Localized Chemogenetic Silencing of Inhibitory Neurons: A novel Mouse Model of Focal Cortical Seizures

AbstractFocal cortical epilepsies are frequently refractory to available anticonvulsant drug therapies. One key factor contributing to this state is the limited availability of animal models that allow to reliably study focal cortical seizures and how they recruit surrounding brain areas in-vivo. In this study, we selectively expressed the inhibitory chemogenetic receptor, hM4D, in GABAergic neurons in focal cortical areas using viral gene transfer. Following focal silencing of GABAergic neurons by administration of Clozapine-N-Oxide (CNO), we demonstrated reliable induction of local epileptiform events in the electroencephalogram (EEG) signal of awake freely moving mice. Experiments in anesthetized mice showed consistent induction of focal seizures in two different brain regions – the barrel cortex (BC) and at the medial prefrontal cortex (mPFC). Seizures were accompanied by high frequency oscillations, a known characteristic of human focal seizures. Seizures propagated, but an analysis of seizure propagation revealed favored propagation pathways. CNO-induced epileptiform events propagated from the BC on one hemisphere to its counterpart and from the BC to the mPFC, but not vice-versa. Lastly, post-CNO epileptiform events in the BC could be triggered by sensory whisker-pad stimulation, indicating that this model, applied to sensory cortices, may be useful to study sensory-evoked seizures. Taken together, our results show that targeted chemogenetic inhibition of GABAergic neurons using hM4D can serve as a novel, versatile and reliable model of focal cortical epilepsy suitable to systematically study cortical ictogenesis in different cortical areas.Significance StatementFocal cortical epilepsies are often hard to alleviate using current anticonvulsant therapies while further drug discovery is impeded by the limited variety of suitable animal models. In this study, we established a novel model of focal cortical seizures induced by spatially-restricted chemogenetic silencing of cortical inhibitory neurons. We have shown this method to be effective at various cortical regions and reliably induce seizures that share key characteristics with known human epilepsy traits, including sensory triggering and seizure propagation. This model may thus be used to advance the discovery of new remedies for focal cortical epilepsies, as well as to improve our understanding of seizure spread along different cortical pathways.

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Statistical Comparison of Spike Responses to Natural Stimuli in Monkey Area V1 With Simulated Responses of a Detailed Laminar Network Model for a Patch of V1

Journal of Neurophysiology ◽

10.1152/jn.00845.2009 ◽

2011 ◽

Vol 105 (2) ◽

pp. 757-778 ◽

Cited By ~ 17

Author(s):

Malte J. Rasch ◽

Klaus Schuch ◽

Nikos K. Logothetis ◽

Wolfgang Maass

Keyword(s):

Network Model ◽

Network Models ◽

Cortical Network ◽

Inhibitory Neurons ◽

Sensory Stimuli ◽

Natural Stimuli ◽

Cortical Areas ◽

Model Response ◽

Spiking Activity

A major goal of computational neuroscience is the creation of computer models for cortical areas whose response to sensory stimuli resembles that of cortical areas in vivo in important aspects. It is seldom considered whether the simulated spiking activity is realistic (in a statistical sense) in response to natural stimuli. Because certain statistical properties of spike responses were suggested to facilitate computations in the cortex, acquiring a realistic firing regimen in cortical network models might be a prerequisite for analyzing their computational functions. We present a characterization and comparison of the statistical response properties of the primary visual cortex (V1) in vivo and in silico in response to natural stimuli. We recorded from multiple electrodes in area V1 of 4 macaque monkeys and developed a large state-of-the-art network model for a 5 × 5-mm patch of V1 composed of 35,000 neurons and 3.9 million synapses that integrates previously published anatomical and physiological details. By quantitative comparison of the model response to the “statistical fingerprint” of responses in vivo, we find that our model for a patch of V1 responds to the same movie in a way which matches the statistical structure of the recorded data surprisingly well. The deviation between the firing regimen of the model and the in vivo data are on the same level as deviations among monkeys and sessions. This suggests that, despite strong simplifications and abstractions of cortical network models, they are nevertheless capable of generating realistic spiking activity. To reach a realistic firing state, it was not only necessary to include both N -methyl-d-aspartate and GABAB synaptic conductances in our model, but also to markedly increase the strength of excitatory synapses onto inhibitory neurons (>2-fold) in comparison to literature values, hinting at the importance to carefully adjust the effect of inhibition for achieving realistic dynamics in current network models.

