Biology subjects

Huguenard, J. R.

Publications and source records attributed to Huguenard, J. R..

12 recordsLinked to original sources

bioRxiv2025

A Dual Inhibitory Network in the Thalamic Reticular Nucleus Delineated by Pallidal and Intra-Reticular Inhibition

Long described as an inhibitory "guardian of the gateway," the thalamic reticular nucleus (TRN) shapes which thalamic signals reach the cortex during attention, arousal, and sensory processing. However, how the inhibitory wiring within TRN supports this flexible gating--from modality-specific tuning to global control--remains poorly defined. Using cell type-specific optogenetic input mapping and whole-cell patch-clamp recordings in mice, we dissect inhibitory connectivity in TRN from two major GABAergic sources: the TRN itself and the external globus pallidus (GPe). All recorded TRN neurons received inhibition from the GPe, whereas a subset also received intra-TRN inhibition. Intra-TRN inhibition arose predominantly from somatostatin-expressing onto parvalbumin-expressing TRN neurons (SOM[->]PV), revealing subtype-specific connectivity recruited by thalamic excitation to form a feedforward motif. These findings delineate a dual inhibitory architecture: local intra-TRN circuits provide spatially selective inhibition, whereas pallidal inputs deliver diffuse inhibition. These complementary mechanisms may support both modality-specific gating and global state-dependent control of thalamic output. Graphical AbstractThe thalamic reticular nucleus (TRN) integrates two distinct inhibitory motifs. Sparse, dendrite-targeting intra-TRN connections from parvalbumin- and somatostatin-expressing neurons provide structured, feedforward inhibition recruited by thalamocortical (TC) inputs. In parallel, robust and widespread inhibition from Npas1-expressing neurons of the external globus pallidus (GPe) supplies a strong external drive that can coordinate activity across the TRN. Together, these complementary motifs define a dual inhibitory architecture that may shape thalamocortical gating and highlight cellular entry points for therapeutic intervention. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=183 SRC="FIGDIR/small/680571v1_ufig1.gif" ALT="Figure 1"> View larger version (36K): org.highwire.dtl.DTLVardef@19035b0org.highwire.dtl.DTLVardef@b4f323org.highwire.dtl.DTLVardef@1c68d8eorg.highwire.dtl.DTLVardef@777c15_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2025

Beyond seizure control: identifying deficits in cognitive networks in absence seizure.

Absence epilepsy is frequently associated with cognitive impairments, yet the direct or indirect involvement of cognitive circuits remains poorly understood, as spike-and-wave discharges are rarely reported in these regions. Here, we investigate the role of a thalamic-prefrontal pathway in a mouse model of absence epilepsy (Scn8a+/-). We find that Scn8a+/- mice exhibit deficits in reversal learning, along with impaired recruitment of medial prefrontal cortex (mPFC) neurons by the Reuniens nucleus of the thalamus. This deficit is accompanied by an altered excitation-inhibition balance and reduced excitability of layer I interneurons in the mPFC, which constitutes the main recipient zone of reuniens inputs to the mPFC. Remarkably, stimulation of Reuniens at 20 Hz significantly reduces seizure incidence and improves performance in reversal learning. Our findings reveal previously unrecognized cognitive circuit dysfunctions in absence epilepsy and highlight the thalamo-prefrontal axis as a promising target for both cognitive and seizure-related interventions.

neuroscience↗

bioRxiv2025

Interpretable Machine Learning Identifies an Emergent Absence Seizure Mechanism

Absence seizures are widespread spike-and-wave oscillations disrupting consciousness. Several consciousness frameworks emphasize intercortical/thalamocortical feedback dynamics, but we lack explicit dynamical mechanisms for how seizures disrupt these circuits. Using interpretable machine learning, we derived dynamical equations directly from seizure electrocorticogram data, reproducing seconds-long multi-regional local field potentials with precision matching inter-mouse variability. The model contained a low-dimensional chaotic seizure attractor emerging from between-region synchronization at preferred phase-lags. Unit recordings revealed corresponding spiking synchrony at single-neuron resolution, linking somatosensory and motor cortex with posterior thalamic nucleus (PO). Model coupling terms predicted tonic and burst firing spatiotemporal organization across regions and guided multisite-optogenetic stimulations. These stimulations showed PO controls corticocortical connectivity gain and that motor/somatosensory corticocortical functional connectivity varies at predicted phase-lags to drive seizures. Our results define absence seizures as dynamics confined to a chaotic attractor within a circuit implicated in anesthetic unconsciousness, linking distributed network chaos to loss of consciousness.

