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Papers by Josef Bischofberger
1. The intracellular calcium concentration ([Ca2+]i) in cultured olfactory bulb neurones of Xenop... more 1. The intracellular calcium concentration ([Ca2+]i) in cultured olfactory bulb neurones of Xenopus laevis tadpoles was imaged using the calcium indicator dyes fluo-3 and Fura Red as well as a laser scanning microscope. 2. Upon extracellular application of brief pulses of a solution with high potassium concentration (high [K+]o), an increase in [Ca2+]i occurred in all neurones observed. During the first 2 days in culture this increase was highest. At later stages (more than 2 days in culture) the increase in [Ca2+]i was non-homogeneous and highest in the dendritic processes. 3. Nifedipine (10 microM) reduced the high [K+]o-induced increase in [Ca2+]i. The reduction was greatest in somata and proximal dendrites. 4. With nifedipine in the bath, the high [K+]o-induced increase of [Ca2+]i was further reduced by the application of omega-conotoxin GVIA (1 microM). The omega-conotoxin-sensitive Ca2+ influx occurred predominantly on dendritic processes. 5. Noradrenaline (NA), as well as the alpha 2-adrenergic receptor agonist clonidine, reduced the high [K+]o-induced increase of [Ca2+]i. This reduction occurred mainly on dendritic processes. 6. Our results suggest a highly non-homogeneous spatial distribution of voltage-gated Ca2+ channels in cultured olfactory bulb neurones. L-type channels were found mainly on somata and their density seemed to decrease on the dendrites with increasing distance from the soma. In contrast, nifedipine-insensitive N-type channels were mainly observed on dendrites and were blocked by omega-conotoxin. NA, as well as clonidine, markedly blocked Ca2+ influx through dendritic N-type Ca2+ channels.
The Journal of neuroscience : the official journal of the Society for Neuroscience, Jan 15, 2002
The presynaptic Ca2+ signal is a key determinant of transmitter release at chemical synapses. In ... more The presynaptic Ca2+ signal is a key determinant of transmitter release at chemical synapses. In cortical synaptic terminals, however, little is known about the kinetic properties of the presynaptic Ca2+ channels. To investigate the timing and magnitude of the presynaptic Ca2+ inflow, we performed whole-cell patch-clamp recordings from mossy fiber boutons (MFBs) in rat hippocampus. MFBs showed large high-voltage-activated Ca(2+) currents, with a maximal amplitude of approximately 100 pA at a membrane potential of 0 mV. Both activation and deactivation were fast, with time constants in the submillisecond range at a temperature of approximately 23 degrees C. An MFB action potential (AP) applied as a voltage-clamp command evoked a transient Ca2+ current with an average amplitude of approximately 170 pA and a half-duration of 580 microsec. A prepulse to +40 mV had only minimal effects on the AP-evoked Ca2+ current, indicating that presynaptic APs open the voltage-gated Ca2+ channels ver...
Nature, 2004
Neural stem cells in various regions of the vertebrate brain continuously generate neurons throug... more Neural stem cells in various regions of the vertebrate brain continuously generate neurons throughout life. In the mammalian hippocampus, a region important for spatial and episodic memory, thousands of new granule cells are produced per day, with the exact number depending on environmental conditions and physical exercise. The survival of these neurons is improved by learning and conversely learning may
Trends in Neurosciences, 2004
The operation of neuronal networks crucially depends on a fast time course of signaling in inhibi... more The operation of neuronal networks crucially depends on a fast time course of signaling in inhibitory interneurons. Synapses that excite interneurons generate fast currents, owing to the expression of glutamate receptors of specific subunit composition. Interneurons generate brief action potentials in response to transient synaptic activation and discharge repetitively at very high frequencies during sustained stimulation. The ability to generate short-duration action potentials at high frequencies depends on the expression of specific voltage-gated K 1 channels. Factors facilitating fast action potential initiation following synaptic excitation include depolarized interneuron resting potential, subthreshold conductances and active dendrites. Finally, GABA release at interneuron output synapses is rapid and highly synchronized, leading to a faster inhibition in postsynaptic interneurons than in principal cells. Thus, the expression of distinct transmitter receptors and voltage-gated ion channels ensures that interneurons operate with high speed and temporal precision.
Science, 1998
It is widely accepted that individual neurons in the central nervous system release only a single... more It is widely accepted that individual neurons in the central nervous system release only a single fast transmitter. The possibility of corelease of fast neurotransmitters was examined by making paired recordings from synaptically connected neurons in spinal cord slices. Unitary inhibitory postsynaptic currents generated at interneuron-motoneuron synapses consisted of a strychnine-sensitive, glycine receptor-mediated component and a bicuculline-sensitive, gamma-aminobutyric acid (GABA)A receptor-mediated component. These results indicate that spinal interneurons release both glycine and GABA to activate functionally distinct receptors in their postsynaptic target cells. A subset of miniature synaptic currents also showed both components, consistent with corelease from individual synaptic vesicles.
