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

2020 ◽  
Author(s):  
Hiromi Tamada ◽  
Jerome Blanc ◽  
Natalya Korogod ◽  
Carl CH Petersen ◽  
Graham W Knott
Keyword(s):  
Dendritic Spines ◽  
Electrical Resistance ◽  
Fixation Method ◽  
Chemical Fixation ◽  
Weak Correlation ◽  
Blood Capillaries ◽  
Neck Width ◽  
Spine Head ◽  
Dendritic Spine Morphology ◽  
Brain Ultrastructure

ABSTRACTPreviously we showed that cryo fixation of brain tissue gave a truer representation of brain ultrastructure in comparison with a standard chemical fixation method (Korogod et al 2005). Extracellular space matched physiological measurements, there were larger numbers of docked vesicles and less glial coverage of synapses and blood capillaries. Here, using the same preservation approaches we compared the morphology of dendritic spines. We show that the length of the spine and the volume of its head is unchanged, however, the spine neck width is thinner by more than 30 % after cryo fixation. In addition, the weak correlation between spine neck width and head volume seen after chemical fixation was not present in cryo-fixed spines. Our data suggest that spine neck geometry is independent of the spine head volume, with cryo fixation showing enhanced spine head compartmentalization and a higher predicted electrical resistance between spine head and parent dendrite.

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

eLife ◽  
2020 ◽  
Vol 9 ◽  
Author(s):  
Hiromi Tamada ◽  
Jerome Blanc ◽  
Natalya Korogod ◽  
Carl CH Petersen ◽  
Graham W Knott
Keyword(s):  
Dendritic Spines ◽  
Adult Mouse ◽  
Fixation Method ◽  
Chemical Fixation ◽  
Adult Mouse Brain ◽  
Blood Capillaries ◽  
Neck Width ◽  
Spine Head ◽  
Dendritic Spine Morphology ◽  
Brain Ultrastructure

Previously, we showed that cryo fixation of adult mouse brain tissue gave a truer representation of brain ultrastructure in comparison with a standard chemical fixation method (Korogod et al., 2015). Extracellular space matched physiological measurements, there were larger numbers of docked vesicles and less glial coverage of synapses and blood capillaries. Here, using the same preservation approaches, we compared the morphology of dendritic spines. We show that the length of the spine and the volume of its head is unchanged; however, the spine neck width is thinner by more than 30% after cryo fixation. In addition, the weak correlation between spine neck width and head volume seen after chemical fixation was not present in cryo-fixed spines. Our data suggest that spine neck geometry is independent of the spine head volume, with cryo fixation showing enhanced spine head compartmentalization and a higher predicted electrical resistance between spine head and parent dendrite.

Self-pressurised rapid freezing, a time-efficient and affordable cryo-fixation method for ultrastructural observations on unhatched cyst nematodes

Nematology ◽  
2019 ◽  
Vol 22 (1) ◽  
pp. 103-110
Author(s):  
Myriam Claeys ◽  
Nurul Dwi Handayani ◽  
Vladimir V. Yushin ◽  
Prabowo Lestari ◽  
Antarjo Dikin ◽  
...  
Keyword(s):  
High Pressure ◽  
Fast Rate ◽  
Low Cost ◽  
Heterodera Schachtii ◽  
Fixation Method ◽  
Rapid Freezing ◽  
Chemical Fixation ◽  
High Pressure Freezing ◽  
Cyst Nematodes ◽  
Second Stage

Summary Ultrastructural analysis of the early development of nematodes is hampered by the impermeability of the eggshell to most commonly used fixatives. High-pressure freezing (HPF), a physical cryo-fixation method, facilitates a fast rate of fixation, and by using this method the issue of the uneven delivery of fixative is circumvented. Although HPF results in a superior preservation of the fine structure, the equipment costs impede a wider application of this method. Self-pressurised rapid freezing (SPRF) is an alternative low-cost cryo-fixation method, and its usefulness was evaluated in an ultrastructural study of the eggshell and the cuticle of unhatched second-stage juveniles (J2) of Globodera rostochiensis and Heterodera schachtii. A comparison with conventional (chemical) fixation demonstrates that SPRF fixation results in a remarkably well-preserved ultrastructure of the entire egg including both the eggshell and the cellular details of the unhatched J2. Therefore, SPRF fixation is proposed as an affordable, relatively easy-to-use and time-efficient technique to study the ultrastructure of unhatched J2 and eggs of nematodes.

