Refine
Has Fulltext
- yes (77)
Is part of the Bibliography
- yes (77) (remove)
Year of publication
Document Type
- Journal article (77) (remove)
Language
- English (77)
Keywords
- Neurobiologie (38)
- Medizin (10)
- active zone (4)
- Hypothalamus (3)
- Prostaglandine (3)
- TRH (3)
- blood pressure (3)
- closed head injury (3)
- traumatic brain injury (3)
- Durchblutung (2)
Institute
- Neurochirurgische Klinik und Poliklinik (73)
- Physiologisches Institut (9)
- Neurologische Klinik und Poliklinik (7)
- Klinik und Poliklinik für Unfall-, Hand-, Plastische und Wiederherstellungschirurgie (Chirurgische Klinik II) (4)
- Center for Computational and Theoretical Biology (3)
- Theodor-Boveri-Institut für Biowissenschaften (3)
- Institut für Medizinische Strahlenkunde und Zellforschung (2)
- Kinderklinik und Poliklinik (2)
- Rudolf-Virchow-Zentrum (2)
- Deutsches Zentrum für Herzinsuffizienz (DZHI) (1)
Traumatic brain injury (TBI) is the leading cause of death and disability in polytrauma and is often accompanied by concomitant injuries. We conducted a retrospective matched-pair analysis of data from a 10-year period from the multicenter database TraumaRegister DGU\(^®\) to analyze the impact of a concomitant femoral fracture on the outcome of TBI patients. A total of 4508 patients with moderate to critical TBI were included and matched by severity of TBI, American Society of Anesthesiologists (ASA) risk classification, initial Glasgow Coma Scale (GCS), age, and sex. Patients who suffered combined TBI and femoral fracture showed increased mortality and worse outcome at the time of discharge, a higher chance of multi-organ failure, and a rate of neurosurgical intervention. Especially those with moderate TBI showed enhanced in-hospital mortality when presenting with a concomitant femoral fracture (p = 0.037). The choice of fracture treatment (damage control orthopedics vs. early total care) did not impact mortality. In summary, patients with combined TBI and femoral fracture have higher mortality, more in-hospital complications, an increased need for neurosurgical intervention, and inferior outcome compared to patients with TBI solely. More investigations are needed to decipher the pathophysiological consequences of a long-bone fracture on the outcome after TBI.
Single-molecule localization microscopy (SMLM) greatly advances structural studies of diverse biological tissues. For example, presynaptic active zone (AZ) nanotopology is resolved in increasing detail. Immunofluorescence imaging of AZ proteins usually relies on epitope preservation using aldehyde-based immunocompetent fixation. Cryofixation techniques, such as high-pressure freezing (HPF) and freeze substitution (FS), are widely used for ultrastructural studies of presynaptic architecture in electron microscopy (EM). HPF/FS demonstrated nearer-to-native preservation of AZ ultrastructure, e.g., by facilitating single filamentous structures. Here, we present a protocol combining the advantages of HPF/FS and direct stochastic optical reconstruction microscopy (dSTORM) to quantify nanotopology of the AZ scaffold protein Bruchpilot (Brp) at neuromuscular junctions (NMJs) of Drosophila melanogaster. Using this standardized model, we tested for preservation of Brp clusters in different FS protocols compared to classical aldehyde fixation. In HPF/FS samples, presynaptic boutons were structurally well preserved with ~22% smaller Brp clusters that allowed quantification of subcluster topology. In summary, we established a standardized near-to-native preparation and immunohistochemistry protocol for SMLM analyses of AZ protein clusters in a defined model synapse. Our protocol could be adapted to study protein arrangements at single-molecule resolution in other intact tissue preparations.