Frontiers in Cellular Neuroscience, 2013
The molecular mechanisms underlying the differentiation of neural progenitor cells (NPCs) remain ... more The molecular mechanisms underlying the differentiation of neural progenitor cells (NPCs) remain poorly understood. In this study we investigated the role of Ca(2+) and cAMP (cyclic adenosine monophosphate) in the differentiation of NPCs extracted from the subventricular zone of E14.5 rat embryos. Patch clamp recordings revealed that increasing cAMP-signaling with Forskolin or IBMX (3-isobutyl-1-methylxantine) significantly facilitated neuronal functional maturation. A continuous application of IBMX to the differentiation medium substantially increased the functional expression of voltage-gated Na(+) and K(+) channels, as well as neuronal firing frequency. Furthermore, we observed an increase in the frequency of spontaneous synaptic currents and in the amplitude of evoked glutamatergic and GABAergic synaptic currents. The most prominent acute effect of applying IBMX was an increase in L-type Ca(2+)currents. Conversely, blocking L-type channels strongly inhibited dendritic outgrowth and synapse formation even in the presence of IBMX, indicating that voltage-gated Ca(2+) influx plays a major role in neuronal differentiation. Finally, we found that nifedipine completely blocks IBMX-induced CREB phosphorylation (cAMP-response-element-binding protein), indicating that the activity of this important transcription factor equally depends on both enhanced cAMP and voltage-gated Ca(2+)-signaling. Taken together, these data indicate that the up-regulation of voltage-gated L-type Ca(2+)-channels and early electrical excitability are critical steps in the cAMP-dependent differentiation of SVZ-derived NPCs into functional neurons. To our knowledge, this is the first demonstration of the acute effects of cAMP on voltage-gated Ca(+2)channels in NPC-derived developing neurons.
Long-term depression (LTD) is a form of synaptic plasticity that can be induced either by low-fre... more Long-term depression (LTD) is a form of synaptic plasticity that can be induced either by low-frequency stimulation of presyn- aptic fibers or in an associative manner by asynchronous pairing of presynaptic and postsynaptic activity. We investigated the induction mechanisms of associative LTD in CA1 pyramidal neu- rons of the hippocampus using whole-cell patch-clamp record- ings and Ca 21 imaging in
Trends in Neurosciences, 2002
Partial quantification of the associative synaptic learning rule of the dentate gyrus. Neuroscien... more Partial quantification of the associative synaptic learning rule of the dentate gyrus. Neuroscience 8, 799-808 6 Markram, H. et al. (1997) Regulation of synaptic efficacy by coincidence of postsynaptic APs and EPSPs. Science 275, 213-215 7 Bell, C.C. et al. (1997) Synaptic plasticity in a cerebellum-like structure depends on temporal order. Nature 387, 278-281 8 Bi, G.Q. and Poo, M.M. (1998) Synaptic modifications in cultured hippocampal neurons: dependence on on spike timing, synaptic strength, and postsynaptic cell type. A critical window for cooperation and competition among developing retinotectal synapses. Nature 395, 37-44 10 Fledman, D.E. (2000) Timing-based LTP and LTD at vertical inputs to layer II/III pyramidal cells in rat barrel cortex. Neuron 27, 45-56 11 Sjostrom, P.J. et al. (2001) Rate, timing, and cooperativity jointly determine cortical synaptic plasticity. Competitive Hebbian learning through spike-timing-dependent synaptic plasticity. Nat. Neurosci. 3, 919-926 15 Rubin, J. et al. (2001) Equilibrium properties of temporally asymmetric Hebbian plasticity. Phys. Rev. Lett. 86, 364-367 16 Senn, W. et al. (2001) An algorithm for modifying neurotransmitter release probability based on pre-and post-synaptic spike timing. Neural Comput. 13, 35-67 17 Froemke, R.C. and Dan, Y. (2002) Spike timingdependent synaptic modification induced by natural spike trains. Nature 416, 433-438 18 Kempter, R. et al. (2001) Intrinsic stabilization of output rates by spike-based Hebbian learning.
The Journal of Physiology, 2014
In the mammalian hippocampus, new granule cells are continuously generated throughout life. Altho... more In the mammalian hippocampus, new granule cells are continuously generated throughout life. Although it is well known that they rapidly form several thousand new glutamatergic synapses, the underlying mechanisms are not well understood. As extrasynaptic NMDA receptors are believed to support the generation of new spines, we have studied the functional properties of extrasynaptic ionotropic glutamate receptors in newborn granule cells in juvenile rats during and after synaptic integration. Using the fast application of glutamate to outside-out membrane patches, we show that all immature granule cells express functional AMPA and NMDA receptors. The density of AMPA receptors was small in cells starting to receive excitatory synaptic input (∼30 pS μm(-2)) but substantially increased during synaptic integration to finally reach ∼120 pS μm(-2) in fully mature cells. Interestingly, AMPA receptors showed a biphasic change in desensitization time constant which was slowest during synaptic integration and substantially faster before and afterwards. This was paralleled by a change in the non-desensitizing current component which was maximal during synaptic integration and about 50% smaller afterwards. Surprisingly, the NMDA receptor kinetics and density in young cells was already comparable to mature cells (∼10 pS μm(-2)), leading to an enhanced NMDA/AMPA receptor density ratio. Similar to somatic outside-out patches, iontophoretic application of glutamate onto dendrites also revealed an enhanced dendritic NMDA/AMPA ratio in young cells. These data indicate that prolonged AMPA receptor currents in newly generated young granule cells might support the effective activation of extrasynaptic NMDA receptors and therefore constitute a competitive advantage over mature cells for new synapse formation.
The Journal of Physiology, 1997
1. Dendritic patch-clamp recordings were obtained from mitral cells in rat olfactory bulb slices,... more 1. Dendritic patch-clamp recordings were obtained from mitral cells in rat olfactory bulb slices, up to 350 microns from the soma. Simultaneous dendritic and somatic whole-cell recordings indicated that action potentials (APs) evoked by somatic or dendritic current injection were initiated near the soma. Both the large amplitude (100.7 +/- 1.1 mV) and the short duration (1.38 +/- 0.07 ms) of the AP were maintained as the AP propagated back into the primary mitral cell dendrites. 2. Outside-out patches isolated from mitral cell dendrites contained voltage-gated Na+ channels (peak conductance density, 90 pS micron-2 at -10 mV). When an AP was used as a somatic voltage-clamp command in the presence of 1 microM tetrodotoxin (TTX), the amplitude of the dendritic potential was attenuated to 48 +/- 14 mV. This shows that dendritic Na+ channels support the active back-propagation of APs. 3. Dendritic patches contained voltage-gated K+ channels with high density (conductance density, 513 pS micron-2 at 30 mV). Dendritic K+ currents were reduced to 35% by 1 mM external tetraethylammonium chloride (TEACl). When an AP was used as a somatic voltage-clamp command in the presence of TEACl, the dendritic potential was markedly prolonged. This indicates that dendritic K+ channels mediate the fast repolarization of dendritic APs. 4. We conclude that voltage-gated Na+ and K+ channels support dendritic APs with large amplitudes and short durations that may trigger fast transmitter release at dendrodendritic synapses in the olfactory bulb.