neuroscience↗

bioRxiv2025

Reticular Thalamic Hyperexcitability Drives Autism Spectrum Disorder Behaviors in the Cntnap2 Model of Autism

Autism spectrum disorders (ASDs) are a group of neurodevelopmental disorders characterized by social communication deficits, repetitive behaviors, and comorbidities such as sensory abnormalities, sleep disturbances, and seizures. Dysregulation of thalamocortical circuits has been implicated in these comorbid features, yet their precise roles in ASD pathophysiology remain elusive. This study focuses on the reticular thalamic nucleus (RT), a key regulator of thalamocortical interactions, to elucidate its contribution to ASD-related behavioral deficits using a Cntnap2 knockout (KO) mouse model. Our behavioral and EEG analyses comparing Cntnap2+/+ and Cntnap2-/- mice demonstrated that Cntnap2 knockout heightened seizure susceptibility, elevated locomotor activity, and produced hallmark ASD phenotypes, including social deficits, and repetitive behaviors. Electrophysiological recordings from thalamic brain slices revealed increased spontaneous and evoked network oscillations with increased RT excitability due to enhanced T-type calcium currents and burst firing. We observed behavior related heightened RT population activity in vivo with fiber photometry. Notably, suppressing RT activity via Z944, a T-type calcium channel blocker, and via C21 and the inhibitory DREADD hM4Di, improved ASD-related behavioral deficits. These findings identify RT hyperexcitability as a mechanistic driver of ASD behaviors and underscore RT as a potential therapeutic target for modulating thalamocortical circuit dysfunction in ASD. TeaserRT hyperexcitability drives ASD behaviors in Cntnap2-/- mice, highlighting RT as a therapeutic target for circuit dysfunction.

neuroscience↗

bioRxiv2025

Actions of the Anti-Seizure Drug Carbamazepine in the Thalamic Reticular Nucleus: Potential Mechanism of Aggravating Absence Seizures

Carbamazepine (CBZ) is a widely used antiepileptic drug effective in managing partial and generalized tonic-clonic seizures. Despite its established therapeutic efficacy, CBZ has been reported to worsen seizures in another form of epilepsy, generalized absence seizures, in both clinical and experimental settings. In this study, we focused on thalamic reticular (RT) neurons, which regulate thalamocortical network activity in absence seizures, to investigate whether CBZ alters their excitability, thereby contributing to the exacerbation of seizures. Using ex vivo whole-cell patch-clamp electrophysiology, we found that CBZ selectively inhibits the tonic firing of RT neurons in a dose-dependent manner without affecting burst firing. At the RT-thalamocortical (RT-TC) synapse, CBZ significantly increases the failure rate of GABAergic synaptic transmission, with greater effects on somatostatin (SST) - than parvalbumin (PV) - expressing RT neurons. In vivo EEG recordings and open-field behavior in Scn8amed+/- mouse model confirmed that CBZ treatment exacerbates absence seizures, increasing both seizure frequency and duration while reducing locomotor activity. In addition, CBZ further amplifies the pre-existing reduction in tonic firing of RT in Scn8amed+/- mice. These findings uncover a novel mechanism by which CBZ exacerbates absence seizures through selective inhibition of RT neuron excitability and disruption of GABAergic synaptic transmission. This work provides mechanistic insights into the paradoxical effects of CBZ and suggest potential avenues for optimizing epilepsy treatment strategies. Scientific SignificanceThis study addresses the clinical paradox in which CBZ, a widely prescribed antiepileptic drug, paradoxically aggravates absence seizures. Understanding the cellular mechanisms behind this phenomenon is critical for improving epilepsy treatments. Here, using electrophysiology recordings from intact thalamocortical slices and SCN8amed+/- mice, an absence seizure animal model, we demonstrate that CBZ selectively inhibits tonic firing of RT neurons and their output to thalamocortical circuits, with a more pronounced effect in SCN8amed+/- mice. These novel findings provide a mechanistic explanation for CBZs paradoxical aggravation of absence seizures, offering a framework for understanding the pharmacological effects of other anti-epilepsy drugs and guiding the development of more effective therapeutic strategies for epilepsy.

physiology↗

bioRxiv2024

Synaptic cell adhesion molecule Cdh6 identifies a class of sensory neurons with novel functions in colonic motility

