Quantitative 3D Ultrastructure of Thalamocortical Synapses from the “Lemniscal” Ventral Posteromedial Nucleus in Mouse Barrel Cortex

Moreno, Javier Rodríguez; Rollenhagen, Astrid; Arlandis, Jaime; Santuy, Andrea; Merchán-Pérez, Ángel; DeFelipe, Javier; Lübke, Joachim H. R.; Clascá, Francisco

doi:10.1093/cercor/bhx187

Cited by 64 publications

(74 citation statements)

References 89 publications

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“…Spine head volume in cryo-fixed tissue was 0.069 μ m 3 , which was not different to the spine volume in chemically-fixed tissue of 0.081 μ m 3 (Figure 2). Our spine volume measurements are similar to other studies in the same region of the mouse brain (0.06 ± 0.04 μ m 3 , layer 4 (Rodriguez-Moreno et al, 2017); 0.075 ± 0.005 μ m 3 - 0.079 ± 0.006 μ m 3 , layer 1, adult and aged mice, layer 1(Calì et al, 2018). Similarly, our measurement of mean spine length after cryo-fixation of 0.77 ± 0.55 μ m was not different from the length of 0.84 ± 0.57 μ m in chemically-fixed tissue (Figure 2), and is similar to other studies, for example rat CA1 hippocampus, 0.45 ± 0.29 μ m (Harris and Stevens, 1989); rat cerebellum, 0.66 ± 0.32 μ m (Harris and Stevens, 1988); and mouse layer 2/3 pyramidal cells, 0.66 ± 0.37 μ m (Arellano et al, 2007).…”

Section: Discussionsupporting

confidence: 90%

Ultrastructural comparison of dendritic spine morphology preserved with cryo and chemical fixation

Petersen

Knott

Tamada

et al. 2020

Preprint

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23Previously we showed that cryo fixation of brain tissue gave a truer 24 representation of brain ultrastructure in comparison with a standard 25 chemical fixation method (Korogod et al 2005). Extracellular space 26 matched physiological measurements, there were larger numbers of 27 docked vesicles and less glial coverage of synapses and blood 28 capillaries. Here, using the same preservation approaches we compared 29 the morphology of dendritic spines. We show that the length of the spine 30 and the volume of its head is unchanged, however, the spine neck width 31 is thinner by more than 30 % after cryo fixation. In addition, the weak 32 correlation between spine neck width and head volume seen after 33 chemical fixation was not present in cryo-fixed spines. Our data suggest 34 that spine neck geometry is independent of the spine head volume, with 35 cryo fixation showing enhanced spine head compartmentalization and a 36 higher predicted electrical resistance between spine head and parent 37 dendrite. 38 39 40 41 42 43 44 45 46 3 INTRODUCTION 47In our previous, parent paper (Korogod et al., 2015), we used a cryo fixation 48 method to study the neuropil of the adult mouse cerebral cortex, comparing it with 49 a standard chemical fixation approach that has been used for many years to 50 preserve the brain for analysis with electron microscopy (eg. Spacek and Harris, 51 1997; Knott et al., 2002). Korogod et al. (2015) found that cryo fixation appeared 52 to be able to preserve an extracellular space matching various previous in vivo 53 measurements, not found in chemically-fixed tissue. Furthermore, synapse 54 density and vesicle docking, as well as astrocytic processes close to synapses 55 and around blood capillaries, appeared to be significantly different between the 56 two fixation methods. This led us in this study to investigate the extent to which 57 dendritic spines might be affected by chemical fixation. 58The dendritic spine is a small dendritic protrusion that carries the majority 59 of the excitatory synaptic connections in the adult brain (Colonnier, 1968) with a 60 size and shape that is closely linked with its function (reviewed by: Holtmaat and 61 Svoboda, 2009; Harris and Kater, 1994). The larger the spine head, the larger its 62 synapse (Harris and Stevens, 1988, Arellano et al., 2007; Knott et al., 2006), the 63 number of its receptors (Kharazia et al., 1999; Nogochi et al., 2005; Nusser et al., 64 1998), and its synaptic strength (Matzusaki et al., 2001). However, the synapse 65 on the spine head is separated from the parent dendrite by the spine neck. This 66 is often thin, compartmentalizing biochemical signals and creating a potentially 67 significant electrical resistance between synapse and dendrite. Changes in the 68 morphology of spine head and neck have been seen after different forms of 69 activity including LTP induction and tetanic stimulation (Lang et al., 2004; 70 4 Matzusaki et al., 2004, Harvey and Svoboda, 2007; Tønnesen et al., 2014; 71 Fifkova and Anderson, 1981). The under...

