Biology subjects

Kole, M. H. P.

Publications and source records attributed to Kole, M. H. P..

16 recordsLinked to original sources

bioRxiv2026

The nanoscopic submyelin space mediates efficient K+ uptake and shapes nodal action potentials

Myelin membranes are tightly connected to the axon, forming an electrical route for rapid saltatory conduction of action potentials from node to node. Beneath the myelin, adjacent to the node, lie voltage-gated potassium (K+) channels, whose fundamental role in conduction remains poorly understood. Constrained by biological data, we developed a finite element model of a node of Ranvier encompassing an adaxonal membrane separating oligodendrocyte cytoplasm from the periaxonal space, and solved the full coupled set of physical equations governing electrodiffusion and voltage profiles at the nanoscale. Remarkably, we find that nodal action potentials invert at the inner adaxonal myelin membrane. The hyperpolarization-driven opening of myelinic Kir4.1 channels produces an instantaneous, powerful K+ prebuffering, clamping the periaxonal K+ concentration and enabling high-frequency action potential generation. Together, these findings indicate that the periaxon maintains an electrical feedback loop with the node, and suggest a key evolutionary advantage of juxtaparanodal K+ channel positioning.

neuroscience↗

bioRxiv2026

Divisive normalization in mouse V1 is unchanged by increased thalamocortical short-term depression

Divisive normalization describes how neuronal responses are scaled by the activity of a broader pool of inputs and accounts for several nonlinear response properties in primary visual cortex (V1). It accurately describes contrast gain control, as well as the response to overlapping gratings. Nevertheless, how this computation is performed by the brain is unclear. One mechanism suggested to underlie divisive normalization in V1 is short-term depression (STD) at thalamocortical synapses. Here, we used a Vglut2-Cre dependent heterozygous deletion of Stxbp1 in mice as an in vivo model for increased STD. This enabled us to test whether STD is responsible for divisive normalization in V1. As expected, responses were shorter in the mutant mice compared to wild-type siblings. Although we did find other differences in visual responses, notably in direction selectivity and response linearity, neither the contrast response function, nor the amount of cross orientation suppression differed between the two groups. We conclude that STD is likely not involved in divisive normalization of visual responses in mouse V1. Instead, short-term plasticity shapes the temporal integration through which selective cortical responses are constructed.

neuroscience↗

bioRxiv2026

Spatiotemporal proteomics elucidates trafficking and localization of Neuroligins to the axon initial segment plasma membrane

Neuronal development and function rely on precise sorting of membrane proteins to distinct neuronal domains, yet the underlying mechanisms remain incompletely understood. Here, we investigated the trafficking of two highly homologous NLGNs (NLGN1 and 2) which distinctly localize and function at excitatory and inhibitory synapses. By using spatiotemporal proteomics, genetic engineering and microscopy in CNS cultured neurons and organotypic slices, we dissected the itinerary of biosynthetic NLGNs, identifying co-cargoes and sorting routes to dendrites and the AIS. At the AIS, which contains only inhibitory synapses, both NLGN1 and NLGN2 are locally exocytosed. While NLGN2 is stably recruited to axo-axonic synapses by its extracellular domain and modulated by activity, NLGN1 is retrieved by endocytic mechanisms. We propose that biosynthetic NLGNs are co-sorted to the AIS PM where they detect pre-synaptic type. These findings may help to elucidate the role of AIS-localized NLGNs in shaping AIS structural and functional plasticity. HighlightsO_LISpatiotemporal proteomics elucidates interactome of biosynthetic NLGN1 in neurons C_LIO_LINLGN1 and NLGN2 are targeted to the AIS by kinesin-1 C_LIO_LINLGN2, but not NLGN1, is retained at axo-axonic synapses and modulated by activity C_LIO_LINLGN stability at the AIS plasma membrane is determined by the ectodomain C_LI Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=194 HEIGHT=200 SRC="FIGDIR/small/733123v1_ufig1.gif" ALT="Figure 1"> View larger version (41K): org.highwire.dtl.DTLVardef@a45909org.highwire.dtl.DTLVardef@1d171b0org.highwire.dtl.DTLVardef@17f132aorg.highwire.dtl.DTLVardef@1c33a8d_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2026

