synapse in cerebellar molec- ular layer interneurons at which the level of presynaptic activity determines the receptor type involved in the postsynaptic re- sponse. When small numbers of parallel fibers are activated, EPSCs are mediated solely by AMPA receptors (AMPARs), despite our finding that NMDA receptors (NMDARs) are present in the dendrites of these cells.
Although the properties and trafficking of AMPA-type glutamate receptors (AMPARs) depend critical... more Although the properties and trafficking of AMPA-type glutamate receptors (AMPARs) depend critically on associated transmembrane AMPAR regulatory proteins (TARPs) such as stargazin (γ-2), no TARP has been described that can specifically regulate the important class of calcium-permeable (CP-) AMPARs. We examined the stargazin-related protein γ-5, which is highly expressed in Bergmann glia, a cell type possessing only CP-AMPARs. γ-5 was
Endogenous polyamines profoundly affect the activity of various ion channels, including that of c... more Endogenous polyamines profoundly affect the activity of various ion channels, including that of calcium-permeable AMPA-type glutamate receptors (CP-AMPARs). Here we show that stargazin, a transmembrane AMPAR regulatory protein (TARP) known to influence transport, gating and desensitization of AMPARs, greatly reduces block of CP-AMPARs by intracellular polyamines. By decreasing CP-AMPAR affinity for cytoplasmic polyamines, stargazin enhances the charge transfer following single
Non-NMDA glutamate receptor subunits of the AMPA- preferring subfamily combine to form ion channe... more Non-NMDA glutamate receptor subunits of the AMPA- preferring subfamily combine to form ion channels with heter- ogeneous functional properties. We have investigated the ef- fects of RNA editing at the Q/R site, splice variation of the "flip/flop" cassette, and multimeric subunit assembly on the single-channel conductance and kinetic properties of the re- combinant AMPA receptors formed from GluR2 and GluR4
Diffuse white matter injury (DWMI), a leading cause of neurodevelopmental disabilities in preterm... more Diffuse white matter injury (DWMI), a leading cause of neurodevelopmental disabilities in preterm infants, is characterized by reduced oligodendrocyte formation. NG2-expressing oligodendrocyte precursor cells (NG2 cells) are exposed to various extrinsic regulatory signals, including the neurotransmitter GABA. We investigated GABAergic signaling to cerebellar white matter NG2 cells in a mouse model of DWMI (chronic neonatal hypoxia). We found that hypoxia caused a loss of GABAA receptor-mediated synaptic input to NG2 cells, extensive proliferation of these cells and delayed oligodendrocyte maturation, leading to dysmyelination. Treatment of control mice with a GABAA receptor antagonist or deletion of the chloride-accumulating transporter NKCC1 mimicked the effects of hypoxia. Conversely, blockade of GABA catabolism or GABA uptake reduced NG2 cell numbers and increased the formation of mature oligodendrocytes both in control and hypoxic mice. Our results indicate that GABAergic signal...
The Journal of neuroscience : the official journal of the Society for Neuroscience, Jan 11, 2015
Presynaptic ionotropic glutamate receptors (iGluRs) play important roles in the control of synapt... more Presynaptic ionotropic glutamate receptors (iGluRs) play important roles in the control of synaptogenesis and neurotransmitter release, yet their regulation is poorly understood. In particular, the contribution of transmembrane auxiliary proteins, which profoundly shape the trafficking and gating of somatodendritic iGluRs, is unknown. Here we examined the influence of transmembrane AMPAR regulatory proteins (TARPs) on presynaptic AMPARs in cerebellar molecular layer interneurons (MLIs). 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), a partial agonist at TARP-associated AMPARs, enhanced spontaneous GABA release in wild-type mice but not in stargazer mice that lack the prototypical TARP stargazin (γ-2). These findings were replicated in mechanically dissociated Purkinje cells with functional adherent synaptic boutons, demonstrating the presynaptic locus of modulation. In dissociated Purkinje cells from stargazer mice, AMPA was able to enhance mIPSC frequency, but only in the presence of...