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4E-BP2–dependent translation in parvalbumin neurons controls epileptic seizure threshold

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2025522118 ◽

2021 ◽

Vol 118 (15) ◽

pp. e2025522118

Author(s):

Vijendra Sharma ◽

Rapita Sood ◽

Danning Lou ◽

Tzu-Yu Hung ◽

Maxime Lévesque ◽

...

Keyword(s):

Animal Models ◽

Mammalian Target Of Rapamycin ◽

Neuronal Cell ◽

Mrna Translation ◽

Translation Initiation Factor ◽

Inhibitory Neurons ◽

Initiation Factor ◽

Seizure Threshold ◽

Parvalbumin Neurons

The mechanistic/mammalian target of rapamycin complex 1 (mTORC1) integrates multiple signals to regulate critical cellular processes such as mRNA translation, lipid biogenesis, and autophagy. Germline and somatic mutations in mTOR and genes upstream of mTORC1, such as PTEN, TSC1/2, AKT3, PIK3CA, and components of GATOR1 and KICSTOR complexes, are associated with various epileptic disorders. Increased mTORC1 activity is linked to the pathophysiology of epilepsy in both humans and animal models, and mTORC1 inhibition suppresses epileptogenesis in humans with tuberous sclerosis and animal models with elevated mTORC1 activity. However, the role of mTORC1-dependent translation and the neuronal cell types mediating the effect of enhanced mTORC1 activity in seizures remain unknown. The eukaryotic translation initiation factor 4E-binding protein 1 (4E-BP1) and 2 (4E-BP2) are translational repressors downstream of mTORC1. Here we show that the ablation of 4E-BP2, but not 4E-BP1, in mice increases the sensitivity to pentylenetetrazole (PTZ)- and kainic acid (KA)–induced seizures. We demonstrate that the deletion of 4E-BP2 in inhibitory, but not excitatory neurons, causes an increase in the susceptibility to PTZ-induced seizures. Moreover, mice lacking 4E-BP2 in parvalbumin, but not somatostatin or VIP inhibitory neurons exhibit a lowered threshold for seizure induction and reduced number of parvalbumin neurons. A mouse model harboring a human PIK3CA mutation that enhances the activity of the PI3K-AKT pathway (Pik3caH1047R-Pvalb) selectively in parvalbumin neurons shows susceptibility to PTZ-induced seizures. Our data identify 4E-BP2 as a regulator of epileptogenesis and highlight the central role of increased mTORC1-dependent translation in parvalbumin neurons in the pathophysiology of epilepsy.

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Restoration of Mecp2 expression in GABAergic neurons is sufficient to rescue multiple disease features in a mouse model of Rett syndrome

eLife ◽

10.7554/elife.14198 ◽

2016 ◽

Vol 5 ◽

Cited By ~ 53

Author(s):

Kerstin Ure ◽

Hui Lu ◽

Wei Wang ◽

Aya Ito-Ishida ◽

Zhenyu Wu ◽

...

Keyword(s):

Social Skills ◽

Mouse Model ◽

Rett Syndrome ◽

Therapeutic Option ◽

Neurodevelopmental Disorder ◽

Gabaergic Neurons ◽

Inhibitory Neurons ◽

Extended Lifespan ◽

Inhibitory Signaling

The postnatal neurodevelopmental disorder Rett syndrome, caused by mutations in MECP2, produces a diverse array of symptoms, including loss of language, motor, and social skills and the development of hand stereotypies, anxiety, tremor, ataxia, respiratory dysrhythmias, and seizures. Surprisingly, despite the diversity of these features, we have found that deleting Mecp2 only from GABAergic inhibitory neurons in mice replicates most of this phenotype. Here we show that genetically restoring Mecp2 expression only in GABAergic neurons of male Mecp2 null mice enhanced inhibitory signaling, extended lifespan, and rescued ataxia, apraxia, and social abnormalities but did not rescue tremor or anxiety. Female Mecp2+/- mice showed a less dramatic but still substantial rescue. These findings highlight the critical regulatory role of GABAergic neurons in certain behaviors and suggest that modulating the excitatory/inhibitory balance through GABAergic neurons could prove a viable therapeutic option in Rett syndrome.

