Biology subjects

Codadu, N. K.

Publications and source records attributed to Codadu, N. K..

9 recordsLinked to original sources

bioRxiv2026

Focal astrocyte Kir4.1 loss drives seizures, spreading depolarizations and postictal impairments

Astrocytic dysfunction is increasingly recognised as an important contributor to epileptogenesis and seizure dynamics. Kir4.1 potassium channels expressed in astrocytes play a critical role in activity-dependent extracellular potassium buffering, and their loss may impair network stability and promote pathological hyperexcitability. In epilepsy, seizures can be accompanied by spreading depolarizations (SDs), propagating waves of neuronal and glial depolarization. While seizure-associated SDs have been proposed to terminate seizures and limit seizure spread, they have also been implicated in postictal dysfunction and sudden unexpected death in epilepsy (SUDEP), and their significance in chronic epilepsy remains unclear. Here, we tested whether focal loss of astrocytic Kir4.1 in the adult hippocampus is sufficient to disrupt potassium buffering, generate spontaneous seizures, and promote seizure-associated SDs. Using astrocyte-targeted viral vector Cre recombinase in adult Kir4.1-floxed mice, we induced focal hippocampal reduction of Kir4.1 expression. This impaired activity-dependent potassium buffering, producing enhanced stimulation-evoked extracellular potassium accumulation and larger DC shifts in hippocampal slices. Chronic wireless EEG recordings demonstrated that focal astrocytic Kir4.1 loss was sufficient to induce spontaneous recurrent seizures and interictal epileptiform activity. To investigate seizure-associated SDs, we combined optogenetic stimulation with graphene-based micro-transistor recordings capable of stable full-bandwidth DC electrophysiology in awake head-fixed mice. Focal hippocampal loss of astrocytic Kir4.1 markedly increased susceptibility to evoked seizures accompanied by SDs. We used chronic wireless DC-coupled video-telemetry recordings to continuously monitor seizure and SD dynamics in freely moving mice. SDs occurred frequently during generalized seizures and were first detected in cortical channels. Seizures accompanied by SDs exhibited greater spectral power, longer duration, and prolonged postictal depression compared with seizures alone. Behaviourally, seizures accompanied by SDs were linked to postictal impairment characterised by behavioural arrest and abnormal motor behaviours. These findings highlight the utility of graphene micro-transistor arrays and chronic DC-coupled telemetry for resolving infraslow (<0.1 Hz) epileptic dynamics that are largely inaccessible using conventional electrophysiological approaches. Ground-truth DC-coupled recordings enabled identification of AC-band electrographic signatures that segregated seizures with SDs from seizures alone, raising the possibility that SD-associated seizures may be retrospectively inferred from conventional AC-coupled epilepsy datasets. We demonstrate that focal astrocytic Kir4.1 loss in the adult brain impairs potassium buffering and is sufficient to drive spontaneous seizures, supporting astrocytic potassium dysregulation as a determinant of seizure and spreading depolarization susceptibility in epilepsy. Furthermore, seizure-associated SDs are strongly linked to increased postictal impairments, supporting the concept that SDs are major determinants of pathological postictal states.

neuroscience↗

bioRxiv2025

Altered GluN2A levels reduce the emergence of seizure-like events in a rat model of GRIN2A haploinsufficiency