Dendritic Spine Remodeling After Spinal Cord Injury Alters Neuronal Signal Processing

2009 ◽  
Vol 102 (4) ◽  
pp. 2396-2409 ◽  
Author(s):  
Andrew M. Tan ◽  
Jin-Sung Choi ◽  
Stephen G. Waxman ◽  
Bryan C. Hains
Keyword(s):  
Spinal Cord ◽  
Spinal Cord Injury ◽  
Synaptic Transmission ◽  
Dendritic Spines ◽  
Dendritic Spine ◽  
Nociceptive Neurons ◽  
Spine Shape ◽  
Cord Injury ◽  
Dendritic Spine Morphology ◽  
Neuronal Signal

Central sensitization, a prolonged hyperexcitability of dorsal horn nociceptive neurons, is a major contributor to abnormal pain processing after spinal cord injury (SCI). Dendritic spines are micron-sized dendrite protrusions that can regulate the efficacy of synaptic transmission. Here we used a computational approach to study whether changes in dendritic spine shape, density, and distribution can individually, or in combination, adversely modify the input–output function of a postsynaptic neuron to create a hyperexcitable neuronal state. The results demonstrate that a conversion from thin-shaped to more mature, mushroom-shaped spine structures results in enhanced synaptic transmission and fidelity, improved frequency-following ability, and reduced inhibitory gating effectiveness. Increasing the density and redistributing spines toward the soma results in a greater probability of action potential activation. Our results demonstrate that changes in dendritic spine morphology, documented in previous studies on spinal cord injury, contribute to the generation of pain following SCI.

Neuronal Activity Regulates Diffusion Across the Neck of Dendritic Spines

Science ◽  
2005 ◽  
Vol 310 (5749) ◽  
pp. 866-869 ◽  
Author(s):  
Brenda L. Bloodgood ◽  
Bernardo L. Sabatini
Keyword(s):  
Neuronal Activity ◽  
Dendritic Spines ◽  
Action Potentials ◽  
Synaptic Activation ◽  
Postsynaptic Potentials ◽  
Electrical Isolation ◽  
Spine Head ◽  
Postsynaptic Action ◽  
Excitatory Neurons

In mammalian excitatory neurons, dendritic spines are separated from dendrites by thin necks. Diffusion across the neck limits the chemical and electrical isolation of each spine. We found that spine/dendrite diffusional coupling is heterogeneous and uncovered a class of diffusionally isolated spines. The barrier to diffusion posed by the neck and the number of diffusionally isolated spines is bidirectionally regulated by neuronal activity. Furthermore, coincident synaptic activation and postsynaptic action potentials rapidly restrict diffusion across the neck. The regulation of diffusional coupling provides a possible mechanism for determining the amplitude of postsynaptic potentials and the accumulation of plasticity-inducing molecules within the spine head.

scholarly journals Dendritic spine geometry and spine apparatus organization govern the spatiotemporal dynamics of calcium

2019 ◽  
Vol 151 (8) ◽  
pp. 1017-1034 ◽  
Author(s):  
Miriam Bell ◽  
Tom Bartol ◽  
Terrence Sejnowski ◽  
Padmini Rangamani
Keyword(s):  
Dendritic Spines ◽  
Reaction Diffusion ◽  
Three Dimensions ◽  
Experimental Investigations ◽  
Calcium Dynamics ◽  
Surface Area Ratio ◽  
Spine Head ◽  
Reaction Diffusion Model ◽  
Spine Apparatus ◽  
Spine Function

Dendritic spines are small subcompartments that protrude from the dendrites of neurons and are important for signaling activity and synaptic communication. These subcompartments have been characterized to have different shapes. While it is known that these shapes are associated with spine function, the specific nature of these shape–function relationships is not well understood. In this work, we systematically investigated the relationship between the shape and size of both the spine head and spine apparatus, a specialized endoplasmic reticulum compartment within the spine head, in modulating rapid calcium dynamics using mathematical modeling. We developed a spatial multicompartment reaction–diffusion model of calcium dynamics in three dimensions with various flux sources, including N-methyl-D-aspartate receptors (NMDARs), voltage-sensitive calcium channels (VSCCs), and different ion pumps on the plasma membrane. Using this model, we make several important predictions. First, the volume to surface area ratio of the spine regulates calcium dynamics. Second, membrane fluxes impact calcium dynamics temporally and spatially in a nonlinear fashion. Finally, the spine apparatus can act as a physical buffer for calcium by acting as a sink and rescaling the calcium concentration. These predictions set the stage for future experimental investigations of calcium dynamics in dendritic spines.

scholarly journals Selective activation of BK channels in small-headed dendritic spines suppresses excitatory postsynaptic potentials

2021 ◽  
Author(s):  
Sabrina Tazerart ◽  
Maxime G. Blanchard ◽  
Soledad Miranda-Rottmann ◽  
Diana E. Mitchell ◽  
Bruno Navea Pina ◽  
...  
Keyword(s):  
Dendritic Spines ◽  
Pyramidal Neurons ◽  
Structural Features ◽  
Bk Channels ◽  
Excitatory Postsynaptic Potentials ◽  
Calcium Signals ◽  
Postsynaptic Potentials ◽  
Synaptic Inputs ◽  
Spine Head ◽  
Small Head

