{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,7,30]],"date-time":"2026-07-30T13:18:40Z","timestamp":1785417520445,"version":"3.56.0"},"reference-count":39,"publisher":"MDPI AG","issue":"14","license":[{"start":{"date-parts":[[2026,7,13]],"date-time":"2026-07-13T00:00:00Z","timestamp":1783900800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100002428","name":"Austrian Science Fund","doi-asserted-by":"publisher","award":["P35219"],"award-info":[{"award-number":["P35219"]}],"id":[{"id":"10.13039\/501100002428","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100002428","name":"Austrian Science Fund","doi-asserted-by":"publisher","award":["P31777"],"award-info":[{"award-number":["P31777"]}],"id":[{"id":"10.13039\/501100002428","id-type":"DOI","asserted-by":"publisher"}]},{"award":["P35219"],"award-info":[{"award-number":["P35219"]}],"id":[{"id":"https:\/\/ror.org\/013tf3c58","id-type":"ROR","asserted-by":"publisher"}]},{"award":["P31777"],"award-info":[{"award-number":["P31777"]}],"id":[{"id":"https:\/\/ror.org\/013tf3c58","id-type":"ROR","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["IJMS"],"abstract":"<jats:p>Toll-like receptors (TLRs) are essential in the innate immune response. Furthermore, neuronal TLRs have been involved in regulating neuronal dendritic outgrowth and excitability. However, a deeper understanding of neuronal-TLR function is essential. We investigated the expression and role of TLR8 using mouse postnatal hippocampal neuronal cultures. We assessed TLR8 (and TLR7) expression by immunocytochemistry and TLR8 functionality via electrophysiological recordings in a high-density multi-electrode array system and calcium flux imaging. Pathway activation following fast TLR8 stimulation was performed via Western blot. TLR8 and TLR7 are expressed in postnatal hippocampal neurons at DIV14 and in neurosphere-derived neurons. TLR8 expression was detected in the cell body and dendrites of GABAergic, parvalbumin-expressing interneurons. Stimulation with the TLR8 agonist TL8-506 led to increased neuronal activity in the short term and enhanced neuronal synchronization in short- and long-term recordings. The calcium flux induced by TLR8 was reduced by blocking NMDA receptors with D-AP5. TLR8 stimulation did not lead to IkB-\u03b1 degradation. Our findings demonstrate that TLR8 and TLR7 are expressed in mouse postnatal hippocampal neurons. TLR8 activation leads to increased neuronal excitability that was decreased by NMDA antagonism. However, acute TLR8 stimulation failed to robustly activate the canonical TLR signaling pathway. We propose that TLR8 activation might lead to the enhancement of excitatory NMDA receptors.<\/jats:p>","DOI":"10.3390\/ijms27146232","type":"journal-article","created":{"date-parts":[[2026,7,14]],"date-time":"2026-07-14T02:34:44Z","timestamp":1783996484000},"page":"6232","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Toll-like Receptor 8 (TLR8) Is Expressed in Mouse Hippocampal Neurons and Modulates Neuronal Excitability"],"prefix":"10.3390","volume":"27","author":[{"given":"Julian","family":"Fenkart","sequence":"first","affiliation":[{"name":"Institute of Pharmacology, Medical University of Innsbruck, Peter Mayr Str. 1, 6020 Innsbruck, Austria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Alice","family":"Santagostino","sequence":"additional","affiliation":[{"name":"Institute of Pharmacology, Medical University of Innsbruck, Peter Mayr Str. 1, 6020 Innsbruck, Austria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Stephanie","family":"Seidlberger","sequence":"additional","affiliation":[{"name":"Institute of Pharmacology, Medical University of Innsbruck, Peter Mayr Str. 1, 6020 Innsbruck, Austria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-1969-1422","authenticated-orcid":false,"given":"Armin","family":"Schmuck","sequence":"additional","affiliation":[{"name":"Institute of Pharmacology, Medical University of Innsbruck, Peter Mayr Str. 1, 6020 Innsbruck, Austria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Katharina","family":"Donat","sequence":"additional","affiliation":[{"name":"Institute of Pharmacology, Medical University of Innsbruck, Peter