scholarly journals DM1 Transgenic Mice Exhibit Abnormal Neurotransmitter Homeostasis and Synaptic Plasticity in Association with RNA Foci and Mis-Splicing in the Hippocampus

2022 ◽  
Vol 23 (2) ◽  
pp. 592
Author(s):  
Brigitte Potier ◽  
Louison Lallemant ◽  
Sandrine Parrot ◽  
Aline Huguet-Lachon ◽  
Geneviève Gourdon ◽  
...  
Keyword(s):  
Time Course ◽  
Pyramidal Neurons ◽  
Granule Cells ◽  
Glutamate Uptake ◽  
Hippocampal Slices ◽  
Synaptic Cleft ◽  
Synaptic Dysfunction ◽  
Functional Changes ◽  
Rna Foci ◽  
The Impact

Myotonic dystrophy type 1 (DM1) is a severe neuromuscular disease mediated by a toxic gain of function of mutant RNAs. The neuropsychological manifestations affect multiple domains of cognition and behavior, but their etiology remains elusive. Transgenic DMSXL mice carry the DM1 mutation, show behavioral abnormalities, and express low levels of GLT1, a critical regulator of glutamate concentration in the synaptic cleft. However, the impact of glutamate homeostasis on neurotransmission in DM1 remains unknown. We confirmed reduced glutamate uptake in the DMSXL hippocampus. Patch clamp recordings in hippocampal slices revealed increased amplitude of tonic glutamate currents in DMSXL CA1 pyramidal neurons and DG granule cells, likely mediated by higher levels of ambient glutamate. Unexpectedly, extracellular GABA levels and tonic current were also elevated in DMSXL mice. Finally, we found evidence of synaptic dysfunction in DMSXL mice, suggestive of abnormal short-term plasticity, illustrated by an altered LTP time course in DG and in CA1. Synaptic dysfunction was accompanied by RNA foci accumulation in localized areas of the hippocampus and by the mis-splicing of candidate genes with relevant functions in neurotransmission. Molecular and functional changes triggered by toxic RNA may induce synaptic abnormalities in restricted brain areas that favor neuronal dysfunction.

scholarly journals GPR68 deletion impairs hippocampal long-term potentiation and passive avoidance behavior

2020 ◽  
Vol 13 (1) ◽  
Author(s):  
Yuanyuan Xu ◽  
Mike T. Lin ◽  
Xiang-ming Zha
Keyword(s):  
Passive Avoidance ◽  
Pyramidal Neurons ◽  
Granule Cells ◽  
Hippocampal Slices ◽  
Synaptic Cleft ◽  
Long Term Potentiation ◽  
Synaptic Function ◽  
Metabotropic Receptor ◽  
Term Potentiation

Abstract Increased neural activities reduced pH at the synaptic cleft and interstitial spaces. Recent studies have shown that protons function as a neurotransmitter. However, it remains unclear whether protons signal through a metabotropic receptor to regulate synaptic function. Here, we showed that GPR68, a proton-sensitive GPCR, exhibited wide expression in the hippocampus, with higher expression observed in CA3 pyramidal neurons and dentate granule cells. In organotypic hippocampal slice neurons, ectopically expressed GPR68-GFP was present in dendrites, dendritic spines, and axons. Recordings in hippocampal slices isolated from GPR68−/− mice showed a reduced fiber volley at the Schaffer collateral-CA1 synapses, a reduced long-term potentiation (LTP), but unaltered paired-pulse ratio. In a step-through passive avoidance test, GPR68−/− mice exhibited reduced avoidance to the dark chamber. These findings showed that GPR68 contributes to hippocampal LTP and aversive fear memory.