An organotypic neocortical slice culture for studying neuroglial interactions

Organotypic slice cultures (OSCs) are widely used to study cellular properties in a functional and developmental tissue context. With the recent advent of transgenic mouse lines and viral tools we postulated that OSCs may enable the study of multicellular glial and neuroglial interactions in development, as well homeostatic and pathological conditions. Here, we made mouse cortical OSCs and used markers for oligodendroglial, microglial states and neuronal types between 1 to 28 days in vitro (DIV). The OSC was characterized by in-vivo like cortical layering, including layer 5 pyramidal neurons and produced highly robust synchronized period bursts resembling Up- and Down states. Glial cells showed a strong cortical layer- and time-dependent development pattern: in the first week (DIV 1-7), slicing-related debris clearance and developmentally restricted sparse oligodendroglial myelination created an environment with highly phagocytic, non-homeostatic microglia (assessed with CD68 and purinergic receptor P2Y12, respectively). Between DIV 14 and 21, however, slices showed stereotypical cortical myelin patterns and the emergence of a homeostatic microglia phenotype while exhibiting continued phagocytosis. Furthermore, live two-photon imaging and morphometric analyses revealed highly ramified microglia and myelinated axons with compact myelination, exceeding lamellae count compared to age-matched in vivo axons. Lastly, from DIV 28 and onwards, myelin integrity became impaired and associated with phagocytic microglia. Together, the results indicate that between DIV14 and 21 cortical OSCs are well suited for live imaging of homeostatic and activity-dependent neuron-glia interactions, bridging the gap between in vivo investigations and primary cell cultures.

neuroscience↗

bioRxiv2025

Tether-mediated extraction of myelinoid bodies by microglia and astrocytes can maintain myelin integrity

Oligodendrocytes make myelin for the electrical insulation of axons and saltatory impulse conduction. Myelin lipids and proteins undergo a slow turnover, but exactly how the multilamellar and compacted membrane sheaths are remodeled without compromising myelin sheath integrity has remained puzzling, in particular at advanced age when myelin abnormalities increase. Earlier EM studies had suggested myelin membranes are shed and subsequently phagocytosed by microglia. However, the formation of multilamellar myelinoid bodies (MBs), leaving a well-ordered myelin sheath behind, is difficult to reconcile with simple shedding mechanisms. Here, we show by three-dimensional FIB-SEM reconstructions of optic nerves in mice and by two-photon live-imaging of myelinated cortical slices that MBs are initially connected to their parental sheaths by long tethers, which are stretched by trogocytosing microglia and astrocytes. We observe ruptured tethers attached to both MBs and sheaths, suggesting a novel mechanism of tension-driven tether scission. Importantly, the successive fusion of the corresponding innermost myelin membranes in an extended tether can preserve myelin sheath integrity. Thus, the remodeling by tether-mediated MB extraction emerges as a mechanism of physiological maintenance of myelin sheaths in the CNS.