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Section: Discussionsupporting

confidence: 90%

Ultrastructural comparison of dendritic spine morphology preserved with cryo and chemical fixation

Petersen

Knott

Tamada

et al. 2020

Preprint

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“…Remarkably, in both S1-L1 and S1-L5a, a significant number (7%) of the Po axonal varicosities that contained a mitochondrion and synaptic vesicles, lacked any evident synaptic contact. Such “non-synaptic boutons” were also observed in MC-L4/3 Po axons but less frequent (2%), but never in the VPM S1-L4 axons (Table 1; see also 27 ).…”

Section: Resultsmentioning

confidence: 84%

“…Virtually all (95%) VPM synaptic boutons were large, containing one or several mitochondria, large vesicle pools, and most of them (53%) contained more than one (up to four) active zones. Only 5% of the VPM synapses lacked a mitochondrion (interbouton synapses), and no VPM axonal segment containing a mitochondrion inside lacked an active zone 25, 27 (Table 1; Fig. 7).…”

Section: Discussionmentioning

confidence: 99%

Area-specific synapse structure in branched axons reveals a subcellular level of complexity in thalamocortical networks

Moreno

Porrero

Rollenhagen

et al. 2019

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37Thalamocortical Posterior nucleus (Po) axons innervating the somatosensory (S1) and 38 motor (MC) vibrissal cortices are key links in the brain neuronal network that allows 39 rodents to explore the environment whisking with their motile vibrissae. Here, using 40 high-end 3D electron microscopy, we demonstrate massive differences between MC vs. 41 S1 Po synapses in a) bouton and active zone size; b) neurotransmitter vesicle pool size; 42 c) mitochondria distribution near synapses; and d) proportion of non-spinous dendrite 43contacts. These differences are as large, or bigger, than those between Po and 44 ventroposterior thalamic nucleus synapses in S1. Moreover, using single-axon 45 transfection labeling, we show that the structure of boutons in the MC vs. S1 branches 46 of individual Po axons is different. These structural differences parallel striking, 47recently-discovered divergences in functional efficacy and plasticity between S1 and 48 MC Po synapses, and overall reveal a new, subcellular level of thalamocortical circuit 49 complexity, unaccounted for in current models. 50 51 Introduction 52 53 Rodents explore their environment by rhythmically "whisking" with their motile facial 54 vibrissae. Time-dependent correlations between motor commands and vibrissal follicle 55 mechanoreceptor signals are used for inferring object position and texture. Such 56 computations are carried out in multilevel, closed-loop neuronal networks 57 encompassing the brainstem, thalamus and neocortex (reviewed in 1 ). 58Two thalamocortical pathways lay at the core of these loops: Ventral Posteromedial 59 thalamic nucleus (VPM) axons arborizing focally on L4 in the vibrissal "barrel" domain 60 of the primary somatosensory cortex (S1); and Posterior thalamic nucleus (Po) axons 61 arborizing mainly in L5a but also L1 of S1 2; 3 . Importantly, Po axons may target, in 62 addition, the motor cortex (MC) middle layers 3, 4, 5 (L5-L3). The VPM axons relay 63 time-locked mechanoreceptive single-whisker trigeminal signals, crucial for computing 64 object location. In turn, Po axons convey information mainly about timing/amplitude 65 differences between ongoing cortical outputs and multi-whisker sensory signals, which 66 may be important for computing whisker position 1, 6, 7 . Po cells are primarily driven by 67 heavy and highly effective L5 cortico-thalamic inputs, while ascending trigeminal 68 inputs to Po are sparser and largely modulatory in character 7, 8 . 69Activation of S1-L4 VPM synapses elicits large currents in cortical neurons 9; 10 and 70 drives their firing with low failure rates 11, 12 . VPM synapses are driven only by 71 ionotropic receptors, depress rapidly upon repetitive stimulation 9 and, after an early 72 postnatal period, show considerable resistance to sensory experience-dependent changes 73 13 . In contrast, synaptic potentials evoked in S1 by Po axons show slower rise and decay 74 times, and elicit smaller currents 10, 14 . The Po S1 synapses involve both ionotropic and 75 metabotropic glutamate conductances, sho...