Science's STKE : signal transduction knowledge environment, Jan 19, 2004
Most excitatory synapses in the brain use the neurotransmitter glutamate to carry impulses betwee... more Most excitatory synapses in the brain use the neurotransmitter glutamate to carry impulses between neurons. During fast transmission, glutamate usually activates a mixture of N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors in the postsynaptic cell. Experimental scrutiny of NMDARs provides insight into their involvement in excitatory synaptic transmission and related processes such as as synaptic plasticity, neural development, and pain perception. There is increasing awareness that subtle variation in NMDAR properties is imparted by specific receptor subunits, and recent studies have started to provide perspective into some of the discrete tasks carried out by individual receptor subtypes.
The Journal of neuroscience : the official journal of the Society for Neuroscience, Jan 15, 2003
NMDA receptors (NMDARs) are thought to be tetrameric assemblies composed of NR1 and at least one ... more NMDA receptors (NMDARs) are thought to be tetrameric assemblies composed of NR1 and at least one type of NR2 subunit. The identity of the NR2 subunit (NR2A, -B, -C, -D) is critical in determining many of the functional properties of the receptor, such as channel conductance and deactivation time. Further diversity may arise from coassembly of more than one type of NR2 subunit, if the resulting triheteromeric assembly (NR1 plus two types of NR2) displays distinct functional properties. We have used gene-ablated mice (NR2D -/-) to examine the effects of the NR2D subunit on NMDAR channels and NMDAR EPSCs in cerebellar Golgi cells. These cells are thought to express both NR2B and NR2D subunits, a combination that occurs widely in the developing nervous system. Our experiments provide direct evidence that the low conductance NMDAR channels in Golgi cells arise from diheteromeric NR1/NR2D assemblies. To investigate whether a functionally distinct triheteromeric assembly was also expressed...
During cerebellar development, granule cells display well char- acterized changes in the expressi... more During cerebellar development, granule cells display well char- acterized changes in the expression of NMDA receptor (NMDAR) NR2 subunits, switching from NR2B to NR2A and NR2C in mature cells. Although various studies, including experiments on mutant mice with one or more NR2 subunit types deleted, sug- gest that NR2A, NR2B, and NR2C subunits contribute to synap- tic NMDARs, changes in
Activity-dependent change in the efficacy of transmission is a basic feature of many excitatory s... more Activity-dependent change in the efficacy of transmission is a basic feature of many excitatory synapses in the central nervous system. The best understood postsynaptic modification involves a change in responsiveness of AMPAR (alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor)-mediated currents following activation of NMDA (N-methyl-D-aspartate) receptors or Ca2+-permeable AMPARs. This process is thought to involve alteration in the number and phosphorylation state of postsynaptic AMPARs. Here we describe a new form of synaptic plasticity--a rapid and lasting change in the subunit composition and Ca2+ permeability of AMPARs at cerebellar stellate cell synapses following synaptic activity. AMPARs lacking the edited GluR2 subunit not only exhibit high Ca2+ permeability but also are blocked by intracellular polyamines. These properties have allowed us to follow directly the involvement of GluR2 subunits in synaptic transmission. Repetitive synaptic activation of Ca2+-permeable AMPARs causes a rapid reduction in Ca2+ permeability and a change in the amplitude of excitatory postsynaptic currents, owing to the incorporation of GluR2-containing AMPARs. Our experiments show that activity-induced Ca2+ influx through GluR2-lacking AMPARs controls the targeting of GluR2-containing AMPARs, implying the presence of a self-regulating mechanism.
