Biology subjects

Raedt, R.

Publications and source records attributed to Raedt, R..

9 recordsLinked to original sources

bioRxiv2026

Seizure control via astrocyte targeted optogenetic extracellular potassium modulation: computational analysis of K+ vs non-selective cation-conducting opsins

Aims: Seizure generation has been strongly linked to the accumulation of extracellular potassium. As astrocytes play a key role in potassium homeostasis, astrocyte targeted optogenetic modulation of extracellular potassium has been proposed as a novel strategy for seizure control. The effectiveness of such modulation is expected to depend strongly on the ion selectivity of the employed opsin. This study aims to mechanistically compare potassium-selective (WiChR) and cation-conducting (ChR2-like, ChR2*) opsins for astrocyte targeted modulation of extracellular potassium, and to determine how astrocytic properties and stimulation parameters influence modulation efficacy. Methods: A conductance-based computational framework was used to model astrocyte-extracellular space interactions, incorporating ion-specific photocurrents, Na+/K+-ATPase activity, and gap junction-mediated coupling within the astrocytic syncytium. Systematic parameter sweeps were performed to evaluate the influence of ion selectivity, astrocytic parameters, and stimulation paradigms on potassium dynamics. Results: WiChR-based modulation consistently produced more effective and robust reductions in [K+]e than ChR2*, via direct K+ inward currents and reduced dependence on pump activity. In contrast, ChR2* primarily limited potassium accumulation rather than reversing it and exhibited greater sensitivity to parameter variations, particularly Na+/K+-ATPase activity. The effectiveness of astrocyte-targeted modulation was strongly dependent on syncytial integrity, with reduced gap junction coupling impairing potassium clearance. Optimal stimulation performance for WiChR was observed for a pulse repetition period of 20 ms, with outcomes determined by the interaction between opsin kinetics and stimulation parameters. Conclusions: These results demonstrate that activation of WiChR opsins in astrocytes can reduce extracellular potassium levels and thereby modulate neuronal excitability. Ion selectivity emerges as a key determinant of modulation efficacy at the astrocytic level, with potassium-selective opsins providing a more direct and reliable approach than non-selective cation-conducting alternatives. Together, these findings establish a mechanistic basis for optogenetic activation of astrocytic potassium buffering as a potential strategy for seizure suppression and other neurological disorders associated with potassium dysregulation.

neuroscience↗

bioRxiv2026

A photoswitchable cannabinoid for precision treatment of refractory seizures in a mouse epilepsy model

Temporal lobe epilepsy (TLE) has an unmet need for precision treatments targeting the seizure focus while avoiding effects on other body parts to minimise side effects. Photopharmacology could enable precision treatment by combining systemic administration of a photoswitchable drug with implantation of an optic fibre in the epileptic focus to induce light-dependent drug conversion from an inactive to an active configuration that interacts with its target receptor to suppress seizures. The photoswitchable {Delta}9-tetrahydrocannabinol ({Delta}9-THC) derivative, azo-THC-3, transitions from an inactive trans to an active cis configuration upon UV irradiation. We demonstrate that local or systemic administration of azo-THC-3 and local UV irradiation in the hippocampus supresses difficult-to-treat seizures in the intrahippocampal kainic acid mouse model of TLE. Furthermore, our findings illustrate that the photoswitch strategy avoids hypolocomotion, a common side effect of systemic {Delta}9-THC administration. As such, we provide the first demonstration of seizure suppression with the systemic administration of a photoswitchable compound and its local photoactivation in the seizure focus. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=133 SRC="FIGDIR/small/720358v1_ufig1.gif" ALT="Figure 1"> View larger version (41K): org.highwire.dtl.DTLVardef@1e42794org.highwire.dtl.DTLVardef@1e26891org.highwire.dtl.DTLVardef@13f2b6forg.highwire.dtl.DTLVardef@3c8e48_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2024

Computational analysis of optogenetic inhibition of CA1 neurons using a data-efficient and interpretable potassium and chloride conducting opsin model

Optogenetic inhibition of excitatory populations has been suggested as a novel technique for the treatment of refractory epilepsy. While this approach holds significant potential, achieving seizure suppression in animal models using optogenetics has proven challenging. This difficulty can be attributed to a suboptimal stimulation method that involves numerous complex variables. To provide insight into these parameters, the behavior of the chloride conducting opsin, GtACR2, was fitted to a mathematical description and combined with a conductance-based model of a pyramidal CA1 neuron. The resulting model was adapted to add the ability to study potassium conducting opsins and used to demonstrate that the effect of an optogenetic modulation setup is highly dependent on its parameters and the physiological conditions of the neuronal environment. Stronger inhibition is observed at higher pulse repetition frequencies and duty cycles. Furthermore, potassium conducting opsins were shown to be more stable in use than chloride conducting ones. The dependence of these observations on the opsin model fit was found to be negligible. To determine this, a simplified model (22OMs) is proposed that permits easy implementation of the experimentally derived parameters describing the opsins opening and closing dynamics into its mathematical description. This model was also employed to determine that the impact of varying the opsins dynamics is insignificant when the opening and closing time constants are altered by a factor between 0.5 and 2. Consequently, this study provides insights into the stimulation and physiological parameters influencing the outcome of an optogenetic inhibition approach and offers a new tool that will facilitate future research into the development of an improved optogenetic modulation protocol for seizure suppression.