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Illuminating the Neural Circuits Underlying Orienting of Attention

Vision ◽

10.3390/vision3010004 ◽

2019 ◽

Vol 3 (1) ◽

pp. 4 ◽

Cited By ~ 1

Author(s):

Michael Posner ◽

Cristopher Niell

Keyword(s):

Animal Models ◽

Superior Colliculus ◽

Large Scale ◽

Neural Circuits ◽

Cell Types ◽

Local Networks ◽

Sensory Stimuli ◽

Cortical Areas ◽

Large Scale Networks ◽

Human Neuroimaging

Human neuroimaging has revealed brain networks involving frontal and parietal cortical areas as well as subcortical areas, including the superior colliculus and pulvinar, which are involved in orienting to sensory stimuli. Because accumulating evidence points to similarities between both overt and covert orienting in humans and other animals, we propose that it is now feasible, using animal models, to move beyond these large-scale networks to address the local networks and cell types that mediate orienting of attention. In this opinion piece, we discuss optogenetic and related methods for testing the pathways involved, and obstacles to carrying out such tests in rodent and monkey populations.

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A NEUROBIOLOGICAL THEORY OF MEANING IN PERCEPTION PART III: MULTIPLE CORTICAL AREAS SYNCHRONIZE WITHOUT LOSS OF LOCAL AUTONOMY

International Journal of Bifurcation and Chaos ◽

10.1142/s0218127403008260 ◽

2003 ◽

Vol 13 (10) ◽

pp. 2845-2856 ◽

Cited By ~ 38

Author(s):

WALTER J. FREEMAN ◽

GYöNGYI GAÁL ◽

REBECKA JORSTEN

Keyword(s):

Information Transfer ◽

Phase Locking ◽

Pulse Frequency ◽

Inhibitory Neurons ◽

Oscillatory Activity ◽

Electrode Arrays ◽

Ensemble Averaging ◽

Pulse Frequency Modulation ◽

Cortical Areas ◽

Gamma Range

Information transfer and integration among functionally distinct areas of cerebral cortex of oscillatory activity require some degree of phase synchrony of the trains of action potentials that carry the information prior to the integration. However, propagation delays are obligatory. Delays vary with the lengths and conduction velocities of the axons carrying the information, causing phase dispersion. In order to determine how synchrony is achieved despite dispersion, we recorded EEG signals from multiple electrode arrays on five cortical areas in cats and rabbits, that had been trained to discriminate visual or auditory conditioned stimuli. Analysis by time-lagged correlation, multiple correlation and PCA, showed that maximal correlation was at zero lag and averaged 0.7, indicating that 50% of the power in the gamma range among the five areas was at zero lag irrespective of phase or frequency. There were no stimulus-related episodes of transiently increased phase locking among the areas, nor EEG "bursts" of transiently increased amplitude above the sustained level of synchrony. Three operations were identified to account for the sustained correlation. Cortices broadcast their outputs over divergent–convergent axonal pathways that performed spatial ensemble averaging; synaptic interactions between excitatory and inhibitory neurons in cortex operated as band pass filters for gamma; and signal coarse-graining by pulse frequency modulation at trigger zones enhanced correlation. The conclusion is that these three operations enable continuous linkage of multiple cortical areas by activity in the gamma range, providing the basis for coordinated cortical output to other parts of the brain, despite varying axonal conduction delays, something like the back plane of a main frame computer.

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Development of subpopulations of GABAergic neurons in cat visual cortical areas

Neuroreport ◽

10.1097/00001756-199212000-00009 ◽

1992 ◽

Vol 3 (12) ◽

pp. 1069-1072 ◽

Cited By ~ 15

Author(s):

Dale Hogan ◽

Erin R. Terwilleger ◽

Nancy E. J. Berman

Keyword(s):

Gabaergic Neurons ◽

Cortical Areas ◽

Visual Cortical

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Regulation of REM Sleep by Inhibitory Neurons in the Dorsomedial Medulla

10.1101/2020.11.30.405530 ◽

2020 ◽

Author(s):

Joseph A. Stucynski ◽

Amanda L. Schott ◽

Justin Baik ◽

Shinjae Chung ◽

Franz Weber

Keyword(s):