The uptake inhibitor L-trans-PDC enhances responses to glutamate but fails to alter the kinetics of excitatory synaptic currents in the hippocampus

1993 ◽  
Vol 70 (5) ◽  
pp. 2187-2191 ◽  
Author(s):  
J. S. Isaacson ◽  
R. A. Nicoll
Keyword(s):  
Time Course ◽  
Glutamate Uptake ◽  
Hippocampal Slices ◽  
Synaptic Cleft ◽  
Gamma Aminobutyric Acid ◽  
Patch Clamp Recording ◽  
Glutamatergic Synapses ◽  
Synaptic Currents ◽  
Ca1 Region ◽  
Transmitter Uptake

1. We have used patch-clamp recording techniques to study the physiological properties of a recently described glutamate uptake blocker, L-trans-pyrrolidine-2,4-dicarboxylic acid (L-trans-PDC), in the CA1 region of the guinea pig hippocampus. 2. L-trans-PDC markedly potentiated the action of exogenously applied glutamate and raised the ambient extracellular levels of glutamate in hippocampal slices. Despite these actions, L-trans-PDC did not affect the time course of either the N-methyl-D-aspartate (NMDA) or non-NMDA receptor-mediated synaptic currents evoked by the stimulation of a large number of neighboring synapses. 3. These findings are consistent with models of fast synaptic transmission in which transmitter is rapidly cleared from the synaptic cleft by diffusion. However, in marked contrast to fast gamma-aminobutyric acid A (GABAA) synapses in the hippocampus, uptake does not appear to play a role in regulating the "spill-over" of transmitter from neighboring, co-activated glutamatergic synapses. Therefore, either diffusion alone can effectively limit the temporal and spatial domain of synaptically released glutamate, or alternatively, L-trans-PDC like other currently available blockers is not sufficiently potent to reveal a role for transmitter uptake at glutamatergic synapses.

Protein Kinase A Mediates the Modulation of the Slow Ca2+-Dependent K+ Current,I sAHP, by the Neuropeptides CRF, VIP, and CGRP in Hippocampal Pyramidal Neurons

2000 ◽  
Vol 83 (4) ◽  
pp. 2071-2079 ◽  
Author(s):  
Trude Haug ◽  
Johan F. Storm
Keyword(s):  
Protein Kinase ◽  
Time Course ◽  
Pyramidal Neurons ◽  
Hippocampal Slices ◽  
Cell Voltage ◽  
Dependent Protein Kinase ◽  
Hippocampal Pyramidal Neurons ◽  
Camp Dependent Protein Kinase ◽  
Dependent Protein ◽  
Camp Cascade

We have studied modulation of the slow Ca2+-activated K+current ( I sAHP) in CA1 hippocampal pyramidal neurons by three peptide transmitters: corticotropin releasing factor (CRF, also called corticotropin releasing hormone, CRH), vasoactive intestinal peptide (VIP), and calcitonin gene–related peptide (CGRP). These peptides are known to be expressed in interneurons. Using whole cell voltage clamp in hippocampal slices from young rats, in the presence of tetrodotoxin (TTX, 0.5 μM) and tetraethylammonium (TEA, 5 mM), I sAHP was measured after a brief depolarizing voltage step eliciting inward Ca2+ current. Each of the peptides CRF (100–250 nM), VIP (400 nM), and CGRP (1 μM) significantly reduced the amplitude of I sAHP. Thus the I sAHP amplitude was reduced to 22% by 100 nM CRF, to 17% by 250 nM CRF, to 22% by 400 nM VIP, and to 40% by 1 μM CGRP. We found no consistent concomitant changes in the Ca2+ current or in the time course of I sAHP for any of the three peptides, suggesting that the suppression of I sAHP was not secondary to a general suppression of Ca2+ channel activity. Because each of these peptides is known to activate the cyclic AMP (cAMP) cascade in various cell types, and I sAHP is known to be suppressed by cAMP via the cAMP-dependent protein kinase (PKA), we tested whether the effects on I sAHP by CRF, VIP, and CGRP are mediated by PKA. Intracellular application of the PKA-inhibitor Rp-cAMPS significantly reduced the suppression of I sAHP by CRF, VIP, and CGRP. Thus with 1 mM Rp-cAMPS in the recording pipette, the average suppression of I sAHP was reduced from 78 to 26% for 100 nM CRF, from 83 to 32% for 250 nM CRF, from 78 to 30% for 400 nM VIP, and from 60 to 7% for 1 μM CGRP. We conclude that CRF, VIP, and CGRP suppress the slow Ca2+-activated K+ current, I sAHP, in CA1 hippocampal pyramidal neurons by activating the cAMP-dependent protein kinase, PKA. Together with the monoamine transmitters norepinephrine, serotonin, histamine, and dopamine, these peptide transmitters all converge on the cAMP cascade modulating I sAHP.