bioengineering↗

bioRxiv2024

tDCS Cranial Nerve Co-Stimulation: Unveiling Brainstem Pathways Involved in Trigeminal Nerve Direct Current Stimulation in Rats

The effects of transcranial direct current stimulation (tDCS) are typically attributed to the polarization of cortical neurons by the weak electric fields it generates in the cortex. However, emerging evidence indicates that certain tDCS effects may be mediated through the co-stimulation of peripheral or cranial nerves, particularly the trigeminal nerve (TN), which projects to critical brainstem nuclei that regulate the release of various neurotransmitters throughout the central nervous system. Despite this, the specific pathways involved remain inadequately characterized. In this study, we examined the effects of acute transcutaneous TN direct current stimulation (TN-DCS) on tonic (i.e. mean spike rate and spike rate over time) and phasic (number of bursts, spike rate per burst, burst duration, and inter-burst interval) activities while simultaneously recording single-neuron activity across three brainstem nuclei in rats: the locus coeruleus (LC), dorsal raphe nucleus (DRN), and median raphe nucleus (MnRN). We found that TN-DCS significantly modulated tonic activity in the LC, with notable interactions between stimulation amplitude, polarity, and time epoch affecting mean spike rates. Similar effects were observed in the DRN regarding tonic activity. Further, phasic activity in the LC was influenced by TN-DCS, with changes in burst number, duration, and inter-burst intervals linked to stimulation parameters. Conversely, MnRN tonic activity following TN-DCS remained unchanged. Importantly, xylocaine administration to block TN abolished the effects on tonic activities in both the LC and DRN. These results suggest that tDCS effects may partially arise from indirect modulation of the TN, leading to altered neuronal activity in DRN and LC. Besides, the differential changes in tonic and phasic LC activities underscore their complementary roles in mediating TN-DCS effects on higher cortical regions. This research bears significant translational implications, providing mechanistic insights that could enhance the efficacy of tDCS applications and deepen our understanding of its neurophysiological effects.

neuroscience↗

bioRxiv2024

Photopharmacological activation of adenosine A1receptor signaling suppresses seizures in a mousemodel for temporal lobe epilepsy

Up to 30% of epilepsy patients suffer from drug-resistant epilepsy (DRE). The search for innovative therapies is therefore important to close the existing treatment gap in these patients. The adenosinergic system possesses potent anticonvulsive effects, mainly through the adenosine A1 receptor (A1R). However, clinical application of A1R agonists is hindered by severe systemic side effects. To achieve local modulation of A1Rs, we employed a photopharmacological approach using a caged version of the A1R agonist N6-cyclopentyladenosine, termed cCPA. We performed the first in vivo study with intracerebroventricularly (ICV) administered cCPA to investigate the potential to uncage sufficient amounts of cCPA in the hippocampus by local illumination in order to suppress hippocampal excitability and seizures in mice. Using hippocampal evoked potential recordings, we showed a reduction in hippocampal neurotransmission after photo-uncaging of cCPA, similar to that obtained with ICV injection of CPA. Furthermore, in the intrahippocampal kainic acid mouse model for DRE, photo-uncaging of CPA in the epileptic hippocampus resulted in a strong suppression of seizures. Finally, we demonstrated that intrahippocampal photo-uncaging of CPA resulted in less impairment of motor performance in the rotarod test compared to ICV administration of CPA. These results provide a proof of concept for photopharmacological A1R modulation as an effective precision treatment for DRE.

neuroscience↗

bioRxiv2024

Feedback Control of Neuronal Excitability and Epileptiform Bursting using a Photocaged Adenosine A1 Agonist

Adenosine is a potent regulator of neurotransmission and neuronal excitability through activation of Gi protein-coupled adenosine A1 receptors (A1Rs). It has gained interest as a potential anticonvulsant due to its endogenous involvement in ending ongoing seizure activity. A recently developed coumarin-caged derivative of the A1R agonist N6-cyclopentyl-adenosine (CPA), cCPA, was used for photo-uncaging of CPA with millisecond flashes of 405 nm light. At population level, CPA reduces Schaffer Collateral stimulated extracellular dendritic field potentials (FPs) in the CA1 region of the hippocampus with an ED50 of 44.1{+/-}2.8 nM and a Hill coefficient of 3. Response onset is CPA dependent and takes less than seconds, while recovery is CPA independent with a time constant of around 20 minutes. A closed-loop feedback system used the amplitude of evoked dendritic FPs to photorelease CPA and was able to control FP amplitude to user defined levels between 10% and 90% of baseline level. In the acute elevated potassium model of epilepsy raising extracellular K+ to 8.5 mM enhances neuronal excitability and induces regularly occurring epileptiform bursts, but FPs evoked with low intensity could still continuously monitor excitability without interfering with bursting. In this model the closed-loop system that controlled CPA release, was able to suppress epileptiform bursting, while maintaining an acceptable level of functional neurotransmission. Including in the control algorithm a second parameter that combined population spike amplitude and number of population spikes, enabled the system to automatically find a level of functional neurotransmission that was just below the threshold for multiple spiking and epileptiform bursting. The combination of photopharmacological adenosinergic modulation with real-time FP monitoring provides a first step towards closed-loop precision treatment for diseases related to neuronal hyperexcitability such as epilepsy.