The Journal of Physiology, 2009
In humans, temporal lobe epilepsy (TLE) is often associated with Ammon's horn sclerosis (AHS) cha... more In humans, temporal lobe epilepsy (TLE) is often associated with Ammon's horn sclerosis (AHS) characterized by hippocampal cell death, gliosis and granule cell dispersion (GCD) in the dentate gyrus. Granule cells surviving TLE have been proposed to be hyperexcitable and to play an important role in seizure generation. However, it is unclear whether this applies to conditions of AHS. We studied granule cells using the intrahippocampal kainate injection mouse model of TLE, brain slice patch-clamp recordings, morphological reconstructions and immunocytochemistry. With progressing AHS and GCD, 'epileptic' granule cells of the injected hippocampus displayed a decreased input resistance, a decreased membrane time constant and an increased rheobase. The resting leak conductance was doubled in epileptic granule cells and roughly 70-80% of this difference were sensitive to K + replacement. Of the increased K + leak, about 50% were sensitive to 1 mm Ba 2+ . Approximately 20-30% of the pathological leak was mediated by a bicuculline-sensitive GABA A conductance. Epileptic granule cells had strongly enlarged inwardly rectifying currents with a low micromolar Ba 2+ IC 50 , reminiscent of classic inward rectifier K + channels (Irk/Kir2). Indeed, protein expression of Kir2 subunits was upregulated in epileptic granule cells. Immunolabelling for two-pore weak inward rectifier K + channels (Twik1/K2P1.1, Twik2/K2P6.1) was also increased. We conclude that the excitability of granule cells in the sclerotic focus of TLE is reduced due to an increased resting conductance mainly due to upregulated K + channel expression. These results point to a local adaptive mechanism that could counterbalance hyperexcitability in epilepsy.
The Journal of Physiology, 2008
Fast-spiking parvalbumin-expressing basket cells (BCs) represent a major type of inhibitory inter... more Fast-spiking parvalbumin-expressing basket cells (BCs) represent a major type of inhibitory interneuron in the hippocampus. These cells inhibit principal cells in a temporally precise manner and are involved in the generation of network oscillations. Although BCs show a unique expression profile of Ca 2+ -permeable receptors, Ca 2+ -binding proteins and Ca 2+ -dependent signalling molecules, physiological Ca 2+ signalling in these interneurons has not been investigated. To study action potential (AP)-induced dendritic Ca 2+ influx and buffering, we combined whole-cell patch-clamp recordings with ratiometric Ca 2+ imaging from the proximal apical dendrites of rigorously identified BCs in acute slices, using the high-affinity Ca 2+ indicator fura-2 or the low-affinity dye fura-FF. Single APs evoked dendritic Ca 2+ transients with small amplitude. Bursts of APs evoked Ca 2+ transients with amplitudes that increased linearly with AP number. Analysis of Ca 2+ transients under steady-state conditions with different fura-2 concentrations and during loading with 200 μM fura-2 indicated that the endogenous Ca 2+ -binding ratio was ∼200 (κ S = 202 ± 26 for the loading experiments). The peak amplitude of the Ca 2+ transients measured directly with 100 μM fura-FF was 39 nM AP −1 . At ∼23 • C, the decay time constant of the Ca 2+ transients was 390 ms, corresponding to an extrusion rate of ∼600 s −1 . At 34 • C, the decay time constant was 203 ms and the corresponding extrusion rate was ∼1100 s −1 . At both temperatures, continuous theta-burst activity with three to five APs per theta cycle, as occurs in vivo during exploration, led to a moderate increase in the global Ca 2+ concentration that was proportional to AP number, whereas more intense stimulation was required to reach micromolar Ca 2+ concentrations and to shift Ca 2+ signalling into a non-linear regime. In conclusion, dentate gyrus BCs show a high endogenous Ca 2+ -binding ratio, a small AP-induced dendritic Ca 2+ influx, and a relatively slow Ca 2+ extrusion. These specific buffering properties of BCs will sharpen the time course of local Ca 2+ signals, while prolonging the decay of global Ca 2+ signals.
The Journal of Physiology, 2007
The modulation of synaptic transmission by presynaptic ionotropic and metabotropic receptors is a... more The modulation of synaptic transmission by presynaptic ionotropic and metabotropic receptors is an important means to control and dynamically adjust synaptic strength. Even though synaptic transmission and plasticity at the hippocampal mossy fibre synapse are tightly controlled by presynaptic receptors, little is known about the downstream signalling mechanisms and targets of the different receptor systems. In the present study, we identified the cellular signalling cascade by which adenosine modulates mossy fibre synaptic transmission. By means of electrophysiological and optical recording techniques, we found that adenosine activates presynaptic A 1 receptors and reduces Ca 2+ influx into mossy fibre terminals. Ca 2+ currents are directly modulated via a membrane-delimited pathway and the reduction of presynaptic Ca 2+ influx can explain the inhibition of synaptic transmission. Specifically, we found that adenosine modulates both P/Q-and N-type presynaptic voltage-dependent Ca 2+ channels and thereby controls transmitter release at the mossy fibre synapse.