scholarly journals Modeling of excitatory amino acid transporters and clearance of synaptic cleft on millisecond time scale

2019 ◽  
Vol 14 (4) ◽  
pp. 407
Author(s):  
Denis Shchepakin ◽  
Leonid Kalachev ◽  
Michael Kavanaugh
Keyword(s):  
Amino Acid ◽  
Time Scale ◽  
Time Course ◽  
Transport Model ◽  
Excitatory Amino Acid ◽  
Synaptic Cleft ◽  
Amino Acid Transporters ◽  
Excitatory Amino Acid Transporters ◽  
Millisecond Time Scale ◽  
The Impact

Excitatory Amino Acid Transporters (EAATs) operate over wide time scales in the brain. They maintain low ambient concentrations of the primary excitatory amino acid neurotransmitter glutamate, but they also seem to play a significant role in clearing glutamate from the synaptic cleft in the millisecond time-scale process of chemical communication that occurs between neurons. The detailed kinetic mechanisms underlying glutamate uptake and clearance remain incompletely understood. In this work we used a combination of methods to model EAAT kinetics and gain insight into the impact of transport on glutamate dynamics in a general sense. We derive reliable estimates of the turnover rates of the three major EAAT subtypes expressed in the mammalian cerebral cortex. Previous studies have provided transporter kinetic estimates that vary over an order of magnitude. The values obtained in this study are consistent with estimates that suggest the unitary transporter rates are approximately 20-fold slower than the time course of glutamate in the synapse. A combined diffusion/transport model provides a possible mechanism for the apparent discrepancy.

scholarly journals Selective Changes in Hippocampal GABAA Receptors during Status Epilepticus

2008 ◽  
Vol 8 (6) ◽  
pp. 170-172
Author(s):  
Gregory C. Mathews
Keyword(s):  
Status Epilepticus ◽  
Ligand Binding ◽  
Pyramidal Neurons ◽  
Granule Cells ◽  
External Medium ◽  
Hippocampal Slices ◽  
Surface Expression ◽  
Hippocampal Pyramidal Neurons ◽  
Electrophysiological Recordings ◽  
Reduced Surface

Subunit-Specific Trafficking of >GABAA Receptors During Status Epilepticus. Goodkin HP, Joshi S, Mtchedlishvili Z, Brar J, Kapur J. J Neurosci 2008 5;28(10):2527–2538. It is proposed that a reduced surface expression of GABAA receptors (GABARs) contributes to the pathogenesis of status epilepticus (SE), a condition characterized by prolonged seizures. This hypothesis was based on the finding that prolonged epileptiform bursting (repetitive bursts of prolonged depolarizations with superimposed action potentials) in cultures of dissociated hippocampal pyramidal neurons (dissociated cultures) results in the increased intracellular accumulation of GABARs. However, it is not known whether this rapid modification in the surface-expressed GABAR pool results from selective, subunit-dependent or nonselective, subunit-independent internalization of GABARs. In hippocampal slices obtained from animals undergoing prolonged SE (SE-treated slices), we found that the surface expression of the GABAR β2/3 and γ2 subunits was reduced, whereas that of the δ subunit was not. Complementary electrophysiological recordings from dentate granule cells in SE-treated slices demonstrated a reduction in GABAR-mediated synaptic inhibition, but not tonic inhibition. A reduction in the surface expression of the γ2 subunit, but not the δ subunit was also observed in dissociated cultures and organotypic hippocampal slice cultures when incubated in an elevated KCl external medium or an elevated KCl external medium supplemented with NMDA, respectively. Additional studies demonstrated that the reduction in the surface expression of the γ2 subunit was independent of direct ligand binding of the GABAR. These findings demonstrate that the regulation of surface-expressed GABAR pool during SE is subunit-specific and occurs independent of ligand binding. The differential modulation of the surface expression of GABARs during SE has potential implications for the treatment of this neurological emergency.