Eye Movement ◽

Rem Sleep ◽

Gabaergic Neurons ◽

Inhibitory Neurons ◽

Sleep Stages ◽

Rapid Eye Movement ◽

Rapid Eye Movement Sleep ◽

Brain Rhythms ◽

Slow Activity ◽

Raphé Nuclei

ABSTRACTThe two major stages of mammalian sleep – rapid eye movement sleep (REMs) and non-REM sleep (NREMs) – are characterized by distinct brain rhythms ranging from millisecond to minute-long (infraslow) oscillations. The mechanisms controlling transitions between sleep stages and how they are synchronized with infraslow rhythms remain poorly understood. Using opto- and chemogenetic manipulation, we show that GABAergic neurons in the dorsomedial medulla (dmM) promote the initiation and maintenance of REMs, in part through their projections to the dorsal and median raphe nuclei. Fiber photometry revealed that dmM GABAergic neurons are strongly activated during REMs. During NREMs, their activity fluctuated in close synchrony with infraslow oscillations in the spindle band of the electroencephalogram, and the phase of this rhythm modulated the latency of optogenetically induced REMs episodes. Thus, dmM inhibitory neurons powerfully promote REMs, and their slow activity fluctuations may coordinate transitions from NREMs to REMs with infraslow brain rhythms.

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Evolution of Neocortex for Sensory Processing

Oxford Research Encyclopedia of Neuroscience ◽

10.1093/acrefore/9780190264086.013.111 ◽

2019 ◽

Author(s):

Jon H. Kaas

Keyword(s):

Sensory Processing ◽

Cortical Neurons ◽

Pyramidal Neurons ◽

Motor Behavior ◽

Single Layer ◽

Small Region ◽

Inhibitory Neurons ◽

Dorsal Cortex ◽

Structural Differentiation ◽

Cortical Areas

The neocortex is a part of the forebrain of mammals that is an innovation of mammal-like “reptilian” synapsid ancestors of early mammals. This neocortex emerged from a small region of dorsal cortex that was present in earlier ancestors and is still found in the forebrain of present-day reptiles. Instead of the thick structure of six layers of cells (five layers) and fibers (one layer) of neocortex of mammals, the dorsal cortex was characterized by a single layer of pyramidal neurons and a scattering of small, largely inhibitory neurons. In reptiles, the dorsal cortex is dominated by visual inputs, with outputs that relate to behavior and memory. The thicker neocortex of six layers in early mammals was already divided into a number of functionally specialized zones called cortical areas that were predominantly sensory in function, while relating to important aspects of motor behavior via subcortical projections. These early sensorimotor areas became modified in various ways as different branches of the mammalian radiation evolved, and neocortex often increased in size and the number of cortical areas, likely by the process of specializations within areas that subdivided areas. At least some areas, perhaps most, subdivided in another way by evolving two or more alternating types of small regions of different functional specializations, now referred to as cortical modules or columns. The specializations within and across cortical areas included those in the sizes of neurons and the extents of their processes, the dendrites and axons, and thus connections with other neurons. As a result, the neocortex of present-day mammals varies greatly within and across phylogenetically related groups (clades), while retaining basic features of organization from early ancestral mammals. In a number of present-day (extant) mammals, brains are relatively small and have little neocortex, with few areas and little structural differentiation, thus resembling early mammals. Other small mammals with little neocortex have specialized some part via selective enlargement and structural modifications to promote certain sensory abilities. Other mammals have a neocortex that is moderately to greatly expanded, with more cortical areas directly related to sensory processing and cognition and memory. The human brain is extreme in this way by having more neocortex in proportion to the rest of the brain, more cortical neurons, and likely more cortical areas.

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Pulmonary surfactant lipids inhibit infections with the pandemic H1N1 influenza virus in several animal models

Journal of Biological Chemistry ◽

10.1074/jbc.ra119.012053 ◽

2019 ◽

Vol 295 (6) ◽

pp. 1704-1715 ◽

Cited By ~ 7

Author(s):

Mari Numata ◽

James R. Mitchell ◽

Jennifer L. Tipper ◽

Jeffrey D. Brand ◽

John E. Trombley ◽

...