Journal of Neuroscience, 2007
Voltage-gated Ca 2ϩ channels in presynaptic terminals initiate the Ca 2ϩ inflow necessary for tra... more Voltage-gated Ca 2ϩ channels in presynaptic terminals initiate the Ca 2ϩ inflow necessary for transmitter release. At a variety of synapses, multiple Ca 2ϩ channel subtypes are involved in synaptic transmission and plasticity. However, it is unknown whether presynaptic Ca 2ϩ channels differ in gating properties and whether they are differentially activated by action potentials or subthreshold voltage signals. We examined Ca 2ϩ channels in hippocampal mossy fiber boutons (MFBs) by presynaptic recording, using the selective blockers -agatoxin IVa, -conotoxin GVIa, and SNX-482 to separate P/Q-, N-, and R-type components. Nonstationary fluctuation analysis combined with blocker application revealed a single MFB contained on average ϳ2000 channels, with 66% P/Q-, 26% N-, and 8% R-type channels. Whereas both P/Q-type and N-type Ca 2ϩ channels showed high activation threshold and rapid activation and deactivation, R-type Ca 2ϩ channels had a lower activation threshold and slower gating kinetics. To determine the efficacy of activation of different Ca 2ϩ channel subtypes by physiologically relevant voltage waveforms, a six-state gating model reproducing the experimental observations was developed. Action potentials activated P/Q-type Ca 2ϩ channels with high efficacy, whereas N-and R-type channels were activated less efficiently. Action potential broadening selectively recruited N-and R-type channels, leading to an equalization of the efficacy of channel activation. In contrast, subthreshold presynaptic events activated R-type channels more efficiently than P/Q-or N-type channels. In conclusion, single MFBs coexpress multiple types of Ca 2ϩ channels, which are activated differentially by subthreshold and suprathreshold presynaptic voltage signals.
Journal of Neuroscience, 2010
Associative long-term depression (LTD) in the hippocampus is a form of spike time-dependent synap... more Associative long-term depression (LTD) in the hippocampus is a form of spike time-dependent synaptic plasticity that is induced by the asynchronous pairing of postsynaptic action potentials and EPSPs. Although metabotropic glutamate receptors (mGluRs) and postsynaptic Ca 2ϩ signaling have been suggested to mediate associative LTD, mechanisms are unclear further downstream. Here we show that either mGluR1 or mGluR5 activation is necessary for LTD induction, which is therefore mediated by group I mGluRs. Inhibition of postsynaptic phospholipase C, inositol-1,4,5-trisphosphate, and PKC prevents associative LTD. Activation of PKC by a phorbol ester causes a presynaptic potentiation of synaptic responses and facilitates LTD induction by a postsynaptic mechanism. Lithium, an inhibitor of the PKC pathway, inhibits LTD and the presynaptic and postsynaptic effects of the phorbol ester. Furthermore, LTD is sensitive to the postsynaptic application of synthetic peptides that inhibit the interaction of AMPA receptors with PDZ domains, suggesting an involvement of protein interacting with C-kinase 1 (PICK1)-mediated receptor endocytosis. Finally, enhanced PKC phosphorylation, induced by behavioral stress, is associated with enhanced LTD. Both increased PKC phosphorylation and stress-induced LTD facilitation can be reversed by lithium, indicating that this clinically used mood stabilizer may act on synaptic depression via PKC modulation. These data suggest that PKC mediates the expression of associative LTD via the PICK1-dependent internalization of AMPA receptors. Moreover, modulation of the PKC activity adjusts the set point for LTD induction in a behavior-dependent manner.
Journal of Neuroscience, 2007
Although dendritic signal processing has been extensively investigated in hippocampal pyramidal c... more Although dendritic signal processing has been extensively investigated in hippocampal pyramidal cells, only little is known about dendritic integration of synaptic potentials in dentate gyrus granule cells, the first stage in the hippocampal trisynaptic circuit. Here we combined dual whole-cell patch-clamp recordings with high-resolution two-photon microscopy to obtain detailed passive cable models of hippocampal granule cells from adult mice. Passive cable properties were determined by direct fitting of the compartmental model to the experimentally measured voltage responses to short and long current pulses. The data are best fit by a cable model with homogenously distributed parameters, including an average specific membrane resistance (R m ) of 38.0 k⍀ cm 2 , a membrane capacitance (C m ) of 1.0 F cm Ϫ2 , and an intracellular resistivity (R i ) of 194 ⍀ cm. Computational analysis shows that signal propagation from somata into dendrites is more efficient in granule cells compared with CA1 pyramidal cells for both steady-state and sinusoidal voltage waveforms up to the gamma frequency range ( f 50% of 74 Hz). Similarly, distal synaptic inputs from entorhinal fibers can efficiently depolarize the somatic membrane of granule cells. Furthermore, the time course of distal dendritic synaptic potentials is remarkably fast, and temporal summation is restricted to a narrow time window in the range of ϳ10 ms attributable to the rapid dendritic charge redistribution during transient voltage signals. Therefore, the structure of the granule cell dendritic tree may be critically important for precise dendritic signal processing and coincidence detection during hippocampus-dependent memory formation and retrieval.
Journal of Neuroscience, 2005
... This mini-symposium presented at the 2005 Society for Neuroscience Meeting will provide insig... more ... This mini-symposium presented at the 2005 Society for Neuroscience Meeting will provide insight into how newly generated neurons ... a fluorescent marker such as green fluorescent protein (GFP), this approach provides adequate time resolution for birth dating and permanent ...