AbstractDendritic spines are the main receptacles of excitatory information in the brain. Their particular morphology, with a small head connected to the dendrite by a slender neck, has inspired theoretical and experimental work to understand how these structural features affect the processing, storage and integration of synaptic inputs in pyramidal neurons (PNs).The activation of glutamate receptors in spines triggers a large voltage change as well as calcium signals at the spine head. Thus, voltage-gated and calcium-activated potassium channels located in the spine head likely play a key role in synaptic transmission. Here we study the presence and function of large conductance calcium-activated potassium (BK) channels in spines from layer 5 PNs. We find that BK channels are localized to dendrites and spines regardless of their size, but their activity can only be detected in spines with small head volumes (≤ 0.09 µm3), which reduces the amplitude of two-photon (2P) uncaging (u) excitatory postsynaptic potentials (EPSPs) recorded at the soma. In addition, we find that calcium signals in spines with small head volumes are significantly larger than those observed in spines with larger head volumes. In accordance with our experimental data, numerical simulations predict that synaptic inputs impinging onto spines with small head volumes generate voltage responses and calcium signals within the spine head itself that are significantly larger than those observed in spines with bigger head volumes, which are sufficient to activate spine BK channels. These results show that BK channels are selectively activated in small-headed spines, suggesting a new level of dendritic spine-mediated regulation of synaptic processing, integration, and plasticity in cortical PNs.

scholarly journals Overexpression of Tropomyosin Isoform Tpm3.1 Does Not Alter Synaptic Function in Hippocampal Neurons

2021 ◽  
Vol 22 (17) ◽  
pp. 9303
Author(s):  
Chanchanok Chaichim ◽  
Tamara Tomanic ◽  
Holly Stefen ◽  
Esmeralda Paric ◽  
Lucy Gamaroff ◽  
...  
Keyword(s):  
Dendritic Spines ◽  
Hippocampal Neurons ◽  
Brain Slices ◽  
Structure And Function ◽  
Spine Morphology ◽  
Dendritic Spine Morphology ◽  
And Function ◽  
Cultured Hippocampal Neurons

Tropomyosin (Tpm) has been regarded as the master regulator of actin dynamics. Tpms regulate the binding of the various proteins involved in restructuring actin. The actin cytoskeleton is the predominant cytoskeletal structure in dendritic spines. Its regulation is critical for spine formation and long-term activity-dependent changes in synaptic strength. The Tpm isoform Tpm3.1 is enriched in dendritic spines, but its role in regulating the synapse structure and function is not known. To determine the role of Tpm3.1, we studied the synapse structure and function of cultured hippocampal neurons from transgenic mice overexpressing Tpm3.1. We recorded hippocampal field excitatory postsynaptic potentials (fEPSPs) from brain slices to examine if Tpm3.1 overexpression alters long-term synaptic plasticity. Tpm3.1-overexpressing cultured neurons did not show a significantly altered dendritic spine morphology or synaptic activity. Similarly, we did not observe altered synaptic transmission or plasticity in brain slices. Furthermore, expression of Tpm3.1 at the postsynaptic compartment does not increase the local F-actin levels. The results suggest that although Tpm3.1 localises to dendritic spines in cultured hippocampal neurons, it does not have any apparent impact on dendritic spine morphology or function. This is contrary to the functional role of Tpm3.1 previously observed at the tip of growing neurites, where it increases the F-actin levels and impacts growth cone dynamics.

scholarly journals Cadherin activity is required for activity-induced spine remodeling

2004 ◽  
Vol 167 (5) ◽  
pp. 961-972 ◽  
Author(s):  
Ko Okamura ◽  
Hidekazu Tanaka ◽  
Yoshiki Yagita ◽  
Yoshinaga Saeki ◽  
Akihiko Taguchi ◽  
...  
Keyword(s):  
Conformational Changes ◽  
Dendritic Spines ◽  
Hippocampal Neurons ◽  
Actin Polymerization ◽  
Fluorescent Protein ◽  
Cytochalasin D ◽  
Dominant Negative ◽  
Spine Head ◽  
Green Fluorescent ◽  
Activity Dependent

Neural activity induces the remodeling of pre- and postsynaptic membranes, which maintain their apposition through cell adhesion molecules. Among them, N-cadherin is redistributed, undergoes activity-dependent conformational changes, and is required for synaptic plasticity. Here, we show that depolarization induces the enlargement of the width of spine head, and that cadherin activity is essential for this synaptic rearrangement. Dendritic spines visualized with green fluorescent protein in hippocampal neurons showed an expansion by the activation of AMPA receptor, so that the synaptic apposition zone may be expanded. N-cadherin-venus fusion protein laterally dispersed along the expanding spine head. Overexpression of dominant-negative forms of N-cadherin resulted in the abrogation of the spine expansion. Inhibition of actin polymerization with cytochalasin D abolished the spine expansion. Together, our data suggest that cadherin-based adhesion machinery coupled with the actin-cytoskeleton is critical for the remodeling of synaptic apposition zone.

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