Biology subjects

Schulze, C.

Publications and source records attributed to Schulze, C..

8 recordsLinked to original sources

bioRxiv2026

Dissecting the molecular triggers of early and late long-term potentiation

The brain stores information by changing the strength of its synapses, a process that has at least two phases: Late long-term potentiation (L-LTP) is thought to result from the consolidation of early LTP (E-LTP), just as long-term memory requires the prior establishment of short-term memory. Recently, inhibitory avoidance experiments under CaMKII inhibition have challenged this notion, demonstrating long-term fear memory without measurable short-term memory. Here we use optogenetic activation and inhibition of CaMKII during induction of spike-timing-dependent potentiation (tLTP) to dissect the signaling pathways. While CaMKII activation in CA1 neurons was sufficient to induce E-LTP, growth of the postsynaptic density and spine neck expansion, we found that CaMKII-induced LTP does not give rise to L-LTP. Conversely, inhibition of CaMKII during tLTP induction prevented E-LTP, but FOS and L-LTP were still expressed, driven by CaMKK and PKM{zeta}. Thus, both long-term memory and L-LTP form in the absence of CaMKII activation.

neuroscience↗

bioRxiv2026

Buffaloed in Brandenburg: Germany's first Brush with Foot-and-Mouth Disease after four Decades of Freedom

Foot-and-mouth disease (FMD) virus is one of the most feared and most consequential pathogens of livestock worldwide. It can be spread rapidly by the transboundary movement of animals, animal products and byproducts. In January 2025, Germany detected its first FMD outbreak since 1988 in extensively reared water buffalo on a small farm in the state of Brandenburg, directly outside Berlin, the federal capital. Immediate control measures including a standstill for movements of susceptible animals and pre-emptive culling were implemented by the veterinary authorities. Whole-genome sequencing identified the virus as serotype O, topotype ME-SA, lineage SA-2018 and revealed extensive recombination, but cross-neutralization assays suggested good heterologous protection by an O/PanAsia-2 vaccine strain. Epidemiological back-calculation placed the time of virus introduction in late December 2024. Although the entry route remains unresolved, human-associated introduction is most likely. Network analysis revealed minimal farm connectivity, and simulations predicted low potential for onward transmission, which is consistent with the outbreak being ultimately restricted to a single herd. This event underscores the constant and unpredictable risk of introduction of the virus. Early detection through increased awareness and comprehensive differential diagnostics as well as the international collaboration of veterinary services, laboratories and experts are essential in the face of the global presence of FMD.

microbiology↗

bioRxiv2020

Evidence of hidden hunger in Darwin's finches as a result of non-native species invasion of the Galapagos cloud forest

Invasive species pose a major threat to forest biodiversity, particularly on islands, such as the Galapagos. Here, invasive plants are threatening the remnants of the unique cloud forest and its iconic Darwins finches. We posit that food web disturbances caused by invasive Rubus niveus (blackberry), but also the management measures used to control it, could contribute to the rapid decline of the insectivourous warbler finch (Certhidae olivacea). We compared changes in long-term management, short-term management and unmanaged areas. We measured C:N ratios, {delta}15N-nitrogen and {delta}13C-carbon signatures in bird blood and arthropods, as indicators of resource use change, in addition to mass abundance and diversity of arthropods. We reconstructed the birds diets using isotope mixing models. The results revealed that finches in (Rubus-invaded) unmanaged areas foraged on abundant yet low quality arthropods and had shorter tarsi. Is this the first evidence of hidden hunger in degraded terrestrial ecosystems in Galapagos?

ecology↗

bioRxiv2020

The vesicular release probability sets the strength of individual Schaffer collateral synapses

Information processing in the brain is controlled by quantal release of neurotransmitters, a tightly regulated process. From ultrastructural analysis, it is known that presynaptic boutons along single axons differ in the number of vesicles docked at the active zone. It is not clear whether the probability of these vesicles to get released (pves) is homogenous or also varies between individual boutons. Here, we optically measure evoked transmitter release at individual Schaffer collateral synapses at different calcium concentrations, using the genetically encoded glutamate sensor iGluSnFR. Fitting a binomial model to measured response amplitude distributions allowed us to extract the quantal parameters N, pves, and q. We find that Schaffer collateral boutons typically release single vesicles under low pves conditions and switch to multivesicular release in high calcium saline. Analyzing the variability of quantal parameters, we conclude that the vesicular release probability rather than the number of readily releasable vesicles or their transmitter content determines the potency of individual boutons.

neuroscience↗

bioRxiv2020

Endoplasmic reticulum visits highly active spines and prevents runaway potentiation of synapses