Mayr Str. 1, 6020 Innsbruck, Austria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2705-9673","authenticated-orcid":false,"given":"Meinrad","family":"Drexel","sequence":"additional","affiliation":[{"name":"Institute of Pharmacology, Medical University of Innsbruck, Peter Mayr Str. 1, 6020 Innsbruck, Austria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4691-3003","authenticated-orcid":false,"given":"Sandra","family":"Santos-Sierra","sequence":"additional","affiliation":[{"name":"Institute of Pharmacology, Medical University of Innsbruck, Peter Mayr Str. 1, 6020 Innsbruck, Austria"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,7,13]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"973","DOI":"10.1016\/S0092-8674(00)80172-5","article-title":"The dorsoventral regulatory gene cassette spatzle\/Toll\/cactus controls the potent antifungal response in Drosophila adults","volume":"86","author":"Lemaitre","year":"1996","journal-title":"Cell"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"394","DOI":"10.1038\/41131","article-title":"A human homologue of the Drosophila Toll protein signals activation of adaptive immunity","volume":"388","author":"Medzhitov","year":"1997","journal-title":"Nature"},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"783","DOI":"10.1016\/j.cell.2006.02.015","article-title":"Pathogen recognition and innate immunity","volume":"124","author":"Akira","year":"2006","journal-title":"Cell"},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"1044","DOI":"10.1016\/j.cell.2020.02.041","article-title":"Toll-like Receptors and the Control of Immunity","volume":"180","author":"Fitzgerald","year":"2020","journal-title":"Cell"},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"350","DOI":"10.1089\/jir.2012.0014","article-title":"Human Toll-like receptor 8 can be cool too: Implications for foreign RNA sensing","volume":"32","author":"Sarvestani","year":"2012","journal-title":"J. Interferon Cytokine Res."},{"key":"ref_6","doi-asserted-by":"crossref","unstructured":"Pluta, L., Yousefi, B., Damania, B., and Khan, A.A. (2019). Endosomal TLR-8 Senses microRNA-1294 Resulting in the Production of NFkB Dependent Cytokines. Front. Immunol., 10.","DOI":"10.3389\/fimmu.2019.02860"},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"11479","DOI":"10.1523\/JNEUROSCI.5566-12.2013","article-title":"TLR7 negatively regulates dendrite outgrowth through the Myd88-c-Fos-IL-6 pathway","volume":"33","author":"Liu","year":"2013","journal-title":"J. Neurosci."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"2727","DOI":"10.1083\/jcb.201712113","article-title":"Endosomal TLR3, TLR7, and TLR8 control neuronal morphology through different transcriptional programs","volume":"217","author":"Hung","year":"2018","journal-title":"J. Cell Biol."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"209","DOI":"10.1083\/jcb.200606016","article-title":"Toll-like receptor 8 functions as a negative regulator of neurite outgrowth and inducer of neuronal apoptosis","volume":"175","author":"Ma","year":"2006","journal-title":"J. Cell Biol."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"319","DOI":"10.1111\/j.1365-2796.2011.02431.x","article-title":"Interleukin-1 type 1 receptor\/Toll-like receptor signalling in epilepsy: The importance of IL-1beta and high-mobility group box 1","volume":"270","author":"Maroso","year":"2011","journal-title":"J. Intern. Med."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"1726","DOI":"10.1089\/ars.2013.5349","article-title":"Disulfide-containing high mobility group box-1 promotes N-methyl-D-aspartate receptor function and excitotoxicity by activating Toll-like receptor 4-dependent signaling in hippocampal neurons","volume":"21","author":"Balosso","year":"2014","journal-title":"Antioxid. Redox Signal."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"12","DOI":"10.1016\/j.nbd.2016.12.007","article-title":"Blockade of the IL-1R1\/TLR4 pathway mediates disease-modification therapeutic effects in a model of acquired epilepsy","volume":"99","author":"Iori","year":"2017","journal-title":"Neurobiol. Dis."