scholarly journals Heterogeneous CaMKII-dependent synaptic compensations in CA1 pyramidal neurons from acute slices with dissected CA3

2021 ◽  
Author(s):  
Pablo Vergara ◽  
Gabriela Pino ◽  
Jorge Vera ◽  
Magdalena Sanhueza
Keyword(s):  
Pyramidal Neurons ◽  
Sensory Deprivation ◽  
Hippocampal Slices ◽  
Suitable Model ◽  
Functional Changes ◽  
Genetic Manipulations ◽  
Ca1 Pyramidal Neurons ◽  
Specific Frequency ◽  
Acute Hippocampal Slices ◽  
Underlying Mechanisms

Prolonged changes in neural activity trigger homeostatic synaptic plasticity (HSP) allowing neuronal networks to operate in functional ranges. Cell-wide or input-specific adaptations can be induced by pharmacological or genetic manipulations of activity, and by sensory deprivation. Reactive functional changes caused by deafferentation may partially share mechanisms with HSP. Acute hippocampal slices constitute a suitable model to investigate relatively rapid (hours) pathway-specific modifications occurring after denervation and explore the underlying mechanisms. As Schaffer collaterals constitute a major glutamatergic input to CA1 pyramidal neurons, we conducted whole-cell recordings of miniature excitatory postsynaptic currents (mEPSCs) to evaluate changes over 12 hours after slice preparation and CA3 dissection. We observed an increment in mEPSCs amplitude and a decrease in decay time, suggesting synaptic AMPA receptor upregulation and subunit content modifications. Sorting mEPSC by rise time, a correlate of synapse location along dendrites, revealed amplitude raises at two separate domains. A specific frequency increase was observed in the same domains and was accompanied by a global, unspecific raise. Amplitude and frequency increments were lower at sites initially more active, consistent with local compensatory processes. Transient preincubation with a specific Ca2+/calmodulin-dependent kinase II (CaMKII) inhibitor either blocked or occluded amplitude and frequency upregulation in different synapse populations. Results are consistent with the concurrent development of different known CaMKII-dependent HSP processes. Our observations support that deafferentation causes rapid and diverse compensations resembling classical slow forms of adaptation to inactivity. These results may contribute to understand fast-developing homeostatic or pathological events after brain injury.

Dual Actions of Volatile Anesthetics on GABAAIPSCs 

1999 ◽  
Vol 90 (1) ◽  
pp. 120-134 ◽  
Author(s):  
Matthew I. Banks ◽  
Robert A. Pearce
Keyword(s):  
Concentration Dependence ◽  
Time Course ◽  
Pyramidal Neurons ◽  
Hippocampal Slices ◽  
Volatile Anesthetics ◽  
Blocking Effect ◽  
Dependent Manner ◽  
Gamma Aminobutyric Acid ◽  
Baseline Noise ◽  
Volatile Agents