neuroscience↗

bioRxiv2025

Spatially resolved mapping of monoacylglycerol lipase activity in the brain

Visualizing signaling systems in the brain with high spatial resolution is critical to understand brain function and to develop therapeutics. Especially enzymes are often regulated on the post-translational level, resulting in a disconnect between protein levels and activity. Conventional antibody-based methods have limitations, including potential cross reactivity and the inability of antibodies to discriminate between active and inactive enzyme states. Monoacylglycerol lipase (MAGL), an enzyme degrading the neuroprotective endocannabinoid 2-arachidonoylglycerol, is the target of inhibitors currently in clinical trials for the treatment of several neurological disorders. To support translational and (pre)clinical studies and fully realize the therapeutic opportunities of MAGL inhibitors, it is essential to map the spatial distribution of MAGL activity throughout the brain in both health and disease. Here, we introduce selective fluorescent activity-based probes for MAGL enabling direct visualization of its enzymatic activity in lysates, cultured cells and tissue sections. We show that oxidative stress, which inactivates MAGL through the oxidation of regulatory cysteines, reduces probe labeling, thereby validating the probes activity-dependence. Extending this approach, we developed an activity-based histology protocol to visualize MAGL activity in fresh-frozen mouse and human brain tissues. This approach revealed robust MAGL activity in astrocytes and presynaptic terminals within the mouse hippocampus, and further allows detection of MAGL activity in the human cerebral cortex. Collectively, these findings establish selective activity-based probes as powerful tools mapping MAGL activity with high spatial resolution across mammalian brain tissue.

neuroscience↗

bioRxiv2025

Robust activity-dependent mitochondrial calcium dynamics at the AIS is dispensable for action potential generation

Mitochondria are diverse and multifaceted intracellular organelles regulating oxidative energy supply, lipid metabolism and calcium (Ca2+) signaling. In neurons the spatial sequestration of cytoplasmic Ca2+ by mitochondria plays a critical role in determining activity-dependent spine plasticity, shaping the presynaptic transmitter release characteristics and contributing to sustained action potential firing. Here, we tested the hypothesis that mitochondria at the axon initial segment (AIS) affect the microdomain cytoplasmic Ca2+ transients, thereby regulating Ca2+-dependent voltage-gated ion channels at the plasma membrane and initiation of action potentials. Using 3D electron microscopy (EM) reconstructions and virally injecting genetically encoded fluorescence indicators we visualized the ultrastructure and distribution of mitochondria selectively in thick-tufted layer 5 pyramidal neurons. We found that most mitochondria were stably clustered to the proximal AIS, while few were observed at distal sites. Simultaneous two-photon imaging of action potential-dependent cytoplasmic and mitochondrial Ca2+, combined with electrophysiological recordings showed the AIS mitochondria exhibit powerful activity-dependent cytosolic Ca2+ uptake. However, while intracellular application of the mitochondrial Ca2+ uniporter inhibitor Ru360 fully blocked mitochondrial Ca2+ import, it did not affect action potential input-output function, action potential dynamics nor the ability to produce high-frequency burst output. Together, the results indicate that AIS mitochondria are dispensable for temporal and rate encoding, suggesting that mt-Ca2+ buffering at the AIS may be involved in non-electrical roles, including AIS maintenance or axonal transport.

neuroscience↗

bioRxiv2023

Visuomotor experience induces functional and structural plasticity of chandelier cells

Detailed characterization of interneuron types in primary visual cortex (V1) has greatly contributed to understanding visual perception, yet the role of chandelier cells (ChCs) in visual processing remains poorly characterized. Using viral tracing we found that V1 ChCs predominantly receive monosynaptic input from local layer 5 pyramidal cells and higher-order cortical regions. Two-photon calcium imaging and convolutional neural network modelling revealed that ChCs are visually responsive but weakly selective for stimulus content. In mice running in a virtual tunnel, ChCs respond strongly to events known to elicit arousal, including locomotion and visuomotor mismatch. Repeated exposure of the mice to the virtual tunnel was accompanied by reduced visual responses of ChCs and structural plasticity of ChC boutons and axon initial segment length. Finally, ChCs only weakly inhibited pyramidal cells. These findings suggest that ChCs provide an arousal-related signal to layer 2/3 pyramidal cells that may modulate their activity and/or gate plasticity of their axon initial segments during behaviorally relevant events.

neuroscience↗

bioRxiv2022

Human voltage-gated Na+ and K+ channel properties underlie sustained fast AP signaling