GluN2A-containing NMDA receptors, encoded by the GRIN2A gene, are critical components of excitatory synaptic transmission and are essential for proper brain development and function. Dysregulation of NMDA receptor activity is strongly implicated in the pathophysiology of epilepsy. While excessive GluN2A-mediated signalling can lead to hyperexcitability and seizure generation, loss-of-function mutations in GRIN2A, which result in reduced GluN2A expression, have also been identified in patients with various forms of epilepsy, including focal epilepsies and epileptic encephalopathies. This paradox highlights the complexity of NMDA receptor contributions to network excitability and suggests that both gain- and loss-of-function mutations can be pathogenic. However, the mechanisms through which reduced GluN2A expression influences seizure susceptibility remains unclear. In this study, we examined the impact of reduced and absence of GluN2A on seizure-like activity using in vitro model system. Hippocampal slices were prepared from wild-type littermate controls (Grin2a+/+), heterozygous (Grin2a+/-) and homozygous (Grin2a-/-) transgenic rats and subjected to pro-convulsant conditions to elicit epileptiform-like events. Specifically, we employed three well established in vitro epilepsy models: (i) 4-aminopyridine (4-AP), (ii) zero-magnesium with elevated potassium (0Mg{superscript 2}/5K), and (iii) high-potassium (high-K+). Local field potentials were recorded from the CA1 pyramidal layer to quantify interictal and seizure-like activity, by measuring latency to onset, event frequency, and duration. Spectral analyses were also conducted to assess alterations in network dynamics. Our findings reveal that reduced GluN2A expression alters the susceptibility of hippocampal circuits to seizure-like activity in a model-dependent manner. In the 4-AP model, Grin2a-/- slices exhibited a significantly lower frequency of interictal events and a delayed onset of seizure-like activity relative to both wild-type and heterozygous slices. In the 0Mg{superscript 2}/5K model, both Grin2a+/- and Grin2a-/- slices displayed reduced seizure susceptibility compared to wild-type. Finally, in the high-K model, Grin2a-/- slices showed a reduced incidence of seizure-like events compared to wild-type controls when extracellular potassium concentration was increased to 7.5 mM, although this effect was less apparent at higher concentrations (9.5 mM). These results suggest that partial or complete loss of GluN2A-containing NMDA receptors reduces the propensity of hippocampal networks to develop epileptiform activity, potentially by altering intrinsic or synaptic excitability. Our findings provide mechanistic insights into how GRIN2A loss-of-function variants may contribute to epilepsy and highlight the need to consider developmental and circuit-level compensations when interpreting the impact of GluN2A disruption.

neuroscience↗

bioRxiv2025

An artefact-resilient wide bandwidth bidirectional graphene neural interface

The ability to simultaneously record and modulate neural activity is critical for next-generation bidirectional neural interfaces aiming to enable adaptive neuromodulation therapies for neurological disorders. Active graphene transistor technologies are particularly promising for neural recordings, as they extend the ability to monitor brain activity at very low frequencies and support multiplexed operation for high-density neural interfaces. However, their limited charge injection capacity makes them unsuitable for stimulation. In this work, we present a bidirectional neural interface that combines nanoporous reduced graphene oxide (rGO) microelectrodes for high charge injection focal stimulation and graphene solution-gated field-effect transistors (gSGFETs) for brain activity monitoring, exploiting the advantages of both technologies in one single device. Using scalable cleanroom microfabrication techniques, we monolithically integrate these two graphene-based technologies into fully flexible probes. We evaluate the performance of the hybrid devices both in saline and in vivo, with a particular focus on transistor performance during stimulation. Our results demonstrate that the recording capability of this bidirectional neural interface, including the monitoring of infraslow and local field potential activity, is not compromised during stimulation. This work highlights the potential of this hybrid neural interface for both basic neurophysiological and clinical translation use.

neuroscience↗

bioRxiv2024

Lifting the degeneracy of optical fiber neural interfaces for optogenetics and electrophysiology by using axialtrodes

Modulating and recording neuronal activity are essential for probing brain function and developing therapies for neurological disorders. However, conventional flat-end optical fibers--widely used for deep brain access-- interact with neural tissue only at their distal tip, limiting spatial resolution across brain layers. To overcome this constraint, we introduce the microfluidic axialtrode: a soft, multimodal neural interface created by controllably angle-cleaving a thermally drawn, multimaterial optical fiber integrated with multiple metal electrodes and microfluidic channels. We demonstrate in vivo that this design enables spatially distributed optogenetics, multisite electrophysiological recording, and targeted drug delivery along the fibers axis, allowing simultaneous interaction with multiple neuronal layers. The axial configuration increases the functional interface with brain tissue, while the soft polymer construction and reduced cross-sectional footprint significantly suppress the inflammatory response compared to conventional silica fibers. Integration with a 3D-printed scaffold, fabricated from FDA-approved biocompatible resin, provides mechanical stability and compatibility with standard experimental hardware. The monolithic integration of these features positions the axialtrode as a scalable and versatile platform for next-generation neural interfacing.

neuroscience↗

bioRxiv2023

RNA sequencing demonstrates ex vivo neocortical transcriptomic changes induced by epileptiform activity in male and female mice