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“…Most strikingly, synaptic boutons beside layer and area-specific differences (see also Rollenhagen 2015Bopp et al 2017;Hsu et al 2017), differ substantially not only in their shape and size, but even more importantly in the number, size and shape of active zones and in the organization and size of the three pools of synaptic vesicles summarized in Table 1. Interestingly, some structural parameters such as bouton size, pre-and postsynaptic density surface area, content of mitochondria, and synaptic vesicles pools are in some cortical synapses well correlated but in others, no or only a weak correlation between several structural subelements are found (Rollenhagen 2015Dufour et al 2016;Hsu et al 2017;Bopp et al 2017;Rodriguez-Moreno et al 2018). The most striking difference at cortical synaptic boutons is the total pool, and the three functionally defined pools of synaptic vesicles, namely the RRP, the RP and resting pools.…”

Section: Synaptic Boutons In the Neocortex Of Rodents And Non-human Pmentioning

confidence: 99%

“…In contrast, only a few coherent and quantitative structural studies exist for synaptic boutons in the rodent neocortex (Rollenhagen et al 2015(Rollenhagen et al , 2018Dufour et al 2016;Bopp et al 2017;Hsu et al 2017;Rodriguez-Moreno et al 2018) and non-human primate neocortex Martin 2006, 2009;Freese and Amaral 2006;Hsu et al 2017). These studies have demonstrated, for example, layer, region and gender specific differences in the density of synaptic boutons (Alonso-Nanclares et al 2008).…”

Section: Synaptic Boutons In the Neocortex Of Rodents And Non-human Pmentioning

confidence: 99%

Synapses: Multitasking Global Players in the Brain

Lübke¹,

Rollenhagen²

2019

Neuroforum

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AbstractSynapses are key elements in the communication between neurons in any given network of the normal adult, developmental and pathologically altered brain. Synapses are composed of nearly the same structural subelements: a presynaptic terminal containing mitochondria with an ultrastructurally visible density at the pre- and postsynaptic apposition zone. The presynaptic density is composed of a cocktail of various synaptic proteins involved in the binding, priming and docking of synaptic vesicles inducing synaptic transmission. Individual presynaptic terminals (synaptic boutons) contain a couple of hundred up to thousands of synaptic vesicles. The pre- and postsynaptic densities are separated by a synaptic cleft. The postsynaptic density, also containing various synaptic proteins and more importantly various neurotransmitter receptors and their subunits specifically composed and arranged at individual synaptic complexes, reside at the target structures of the presynaptic boutons that could be somata, dendrites, spines or initial segments of axons.Beside the importance of the network in which synapses are integrated, their individual structural composition critically determines the dynamic properties within a given connection or the computations of the entire network, in particular, the number, size and shape of the active zone, the structural equivalent to a functional neurotransmitter release site, together with the size and organization of the three functionally defined pools of synaptic vesicles, namely the readily releasable, the recycling and the resting pool, are important structural subelements governing the ‘behavior’ of synaptic complexes within a given network such as the cortical column.In the late last century, neuroscientists started to generate quantitative 3D-models of synaptic boutons and their target structures that is one possible way to correlate structure with function, thus allowing reliable predictions about their function. The re-introduction of electron microscopy (EM) as an important tool achieved by modern high-end, high-resolution transmission-EM, focused ion beam scanning-EM, CRYO-EM and EM-tomography have enormously improved our knowledge about the synaptic organization of the brain not only in various animal species, but also allowed new insights in the ‘microcosms’ of the human brain in health and disease.

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Quantitative 3D Ultrastructure of Thalamocortical Synapses from the “Lemniscal” Ventral Posteromedial Nucleus in Mouse Barrel Cortex

Cited by 64 publications

References 89 publications

Ultrastructural comparison of dendritic spine morphology preserved with cryo and chemical fixation

Ultrastructural comparison of dendritic spine morphology preserved with cryo and chemical fixation

Area-specific synapse structure in branched axons reveals a subcellular level of complexity in thalamocortical networks

Synapses: Multitasking Global Players in the Brain

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