Human cortical pyramidal neurons are large, have extensive dendritic trees, and yet have surprisingly fast input-output properties: rapid subthreshold synaptic membrane potential changes are reliably encoded in timing of action potentials (APs). Here, we tested whether biophysical properties of voltage-gated sodium (Na+) and potassium (K+) currents in human pyramidal neurons can explain their fast input-output properties. Human Na+ and K+ currents exhibited more depolarized voltage-dependence, slower inactivation and faster recovery from inactivation compared with their mouse counterparts. Computational modeling showed that despite lower Na+ channel densities in human neurons, the biophysical properties of Na+ channels resulted in higher channel availability and contributed to fast AP kinetics stability. Finally, human Na+ channel properties also resulted in a larger dynamic range for encoding of subthreshold membrane potential changes. Thus, biophysical adaptations of voltage-gated Na+ and K+ channels enable fast input-output properties of large human pyramidal neurons. One-Sentence SummaryBiophysical properties of Na+ and K+ ion channels enable human neurons to reliably encode fast inputs into output.

neuroscience↗

bioRxiv2022

Sodium channel endocytosis drives axon initial segment plasticity

Activity-dependent plasticity of the axon initial segment (AIS) endows neurons with the ability to adapt action potential output to changes in network activity. Action potential initiation at the AIS highly depends on the clustering of voltage-gated sodium channels, however the molecular mechanisms regulating their plasticity remain largely unknown. Here, we used novel genetic tools to endogenously label sodium channels and their scaffolding protein, to reveal their nanoscale organization and longitudinally image AIS plasticity in hippocampal neurons, in slices and primary cultures. We find that induction of NMDA receptor-mediated long-term synaptic depression is linked to a rapid and local endocytosis of sodium channels from the distal AIS. These data reveal a novel fundamental mechanism for rapid activity-dependent AIS reorganization sharing conserved features with synaptic plasticity.

neuroscience↗

bioRxiv2022

Myelination-dependent mitochondria clustering and calcium buffering in parvalbumin interneuron axons

Parvalbumin-expressing (PV+) basket cells are fast-spiking interneurons that exert critical control over local neuronal circuit activity and oscillations. PV+ interneuron axons are partially myelinated but the electrical and metabolic roles of myelin in axonal functions remain poorly understood. Here, we developed Cre-dependent AAV vectors for cell type-specific investigation of mitochondria with genetically encoded fluorescent probes. Single-cell reconstructions and mining of ultrastructural data revealed that mitochondria selectively cluster to myelinated segments of PV+ basket cell axons. Cuprizone-induced demyelination abolished mitochondrial clustering in PV+ axons but increased axonal mitochondrial densities in excitatory axons. The internodal clustering of mitochondria was preserved with genetic deletion of myelin basic protein, suggesting that noncompacted myelin is sufficient. Finally, two-photon imaging of action potential-evoked mitochondrial calcium (mt-Ca2+) responses showed that internodal mitochondria did not contribute in buffering activity-dependent Ca2+ influx. These findings suggest that oligodendrocyte-PV+ axon signaling assembles mitochondria to branch selectively fine-tune metabolic demands.

neuroscience↗

bioRxiv2021

Myelin speeds cortical oscillations by consolidating phasic parvalbumin-mediated inhibition

Parvalbumin-positive (PV+) {gamma}-aminobutyric acid (GABA) interneurons are critically involved in producing rapid network oscillations and cortical microcircuit computations but the significance of PV+ axon myelination to the temporal features of inhibition remains elusive. Here using toxic and genetic models of demyelination and dysmyelination, respectively, we find that loss of compact myelin reduces PV+ interneuron presynaptic terminals, increases failures and the weak phasic inhibition of pyramidal neurons abolishes optogenetically driven gamma oscillations in vivo. Strikingly, during periods of quiet wakefulness selectively theta rhythms are amplified and accompanied by highly synchronized interictal epileptic discharges. In support of a causal role of impaired PV-mediated inhibition, optogenetic activation of myelin-deficient PV+ interneurons attenuated the power of slow theta rhythms and limited interictal spike occurrence. Thus, myelination of PV axons is required to consolidate fast inhibition of pyramidal neurons and enable behavioral state-dependent modulation of local circuit synchronization.