The assumption that synaptic and extrasynaptic glutamate re- ceptors are similar underpins many s... more The assumption that synaptic and extrasynaptic glutamate re- ceptors are similar underpins many studies that have sought to relate the behavior of channels in excised patches to the mac- roscopic properties of the EPSC. We have examined this issue for NMDA receptors in cerebellar granule cells, the small size of which allows the opening of individual synaptic NMDA chan- nels
Many neurons express a multiplicity of GABAA receptor subunit isoforms. Despite having only a sin... more Many neurons express a multiplicity of GABAA receptor subunit isoforms. Despite having only a single source of inhibitory input, the cerebellar granule cell displays, at various stages of devel- opment, more than 10 different GABAA subunit types. This subunit diversity would be expected to result in significant receptor heterogeneity, yet the functional consequences of such heterogeneity remain poorly understood. Here
In many neurons, responses to individual quanta of transmitter exhibit large variations in amplit... more In many neurons, responses to individual quanta of transmitter exhibit large variations in amplitude. The origin of this variability, although central to our understanding of synaptic transmission and plasticity, remains controversial. To examine the relationship between quantal amplitude and postsynaptic receptor number, we adopted a novel approach, combining patch-clamp recording of synaptic currents with quantitative immunogold localization of synaptic receptors.
High-frequency synaptic stimulation is thought to cause a rapid and lasting change in the express... more High-frequency synaptic stimulation is thought to cause a rapid and lasting change in the expression of GluR2 subunit- containing AMPA receptors (AMPARs) at synapses in cere- bellar stellate cells. We examined whether spontaneous synaptic activity affects the expression of GluR2-containing synaptic AMPARs and whether the change in AMPAR sub- types alters their Ca 2 permeability and kinetic properties. We used
Many neurons receive a continuous, or `tonic', synaptic input, which increases their membrane... more Many neurons receive a continuous, or `tonic', synaptic input, which increases their membrane conductance, and so modifies the spatial and temporal integration of excitatory signals. In cerebellar granule cells, although the frequency of inhibitory synaptic currents is relatively low, the spillover of synaptically released GABA (gamma-aminobutyric acid) gives rise to a persistent conductance mediated by the GABA A receptor that
We have identified an excitatory synapse in cerebellar molec- ular layer interneurons at which th... more We have identified an excitatory synapse in cerebellar molec- ular layer interneurons at which the level of presynaptic activity determines the receptor type involved in the postsynaptic re- sponse. When small numbers of parallel fibers are activated, EPSCs are mediated solely by AMPA receptors (AMPARs), despite our finding that NMDA receptors (NMDARs) are present in the dendrites of these cells.
Although the properties and trafficking of AMPA-type glutamate receptors (AMPARs) depend critical... more Although the properties and trafficking of AMPA-type glutamate receptors (AMPARs) depend critically on associated transmembrane AMPAR regulatory proteins (TARPs) such as stargazin (γ-2), no TARP has been described that can specifically regulate the important class of calcium-permeable (CP-) AMPARs. We examined the stargazin-related protein γ-5, which is highly expressed in Bergmann glia, a cell type possessing only CP-AMPARs. γ-5 was
Endogenous polyamines profoundly affect the activity of various ion channels, including that of c... more Endogenous polyamines profoundly affect the activity of various ion channels, including that of calcium-permeable AMPA-type glutamate receptors (CP-AMPARs). Here we show that stargazin, a transmembrane AMPAR regulatory protein (TARP) known to influence transport, gating and desensitization of AMPARs, greatly reduces block of CP-AMPARs by intracellular polyamines. By decreasing CP-AMPAR affinity for cytoplasmic polyamines, stargazin enhances the charge transfer following single
Non-NMDA glutamate receptor subunits of the AMPA- preferring subfamily combine to form ion channe... more Non-NMDA glutamate receptor subunits of the AMPA- preferring subfamily combine to form ion channels with heter- ogeneous functional properties. We have investigated the ef- fects of RNA editing at the Q/R site, splice variation of the "flip/flop" cassette, and multimeric subunit assembly on the single-channel conductance and kinetic properties of the re- combinant AMPA receptors formed from GluR2 and GluR4
Diffuse white matter injury (DWMI), a leading cause of neurodevelopmental disabilities in preterm... more Diffuse white matter injury (DWMI), a leading cause of neurodevelopmental disabilities in preterm infants, is characterized by reduced oligodendrocyte formation. NG2-expressing oligodendrocyte precursor cells (NG2 cells) are exposed to various extrinsic regulatory signals, including the neurotransmitter GABA. We investigated GABAergic signaling to cerebellar white matter NG2 cells in a mouse model of DWMI (chronic neonatal hypoxia). We found that hypoxia caused a loss of GABAA receptor-mediated synaptic input to NG2 cells, extensive proliferation of these cells and delayed oligodendrocyte maturation, leading to dysmyelination. Treatment of control mice with a GABAA receptor antagonist or deletion of the chloride-accumulating transporter NKCC1 mimicked the effects of hypoxia. Conversely, blockade of GABA catabolism or GABA uptake reduced NG2 cell numbers and increased the formation of mature oligodendrocytes both in control and hypoxic mice. Our results indicate that GABAergic signal...