Intrinsic sensory neurons are an essential part of the enteric nervous system (ENS) and play a crucial role in gastrointestinal tract motility and digestion. Neuronal subtypes in the ENS have been distinguished by their electrophysiological properties, morphology, and expression of characteristic markers, notably neurotransmitters and neuropeptides. Here we investigated synaptic cell adhesion molecules as novel cell type markers in the ENS. Our work identifies two Type II classic cadherins, Cdh6 and Cdh8, specific to sensory neurons in the mouse colon. We show that Cdh6+ neurons demonstrate all other distinguishing classifications of enteric sensory neurons including marker expression of Calcb and Nmu, Dogiel type II morphology and AH-type electrophysiology and IH current. Optogenetic activation of Cdh6+ sensory neurons in distal colon evokes retrograde colonic motor complexes (CMCs), while pharmacologic blockade of rhythmicity-associated current IH disrupts the spontaneous generation of CMCs. These findings provide the first demonstration of selective activation of a single neurochemical and functional class of enteric neurons, and demonstrate a functional and critical role for sensory neurons in the generation of CMCs. One-Sentence SummaryIntrinsic sensory neurons of the enteric nervous system in the mouse distal colon exclusively express synaptic cell adhesion molecules Cdh6 and Cdh8, evoke retrograde colonic motor complexes (CMCs) when stimulated, and possess rhythmicity-associated IH current, involved in producing spontaneous CMCs.

neuroscience↗

bioRxiv2024

Reuniens thalamus recruits recurrent excitation in medial prefrontal cortex.

Medial prefrontal cortex (mPFC) and hippocampus are critical for memory retrieval, decision making and emotional regulation. While ventral CA1 (vCA1) shows direct and reciprocal connections with mPFC, dorsal CA1 (dCA1) forms indirect pathways to mPFC, notably via the thalamic Reuniens nucleus (Re). Neuroanatomical tracing has documented structural connectivity of this indirect pathway through Re however, its functional operation is largely unexplored. Here we used in vivo and in vitro electrophysiology along with optogenetics to address this question. Whole-cell patch-clamp recordings in acute mouse brain slices revealed both monosynaptic excitatory responses and disynaptic feedforward inhibition at Re-mPFC synapses. However, we also identified a novel prolonged excitation of mPFC by Re. These early monosynaptic and late recurrent components are in marked contrast to the primarily feedforward inhibition characteristic of thalamic inputs to neocortex. Local field potential recordings in mPFC brain slices revealed prolonged synaptic activity throughout all cortical lamina upon Re activation, with the late excitation enhanced by blockade of parvalbumin neurons and GABAARs. In vivo Neuropixels recordings in head-fixed awake mice revealed a similar prolonged excitation of mPFC units by Re activation. In summary, Re output produces recurrent feedforward excitation within mPFC suggesting a potent amplification system in the Re-mPFC network. This may facilitate amplification of dCA1->mPFC signals for which Re acts as the primary conduit, as there is little direct connectivity. In addition, the capacity of mPFC neurons to fire bursts of action potentials in response to Re input suggests that these synapses have a high gain. Significance statementThe interactions between medial prefrontal cortex and hippocampus are crucial for memory formation and retrieval. Yet, it is still poorly understood how the functional connectivity of direct and indirect pathways underlies these functions. This research explores the synaptic connectivity of the indirect pathway through the Reuniens nucleus of the thalamus using electrophysiological recordings and optogenetic manipulations. The study found that Reuniens stimulation recruits recurrent and long-lasting activity in mPFC - a phenomenon not previously recorded. This recurrent activity might create a temporal window ideal for coincidence detection and be an underlying mechanism for memory formation and retrieval.

neuroscience↗

bioRxiv2023

Human assembloids reveal the consequences of CACNA1G gene variants in the thalamocortical pathway

Abnormalities in crosstalk between the thalamus and the cerebral cortex are thought to lead to severe neuropsychiatric disorders, such as epilepsy and psychotic disorders. Pathogenic variants in the CACNA1G gene, which encodes the 1G subunit of the thalamus-enriched T-type voltage-gated calcium channel CaV3.1, are associated with absence seizures, intellectual disability, and schizophrenia, but the cellular and circuit level consequences of these genetic variants in humans remain unknown. Here, we developed an in vitro human assembloid model of the thalamocortical pathway to systematically dissect the contribution of genetic variants in T-type calcium channels. We discovered that a CACNA1G variant (M1531V) associated with seizures led to changes in T-type currents in human thalamic neurons, as well as correlated hyperactivity of thalamic and cortical neurons in thalamo-cortical assembloids. In contrast, CACNA1G loss, which has been associated with risk of schizophrenia, resulted in abnormal thalamocortical connectivity that was related to both increased spontaneous thalamic activity and aberrant thalamic axonal projections. Taken together, these results illustrate the utility of organoid and assembloid systems for interrogating human genetic disease risk variants at both cellular and circuit level.

