Structural determinants and regulation of spontaneous activity in GABAA receptors

AbstractGABAA receptors are vital for controlling neuronal excitability and can display significant levels of constitutive activity that contributes to tonic inhibition. However, the mechanisms underlying spontaneity are poorly understood. Here we demonstrate a strict requirement for β3 subunit incorporation into receptors for spontaneous gating, facilitated by α4, α6 and δ subunits. The crucial molecular determinant involves four amino acids (GKER) in the β3 subunit’s extracellular domain, which interacts with adjacent receptor subunits to promote transition to activated, open channel conformations. Spontaneous activity is further regulated by β3 subunit phosphorylation and by allosteric modulators including neurosteroids and benzodiazepines. Promoting spontaneous activity reduced neuronal excitability, indicating that spontaneous currents will alter neural network activity. This study demonstrates how regional diversity in GABAA receptor isoform, protein kinase activity, and neurosteroid levels, can impact on tonic inhibition through the modulation of spontaneous GABAA receptor gating.

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A supervised machine learning approach to characterize spinal network function

Journal of Neurophysiology ◽

10.1152/jn.00763.2018 ◽

2019 ◽

Vol 121 (6) ◽

pp. 2001-2012 ◽

Cited By ~ 4

Author(s):

A. N. Dalrymple ◽

S. A. Sharples ◽

N. Osachoff ◽

A. P. Lognon ◽

P. J. Whelan

Keyword(s):

Machine Learning ◽

Spinal Cord ◽

Nervous System ◽

Spontaneous Activity ◽

Machine Learning Algorithms ◽

Supervised Machine Learning ◽

Network Activity ◽

Multilayer Perceptrons ◽

Network Development ◽

Newborn Mice

Spontaneous activity is a common feature of immature neuronal networks throughout the central nervous system and plays an important role in network development and consolidation. In postnatal rodents, spontaneous activity in the spinal cord exhibits complex, stochastic patterns that have historically proven challenging to characterize. We developed a software tool for quickly and automatically characterizing and classifying episodes of spontaneous activity generated from developing spinal networks. We recorded spontaneous activity from in vitro lumbar ventral roots of 16 neonatal [postnatal day (P)0–P3] mice. Recordings were DC coupled and detrended, and episodes were separated for analysis. Amplitude-, duration-, and frequency-related features were extracted from each episode and organized into five classes. Paired classes and features were used to train and test supervised machine learning algorithms. Multilayer perceptrons were used to classify episodes as rhythmic or multiburst. We increased network excitability with potassium chloride and tested the utility of the tool to detect changes in features and episode class. We also demonstrate usability by having a novel experimenter use the program to classify episodes collected at a later time point (P5). Supervised machine learning-based classification of episodes accounted for changes that traditional approaches cannot detect. Our tool, named SpontaneousClassification, advances the detail in which we can study not only developing spinal networks, but also spontaneous networks in other areas of the nervous system.NEW & NOTEWORTHY Spontaneous activity is important for nervous system network development and consolidation. Our software uses machine learning to automatically and quickly characterize and classify episodes of spontaneous activity in the spinal cord of newborn mice. It detected changes in network activity following KCl-enhanced excitation. Using our software to classify spontaneous activity throughout development, in pathological models, or with neuromodulation, may offer insight into the development and organization of spinal circuits.

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Oxytocin shapes spontaneous activity patterns in the developing visual cortex by activating somatostatin interneurons

10.1101/866251 ◽

2019 ◽

Cited By ~ 1

Author(s):

Paloma P Maldonado ◽

Alvaro Nuno-Perez ◽

Jan Kirchner ◽

Elizabeth Hammock ◽

Julijana Gjorgjieva ◽

...

Keyword(s):

Visual Cortex ◽

Spontaneous Activity ◽

Sensory Processing ◽

Activity Patterns ◽

Network Activity ◽

Synaptic Connections ◽

Pairwise Correlations ◽

Early Brain Development

SummarySpontaneous network activity shapes emerging neuronal circuits during early brain development, however how neuromodulation influences this activity is not fully understood. Here, we report that the neuromodulator oxytocin powerfully shapes spontaneous activity patterns. In vivo, oxytocin strongly decreased the frequency and pairwise correlations of spontaneous activity events in visual cortex (V1), but not in somatosensory cortex (S1). This differential effect was a consequence of oxytocin only increasing inhibition in V1 and increasing both inhibition and excitation in S1. The increase in inhibition was mediated by the depolarization and increase in excitability of somatostatin+ (SST) interneurons specifically. Accordingly, silencing SST+ neurons pharmacogenetically fully blocked oxytocin’s effect on inhibition in vitro as well its effect on spontaneous activity patterns in vivo. Thus, oxytocin decreases the excitatory/inhibitory ratio and modulates specific features of V1 spontaneous activity patterns that are crucial for refining developing synaptic connections and sensory processing later in life.

