Biology subjects

Stellwagen, D.

Publications and source records attributed to Stellwagen, D..

5 recordsLinked to original sources

bioRxiv2026

GPCR-mediated regulation of glial TNF production

Neuromodulators generally act through G-protein-coupled receptors, but their effects on glia are not well defined. Here we examine the impact of various G-protein-coupled signaling pathways on glia, using the production of the pro-inflammatory cytokine tumor necrosis factor alpha (TNF) as a measure of activation. TNF is a major component of the innate immune response but is also an important regulator of synaptic function and can be released by both astrocytes and microglia. Using pharmacological and chemogenetic approaches, we characterized the response to activation of the Gi, Gq, and Gs signaling pathways in rat astrocyte and microglia cultures and human induced pluripotent stem cells (hiPSCs) derived astrocytes. Across all tested glia, activation of the Gs pathway results in a stark decrease in TNF expression. Similarly, activation of Gq signaling also results in a reduction in TNF mRNA levels. Conversely, Gi activation in astrocytes and microglia increases TNF levels both in vitro and in vivo. The impacts of GPCRs on TNF production were not consistent for other pro-inflammatory cytokines. Overall, this work demonstrates that G protein-mediated activation and inhibition in glia should be considered separately from the effects seen in neurons.

neuroscience↗

bioRxiv2026

Transregional astrocyte-dependent metaplasticity in the hippocampus

Learning-related synaptic plasticity is regulated by metaplasticity, which adjusts plasticity thresholds in an activity-dependent manner. We have previously described a heterodendritic form of metaplasticity whereby priming stimulation in stratum oriens (SO) inhibits subsequent long-term potentiation (LTP) in the neighboring stratum radiatum of the hippocampal CA1 region. Here, we report that this metaplasticity is, in fact, transregional, in that the SO priming stimulation also inhibits later LTP induction at dentate gyrus (DG) middle molecular layer (MML) synapses, both in vitro and in vivo. This effect operates across the hippocampal fissure since it occurs in the absence of CA3, thus highlighting a previously unappreciated reverse-direction and long-distance hippocampal crosstalk. Our findings demonstrate an essential role of astrocytes as SO priming elicited a sustained increase in the frequency of calcium (Ca2+) events in astrocytes in the DG MML, while the metaplasticity effect was blocked by calcium-buffering in MML astrocytes. It could be triggered by either activation of M1 muscarinic acetylcholine receptors or group II metabotropic glutamate receptors, and was critically dependent on inositol 1,4,5-trisphosphate receptor type 2 signaling. The transregional inhibition of LTP was mediated by astrocytic release of tumor necrosis factor (TNF), which likely acts in an autocrine fashion on astrocytic TNF type 1 receptors (TNFR1s). Downstream of TNF-TNFR1 signaling, the inhibition of MML LTP was mediated by the activation of GluN2B-containing N-methyl-D-aspartate receptors. Thus, a complex, bidirectional neuron-glia signaling cascade orchestrates long-distance metaplasticity across hippocampal subregions, providing a novel framework for understanding how hippocampal neuronal networks dynamically regulate plasticity thresholds across space and time. Significance StatementThis study documents the existence of a transregional metaplasticity that traverses from area CA1 to the dentate gyrus across the hippocampal fissure. This reveals a novel long-distance crosstalk within the hippocampus, in addition to the classical pathways of information transfer. This form of metaplasticity entails an essential contribution by astrocytes that integrate neuronal activity and use a complex Ca2+-dependent neuron-glia-neuron signaling cascade to dynamically regulate LTP thresholds in the hippocampal dentate gyrus.

neuroscience↗

bioRxiv2022

PP1 inhibitor-2 promotes PP1γ positive regulation of synaptic transmission

Inhibitor-2 (I-2) is a prototypic inhibitor of protein phosphatase-1 (PP1), a major serine-threonine phosphatase that regulates synaptic plasticity and learning and memory. Although I-2 is a potent inhibitor of PP1 in vitro, our previous work has elucidated that, in vivo, I-2 may act as a positive regulator of PP1. Here we show that I-2 and PP1{gamma}, but not PP1, positively regulate synaptic transmission in hippocampal neurons. Moreover, we demonstrated that I-2 enhances PP1{gamma} interaction with its major synaptic scaffold, neurabin, by Forster resonance energy transfer (FRET)/Fluorescence lifetime imaging microscopy (FLIM) studies, while having a limited effect on PP1 autoinhibitory phosphorylation. Furthermore, our study indicates that the effect of I-2 on PP1 activity in vivo is dictated by I-2 threonine-72 phosphorylation. Our work thus demonstrates a molecular mechanism by which I-2 positively regulates PP1 function in synaptic transmission.

neuroscience↗

bioRxiv2021

Sustained TNF signaling is required for the synaptic and behavioral response to acute stress

Acute stress triggers plasticity of forebrain synapses as well as behavioral changes. Here we reveal that Tumor Necrosis Factor (TNF) is a required downstream mediator of the stress response in mice, necessary for stress-induced synaptic potentiation in the ventral hippocampus and for an increase in anxiety-like behaviour. Acute stress is sufficient to activate microglia, triggering the long-term release TNF. Critically, on-going TNF signaling in the ventral hippocampus is necessary to sustain both the stress-induced synaptic and behavioral changes, as these could be reversed hours after induction by antagonizing TNF signaling. This demonstrates that TNF maintains the synaptic and behavioral stress response in vivo, making TNF a potential novel therapeutic target for stress disorders.

neuroscience↗

bioRxiv2019

Depolarizing GABA Transmission Restrains Activity-Dependent Glutamatergic Synapse Formation in the Developing Hippocampal Circuit

GABA is the main inhibitory neurotransmitter in the mature brain but has the paradoxical property of depolarizing neurons during early development. Depolarization provided by GABAA transmission during this early phase regulates neural stem cell proliferation, neural migration, neurite outgrowth, synapse formation, and circuit refinement, making GABA a key factor in neural circuit development. Importantly, depending on the context, depolarizing GABAA transmission can either drive neural activity, or inhibit it through shunting inhibition. The varying roles of depolarizing GABAA transmission during development, and its ability to both drive and inhibit neural activity, makes it a difficult developmental cue to study. This is particularly true in the later stages of development, when the majority of synapses form and GABAA transmission switches from depolarizing to hyperpolarizing. Here we addressed the importance of depolarizing but inhibitory (or shunting) GABAA transmission in glutamatergic synapse formation in hippocampal CA1 pyramidal neurons. We first showed that the developmental depolarizing-to-hyperpolarizing switch in GABAA transmission is recapitulated in organotypic hippocampal slice cultures. Based on the expression profile of K+-Cl- co-transporter 2 (KCC2) and changes in the GABA reversal potential, we pinpointed the timing of the switch from depolarizing to hyperpolarizing GABAA transmission in CA1 neurons. We found that blocking depolarizing but shunting GABAA transmission increased excitatory synapse number and strength, indicating that depolarizing GABAA transmission can restrain glutamatergic synapse formation. The increase in glutamatergic synapses was activity-dependent, but independent of BDNF signalling. Importantly, the elevated number of synapses was stable for more than a week after GABAA inhibitors were washed out. Together these findings point to the ability of immature GABAergic transmission to restrain glutamatergic synapse formation and suggest an unexpected role for depolarizing GABAA transmission in shaping excitatory connectivity during neural circuit development.

neuroscience↗