Seizures are generally associated with epilepsy but may also be a symptom of many other neurological conditions. A hallmark of a seizure is the intensity of the local neuronal activation, which can drive large-scale gene transcription changes. Such changes in the transcriptional profile are likely to alter neuronal function, thereby contributing to the pathological process. Therefore, there is a strong clinical imperative to characterie how gene expression is changed by seizure activity. To this end, we developed a simplified ex vivo technique for studying seizure-induced transcriptional changes. We compared the RNA sequencing profile in mouse neocortical tissue that had up to 3 hours of epileptiform activity induced by 4-aminopyridine (4AP), relative to control brain slices not exposed to the drug. We identified over 100 genes with significantly altered expression after 4AP treatment, including multiple genes involved in MAPK, TNF, and neuroinflammatory signalling pathways, all of which have been linked to epilepsy previously. Notably, the patterns in male and female brain slices were almost identical. Various immediate early genes were among those showing the largest upregulation. The set of down-regulated genes included ones that might be expected either to increase or to decrease neuronal excitability. In summary, we found the seizure-induced transcriptional profile to be complex, but the changes aligned well with an analysis of published epilepsy-associated genes. We discuss how simple models may provide new angles for investigating seizure-induced transcriptional changes. Significance StatementIt is well-established that strong neuronal activation results in large-scale transcriptomic changes. Understanding this process is of particular importance in epilepsy, which is characterized by paroxysmal pathological discharges. The complexity of in vivo activity patterns, however, present many difficulties for interpretation of the transcriptional changes. In contrast, ex vivo seizure models provide better experimental control and quantification of activity patterns, with lower welfare impact. Importantly, we now show that these models also replicate the transcriptional patterns previously reported in chronic human and animal epilepsy, thus validating their use in these kinds of study.

neuroscience↗

bioRxiv2022

Xenon LFP Analysis Platform is a Novel Graphical User Interface for Analysis of Local Field Potential from Large-Scale MEA Recordings

High-density multi-electrode array (HD-MEA) has enabled neuronal measurements at high spatial resolution to record local field potentials (LFP), extracellular spikes, and network activity with ease. Whilst we have advanced recording systems with over 4000 electrodes, capable of recording data at over 20 kHz, it still presents computational challenges to handle, process, extract, and view information from these large recordings. It can be challenging for researchers to extract and view even a single channel that has more than a billion data points, let alone process a group of channels. We have created a computational method, and an open-source toolkit built on Python, rendered on a web browser using Plotlys Dash for extracting and viewing the data, and creating interactive visualization. In addition to extracting and viewing entire or small chunks of data sampled at lower or higher frequencies, respectively, it provides a framework to collect user inputs, analyze channel groups, generate raster plots, view quick summary measures for LFP activity, detect and isolate noise channels, and generate plots and visualization in both time and frequency domain. Incorporated into our Graphical User Interface (GUI), we also have created a novel seizure detection method, which can be used to detect the onset of seizures in all or a selected group of channels and provide the following measures of seizures: distance, duration, and propagation across the region of interest. We demonstrate the utility of this toolkit, using datasets collected from the 3Brain BioCAM duplex system. For the current analysis, we demonstrate the toolkit and methods with a low sampling frequency dataset (300 Hz) and a group of approximately 400 channels. Using this toolkit, we present novel data demonstrating increased seizure propagation speed from slices of Scn1aHet mice compared to littermate controls. With advances in HD-MEA recording systems with high spatial and temporal resolution, limited tools are available for researchers to view and process these big datasets. We now provide a user-friendly toolkit to analyze LFP activity obtained from large-scale MEA recordings with translatable applications to EEG recordings, and demonstrate the utility of this new graphic user interface with novel biological findings.

neuroscience↗

bioRxiv2019

Divergent paths to seizure-like events.

AimMuch debate exists about how the brain transitions into an epileptic seizure. One source of confusion is that there are likely to be critical differences between experimental seizure models. To address this, we compared the evolving activity patterns in two, widely used, in vitro models of epileptic discharges.\n\nMethodsWe compared brain slices, prepared in the same way from young adult mice, that were bathed either in 0 Mg2+, or 100{micro}M 4AP, artificial cerebrospinal fluid.\n\nResultsWe find that while local field potential recordings of epileptiform discharges in the two models appear broadly similar, patch-clamp analysis reveals an important difference in the relative degree of glutamatergic involvement. 4AP affects parvalbumin-expressing interneurons more than other cortical populations, destabilizing their resting state and inducing spontaneous bursting behavior. Consequently, the most prominent pattern of transient discharge (\"interictal event\") in this model is almost purely GABAergic, although the transition to seizure-like events (SLEs) involves pyramidal recruitment. In contrast, interictal discharges in 0 Mg2+ are only maintained by a very large glutamatergic component that also involves transient discharges of the interneurons. Seizure-like events in 0 Mg2+ have significantly higher power in the high gamma frequency band (60-120Hz) than these events do in 4AP, and are greatly delayed in onset by diazepam, unlike 4AP events.\n\nConclusionsThe 0 Mg2+ and 4AP models display fundamentally different levels of glutamatergic drive, demonstrating how ostensibly similar pathological discharges can arise from different sources. We contend that similar interpretative issues will also be relevant to clinical practice.

