Biology subjects

Greger, I. H.

Publications and source records attributed to Greger, I. H..

7 recordsLinked to original sources

bioRxiv2026

Vesicular acidification modulates the synaptic current: a hybrid diffusion reaction model analysis

Glutamate synaptic vesicles co-release protons, producing a brief acidification of the synaptic cleft that could modulate AMPA receptor (AMPARs) operation. To evaluate the extent of receptor acidification, we develop a diffusion-reaction model that couples vesicle-evoked proton and glutamate transients to AMPAR dynamics. Our simulations reveal that the rapid diffusion of protons and glutamate within the flat-cylindrical synaptic cleft leads to a mixture of protonated, singly glutamate-bound and doubly glutamate-bound AMPARs. We studied four postsynaptic AMPAR distributions - uniform disk, sub-disk, Gaussian cluster, and point-like cluster - and showed a [~] 50% increase in the number of acidified receptors when AMPARs are clustered on the postsynaptic cleft compared to a uniform arrangement. We further explored the impact of pH revealing that at acidic conditions (pH [~] 5), approximately 80-90% of open receptors are non-acidified, whereas under strongly acidic conditions (pH [~] 3), about 80-90% of open receptors exist in the protonated form. Finally, we explored how acidification modulates AMPARs during paired-pulse stimulation, a measure of short-term synaptic depression. While the presence of protons does not markedly alter the overall trends, acidified receptor states reduce the occupancies of their neutral counterparts by roughly 10-15%, indicating a mild redistribution toward protonated receptor conformations. To conclude, our model suggests that AMPAR protonation can influence the synaptic current, and we predict that this effect is determined primarily by the dissociation kinetics of glutamate and protons from AMPAR.

neuroscience↗

bioRxiv2026

Pathological TDP-43 filaments accumulate at synapses and cause synaptic dysfunction

The assembly of TAR DNA-binding protein 43 (TDP-43) into amyloid filaments within neurons is a hallmark of multiple neurodegenerative diseases, including motor neuron diseases (MND), frontotemporal dementias (FTD) and limbic-predominant age-related TDP-43 encephalopathy (LATE). These diseases result from the deterioration and loss of neurons, with synaptic dysfunction and neuronal hyperexcitability being prominent early events. Pathogenic mutations in the TDP-43 gene, TARDBP, that promote filament formation have established a causal role for TDP-43 assembly in neurodegenerative diseases. However, the molecular mechanisms underlying filament accumulation and their contribution to neurodegeneration are poorly understood. TDP-43 filaments can propagate between neurons in a prion-like manner, which may underlie the progressive spread and accumulation of TDP-43 pathology in disease. Here, we studied early stages of TDP-43 filament accumulation following internalisation of patient-derived TDP-43 filaments by mouse and human cortical neurons. Using proximity labelling, we identified molecular environments and putative interactions of TDP-43 filaments. We found that TDP-43 filaments accumulated at synapses, particularly in proximity to the presynaptic active zone, which we confirmed in FTD patient brain sections. Electron cryo-tomography (cryo-ET) directly visualised abundant TDP-43 filaments spanning the presynaptic cytoplasm in situ, which contacted synaptic vesicles and the plasma membrane. Functional measurements revealed that the accumulation of TDP-43 filaments led to presynaptic dysfunction and subsequent neuronal hyperexcitability. These findings suggest that synapses are a major early site of TDP-43 filament accumulation, relevant to their propagation, and directly link TDP-43 filament gain of function to synaptic dysfunction.

neuroscience↗

bioRxiv2024

'Mini analysis' is an unreliable reporter of synaptic changes

Analysis of miniature postsynaptic currents (mPSCs, or minis) is one of the most extensively employed approaches to determine the functional properties of synaptic connections. The popularity of this technique stems from its simplicity. Patch-clamp recording is used to observe spontaneous transmission occurring at synapses throughout a neurons dendritic tree. These events are analysed in an attempt to determine quantal synaptic parameters and changes during experimental manipulation. For decades, changes in the amplitude or frequency of mPSCs have been interpreted as evidence for specific synaptic modifications, including changes in presynaptic release sites, postsynaptic receptor abundance or even nanoscale changes in the alignment of synaptic machinery. However, at the majority of brain synapses, these events are small, with many undetectable due to recording noise. Here, using both simulated and experimental data, we demonstrate that interpreting synaptic changes from mPSC datasets is fundamentally fallible. Due to incomplete detection of event distributions, seemingly specific changes in mPSC amplitude or frequency falsely report actual synaptic changes. In addition, probabilistic detection of small events gives false confidence in the completeness of detection and inaccurate determination of quantal size. We not only demonstrate the dense pitfalls of mini analysis, but also establish a method for experimental detection of the detection limit, allowing more robust data analysis and scientific interpretation.

neuroscience↗

bioRxiv2024

Dopamine increases protein synthesis in hippocampal neurons enabling dopamine-dependent LTP