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The Dynamic Modulation of GABAA Receptor Trafficking and Its Role in Regulating the Plasticity of Inhibitory Synapses

Physiological Reviews ◽

10.1152/physrev.00015.2010 ◽

2011 ◽

Vol 91 (3) ◽

pp. 1009-1022 ◽

Cited By ~ 127

Author(s):

Mansi Vithlani ◽

Miho Terunuma ◽

Stephen J. Moss

Keyword(s):

Neuronal Excitability ◽

Tonic Inhibition ◽

Inhibitory Synapses ◽

General Anesthetics ◽

Selective Stabilization ◽

Neuronal Plasma Membrane ◽

Sites Of Action ◽

And Behavior ◽

The Impact ◽

The Brain

Inhibition in the adult mammalian central nervous system (CNS) is mediated by γ-aminobutyric acid (GABA). The fast inhibitory actions of GABA are mediated by GABA type A receptors (GABAARs); they mediate both phasic and tonic inhibition in the brain and are the principle sites of action for anticonvulsant, anxiolytic, and sedative-hypnotic agents that include benzodiazepines, barbiturates, neurosteroids, and some general anesthetics. GABAARs are heteropentameric ligand-gated ion channels that are found concentrated at inhibitory postsynaptic sites where they mediate phasic inhibition and at extrasynaptic sites where they mediate tonic inhibition. The efficacy of inhibition and thus neuronal excitability is critically dependent on the accumulation of specific GABAAR subtypes at inhibitory synapses. Here we evaluate how neurons control the number of GABAARs on the neuronal plasma membrane together with their selective stabilization at synaptic sites. We then go on to examine the impact that these processes have on the strength of synaptic inhibition and behavior.

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Control of motor coordination by astrocytic tonic GABA release through modulation of excitation/inhibition balance in cerebellum

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1721187115 ◽

2018 ◽

Vol 115 (19) ◽

pp. 5004-5009 ◽

Cited By ~ 22

Author(s):

Junsung Woo ◽

Joo Ok Min ◽

Dae-Si Kang ◽

Yoo Sung Kim ◽

Guk Hwa Jung ◽

...

Keyword(s):

Synaptic Transmission ◽

Motor Performance ◽

Neuronal Excitability ◽

Motor Coordination ◽

Granule Cells ◽

Cerebellar Granule Cells ◽

Gaba Release ◽

In Vivo Microdialysis ◽

Tonic Inhibition

Tonic inhibition in the brain is mediated through an activation of extrasynaptic GABAA receptors by the tonically released GABA, resulting in a persistent GABAergic inhibitory action. It is one of the key regulators for neuronal excitability, exerting a powerful action on excitation/inhibition balance. We have previously reported that astrocytic GABA, synthesized by monoamine oxidase B (MAOB), mediates tonic inhibition via GABA-permeable bestrophin 1 (Best1) channel in the cerebellum. However, the role of astrocytic GABA in regulating neuronal excitability, synaptic transmission, and cerebellar brain function has remained elusive. Here, we report that a reduction of tonic GABA release by genetic removal or pharmacological inhibition of Best1 or MAOB caused an enhanced neuronal excitability in cerebellar granule cells (GCs), synaptic transmission at the parallel fiber-Purkinje cell (PF-PC) synapses, and motor performance on the rotarod test, whereas an augmentation of tonic GABA release by astrocyte-specific overexpression of MAOB resulted in a reduced neuronal excitability, synaptic transmission, and motor performance. The bidirectional modulation of astrocytic GABA by genetic alteration of Best1 or MAOB was confirmed by immunostaining and in vivo microdialysis. These findings indicate that astrocytes are the key player in motor coordination through tonic GABA release by modulating neuronal excitability and could be a good therapeutic target for various movement and psychiatric disorders, which show a disturbed excitation/inhibition balance.

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Spontaneous dynamics of neural networks in deep layers of prefrontal cortex

Journal of Neurophysiology ◽

10.1152/jn.00295.2016 ◽

2017 ◽

Vol 117 (4) ◽

pp. 1581-1594 ◽

Cited By ~ 4

Author(s):

Andrew S. Blaeser ◽

Barry W. Connors ◽

Arto V. Nurmikko

Keyword(s):

