article published yes Peter Koppensteiner author 3B8B25A8-F248-11E8-B48F-1D18A9856A870000-0002-3509-1948 Pradeep Bhandari author 45EDD1BC-F248-11E8-B48F-1D18A9856A870000-0003-0863-4481 Hüseyin C Önal author 4659D740-F248-11E8-B48F-1D18A9856A870000-0002-2771-2011 Carolina Borges Merjane author 4305C450-F248-11E8-B48F-1D18A9856A870000-0003-0005-401X Elodie Le Monnier author 3B59276A-F248-11E8-B48F-1D18A9856A87 Utsa Roy author 4d26cf11-5355-11ee-ae5a-eb05e255b9b2 Yukihiro Nakamura author Tetsushi Sadakata author Makoto Sanbo author Masumi Hirabayashi author JeongSeop Rhee author Nils Brose author Peter M Jonas author 353C1B58-F248-11E8-B48F-1D18A9856A870000-0001-5001-4804 Ryuichi Shigemoto author 499F3ABC-F248-11E8-B48F-1D18A9856A870000-0001-8761-9444 RySh department PeJo department In situ analysis of single channel subunit composition in neurons: physiological implication in synaptic plasticity and behaviour project International IST Doctoral Program project GABAB receptor (GBR) activation inhibits neurotransmitter release in axon terminals in the brain, except in medial habenula (MHb) terminals, which show robust potentiation. However, mechanisms underlying this enigmatic potentiation remain elusive. Here, we report that GBR activation on MHb terminals induces an activity-dependent transition from a facilitating, tonic to a depressing, phasic neurotransmitter release mode. This transition is accompanied by a 4.1-fold increase in readily releasable vesicle pool (RRP) size and a 3.5-fold increase of docked synaptic vesicles (SVs) at the presynaptic active zone (AZ). Strikingly, the depressing phasic release exhibits looser coupling distance than the tonic release. Furthermore, the tonic and phasic release are selectively affected by deletion of synaptoporin (SPO) and Ca <jats:sup>2+</jats:sup> -dependent activator protein for secretion 2 (CAPS2), respectively. SPO modulates augmentation, the short-term plasticity associated with tonic release, and CAPS2 retains the increased RRP for initial responses in phasic response trains. The cytosolic protein CAPS2 showed a SV-associated distribution similar to the vesicular transmembrane protein SPO, and they were colocalized in the same terminals. We developed the “Flash and Freeze-fracture” method, and revealed the release of SPO-associated vesicles in both tonic and phasic modes and activity-dependent recruitment of CAPS2 to the AZ during phasic release, which lasted several minutes. Overall, these results indicate that GBR activation translocates CAPS2 to the AZ along with the fusion of CAPS2-associated SVs, contributing to persistency of the RRP increase. Thus, we identified structural and molecular mechanisms underlying tonic and phasic neurotransmitter release and their transition by GBR activation in MHb terminals. https://research-explorer.ista.ac.at/download/15084/15110/2024_PNAS_Koppensteiner.pdf application/pdfno https://creativecommons.org/licenses/by-nc-nd/4.0/ National Academy of Sciences2024 eng 0027-8424 1091-6490 38346189 00120856730000610.1073/pnas.2301449121 1218 https://research-explorer.ista.ac.at/record/13173 https://research-explorer.ista.ac.at/record/19271 https://ista.ac.at/en/news/neuronal-insights-flash-and-freeze-fracture/ P. Koppensteiner, P. Bhandari, C. Önal, C. Borges Merjane, E. Le Monnier, U. Roy, Y. Nakamura, T. Sadakata, M. Sanbo, M. Hirabayashi, J. Rhee, N. Brose, P.M. Jonas, R. Shigemoto, Proceedings of the National Academy of Sciences of the United States of America 121 (2024). P. Koppensteiner <i>et al.</i>, “GABAB receptors induce phasic release from medial habenula terminals through activity-dependent recruitment of release-ready vesicles,” <i>Proceedings of the National Academy of Sciences of the United States of America</i>, vol. 121, no. 8. National Academy of Sciences, 2024. Koppensteiner, P., Bhandari, P., Önal, C., Borges Merjane, C., Le Monnier, E., Roy, U., … Shigemoto, R. (2024). GABAB receptors induce phasic release from medial habenula terminals through activity-dependent recruitment of release-ready vesicles. <i>Proceedings of the National Academy of Sciences of the United States of America</i>. National Academy of Sciences. <a href="https://doi.org/10.1073/pnas.2301449121">https://doi.org/10.1073/pnas.2301449121</a> Koppensteiner P, Bhandari P, Önal C, et al. GABAB receptors induce phasic release from medial habenula terminals through activity-dependent recruitment of release-ready vesicles. <i>Proceedings of the National Academy of Sciences of the United States of America</i>. 2024;121(8). doi:<a href="https://doi.org/10.1073/pnas.2301449121">10.1073/pnas.2301449121</a> Koppensteiner, Peter, Pradeep Bhandari, Cihan Önal, Carolina Borges Merjane, Elodie Le Monnier, Utsa Roy, Yukihiro Nakamura, et al. “GABAB Receptors Induce Phasic Release from Medial Habenula Terminals through Activity-Dependent Recruitment of Release-Ready Vesicles.” <i>Proceedings of the National Academy of Sciences of the United States of America</i>. National Academy of Sciences, 2024. <a href="https://doi.org/10.1073/pnas.2301449121">https://doi.org/10.1073/pnas.2301449121</a>. Koppensteiner, Peter, et al. “GABAB Receptors Induce Phasic Release from Medial Habenula Terminals through Activity-Dependent Recruitment of Release-Ready Vesicles.” <i>Proceedings of the National Academy of Sciences of the United States of America</i>, vol. 121, no. 8, e2301449121, National Academy of Sciences, 2024, doi:<a href="https://doi.org/10.1073/pnas.2301449121">10.1073/pnas.2301449121</a>. Koppensteiner P, Bhandari P, Önal C, Borges Merjane C, Le Monnier E, Roy U, Nakamura Y, Sadakata T, Sanbo M, Hirabayashi M, Rhee J, Brose N, Jonas PM, Shigemoto R. 2024. GABAB receptors induce phasic release from medial habenula terminals through activity-dependent recruitment of release-ready vesicles. Proceedings of the National Academy of Sciences of the United States of America. 121(8), e2301449121. 150842024-03-05T09:23:55Z2026-05-16T22:30:29Z