neuroscience↗

bioRxiv2021

Complement-associated loss of CA2 inhibitory synapses in the demyelinated hippocampus impairs memory

The complement system is implicated in synapse loss in the MS hippocampus, but the functional consequences of synapse loss remain poorly understood. Here, in post-mortem MS hippocampi with demyelination we find that deposits of the complement component C1q are enriched in the CA2 subfield, are linked to loss of inhibitory synapses and are significantly higher in MS patients with cognitive impairments compared to those with preserved cognitive functions. Using the cuprizone mouse model of demyelination, we corroborated that C1q deposits are highest within the demyelinated dorsal hippocampal CA2 pyramidal layer, and co-localized with inhibitory synapses engulfed by microglia/macrophages. In agreement with the loss of inhibitory perisomatic synapses, we further found that Schaffer collateral feedforward inhibition but not excitation was impaired in CA2 pyramidal neurons and accompanied by a reduced spike output. Ultimately, we show that these electrophysiological changes were associated with an impaired encoding of social memories. Together, our findings identify CA2 as a critical circuit in demyelinated intrahippocampal lesions and memory dysfunctions in MS.

neuroscience↗

bioRxiv2020

REALM: AO-based localization microscopy deep in complex tissue

Performing Single-Molecule Localization Microscopy (SMLM) in complex biological tissues, where sample-induced aberrations hamper detection and localization, has remained a challenge. Here we establish REALM (Robust and Effective Adaptive Optics in Localization Microscopy), which corrects aberrations of [≤]1 rad RMS using 297 frames of blinking molecules to improve single-molecule localization. We demonstrate this method by resolving the periodic cytoskeleton of the axon initial segment at 50 m depth in brain tissue.

cell biology↗

bioRxiv2020

Sensory input drives rapid homeostatic scaling of the axon initial segment in mouse barrel cortex

The axon initial segment (AIS) is an important axonal microdomain for action potential initiation and implicated in the regulation of neuronal excitability during activity-dependent cortical plasticity. While structural AIS plasticity has been suggested to fine-tune neuronal activity when network states change, whether it acts as a homeostatic regulatory mechanism in behaviorally relevant contexts remains poorly understood. Using an in vivo model of the mouse whisker-to-barrel pathway in combination with immunofluorescence, confocal analysis and patch-clamp electrophysiological recordings, we observed bidirectional AIS plasticity. Furthermore, we find that structural and functional AIS remodeling occurs in distinct temporal domains: long-term sensory deprivation elicits an AIS length increase, accompanied with an increase in neuronal excitability, while sensory enrichment results in a rapid AIS shortening, accompanied by a decrease in action potential generation. Our findings highlight a central role of the AIS in the homeostatic regulation of neuronal input-output relations.

neuroscience↗

bioRxiv2019

HCN channel-mediated neuromodulation can control action potential velocity and fidelity in central axons

Hyperpolarization-activated cyclic-nucleotide-gated (HCN) channels control electrical rhythmicity and excitability in the heart and brain, but the function of HCN channels at subcellular level in axons remains poorly understood. Here, we show that the action potential conduction velocity in both myelinated and unmyelinated central axons can bidirectionally be modulated by HCN channel blockers, cyclic adenosine monophosphate (cAMP), and neuromodulators. Recordings from mice cerebellar mossy fiber boutons show that HCN channels ensure reliable high-frequency firing and are strongly modulated by cAMP (EC50 40 {micro}M; estimated endogenous cAMP concentration 13 {micro}M). In accord, immunogold-electron microscopy revealed HCN2 as the dominating subunit in cerebellar mossy fibers. Computational modeling indicated that HCN2 channels control conduction velocity primarily via altering the resting membrane potential and was associated with significant metabolic costs. These results suggest that the cAMP-HCN pathway provides neuromodulators an opportunity to finely tune energy consumption and temporal delays across axons in the brain.

neuroscience↗