Science, 2006
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1. The intracellular calcium concentration ([Ca2+]i) in cultured olfactory bulb neurones of Xenop... more 1. The intracellular calcium concentration ([Ca2+]i) in cultured olfactory bulb neurones of Xenopus laevis tadpoles was imaged using the calcium indicator dyes fluo-3 and Fura Red as well as a laser scanning microscope. 2. Upon extracellular application of brief pulses of a solution with high potassium concentration (high [K+]o), an increase in [Ca2+]i occurred in all neurones observed. During the first 2 days in culture this increase was highest. At later stages (more than 2 days in culture) the increase in [Ca2+]i was non-homogeneous and highest in the dendritic processes. 3. Nifedipine (10 microM) reduced the high [K+]o-induced increase in [Ca2+]i. The reduction was greatest in somata and proximal dendrites. 4. With nifedipine in the bath, the high [K+]o-induced increase of [Ca2+]i was further reduced by the application of omega-conotoxin GVIA (1 microM). The omega-conotoxin-sensitive Ca2+ influx occurred predominantly on dendritic processes. 5. Noradrenaline (NA), as well as the alpha 2-adrenergic receptor agonist clonidine, reduced the high [K+]o-induced increase of [Ca2+]i. This reduction occurred mainly on dendritic processes. 6. Our results suggest a highly non-homogeneous spatial distribution of voltage-gated Ca2+ channels in cultured olfactory bulb neurones. L-type channels were found mainly on somata and their density seemed to decrease on the dendrites with increasing distance from the soma. In contrast, nifedipine-insensitive N-type channels were mainly observed on dendrites and were blocked by omega-conotoxin. NA, as well as clonidine, markedly blocked Ca2+ influx through dendritic N-type Ca2+ channels.
The Journal of neuroscience : the official journal of the Society for Neuroscience, Jan 15, 2002
The presynaptic Ca2+ signal is a key determinant of transmitter release at chemical synapses. In ... more The presynaptic Ca2+ signal is a key determinant of transmitter release at chemical synapses. In cortical synaptic terminals, however, little is known about the kinetic properties of the presynaptic Ca2+ channels. To investigate the timing and magnitude of the presynaptic Ca2+ inflow, we performed whole-cell patch-clamp recordings from mossy fiber boutons (MFBs) in rat hippocampus. MFBs showed large high-voltage-activated Ca(2+) currents, with a maximal amplitude of approximately 100 pA at a membrane potential of 0 mV. Both activation and deactivation were fast, with time constants in the submillisecond range at a temperature of approximately 23 degrees C. An MFB action potential (AP) applied as a voltage-clamp command evoked a transient Ca2+ current with an average amplitude of approximately 170 pA and a half-duration of 580 microsec. A prepulse to +40 mV had only minimal effects on the AP-evoked Ca2+ current, indicating that presynaptic APs open the voltage-gated Ca2+ channels ver...
Nature, 2004
Neural stem cells in various regions of the vertebrate brain continuously generate neurons throug... more Neural stem cells in various regions of the vertebrate brain continuously generate neurons throughout life. In the mammalian hippocampus, a region important for spatial and episodic memory, thousands of new granule cells are produced per day, with the exact number depending on environmental conditions and physical exercise. The survival of these neurons is improved by learning and conversely learning may
Trends in Neurosciences, 2004
The operation of neuronal networks crucially depends on a fast time course of signaling in inhibi... more The operation of neuronal networks crucially depends on a fast time course of signaling in inhibitory interneurons. Synapses that excite interneurons generate fast currents, owing to the expression of glutamate receptors of specific subunit composition. Interneurons generate brief action potentials in response to transient synaptic activation and discharge repetitively at very high frequencies during sustained stimulation. The ability to generate short-duration action potentials at high frequencies depends on the expression of specific voltage-gated K 1 channels. Factors facilitating fast action potential initiation following synaptic excitation include depolarized interneuron resting potential, subthreshold conductances and active dendrites. Finally, GABA release at interneuron output synapses is rapid and highly synchronized, leading to a faster inhibition in postsynaptic interneurons than in principal cells. Thus, the expression of distinct transmitter receptors and voltage-gated ion channels ensures that interneurons operate with high speed and temporal precision.
Science, 1998
It is widely accepted that individual neurons in the central nervous system release only a single... more It is widely accepted that individual neurons in the central nervous system release only a single fast transmitter. The possibility of corelease of fast neurotransmitters was examined by making paired recordings from synaptically connected neurons in spinal cord slices. Unitary inhibitory postsynaptic currents generated at interneuron-motoneuron synapses consisted of a strychnine-sensitive, glycine receptor-mediated component and a bicuculline-sensitive, gamma-aminobutyric acid (GABA)A receptor-mediated component. These results indicate that spinal interneurons release both glycine and GABA to activate functionally distinct receptors in their postsynaptic target cells. A subset of miniature synaptic currents also showed both components, consistent with corelease from individual synaptic vesicles.