The Journal of neuroscience : the official journal of the Society for Neuroscience, Jan 11, 2015
Presynaptic ionotropic glutamate receptors (iGluRs) play important roles in the control of synapt... more Presynaptic ionotropic glutamate receptors (iGluRs) play important roles in the control of synaptogenesis and neurotransmitter release, yet their regulation is poorly understood. In particular, the contribution of transmembrane auxiliary proteins, which profoundly shape the trafficking and gating of somatodendritic iGluRs, is unknown. Here we examined the influence of transmembrane AMPAR regulatory proteins (TARPs) on presynaptic AMPARs in cerebellar molecular layer interneurons (MLIs). 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), a partial agonist at TARP-associated AMPARs, enhanced spontaneous GABA release in wild-type mice but not in stargazer mice that lack the prototypical TARP stargazin (γ-2). These findings were replicated in mechanically dissociated Purkinje cells with functional adherent synaptic boutons, demonstrating the presynaptic locus of modulation. In dissociated Purkinje cells from stargazer mice, AMPA was able to enhance mIPSC frequency, but only in the presence of...
Science's STKE : signal transduction knowledge environment, Jan 19, 2004
Most excitatory synapses in the brain use the neurotransmitter glutamate to carry impulses betwee... more Most excitatory synapses in the brain use the neurotransmitter glutamate to carry impulses between neurons. During fast transmission, glutamate usually activates a mixture of N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors in the postsynaptic cell. Experimental scrutiny of NMDARs provides insight into their involvement in excitatory synaptic transmission and related processes such as as synaptic plasticity, neural development, and pain perception. There is increasing awareness that subtle variation in NMDAR properties is imparted by specific receptor subunits, and recent studies have started to provide perspective into some of the discrete tasks carried out by individual receptor subtypes.
The Journal of neuroscience : the official journal of the Society for Neuroscience, Jan 15, 2003
NMDA receptors (NMDARs) are thought to be tetrameric assemblies composed of NR1 and at least one ... more NMDA receptors (NMDARs) are thought to be tetrameric assemblies composed of NR1 and at least one type of NR2 subunit. The identity of the NR2 subunit (NR2A, -B, -C, -D) is critical in determining many of the functional properties of the receptor, such as channel conductance and deactivation time. Further diversity may arise from coassembly of more than one type of NR2 subunit, if the resulting triheteromeric assembly (NR1 plus two types of NR2) displays distinct functional properties. We have used gene-ablated mice (NR2D -/-) to examine the effects of the NR2D subunit on NMDAR channels and NMDAR EPSCs in cerebellar Golgi cells. These cells are thought to express both NR2B and NR2D subunits, a combination that occurs widely in the developing nervous system. Our experiments provide direct evidence that the low conductance NMDAR channels in Golgi cells arise from diheteromeric NR1/NR2D assemblies. To investigate whether a functionally distinct triheteromeric assembly was also expressed...
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