The reward and novelty related neuromodulator dopamine plays an important role in hippocampal long- term memory, which is thought to involve protein synthesis-dependent synaptic plasticity. However, the direct effects of dopamine on protein synthesis, and the functional implications of newly synthesized proteins for synaptic plasticity, have not yet been investigated. We have previously reported that timing- dependent synaptic depression (t-LTD) can be converted into potentiation by dopamine application during synaptic stimulation (Brzosko et al., 2015) or postsynaptic burst activation (Fuchsberger et al., 2022). Here we show that dopamine increases protein synthesis in mouse hippocampal CA1 neurons, enabling dopamine-dependent long-term potentiation (DA-LTP), which is mediated via the Ca2+-sensitive adenylate cyclase (AC) subtypes 1/8, cAMP, and cAMP-dependent protein kinase (PKA). We found that neuronal activity is required for the dopamine-induced increase in protein synthesis. Furthermore, dopamine induced a protein synthesis-dependent increase in the AMPA receptor subunit GluA1, but not GluA2. We found that DA-LTP is absent in GluA1 knock-out mice and that it requires calcium-permeable AMPA receptors. Taken together, our results suggest that dopamine together with neuronal activity controls synthesis of plasticity-related proteins, including GluA1, which enable DA-LTP via a signalling pathway distinct from that of conventional LTP.

neuroscience↗

bioRxiv2022

Modulatory mechanisms of TARP γ8-selective AMPA receptor therapeutics

AMPA glutamate receptors (AMPARs) mediate excitatory neurotransmission throughout the brain. Their signalling is uniquely diversified by brain region-specific auxiliary subunits, providing an opportunity for the development of selective therapeutics. AMPARs associated with TARP {gamma}8 are enriched in the hippocampus, and are targets of emerging anti-epileptic drugs. To understand their therapeutic activity, we determined cryo-EM structures of the GluA1/2-{gamma}8 receptor associated with three potent, chemically diverse drugs. We find that despite sharing a lipid-exposed and water-accessible binding pocket, drug action is differentially affected by binding-site mutants. Together with patch-clamp recordings and MD simulations we demonstrate that ligand-triggered reorganisation of the AMPAR-TARP interface contributes to modulation. Unexpectedly, one ligand (JNJ-61432059) acts bifunctionally, negatively affecting GluA1 but exerting positive modulatory action on GluA2-containing AMPARs, in a TARP stoichiometry-dependent manner. These results further illuminate the action of TARPs, demonstrate the sensitive balance between positive and negative modulatory action, and provide a mechanistic platform for development of both positive and negative selective AMPAR modulators.

neuroscience↗

bioRxiv2020

Gating transitions and modulation of a hetero-octameric AMPA glutamate receptor

AMPA glutamate receptors (AMPARs) mediate the majority of excitatory transmission in the brain, and enable synaptic plasticity that underlies learning 1. A diverse array of AMPAR signaling complexes are established by receptor auxiliary subunits, associating in various combinations to modulate trafficking, gating and synaptic strength 2. However, their mechanisms of action are poorly understood. Here, we determine cryo-electron microscopy structures of the heteromeric GluA1/2 receptor assembled with both TARP-{gamma}8 and CNIH2, the predominant AMPAR complex in the forebrain, in both resting and active states (at 3.2 and 3.7 [A], respectively). Consequential for gating regulation, two {gamma}8 and two CNIH2 subunits lodge at distinct sites beneath the ligand-binding domains of the receptor tetramer, with site-specific lipids shaping each interaction. Activation leads to a stark asymmetry between GluA1 and GluA2 along the ion conduction path, and an outward expansion of the channel triggers counter-rotations of both auxiliary subunit pairs, that promotes the active-state conformation. In addition, both {gamma}8 and CNIH2 pivot towards the pore exit on activation, extending their reach for cytoplasmic receptor elements. CNIH2 achieves this through its uniquely extended M2 helix, which has transformed this ER-export factor into a powerful positive AMPAR modulator, capable of providing hippocampal pyramidal neurons with their integrative synaptic properties.

neuroscience↗

bioRxiv2020

An inhalation anaesthesia approach for neonatal mice allowing streamlined stereotactic injection in the brain

Investigating brain function requires tools and techniques to visualise, modify and manipulate neuronal tissue. One powerful and popular method is intracerebral injection of customised viruses, allowing expression of exogenous transgenes. This technique is a standard procedure for adult mice, and is used by laboratories worldwide. Use of neonatal animals in scientific research allows investigation of developing tissues, and enables long-term study of cell populations. However, procedures on neonatal mice are more challenging, due to the lack of reliable methods and apparatus for anaesthesia of these animals. Here, we report an inhalation-based protocol for anaesthesia of neonatal (P0-2) mice, and present a custom 3D-printed apparatus for maintenance of anaesthesia during surgical procedures. This approach significantly enhances animal welfare and facilitates wider and simpler use of neonatal rodents in scientific research. Our optimised method of anaesthesia enables a rapid method of stereotactic injection in neonatal mice for transduction of brain tissue. We demonstrate this procedure for targeted labelling of specific brain regions, and in vivo modification of tissue prior to organotypic culture. This anaesthetic approach can be readily employed by any laboratory, and will enable safer use of neonatal rodents across a diverse spectrum of scientific disciplines. HighlightsO_LIDevelopment of inhalation-based anaesthesia for early postnatal (P0-2) mice C_LIO_LI3D-printed mould allows anaesthetic maintenance for neonatal surgery C_LIO_LIImproved mouse welfare through reliable neonatal inhalation anaesthesia C_LIO_LIRapid procedure for brain transduction of mouse litter in under 2 hours C_LI

neuroscience↗