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"3171","DOI":"10.1007\/s12035-020-01927-0","article-title":"Compromised Hippocampal Neuroplasticity in the Interferon-alpha and Toll-like Receptor-3 Activation-Induced Mouse Depression Model","volume":"57","author":"Dzyubenko","year":"2020","journal-title":"Mol. Neurobiol."},{"key":"ref_14","doi-asserted-by":"crossref","unstructured":"Seizer, L., Rahimi, S., Santos-Sierra, S., and Drexel, M. (2022). Expression of toll like receptor 8 (TLR8) in specific groups of mouse hippocampal interneurons. PLoS ONE, 17.","DOI":"10.1371\/journal.pone.0267860"},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"1526","DOI":"10.1126\/science.1093620","article-title":"Species-specific recognition of single-stranded RNA via toll-like receptor 7 and 8","volume":"303","author":"Heil","year":"2004","journal-title":"Science"},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"5598","DOI":"10.1073\/pnas.0400937101","article-title":"Recognition of single-stranded RNA viruses by Toll-like receptor 7","volume":"101","author":"Lund","year":"2004","journal-title":"Proc. Natl. Acad. Sci. USA"},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"1529","DOI":"10.1126\/science.1093616","article-title":"Innate antiviral responses by means of TLR7-mediated recognition of single-stranded RNA","volume":"303","author":"Diebold","year":"2004","journal-title":"Science"},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"13978","DOI":"10.1523\/JNEUROSCI.2140-08.2008","article-title":"Toll-like receptor 3 is a negative regulator of embryonic neural progenitor cell proliferation","volume":"28","author":"Lathia","year":"2008","journal-title":"J. Neurosci."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"499","DOI":"10.1158\/1078-0432.CCR-11-1625","article-title":"VTX-2337 is a novel TLR8 agonist that activates NK cells and augments ADCC","volume":"18","author":"Lu","year":"2012","journal-title":"Clin. Cancer Res."},{"key":"ref_20","doi-asserted-by":"crossref","unstructured":"Moutin, E., Hemonnot, A.L., Seube, V., Linck, N., Rassendren, F., Perroy, J., and Compan, V. (2020). Procedures for Culturing and Genetically Manipulating Murine Hippocampal Postnatal Neurons. Front. Synaptic Neurosci., 12.","DOI":"10.3389\/fnsyn.2020.00019"},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"1281","DOI":"10.1016\/j.bbi.2011.03.018","article-title":"IL-1 receptor\/Toll-like receptor signaling in infection, inflammation, stress and neurodegeneration couples hyperexcitability and seizures","volume":"25","author":"Vezzani","year":"2011","journal-title":"Brain Behav. Immun."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"93","DOI":"10.1016\/j.tiv.2018.12.001","article-title":"Assessing seizure liability using multi-electrode arrays (MEA)","volume":"55","author":"Fan","year":"2019","journal-title":"Toxicol. In Vitro"},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"497","DOI":"10.1002\/ana.25698","article-title":"Toll-like Receptor 4 Signaling in Neurons Enhances Calcium-Permeable AMPA Receptor Currents and Drives Post-Traumatic Epileptogenesis","volume":"87","author":"Korgaonkar","year":"2020","journal-title":"Ann. Neurol."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"816","DOI":"10.1038\/sj.cdd.4401850","article-title":"TLR signaling","volume":"13","author":"Kawai","year":"2006","journal-title":"Cell Death Differ."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"1259","DOI":"10.4049\/jimmunol.174.3.1259","article-title":"Synthetic TLR agonists reveal functional differences between human TLR7 and TLR8","volume":"174","author":"Gorden","year":"2005","journal-title":"J. Immunol."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"93","DOI":"10.1016\/j.neuroscience.2014.03.039","article-title":"The role of TLR4-mediated PTEN\/PI3K\/AKT\/NF-kappaB signaling pathway in neuroinflammation in hippocampal neurons","volume":"269","author":"Zhao","year":"2014","journal-title":"Neuroscience"},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"1619","DOI":"10.1152\/physrev.00007.2017","article-title":"Hippocampal GABAergic Inhibitory Interneurons","volume":"97","author":"Pelkey","year":"2017","journal-title":"Physiol. Rev."