Keyword(s):

Animal Models ◽

Influenza A ◽

Lethal Dose ◽

Viral Gene Expression ◽

Viral Gene ◽

Infection Model ◽

Viral Spread ◽

Viral Burden ◽

Influenza A H1n1

The influenza A (H1N1)pdm09 outbreak in 2009 exemplified the problems accompanying the emergence of novel influenza A virus (IAV) strains and their unanticipated virulence in populations with no pre-existing immunity. Neuraminidase inhibitors (NAIs) are currently the drugs of choice for intervention against IAV outbreaks, but there are concerns that NAI-resistant viruses can transmit to high-risk populations. These issues highlight the need for new approaches that address the annual influenza burden. In this study, we examined whether palmitoyl-oleoyl-phosphatidylglycerol (POPG) and phosphatidylinositol (PI) effectively antagonize (H1N1)pdm09 infection. POPG and PI markedly suppressed cytopathic effects and attenuated viral gene expression in (H1N1)pdm09-infected Madin-Darby canine kidney cells. POPG and PI bound to (H1N1)pdm09 with high affinity and disrupted viral spread from infected to noninfected cells in tissue culture and also reduced (H1N1)pdm09 propagation by a factor of 102 after viral infection was established in vitro. In a mouse infection model of (H1N1)pdm09, POPG and PI significantly reduced lung inflammation and viral burden. Of note, when mice were challenged with a typically lethal dose of 1000 plaque-forming units of (H1N1)pdm09, survival after 10 days was 100% (14 of 14 mice) with the POPG treatment compared with 0% (0 of 14 mice) without this treatment. POPG also significantly reduced inflammatory infiltrates and the viral burden induced by (H1N1)pdm09 infection in a ferret model. These findings indicate that anionic phospholipids potently and efficiently disrupt influenza infections in animal models.

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Abstract TMP34: Longitudinal Calcium Imaging Reveals Circuit Switching and Abnormal Response Fidelity in Somatosensory Vip Interneuron Circuits in the Stroke Damaged Brain

Stroke ◽

10.1161/str.51.suppl_1.tmp34 ◽

2020 ◽

Vol 51 (Suppl_1) ◽

Author(s):

Craig E Brown ◽

Mohammad Motaharinia

Keyword(s):

Critical Role ◽

Significant Loss ◽

Inhibitory Neurons ◽

Circuit Switching ◽

Highly Active ◽

Cortical Interneurons ◽

Before And After ◽

Sensory Responses ◽

Sensory Evoked ◽

And Function

Although inhibitory cortical interneurons play a critical role in regulating brain excitability and function, the effects of stroke on these neurons is poorly understood. In particular, interneurons expressing vasoactive intestinal peptide (VIP) specialize in inhibiting other classes of inhibitory neurons, and thus serve to modulate cortical sensory processing. To understand how stroke affects this circuit, we imaged VIP neuron structure and function (using GCaMP6s) before and after focal stroke in forelimb somatosensory cortex. Stroke led to a significant loss of peri-infarct pre-synaptic boutons and dendritic spines that was followed by a wave of bouton/spine production. Larger-scale changes, such as pruning/growth of axons or dendritic branches was observed, albeit on a limited scale. Functionally, the fraction of forelimb responsive VIP interneurons and their response fidelity (defined as the % of forelimb responsive trials) was significantly reduced in the first week after stroke. The loss of responsiveness was most evident in highly active VIP neurons (defined by their level of responsiveness before stroke), whereas less active neurons were minimally affected. Of note, a small fraction of VIP neurons that were minimally active before stroke, became responsive afterwards suggesting that stroke may unmask sensory responses in some neurons. Although VIP responses to forepaw stimulation generally improved although not fully from 2-5 weeks recovery, the variance in response fidelity after stroke was comparatively high and therefore less predictable than that observed before stroke. Lastly, stroke related changes to synaptic structure and response properties were both restricted to within 400μm of the infarct border. These findings reveal the dynamic and resilient nature of VIP neurons and suggest that a sub-population of these cells are more apt to lose sensory responsiveness during the initial phase of stroke, whereas some minimally responsive cells are progressively recruited into the forelimb sensory circuit. Furthermore, stroke appears to disrupt the predictability of sensory evoked responses in these cortical interneurons which could have important consequences for sensory perception.

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