neuroscience↗

bioRxiv2022

Prefrontal PV interneurons facilitate attention and are linked to attentional dysfunction in a mouse model of absence epilepsy

Absence seizures are characterized by brief periods of unconsciousness accompanied by a lapse in motor function that can occur hundreds of times throughout the day. Outside of these frequent moments of unconsciousness, approximately a third of patients experience treatment-resistant attention impairments. Convergent evidence suggests prefrontal cortex (PFC) dysfunction may underlie attention impairments in affected patients. To test this, we use a combination of slice physiology, fiber photometry, electrocorticography (ECoG), optogenetics, and behavior in the Scn8a+/- mouse model of absence epilepsy. In these mice, we find decreased parvalbumin interneuron (PVIN) recruitment in the medial PFC (mPFC) in vitro and hypoactivity during cue presentation in vivo that is linked to attention dysfunction. Further, we find that low levels of mPFC PVIN activity are predictive of poorer performance in WT littermates. This highlights cue-evoked PVIN activity as an important mechanism for attention and suggests PVINs may represent a therapeutic target for cognitive comorbidities in absence epilepsy.

neuroscience↗

bioRxiv2020

Precise spatiotemporal control of voltage-gated sodium channels by photocaged saxitoxin

Here we report the pharmacologic blockade of voltage-gated sodium ion channels (NaV) by a synthetic saxitoxin derivative affixed to a photocleavable protecting group. We demonstrate that a functionalized saxitoxin (STX-eac) enables exquisite spatiotemporal control of NaV blockade to interrupt action potentials (APs) in dissociated neurons and nerve fiber bundles. The photo-uncaged inhibitor (STX-ea) is a nanomolar potent, reversible binder of NaVs. We use STX-eac to reveal differential susceptibility of myelinated and unmyelinated axons in the corpus callosum to NaV-dependent alterations in AP propagation, with unmyelinated axons preferentially showing reduced AP fidelity under conditions of partial NaV blockade. These results validate STX-eac as a high precision tool for robust photocontrol of neuronal excitability and AP generation.

neuroscience↗

bioRxiv2020

Nonlinearities between inhibition and T-type calcium channel activity bidirectionally regulate thalamic network oscillations

Absence seizures result from 3-5 Hz generalized thalamocortical oscillations that depend on highly regulated inhibitory neurotransmission in the thalamus. Efficient reuptake of the inhibitory neurotransmitter GABA is essential, and reuptake failure worsens seizures. Here, we show that blocking GABA transporters (GATs) in acute brain slices containing key parts of the thalamocortical seizure network modulates epileptiform activity. As expected, we found that blocking either GAT1 or GAT3 prolonged oscillations. However, blocking both GATs unexpectedly suppressed oscillations. Integrating experimental observations into single-neuron and network-level computational models shows how a non-linear dependence of T-type calcium channel opening on GABAB receptor activity regulates network oscillations. Receptor activity that is either too brief or too protracted fails to sufficiently open T-type channels necessary for sustaining oscillations. Only within a narrow range does prolonging GABAB receptor activity promote channel opening and intensify oscillations. These results have implications for therapeutics that modulate GABA transporters.

neuroscience↗

bioRxiv2020

Thalamic activity patterns unfolding over multiple time scales predict seizure onset in absence epilepsy

The brain has a remarkable, yet poorly understood, capacity to perform rapid dynamic switching between different cognitive states. Absence epilepsy, characterized by sudden transitions to and from highly synchronous thalamocortical oscillations, provides a unique window to investigate rapid state switching. Here we explored the transition into seizures in detail using simultaneous extracellular unit recordings from the thalamocortical circuit in the Scn8a mouse, a validated murine model of absence epilepsy. We find that trial-averaged neural firing in the thalamus, but not cortex, was transiently elevated several seconds prior to seizure onset. However, we observed large single-trial variability in pre-ictal dynamics both within and across subjects, suggesting possible heterogeneous transition dynamics into absence seizures. To quantify the single-trial amplitude and temporal variability, we developed a statistical model, which revealed that individual seizures are preceded by low dimensional neural dynamics that vary in amplitude and time across seizures. Interestingly, the single-trial pre-seizure amplitude modulation uncovered by the model showed strong periodicity over trials, suggesting that pre-ictal dynamics may co-modulate with arousal state. To our knowledge, our results are the first characterization of single-unit pre-ictal firing dynamics across the thalamocortical circuit in absence epilepsy. Our results argue that seizure-monitoring devices may be able to capitalize on seizure-by-seizure changes in pre-ictal activity to better predict seizure onset, and that the thalamus may be a source of clinically useful pre-ictal signatures.

neuroscience↗