In hippocampal pyramidal cells, a small subset of dendritic spines contain endoplasmic reticulum (ER). In large spines, ER frequently forms a spine apparatus, while smaller spines contain just a single tubule of smooth ER. Here we show that the ER visits dendritic spines in a non-random manner, targeting spines during periods of high synaptic activity. When we blocked ER motility using a dominant negative approach against myosin V, spine synapses became stronger compared to controls. We were not able to further potentiate these maxed-out synapses, but LTD was readily induced by low-frequency stimulation. We conclude that the brief ER visits to active spines have the important function of preventing runaway potentiation of individual spine synapses, keeping most of them at an intermediate strength level from which both LTP and LTD are possible.

neuroscience↗

bioRxiv2019

Freeze-frame imaging of synaptic activity using SynTagMA

Information within the brain travels from neuron to neuron across synapses. At any given moment, only a few synapses within billions will be active and are thought to transmit key information about the environment, a behavior being executed or memory being recalled. Here we present SynTagMA, which marks active synapses within a ~2 s time window. Upon violet illumination, the genetically expressed tag converts from green to red fluorescence if bound to calcium. Targeted to presynaptic terminals, preSynTagMA allows discrimination between active and silent axons. Targeted to excitatory postsynapses, postSynTagMA creates a snapshot of synapses active just before photoconversion. To analyze large datasets, we developed an analysis program that automatically identifies and tracks the fluorescence of thousands of individual synapses in tissue. Together, these tools provide a high throughput method for repeatedly mapping active synapses in vitro and in vivo.

neuroscience↗

bioRxiv2018

Strong diffusional coupling between spines and dendrites promotes long-term potentiation of Schaffer collateral synapses

Dendritic spines on CA1 pyramidal cells are highly variable in size and shape. For some spine synapses, long and narrow spine necks provide strong diffusional and electrical isolation from the main dendrite, and it has been speculated that synapses on well isolated spines could be more plastic than synapses on spines with low resistance necks. Here we test this hypothesis by first measuring the diffusional resistance of spine necks, then pairing two-photon glutamate uncaging with bursts of back-propagating action potentials. Paired stimulation induced significant (155%) long-term potentiation (LTP) of synapses on weakly isolated spines, but no net functional change of synapses on highly isolated spines. No correlation was found between spine head volume and functional plasticity of the synapses. We conclude that contrary to our expectations, diffusional isolation makes potentiation of synapses more difficult. Our results support the concept that delivery of plasticity-related proteins from the dendrite into the spine is a limiting factor for LTP.

neuroscience↗

bioRxiv2017

Ultrafast glutamate sensors resolve synaptic short-term plasticity

Glutamatergic synapses display a rich repertoire of plasticity mechanisms on many different time scales, involving dynamic changes in the efficacy of transmitter release as well as changes in the number and function of postsynaptic glutamate receptors. The genetically encoded glutamate sensor iGluSnFR enables visualization of glutamate release from presynaptic terminals at frequencies up to [~]10 Hz. However, to resolve glutamate dynamics during high frequency bursts, faster indicators are required. Here we report the development of fast (iGluf) and ultrafast (iGluu) variants with comparable brightness, but increased Kd for glutamate (137 M and 600 M, respectively). Compared to iGluSnFR, iGluu has a 6-fold faster dissociation rate in vitro and 5-fold faster kinetics in synapses. Fitting a three-state model to kinetic data, we identify the large conformational change after glutamate binding as the rate-limiting step. In rat hippocampal slice culture stimulated at 100 Hz, we find that iGluu is sufficiently fast to resolve individual glutamate release events, revealing that glutamate is rapidly cleared from the synaptic cleft. Depression of iGluu responses during 100 Hz trains correlates with depression of postsynaptic EPSPs, indicating that depression during high frequency stimulation is purely presynaptic in origin. At individual boutons, the recovery from depression could be predicted from the amount of glutamate released on the second pulse (paired pulse facilitation/depression), demonstrating differential frequency-dependent filtering of spike trains at Schaffer collateral boutons.\n\nSignificance StatementExcitatory synapses convert presynaptic action potentials into chemical signals that are sensed by postsynaptic glutamate receptors. To eavesdrop on synaptic transmission, genetically encoded fluorescent sensors for glutamate have been developed. However, even the best available sensors lag behind the very fast glutamate dynamics in the synaptic cleft. Here we report the development of an ultrafast genetically encoded glutamate sensor, iGluu, which allowed us to image glutamate clearance and synaptic depression during 100 Hz spike trains. We found that only boutons showing paired-pulse facilitation were able to rapidly recover from depression. Thus, presynaptic boutons act as frequency-specific filters to transmit select features of the spike train to specific postsynaptic cells.

neuroscience↗