neuroscience↗

bioRxiv2018

Excitatory GABAergic signalling is associated with acquired benzodiazepine resistance in status epilepticus

Status epilepticus (SE) is defined as a state of unrelenting seizure activity. It is associated with a rapidly rising mortality rate, and thus constitutes a medical emergency. Benzodiazepines, which act as positive modulators of chloride (Cl-) permeable GABAA receptors, are indicated as the first line of treatment, but this is ineffective in many cases. We found that 48% of children presenting with SE were unresponsive to benzodiazepine treatment, and critically, that the duration of SE at the time of treatment is an important predictor of non-responsiveness. We therefore investigated the cellular mechanisms that underlie acquired benzodiazepine resistance, using rodent organotypic brain slices. Removing Mg2+ ions leads to an evolving pattern of epileptiform activity, and eventually to a persistent state of repetitive discharges that strongly resembles clinical EEG recordings of SE. We show that the persistent SE-like activity is associated with a reduction in GABAA receptor conductance and Cl- extrusion capability. We explored the effect on intraneuronal Cl- using both gramicidin, perforated-patch clamp recordings and Cl- imaging. This showed that during SE-like activity, reduced Cl- extrusion capacity was further exacerbated by activity-dependent Cl- loading, resulting in a persistently high intraneuronal Cl-. Consistent with these results, we found that optogenetic stimulation of GABAergic interneurons in the SE-like state, actually enhanced epileptiform activity in a GABAAR dependent manner. Together our findings describe a novel potential mechanism underlying benzodiazepine-resistant SE, with relevance to how this life-threatening condition should be managed in the clinic.

neuroscience↗

bioRxiv2018

Region-specific differences and areal interactions underlying transitions in epileptiform activity

Understanding the nature of epileptic state transitions remains a major goal for epilepsy research. Simple in vitro models offer unique experimental opportunities, which we exploit to show that such transitions can arise from shifts in the ictal source of the activity. These transitions reflect the fact that cortical territories differ both in the type of epileptiform activity they can sustain, and their susceptibility to drug manipulation. In the zero Mg2+ model, the earliest epileptiform activity is restricted to neocortical and entorhinal networks. Hippocampal bursting only starts much later, and triggers a marked transition in neo-/entorhinal cortical activity. Thereafter, the hippocampal activity acts as a pacemaker, entraining the other territories to their discharge pattern. This entrainment persists following transection of the major axonal pathways between hippocampus and cortex, indicating that it can be mediated through a non-synaptic route. Neuronal discharges are associated with large rises in extracellular [K+], but we show that these are very localised, and therefore are not the means of entraining distant cortical areas. We conclude instead that the entrainment occurs through weak field effects distant from the pacemaker, but which are highly effective at recruiting other brain territories that are already hyperexcitable. The hippocampal epileptiform activity appears unusually susceptible to drugs that impact on K+ conductances. These findings demonstrate that the local circuitry gives rise to stereotypical epileptic activity patterns, but these are also influenced by both synaptic and non-synaptic long-range effects. Our results have important implications for our understanding of epileptic propagation, and anti-epileptic drug action.\n\nKey pointsO_LILocal neocortical and hippocampal territories show different and sterotypical patterns of acutely evolving, epileptiform activity.\nC_LIO_LINeocortical and entorhinal networks show tonic-clonic-like events, but the main hippocampal territories do not, unless it is relayed from the other areas.\nC_LIO_LITransitions in the pattern of locally recorded epileptiform activity can be indicative of a shift in the source of pathological activity, and which may spread through both synaptic and non-synaptic means.\nC_LIO_LIHippocampal epileptiform activity is promoted by 4-aminopyridine and inhibited by GABAB agonists, and appears far more sensitive to these drugs than neocortical activity.\nC_LIO_LIThese signature features of local epileptiform activity can provide useful insight into the primary source of ictal activity, aiding both experimental and clinical investigation.\nC_LI

neuroscience↗