Background Volatile agents alter inhibitory postsynaptic currents (IPSCs) at clinically relevant concentrations, an action that is thought to make an important contribution to their behavioral effects. The authors investigated the mechanisms underlying these effects by evaluating the concentration dependence of modulation by enflurane, isoflurane, and halothane of IPSCs in rat hippocampal slices. Methods Action potential-independent gamma-aminobutyric acid(A) IPSCs (miniature IPSCs [mIPSCs]) were recorded from CA1 pyramidal neurons. The effects on mIPSC amplitude were used to distinguish between presynaptic (altered release) and postsynaptic (altered receptor response) actions of volatile agents. The concentration dependence of blocking and prolonging actions was compared among the volatile agents to determine whether a single modulatory process could account for both effects. Results The application of volatile anesthetics prolonged the decay and reduced the amplitude of mIPSCs in a dose-dependent manner. The effects on decay time for isoflurane and enflurane could not be distinguished. However, the blocking effect of enflurane was significantly greater than that of isoflurane at all concentrations. Despite the blocking effect, the net action of these agents was enhanced inhibition, because charge transfer was always significantly greater than control. Isoflurane, and to a lesser extent enflurane and halothane, caused a picrotoxin-sensitive increase in baseline noise. Moderate increases in mIPSC frequency were also observed for all agents. Conclusions These results show that enflurane, isoflurane, and halothane reduce IPSC amplitude through a direct postsynaptic action. Furthermore, the concentration dependence of the actions of the agents reveals a dissociation between the effects on the amplitude and the time course of IPSCs, suggesting that distinct mechanisms underlie the two actions.

Enhanced intrinsic excitability and EPSP-spike coupling accompany enriched environment-induced facilitation of LTP in hippocampal CA1 pyramidal neurons

2012 ◽  
Vol 107 (5) ◽  
pp. 1366-1378 ◽  
Author(s):  
Ruchi Malik ◽  
Sumantra Chattarji
Keyword(s):  
Environmental Enrichment ◽  
Pyramidal Neurons ◽  
Hippocampal Slices ◽  
Long Term Potentiation ◽  
Intrinsic Excitability ◽  
Excitatory Postsynaptic Potential ◽  
Ca1 Neurons ◽  
Ca1 Pyramidal Neurons ◽  
Hippocampal Ca1 ◽  
The Impact

Environmental enrichment (EE) is a well-established paradigm for studying naturally occurring changes in synaptic efficacy in the hippocampus that underlie experience-induced modulation of learning and memory in rodents. Earlier research on the effects of EE on hippocampal plasticity focused on long-term potentiation (LTP). Whereas many of these studies investigated changes in synaptic weight, little is known about potential contributions of neuronal excitability to EE-induced plasticity. Here, using whole-cell recordings in hippocampal slices, we address this gap by analyzing the impact of EE on both synaptic plasticity and intrinsic excitability of hippocampal CA1 pyramidal neurons. Consistent with earlier reports, EE increased contextual fear memory and dendritic spine density on CA1 cells. Furthermore, EE facilitated LTP at Schaffer collateral inputs to CA1 pyramidal neurons. Analysis of the underlying causes for enhanced LTP shows EE to increase the frequency but not amplitude of miniature excitatory postsynaptic currents. However, presynaptic release probability, assayed using paired-pulse ratios and use-dependent block of N-methyl-d-aspartate receptor currents, was not affected. Furthermore, CA1 neurons fired more action potentials (APs) in response to somatic depolarization, as well as during the induction of LTP. EE also reduced spiking threshold and after-hyperpolarization amplitude. Strikingly, this EE-induced increase in excitability caused the same-sized excitatory postsynaptic potential to fire more APs. Together, these findings suggest that EE may enhance the capacity for plasticity in CA1 neurons, not only by strengthening synapses but also by enhancing their efficacy to fire spikes—and the two combine to act as an effective substrate for amplifying LTP.

scholarly journals Disruption of Glutamate Transport and Homeostasis by Acute Metabolic Stress

2021 ◽  
Vol 15 ◽  
Author(s):  
Stefan Passlick ◽  
Christine R. Rose ◽  
Gabor C. Petzold ◽  
Christian Henneberger
Keyword(s):  
Glutamate Uptake ◽  
Metabolic Stress ◽  
Glutamate Transporters ◽  
Synaptic Cleft ◽  
Resting Membrane Potential ◽  
Extracellular Glutamate ◽  
Altered Expression ◽  
Rapid Changes ◽  
Primary Means ◽  
The Impact