Prefrontal Cortex ◽

Spontaneous Activity ◽

Calcium Imaging ◽

Cortical Neurons ◽

Rhythmic Activity ◽

Network Activity ◽

Local Networks ◽

Spatiotemporal Scale ◽

Deep Layers ◽

Delta Oscillations

Cortical systems maintain and process information through the sustained activation of recurrent local networks of neurons. Layer 5 is known to have a major role in generating the recurrent activation associated with these functions, but relatively little is known about its intrinsic dynamics at the mesoscopic level of large numbers of neighboring neurons. Using calcium imaging, we measured the spontaneous activity of networks of deep-layer medial prefrontal cortical neurons in an acute slice model. Inferring the simultaneous activity of tens of neighboring neurons, we found that while the majority showed only sporadic activity, a subset of neurons engaged in sustained delta frequency rhythmic activity. Spontaneous activity under baseline conditions was weakly correlated between pairs of neurons, and rhythmic neurons showed little coherence in their oscillations. However, we consistently observed brief bouts of highly synchronous activity that must be attributed to network activity. NMDA-mediated stimulation enhanced rhythmicity, synchrony, and correlation within these local networks. These results characterize spontaneous prefrontal activity at a previously unexplored spatiotemporal scale and suggest that medial prefrontal cortex can act as an intrinsic generator of delta oscillations. NEW & NOTEWORTHY Using calcium imaging and a novel analytic framework, we characterized the spontaneous and NMDA-evoked activity of layer 5 prefrontal cortex at a largely unexplored spatiotemporal scale. Our results suggest that the mPFC microcircuitry is capable of intrinsically generating delta oscillations and sustaining synchronized network activity that is potentially relevant for understanding its contribution to cognitive processes.

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Microglia Control Neuronal Network Excitability via BDNF Signalling

Neural Plasticity ◽

10.1155/2013/429815 ◽

2013 ◽

Vol 2013 ◽

pp. 1-11 ◽

Cited By ~ 138

Author(s):

Francesco Ferrini ◽

Yves De Koninck

Keyword(s):

Neural Network ◽

Nitric Oxide ◽

Neurological Disorders ◽

Neuronal Excitability ◽

Current Knowledge ◽

Glycine Receptor ◽

Network Activity ◽

Biophysical Mechanism ◽

Neural Dysfunctions ◽

Novel Therapeutic

Microglia-neuron interactions play a crucial role in several neurological disorders characterized by altered neural network excitability, such as epilepsy and neuropathic pain. While a series of potential messengers have been postulated as substrates of the communication between microglia and neurons, including cytokines, purines, prostaglandins, and nitric oxide, the specific links between messengers, microglia, neuronal networks, and diseases have remained elusive. Brain-derived neurotrophic factor (BDNF) released by microglia emerges as an exception in this riddle. Here, we review the current knowledge on the role played by microglial BDNF in controlling neuronal excitability by causing disinhibition. The efforts made by different laboratories during the last decade have collectively provided a robust mechanistic paradigm which elucidates the mechanisms involved in the synthesis and release of BDNF from microglia, the downstream TrkB-mediated signals in neurons, and the biophysical mechanism by which disinhibition occurs, via the downregulation of the K+-Cl−cotransporter KCC2, dysrupting Cl−homeostasis, and hence the strength ofGABAA- and glycine receptor-mediated inhibition. The resulting altered network activity appears to explain several features of the associated pathologies. Targeting the molecular players involved in this canonical signaling pathway may lead to novel therapeutic approach for ameliorating a wide array of neural dysfunctions.

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Loss of the glial glutamate transporter eaat2a leads to a combined developmental and epileptic encephalopathy in zebrafish

10.1101/2021.03.16.435577 ◽

2021 ◽

Author(s):

Adriana L. Hotz ◽

Ahmed Jamali ◽

Nicolas N. Rieser ◽

Stephanie Niklaus ◽

Ecem Aydin ◽

...

Keyword(s):

Neuronal Excitability ◽

Excitatory Amino Acid ◽

Brain Activity ◽

Glutamate Transporter ◽

Epileptic Seizures ◽

Synaptic Cleft ◽

Epileptic Encephalopathy ◽

Network Activity ◽

Excitatory Amino Acid Transporter ◽

The Impact

ABSTRACTAstroglial excitatory amino acid transporter 2 (EAAT2, GLT-1, SLC1A2) regulates the duration and extent of neuronal excitation by removing glutamate from the synaptic cleft. Human patients with altered EAAT2 function exhibit epileptic seizures, suggesting an important role for astroglial glutamate transporters in balancing neuronal excitability. To study the impact of EAAT2 function at the neural network levels, we generated eaat2a mutant zebrafish. We observed that eaat2a-/- mutant zebrafish larvae display recurrent spontaneous and light-induced seizures in neurons and astroglia, which coincide with an abrupt increase in extracellular glutamate levels. In stark contrast to this hyperexcitability, basal brain activity was surprisingly reduced in eaat2a-/- mutant animals, which manifested in decreased locomotion, neuronal and astroglial calcium signals. Our results reveal an unexpected key role of the astroglial EAAT2a in balancing brain excitability, affecting both neuronal and astroglial network activity.