neuroscience↗

bioRxiv2023

Quantitative Analysis of the Optogenetic Excitability of CA1 Neurons

Optogenetics has emerged as a promising technique for modulating neuronal activity and holds potential for the treatment of neurological disorders such as temporal lobe epilepsy (TLE). However, clinical translation still faces many challenges. This in-silico study aims to enhance the understanding of optogenetic excitability in CA1 cells and to identify strategies for improving stimulation protocols. Employing state-of-the-art computational models, the optogenetic excitability of four CA1 cells, two pyramidal and two interneurons, expressing ChR2(H134R) is investigated. The results demonstrate that confining the opsin to specific neuronal membrane compartments significantly improves excitability. An improvement is also achieved by focusing the light beam on the most excitable cell region. Moreover, the perpendicular orientation of the optical fiber relative to the somato-dendritic axis yields superior results. Inter-cell variability is observed, highlighting the importance of considering neuron degeneracy when designing optogenetic tools. Opsin confinement to the basal dendrites of the pyramidal cells renders the neuron the most excitability. A global sensitivity analysis identified opsin location and expression level as having the greatest impact on simulation outcomes. The error reduction of simulation outcome due to coupling of neuron modeling with light propagation is shown. The results promote spatial confinement and increased opsin expression levels as important improvement strategies. On the other hand, uncertainties in these parameters limit precise determination of the irradiance thresholds. This study provides valuable insights on optogenetic excitability of CA1 cells useful for the development of improved optogenetic stimulation protocols for, for instance, TLE treatment.

neuroscience↗

bioRxiv2023

Modulation of locus coeruleus neurons and strong release of noradrenaline during acute hippocampal seizures in rats

The locus coeruleus (LC), a brainstem nucleus, is the sole source of noradrenaline in the neocortex, hippocampus and cerebellum. Noradrenaline is a powerful neuromodulator involved in the regulation of excitability and plasticity of large-scale brain networks. In this study, we assessed the activity of locus coeruleus neurons and changes in noradrenergic transmission during acute hippocampal seizures evoked with perforant path stimulation. LC neurons were recorded in anesthetized rats using a multichannel electrophysiology probe and were identified based on electrophysiological characteristics or optogenetic tagging. The majority of LC neurons (55%) were inhibited during seizures, while only a subset of LC neurons (28%) was excited during seizures. Topographic analysis of multi-unit activity showed anatomical separation of neurons that were excited and inhibited during seizures. Changes in hippocampal noradrenaline transmission during seizures were assessed using a fluorescent biosensor for noradrenaline, GRABNE2m, in combination with fiber photometry in both anesthetized and awake rats. Our results indicate that acute electrically evoked hippocampal seizures are associated with strong changes in LC unit activity and strong and consistent time-locked release of noradrenaline. Understanding the role of mass release of noradrenaline during hippocampal seizures is likely to be important to understand seizure pathophysiology.

neuroscience↗

bioRxiv2020

Hodgkin and Huxley Opsin Model for Computationally Efficient Optogenetic Neurostimulation in Cells and Networks

Optogenetics has a lot of potential to become an effective neuromodulative therapy for clinical application. Selecting the correct opsin is crucial to have an optimal optogenetic tool. With computational modeling, the neuronal response to the current dynamics of an opsin can be extensively and systematically tested. Unlike electrical stimulation where the effect is directly defined by the applied field, the stimulation in optogenetics is indirect, depending on the selected opsins non-linear kinetics. With the continuous expansion of opsin possibilities, computational studies are difficult due to the need for an accurate model of the selected opsin first. To this end, we propose a Hodgkin-and-Huxley based model (22HH) as alternative to the conventional three and four state Markov models used for opsin modeling. Furthermore, we provide a fitting procedure, which allows for nearly automatic model fitting starting from a vast parameter space. With this procedure, we successfully fitted two distinctive opsins ChR2(H134R) and MerMAID. Both models are able to represent the experimental data with great accuracy and were obtained within an acceptable time frame. This is due to the absence of differential equations in the fitting procedure, with an enormous reduction in computational cost as result. The performance of the proposed model with a fit to ChR2(H134R) was tested, by comparing the neural response in a regular spiking neuron to the response obtained with the non-instantaneous, four state Markov model (4SB), derived by Williams et al. (2013) [1]. Finally, a computational speed gain was observed with the 22HH model in a regular spiking and sparse Pyramidal-Interneuron-Network-Gamma (sPING) network simulation with respect to the 4SB-model, due to the former having two differential equations less. Consequently, the proposed model allows for computationally efficient optogenetic neurostimulation and with the proposed fitting procedure will be valuable for further research in the field of optogenetics.

bioengineering↗