High-affinity, Na+-dependent glutamate transporters are the primary means by which synaptically released glutamate is removed from the extracellular space. They restrict the spread of glutamate from the synaptic cleft into the perisynaptic space and reduce its spillover to neighboring synapses. Thereby, glutamate uptake increases the spatial precision of synaptic communication. Its dysfunction and the entailing rise of the extracellular glutamate concentration accompanied by an increased spread of glutamate result in a loss of precision and in enhanced excitation, which can eventually lead to neuronal death via excitotoxicity. Efficient glutamate uptake depends on a negative resting membrane potential as well as on the transmembrane gradients of the co-transported ions (Na+, K+, and H+) and thus on the proper functioning of the Na+/K+-ATPase. Consequently, numerous studies have documented the impact of an energy shortage, as occurring for instance during an ischemic stroke, on glutamate clearance and homeostasis. The observations range from rapid changes in the transport activity to altered expression of glutamate transporters. Notably, while astrocytes account for the majority of glutamate uptake under physiological conditions, they may also become a source of extracellular glutamate elevation during metabolic stress. However, the mechanisms of the latter phenomenon are still under debate. Here, we review the recent literature addressing changes of glutamate uptake and homeostasis triggered by acute metabolic stress, i.e., on a timescale of seconds to minutes.

α7 Nicotinic Acetylcholine Receptors on GABAergic Interneurons Evoke Dendritic and Somatic Inhibition of Hippocampal Neurons

2002 ◽  
Vol 87 (1) ◽  
pp. 548-557 ◽  
Author(s):  
A. V. Buhler ◽  
T. V. Dunwiddie
Keyword(s):  
Nicotinic Acetylcholine Receptors ◽  
Acetylcholine Receptors ◽  
Pyramidal Neurons ◽  
Hippocampal Slices ◽  
Pyramidal Cells ◽  
Gabaergic Interneurons ◽  
Nicotinic Acetylcholine ◽  
Α7 Nicotinic Acetylcholine Receptors ◽  
The Impact ◽  
Two Populations

GABAergic interneurons in the hippocampus express high levels of α7 nicotinic acetylcholine receptors, but because of the diverse roles played by hippocampal interneurons, the impact of activation of these receptors on hippocampal output neurons (i.e., CA1 pyramidal cells) is unclear. Activation of hippocampal interneurons could directly inhibit pyramidal neuron activity but could also produce inhibition of other GABAergic cells leading to disinhibition of pyramidal cells. To characterize the inhibitory circuits activated by these receptors, exogenous acetylcholine was applied directly to CA1 interneurons in hippocampal slices, and the resulting postsynaptic responses were recorded from pyramidal neurons or interneurons. Inhibitory currents mediated by GABAA receptors were observed in 27/131 interneuron/pyramidal cell pairs, but no instances of disinhibition of spontaneous inhibitory events or GABAB receptor-mediated responses were observed. Two populations of bicuculline-sensitive GABAAreceptor-mediated currents could be distinguished based on their kinetics and amplitude. Anatomical reconstructions of the interneurons in a subset of connected pairs support the hypothesis that these two populations correspond to inhibitory synapses located either on the somata or dendrites of pyramidal cells. In 11 interneuron/interneuron cell pairs, one presynaptic neuron was observed that produced strong inhibitory currents in several nearby interneurons, suggesting that disinhibition of pyramidal neurons may also occur. All three types of inhibitory responses (somatic-pyramidal, dendritic-pyramidal, and interneuronal) were blocked by the α7 receptor-selective antagonist methyllycaconitine. These data suggest activation of these functionally distinct circuits by α7 receptors results in significant inhibition of both hippocampal pyramidal neurons as well as interneurons.

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