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. 2022 Aug 11;14:968404. doi: 10.3389/fnsyn.2022.968404

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Copyright © 2022 Gore, Yurina, Yukevich-Mussomeli and Nahmani.

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

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Spinule-bearing presynaptic boutons (SBBs) are larger and stronger than presynaptic boutons without spinules (non-SBBs). (A) Successive FIB-SEM images showing a spinule from an adjacent presynaptic bouton (AdjAx; green) with a spinule projecting into and enveloped by an SBB (purple). (B) 3D reconstruction of the same SBB (purple) and AdjAx spinule (green) as shown in panel (A), displaying an annulus-shaped perforated PSD (red) and a CT spinule (pink) from a postsynaptic spine (not shown). (C) Field of 19 3D reconstructed SBBs (purple) in their approximate neuropil locations within the FIB-SEM image stack; some non-SBBs have been rotated to display their PSDs (red) and spinule invagination sites (green). (D) Successive FIB-SEM images showing a presynaptic non-SBB (light blue) with a synapse (dark PSD above bouton) onto a postsynaptic spine. Note that this postsynaptic spine is enveloped by an inhibitory presynaptic bouton (top of right FIB-SEM image) and has a long no-CT spinule into this inhibitory bouton (see yellow spinule in Figure 1G₅). (E) 3D reconstruction of the same non-SBB (light blue) and PSD (red) as shown in panel (D). (F) Field of 20 non-SBBs (light blue) in their approximate neuropil locations within the FIB-SEM image stack; some SBBs have been rotated to display their PSDs (red). (G) Same 3D reconstructions of SBB and non-SBB shown in panels (B,E), shown side by side for comparison. (H) Box plots showing the presynaptic bouton volume for SBBs and non-SBBs (n = 87 and 51, respectively). For all boxplots, center lines show medians, box limits indicate the 25th and 75th percentiles, whiskers extend to the 5th and 95th percentiles, width of boxes is proportional to the square root of the sample size, and raw data points are plotted as filled circles. (I) Zoomed-in view of the 3D reconstructions in panel (G) showing PSDs from an SBB (left) and a non-SBB (right). (J) Boxplots of PSD surface area for SBBs and non-SBBs (n = 107 and 52, respectively). (K) 3D reconstructions of SBBs with no-CT (above, light blue) and CT (below, pink) spinules, displaying their PSDs (red). (L) Boxplots of PSD surface area for SBBs with only no-CT spinules and SBBs with only CT spinules. (M) 3D reconstructions of representative PSDs from SBBs containing AdjAx (green), adjacent spine (AdjS, yellow), and postsynaptic spine (PSs, magenta) spinules. (N) Boxplots of PSD surface area for SBBs containing spinules from AdjAx, AdjS, and PSs origins. Scale bars (A,D) 0.5 μm; All scale cubes = 0.5 μm per side.