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"8166","DOI":"10.1523\/JNEUROSCI.3456-16.2017","article-title":"Selective Silencing of Hippocampal Parvalbumin Interneurons Induces Development of Recurrent Spontaneous Limbic Seizures in Mice","volume":"37","author":"Drexel","year":"2017","journal-title":"J. Neurosci."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"2987","DOI":"10.1002\/eji.200324238","article-title":"The Toll-like receptor 7 (TLR7)-specific stimulus loxoribine uncovers a strong relationship within the TLR7, 8 and 9 subfamily","volume":"33","author":"Heil","year":"2003","journal-title":"Eur. J. Immunol."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"pe14","DOI":"10.1126\/scisignal.2005407","article-title":"Location is everything: Let-7b microRNA and TLR7 signaling results in a painful TRP","volume":"7","author":"Winkler","year":"2014","journal-title":"Sci. Signal."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"55","DOI":"10.1016\/j.imlet.2017.03.019","article-title":"Activation of cell membrane-localized Toll-like receptor 3 by siRNA","volume":"189","author":"Pirher","year":"2017","journal-title":"Immunol. Lett."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"6119","DOI":"10.1038\/ncomms7119","article-title":"Targeting cell surface TLR7 for therapeutic intervention in autoimmune diseases","volume":"6","author":"Kanno","year":"2015","journal-title":"Nat. Commun."},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"1231","DOI":"10.1189\/jlb.0413206","article-title":"Human TLR8 is activated upon recognition of Borrelia burgdorferi RNA in the phagosome of human monocytes","volume":"94","author":"Cervantes","year":"2013","journal-title":"J. Leukoc. Biol."},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"109","DOI":"10.1016\/j.chom.2012.05.015","article-title":"Neutrophil extracellular traps mediate a host defense response to human immunodeficiency virus-1","volume":"12","author":"Saitoh","year":"2012","journal-title":"Cell Host Microbe"},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"1490","DOI":"10.1038\/nprot.2007.207","article-title":"Isolation and culture of adult neurons and neurospheres","volume":"2","author":"Brewer","year":"2007","journal-title":"Nat. Protoc."},{"key":"ref_36","doi-asserted-by":"crossref","unstructured":"Hinkelmann, L., Brehm, M., Kumbol, V., McGurran, H., Kr\u00fcger, C., Kleinau, G., Scheerer, P., Golenbock, D., Alexopoulou, L., and Gantier, M.P. (2025). Murine Toll-like receptor 8 is a nucleic acid multi-sensor detecting 2\u2032,3\u2032-cyclic monophosphate guanosine as well as combinations of ribo-, deoxy-, cyclic nucleotides, and nucleosides. bioRxiv.","DOI":"10.1101\/2025.10.14.682277"},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"995","DOI":"10.1016\/j.eplepsyres.2014.04.001","article-title":"Physiological bases of the K+ and the glutamate\/GABA hypotheses of epilepsy","volume":"108","author":"DiNuzzo","year":"2014","journal-title":"Epilepsy Res."},{"key":"ref_38","doi-asserted-by":"crossref","unstructured":"Sharif, O., Bolshakov, V.N., Raines, S., Newham, P., and Perkins, N.D. (2007). Transcriptional profiling of the LPS induced NF-kappaB response in macrophages. BMC Immunol., 8.","DOI":"10.1186\/1471-2172-8-1"},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"2018","DOI":"10.1038\/emboj.2009.158","article-title":"Mal connects TLR2 to PI3Kinase activation and phagocyte polarization","volume":"28","author":"Deshmukh","year":"2009","journal-title":"EMBO J."}],"container-title":["International Journal of Molecular Sciences"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1422-0067\/27\/14\/6232\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,7,14]],"date-time":"2026-07-14T02:35:56Z","timestamp":1783996556000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1422-0067\/27\/14\/6232"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,7,13]]},"references-count":39,"journal-issue":{"issue":"14","published-online":{"date-parts":[[2026,7]]}},"alternative-id":["ijms27146232"],"URL":"https:\/\/doi.org\/10.3390\/ijms27146232","relation":{},"ISSN":["1422-0067"],"issn-type":[{"value":"1422-0067","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,7,13]]}}}