Frontiers in Cellular Neuroscience, 2013
The molecular mechanisms underlying the differentiation of neural progenitor cells (NPCs) remain ... more The molecular mechanisms underlying the differentiation of neural progenitor cells (NPCs) remain poorly understood. In this study we investigated the role of Ca(2+) and cAMP (cyclic adenosine monophosphate) in the differentiation of NPCs extracted from the subventricular zone of E14.5 rat embryos. Patch clamp recordings revealed that increasing cAMP-signaling with Forskolin or IBMX (3-isobutyl-1-methylxantine) significantly facilitated neuronal functional maturation. A continuous application of IBMX to the differentiation medium substantially increased the functional expression of voltage-gated Na(+) and K(+) channels, as well as neuronal firing frequency. Furthermore, we observed an increase in the frequency of spontaneous synaptic currents and in the amplitude of evoked glutamatergic and GABAergic synaptic currents. The most prominent acute effect of applying IBMX was an increase in L-type Ca(2+)currents. Conversely, blocking L-type channels strongly inhibited dendritic outgrowth and synapse formation even in the presence of IBMX, indicating that voltage-gated Ca(2+) influx plays a major role in neuronal differentiation. Finally, we found that nifedipine completely blocks IBMX-induced CREB phosphorylation (cAMP-response-element-binding protein), indicating that the activity of this important transcription factor equally depends on both enhanced cAMP and voltage-gated Ca(2+)-signaling. Taken together, these data indicate that the up-regulation of voltage-gated L-type Ca(2+)-channels and early electrical excitability are critical steps in the cAMP-dependent differentiation of SVZ-derived NPCs into functional neurons. To our knowledge, this is the first demonstration of the acute effects of cAMP on voltage-gated Ca(+2)channels in NPC-derived developing neurons.
Long-term depression (LTD) is a form of synaptic plasticity that can be induced either by low-fre... more Long-term depression (LTD) is a form of synaptic plasticity that can be induced either by low-frequency stimulation of presyn- aptic fibers or in an associative manner by asynchronous pairing of presynaptic and postsynaptic activity. We investigated the induction mechanisms of associative LTD in CA1 pyramidal neu- rons of the hippocampus using whole-cell patch-clamp record- ings and Ca 21 imaging in
Trends in Neurosciences, 2002
Partial quantification of the associative synaptic learning rule of the dentate gyrus. Neuroscien... more Partial quantification of the associative synaptic learning rule of the dentate gyrus. Neuroscience 8, 799-808 6 Markram, H. et al. (1997) Regulation of synaptic efficacy by coincidence of postsynaptic APs and EPSPs. Science 275, 213-215 7 Bell, C.C. et al. (1997) Synaptic plasticity in a cerebellum-like structure depends on temporal order. Nature 387, 278-281 8 Bi, G.Q. and Poo, M.M. (1998) Synaptic modifications in cultured hippocampal neurons: dependence on on spike timing, synaptic strength, and postsynaptic cell type. A critical window for cooperation and competition among developing retinotectal synapses. Nature 395, 37-44 10 Fledman, D.E. (2000) Timing-based LTP and LTD at vertical inputs to layer II/III pyramidal cells in rat barrel cortex. Neuron 27, 45-56 11 Sjostrom, P.J. et al. (2001) Rate, timing, and cooperativity jointly determine cortical synaptic plasticity. Competitive Hebbian learning through spike-timing-dependent synaptic plasticity. Nat. Neurosci. 3, 919-926 15 Rubin, J. et al. (2001) Equilibrium properties of temporally asymmetric Hebbian plasticity. Phys. Rev. Lett. 86, 364-367 16 Senn, W. et al. (2001) An algorithm for modifying neurotransmitter release probability based on pre-and post-synaptic spike timing. Neural Comput. 13, 35-67 17 Froemke, R.C. and Dan, Y. (2002) Spike timingdependent synaptic modification induced by natural spike trains. Nature 416, 433-438 18 Kempter, R. et al. (2001) Intrinsic stabilization of output rates by spike-based Hebbian learning.
The Journal of Physiology, 2014
In the mammalian hippocampus, new granule cells are continuously generated throughout life. Altho... more In the mammalian hippocampus, new granule cells are continuously generated throughout life. Although it is well known that they rapidly form several thousand new glutamatergic synapses, the underlying mechanisms are not well understood. As extrasynaptic NMDA receptors are believed to support the generation of new spines, we have studied the functional properties of extrasynaptic ionotropic glutamate receptors in newborn granule cells in juvenile rats during and after synaptic integration. Using the fast application of glutamate to outside-out membrane patches, we show that all immature granule cells express functional AMPA and NMDA receptors. The density of AMPA receptors was small in cells starting to receive excitatory synaptic input (∼30 pS μm(-2)) but substantially increased during synaptic integration to finally reach ∼120 pS μm(-2) in fully mature cells. Interestingly, AMPA receptors showed a biphasic change in desensitization time constant which was slowest during synaptic integration and substantially faster before and afterwards. This was paralleled by a change in the non-desensitizing current component which was maximal during synaptic integration and about 50% smaller afterwards. Surprisingly, the NMDA receptor kinetics and density in young cells was already comparable to mature cells (∼10 pS μm(-2)), leading to an enhanced NMDA/AMPA receptor density ratio. Similar to somatic outside-out patches, iontophoretic application of glutamate onto dendrites also revealed an enhanced dendritic NMDA/AMPA ratio in young cells. These data indicate that prolonged AMPA receptor currents in newly generated young granule cells might support the effective activation of extrasynaptic NMDA receptors and therefore constitute a competitive advantage over mature cells for new synapse formation.
The Journal of Physiology, 1997
1. Dendritic patch-clamp recordings were obtained from mitral cells in rat olfactory bulb slices,... more 1. Dendritic patch-clamp recordings were obtained from mitral cells in rat olfactory bulb slices, up to 350 microns from the soma. Simultaneous dendritic and somatic whole-cell recordings indicated that action potentials (APs) evoked by somatic or dendritic current injection were initiated near the soma. Both the large amplitude (100.7 +/- 1.1 mV) and the short duration (1.38 +/- 0.07 ms) of the AP were maintained as the AP propagated back into the primary mitral cell dendrites. 2. Outside-out patches isolated from mitral cell dendrites contained voltage-gated Na+ channels (peak conductance density, 90 pS micron-2 at -10 mV). When an AP was used as a somatic voltage-clamp command in the presence of 1 microM tetrodotoxin (TTX), the amplitude of the dendritic potential was attenuated to 48 +/- 14 mV. This shows that dendritic Na+ channels support the active back-propagation of APs. 3. Dendritic patches contained voltage-gated K+ channels with high density (conductance density, 513 pS micron-2 at 30 mV). Dendritic K+ currents were reduced to 35% by 1 mM external tetraethylammonium chloride (TEACl). When an AP was used as a somatic voltage-clamp command in the presence of TEACl, the dendritic potential was markedly prolonged. This indicates that dendritic K+ channels mediate the fast repolarization of dendritic APs. 4. We conclude that voltage-gated Na+ and K+ channels support dendritic APs with large amplitudes and short durations that may trigger fast transmitter release at dendrodendritic synapses in the olfactory bulb.