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Neuromodulation or energy failure? Metabolic limitations silence network output in the hypoxic amphibian brainstem

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00209.2020 ◽

2020 ◽

Author(s):

Sasha Adams ◽

Tanya Zubov ◽

Nikolaus Bueschke ◽

Joseph M. Santin

Keyword(s):

Neuronal Excitability ◽

Atp Synthesis ◽

Network Activity ◽

Hypoxia Tolerance ◽

Support Network ◽

Network Function ◽

Respiratory Network ◽

Network Output ◽

Energy Failure ◽

Arrest Activity

Hypoxia tolerance in the vertebrate brain often involves chemical modulators that arrest neuronal activity to conserve energy. However, in intact networks, it can be difficult to determine whether hypoxia triggers modulators to stop activity in a protective manner or whether activity stops because rates of ATP synthesis are insufficient to support network function. Here, we assessed the extent to which neuromodulation or metabolic limitations arrest activity in the respiratory network of bullfrogs-a circuit that survives moderate periods of oxygen deprivation, presumably, by activating an inhibitory noradrenergic pathway. We confirmed that hypoxia and norepinephrine (NE) reduce network output, consistent with the view that hypoxia may cause the release of NE to inhibit activity. However, these responses differed qualitatively; hypoxia, but not NE, elicited a large motor burst and silenced the network. The stereotyped response to hypoxia persisted in the presence of both NE and an adrenergic receptor blocker that eliminates sensitivity to NE, indicating that noradrenergic signaling does not cause the arrest. Pharmacological inhibition of glycolysis and mitochondrial respiration recapitulated all features of hypoxia, implying that reduced ATP synthesis underlies the effects of hypoxia on network activity. Finally, activating modulatory mechanisms that dampen neuronal excitability when ATP falls, KATP channels and AMP-dependent protein kinase, did not resemble the hypoxic response. These results suggest energy failure- rather than inhibitory modulation- silences the respiratory network during hypoxia and emphasize the need to account for metabolic limitations before concluding that modulators arrest activity as an adaptation for energy conservation in the nervous system.

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Na+-K+-ATPase functions in the developing hippocampus: regional differences in CA1 and CA3 neuronal excitability and role in epileptiform network bursting

Journal of Neurophysiology ◽

10.1152/jn.00453.2020 ◽

2021 ◽

Vol 125 (1) ◽

pp. 1-11

Author(s):

Li-Rong Shao ◽

Remi Janicot ◽

Carl E. Stafstrom

Keyword(s):

Transmitter Release ◽

Regional Differences ◽

Neuronal Excitability ◽

Neuronal Firing ◽

Developing Brain ◽

Network Activity ◽

Extensive Literature ◽

Ca1 Neurons ◽

Pump Activity ◽

Neuronal Functions

Despite the extensive literature showing the importance of the Na+-K+ pump in various neuronal functions, its roles in the developing brain are not well understood. This study reveals that the Na+-K+ pump differentially regulates the excitability of CA3 and CA1 neurons in the developing hippocampus, and the pump activity is crucial for maintaining network activity. Compromised Na+-K+ pump activity desynchronizes neuronal firing and transmitter release, leading to cessation of ongoing epileptiform network bursting.

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COUP-TFI/Nr2f1 Orchestrates Intrinsic Neuronal Activity during Development of the Somatosensory Cortex

Cerebral Cortex ◽

10.1093/cercor/bhaa137 ◽

2020 ◽

Vol 30 (11) ◽

pp. 5667-5685 ◽

Cited By ~ 1

Author(s):

Isabel Del Pino ◽

Chiara Tocco ◽

Elia Magrinelli ◽

Andrea Marcantoni ◽

Celeste Ferraguto ◽

...

Keyword(s):

Neuronal Excitability ◽

Pyramidal Neurons ◽

Time Windows ◽

Critical Time ◽

Network Activity ◽

Intrinsic Excitability ◽

Developmental Sequence ◽

Genetic Mechanisms ◽

Layer V ◽

Voltage Gated Ion Channels

Abstract The formation of functional cortical maps in the cerebral cortex results from a timely regulated interaction between intrinsic genetic mechanisms and electrical activity. To understand how transcriptional regulation influences network activity and neuronal excitability within the neocortex, we used mice deficient for Nr2f1 (also known as COUP-TFI), a key determinant of primary somatosensory (S1) area specification during development. We found that the cortical loss of Nr2f1 impacts on spontaneous network activity and synchronization of S1 cortex at perinatal stages. In addition, we observed alterations in the intrinsic excitability and morphological features of layer V pyramidal neurons. Accordingly, we identified distinct voltage-gated ion channels regulated by Nr2f1 that might directly influence intrinsic bioelectrical properties during critical time windows of S1 cortex specification. Altogether, our data suggest a tight link between Nr2f1 and neuronal excitability in the developmental sequence that ultimately sculpts the emergence of cortical network activity within the immature neocortex.

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