The Journal of Physiology, 2009
In humans, temporal lobe epilepsy (TLE) is often associated with Ammon's horn sclerosis (AHS) cha... more In humans, temporal lobe epilepsy (TLE) is often associated with Ammon's horn sclerosis (AHS) characterized by hippocampal cell death, gliosis and granule cell dispersion (GCD) in the dentate gyrus. Granule cells surviving TLE have been proposed to be hyperexcitable and to play an important role in seizure generation. However, it is unclear whether this applies to conditions of AHS. We studied granule cells using the intrahippocampal kainate injection mouse model of TLE, brain slice patch-clamp recordings, morphological reconstructions and immunocytochemistry. With progressing AHS and GCD, 'epileptic' granule cells of the injected hippocampus displayed a decreased input resistance, a decreased membrane time constant and an increased rheobase. The resting leak conductance was doubled in epileptic granule cells and roughly 70-80% of this difference were sensitive to K + replacement. Of the increased K + leak, about 50% were sensitive to 1 mm Ba 2+ . Approximately 20-30% of the pathological leak was mediated by a bicuculline-sensitive GABA A conductance. Epileptic granule cells had strongly enlarged inwardly rectifying currents with a low micromolar Ba 2+ IC 50 , reminiscent of classic inward rectifier K + channels (Irk/Kir2). Indeed, protein expression of Kir2 subunits was upregulated in epileptic granule cells. Immunolabelling for two-pore weak inward rectifier K + channels (Twik1/K2P1.1, Twik2/K2P6.1) was also increased. We conclude that the excitability of granule cells in the sclerotic focus of TLE is reduced due to an increased resting conductance mainly due to upregulated K + channel expression. These results point to a local adaptive mechanism that could counterbalance hyperexcitability in epilepsy.
The Journal of Physiology, 2008
Fast-spiking parvalbumin-expressing basket cells (BCs) represent a major type of inhibitory inter... more Fast-spiking parvalbumin-expressing basket cells (BCs) represent a major type of inhibitory interneuron in the hippocampus. These cells inhibit principal cells in a temporally precise manner and are involved in the generation of network oscillations. Although BCs show a unique expression profile of Ca 2+ -permeable receptors, Ca 2+ -binding proteins and Ca 2+ -dependent signalling molecules, physiological Ca 2+ signalling in these interneurons has not been investigated. To study action potential (AP)-induced dendritic Ca 2+ influx and buffering, we combined whole-cell patch-clamp recordings with ratiometric Ca 2+ imaging from the proximal apical dendrites of rigorously identified BCs in acute slices, using the high-affinity Ca 2+ indicator fura-2 or the low-affinity dye fura-FF. Single APs evoked dendritic Ca 2+ transients with small amplitude. Bursts of APs evoked Ca 2+ transients with amplitudes that increased linearly with AP number. Analysis of Ca 2+ transients under steady-state conditions with different fura-2 concentrations and during loading with 200 μM fura-2 indicated that the endogenous Ca 2+ -binding ratio was ∼200 (κ S = 202 ± 26 for the loading experiments). The peak amplitude of the Ca 2+ transients measured directly with 100 μM fura-FF was 39 nM AP −1 . At ∼23 • C, the decay time constant of the Ca 2+ transients was 390 ms, corresponding to an extrusion rate of ∼600 s −1 . At 34 • C, the decay time constant was 203 ms and the corresponding extrusion rate was ∼1100 s −1 . At both temperatures, continuous theta-burst activity with three to five APs per theta cycle, as occurs in vivo during exploration, led to a moderate increase in the global Ca 2+ concentration that was proportional to AP number, whereas more intense stimulation was required to reach micromolar Ca 2+ concentrations and to shift Ca 2+ signalling into a non-linear regime. In conclusion, dentate gyrus BCs show a high endogenous Ca 2+ -binding ratio, a small AP-induced dendritic Ca 2+ influx, and a relatively slow Ca 2+ extrusion. These specific buffering properties of BCs will sharpen the time course of local Ca 2+ signals, while prolonging the decay of global Ca 2+ signals.
The Journal of Physiology, 2007
The modulation of synaptic transmission by presynaptic ionotropic and metabotropic receptors is a... more The modulation of synaptic transmission by presynaptic ionotropic and metabotropic receptors is an important means to control and dynamically adjust synaptic strength. Even though synaptic transmission and plasticity at the hippocampal mossy fibre synapse are tightly controlled by presynaptic receptors, little is known about the downstream signalling mechanisms and targets of the different receptor systems. In the present study, we identified the cellular signalling cascade by which adenosine modulates mossy fibre synaptic transmission. By means of electrophysiological and optical recording techniques, we found that adenosine activates presynaptic A 1 receptors and reduces Ca 2+ influx into mossy fibre terminals. Ca 2+ currents are directly modulated via a membrane-delimited pathway and the reduction of presynaptic Ca 2+ influx can explain the inhibition of synaptic transmission. Specifically, we found that adenosine modulates both P/Q-and N-type presynaptic voltage-dependent Ca 2+ channels and thereby controls transmitter release at the mossy fibre synapse.
Journal of Neuroscience, 2007
Voltage-gated Ca 2ϩ channels in presynaptic terminals initiate the Ca 2ϩ inflow necessary for tra... more Voltage-gated Ca 2ϩ channels in presynaptic terminals initiate the Ca 2ϩ inflow necessary for transmitter release. At a variety of synapses, multiple Ca 2ϩ channel subtypes are involved in synaptic transmission and plasticity. However, it is unknown whether presynaptic Ca 2ϩ channels differ in gating properties and whether they are differentially activated by action potentials or subthreshold voltage signals. We examined Ca 2ϩ channels in hippocampal mossy fiber boutons (MFBs) by presynaptic recording, using the selective blockers -agatoxin IVa, -conotoxin GVIa, and SNX-482 to separate P/Q-, N-, and R-type components. Nonstationary fluctuation analysis combined with blocker application revealed a single MFB contained on average ϳ2000 channels, with 66% P/Q-, 26% N-, and 8% R-type channels. Whereas both P/Q-type and N-type Ca 2ϩ channels showed high activation threshold and rapid activation and deactivation, R-type Ca 2ϩ channels had a lower activation threshold and slower gating kinetics. To determine the efficacy of activation of different Ca 2ϩ channel subtypes by physiologically relevant voltage waveforms, a six-state gating model reproducing the experimental observations was developed. Action potentials activated P/Q-type Ca 2ϩ channels with high efficacy, whereas N-and R-type channels were activated less efficiently. Action potential broadening selectively recruited N-and R-type channels, leading to an equalization of the efficacy of channel activation. In contrast, subthreshold presynaptic events activated R-type channels more efficiently than P/Q-or N-type channels. In conclusion, single MFBs coexpress multiple types of Ca 2ϩ channels, which are activated differentially by subthreshold and suprathreshold presynaptic voltage signals.
Journal of Neuroscience, 2010
Associative long-term depression (LTD) in the hippocampus is a form of spike time-dependent synap... more Associative long-term depression (LTD) in the hippocampus is a form of spike time-dependent synaptic plasticity that is induced by the asynchronous pairing of postsynaptic action potentials and EPSPs. Although metabotropic glutamate receptors (mGluRs) and postsynaptic Ca 2ϩ signaling have been suggested to mediate associative LTD, mechanisms are unclear further downstream. Here we show that either mGluR1 or mGluR5 activation is necessary for LTD induction, which is therefore mediated by group I mGluRs. Inhibition of postsynaptic phospholipase C, inositol-1,4,5-trisphosphate, and PKC prevents associative LTD. Activation of PKC by a phorbol ester causes a presynaptic potentiation of synaptic responses and facilitates LTD induction by a postsynaptic mechanism. Lithium, an inhibitor of the PKC pathway, inhibits LTD and the presynaptic and postsynaptic effects of the phorbol ester. Furthermore, LTD is sensitive to the postsynaptic application of synthetic peptides that inhibit the interaction of AMPA receptors with PDZ domains, suggesting an involvement of protein interacting with C-kinase 1 (PICK1)-mediated receptor endocytosis. Finally, enhanced PKC phosphorylation, induced by behavioral stress, is associated with enhanced LTD. Both increased PKC phosphorylation and stress-induced LTD facilitation can be reversed by lithium, indicating that this clinically used mood stabilizer may act on synaptic depression via PKC modulation. These data suggest that PKC mediates the expression of associative LTD via the PICK1-dependent internalization of AMPA receptors. Moreover, modulation of the PKC activity adjusts the set point for LTD induction in a behavior-dependent manner.
Journal of Neuroscience, 2007
Although dendritic signal processing has been extensively investigated in hippocampal pyramidal c... more Although dendritic signal processing has been extensively investigated in hippocampal pyramidal cells, only little is known about dendritic integration of synaptic potentials in dentate gyrus granule cells, the first stage in the hippocampal trisynaptic circuit. Here we combined dual whole-cell patch-clamp recordings with high-resolution two-photon microscopy to obtain detailed passive cable models of hippocampal granule cells from adult mice. Passive cable properties were determined by direct fitting of the compartmental model to the experimentally measured voltage responses to short and long current pulses. The data are best fit by a cable model with homogenously distributed parameters, including an average specific membrane resistance (R m ) of 38.0 k⍀ cm 2 , a membrane capacitance (C m ) of 1.0 F cm Ϫ2 , and an intracellular resistivity (R i ) of 194 ⍀ cm. Computational analysis shows that signal propagation from somata into dendrites is more efficient in granule cells compared with CA1 pyramidal cells for both steady-state and sinusoidal voltage waveforms up to the gamma frequency range ( f 50% of 74 Hz). Similarly, distal synaptic inputs from entorhinal fibers can efficiently depolarize the somatic membrane of granule cells. Furthermore, the time course of distal dendritic synaptic potentials is remarkably fast, and temporal summation is restricted to a narrow time window in the range of ϳ10 ms attributable to the rapid dendritic charge redistribution during transient voltage signals. Therefore, the structure of the granule cell dendritic tree may be critically important for precise dendritic signal processing and coincidence detection during hippocampus-dependent memory formation and retrieval.
Journal of Neuroscience, 2005
... This mini-symposium presented at the 2005 Society for Neuroscience Meeting will provide insig... more ... This mini-symposium presented at the 2005 Society for Neuroscience Meeting will provide insight into how newly generated neurons ... a fluorescent marker such as green fluorescent protein (GFP), this approach provides adequate time resolution for birth dating and permanent ...
Science, 2006
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