Based on recent findings that show that depletion of factor XII (FXII) leads to better posttraumatic neurological recovery, we studied the effect of FXII-deficiency on post-traumatic cognitive and behavioral outcomes in female and male mice. In agreement with our previous findings, neurological deficits on day 7 after weight-drop traumatic brain injury (TBI) were significantly reduced in FXII\(^{−/−}\) mice compared to wild type (WT) mice. Also, glycoprotein Ib (GPIb)-positive platelet aggregates were more frequent in brain microvasculature of WT than FXII\(^{−/−}\) mice 3 months after TBI. Six weeks after TBI, memory for novel object was significantly reduced in both female and male WT but not in FXII\(^{−/−}\) mice compared to sham-operated mice. In the setting of automated home-cage monitoring of socially housed mice in IntelliCages, female WT mice but not FXII\(^{−/−}\) mice showed decreased exploration and reacted negatively to reward extinction one month after TBI. Since neuroendocrine stress after TBI might contribute to trauma-induced cognitive dysfunction and negative emotional contrast reactions, we measured peripheral corticosterone levels and the ration of heart, lung, and spleen weight to bodyweight. Three months after TBI, plasma corticosterone levels were significantly suppressed in both female and male WT but not in FXII\(^{−/−}\) mice, while the relative heart weight increased in males but not in females of both phenotypes when compared to sham-operated mice. Our results indicate that FXII deficiency is associated with efficient post-traumatic behavioral and neuroendocrine recovery.
Ultrastructural analysis of wild-type and RIM1α knockout active zones in a large cortical synapse
(2022)
Rab3A-interacting molecule (RIM) is crucial for fast Ca\(^{2+}\)-triggered synaptic vesicle (SV) release in presynaptic active zones (AZs). We investigated hippocampal giant mossy fiber bouton (MFB) AZ architecture in 3D using electron tomography of rapid cryo-immobilized acute brain slices in RIM1α\(^{−/−}\) and wild-type mice. In RIM1α\(^{−/−}\), AZs are larger with increased synaptic cleft widths and a 3-fold reduced number of tightly docked SVs (0–2 nm). The distance of tightly docked SVs to the AZ center is increased from 110 to 195 nm, and the width of their electron-dense material between outer SV membrane and AZ membrane is reduced. Furthermore, the SV pool in RIM1α\(^{−/−}\) is more heterogeneous. Thus, RIM1α, besides its role in tight SV docking, is crucial for synaptic architecture and vesicle pool organization in MFBs.
Neurotransmitter release is stabilized by homeostatic plasticity. Presynaptic homeostatic potentiation (PHP) operates on timescales ranging from minute- to life-long adaptations and likely involves reorganization of presynaptic active zones (AZs). At Drosophila melanogaster neuromuscular junctions, earlier work ascribed AZ enlargement by incorporating more Bruchpilot (Brp) scaffold protein a role in PHP. We use localization microscopy (direct stochastic optical reconstruction microscopy [dSTORM]) and hierarchical density-based spatial clustering of applications with noise (HDBSCAN) to study AZ plasticity during PHP at the synaptic mesoscale. We find compaction of individual AZs in acute philanthotoxin-induced and chronic genetically induced PHP but unchanged copy numbers of AZ proteins. Compaction even occurs at the level of Brp subclusters, which move toward AZ centers, and in Rab3 interacting molecule (RIM)-binding protein (RBP) subclusters. Furthermore, correlative confocal and dSTORM imaging reveals how AZ compaction in PHP translates into apparent increases in AZ area and Brp protein content, as implied earlier.
Medulloblastoma is the most common high-grade brain tumor in childhood. Medulloblastomas with c-myc amplification, classified as group 3, are the most aggressive among the four disease subtypes resulting in a 5-year overall survival of just above 50%. Despite current intensive therapy regimens, patients suffering from group 3 medulloblastoma urgently require new therapeutic options. Using a recently established c-myc amplified human medulloblastoma cell line, we performed an in-vitro-drug screen with single and combinatorial drugs that are either already clinically approved or agents in the advanced stage of clinical development. Candidate drugs were identified in vitro and then evaluated in vivo. Tumor growth was closely monitored by BLI. Vessel development was assessed by 3D light-sheet-fluorescence-microscopy. We identified the combination of gemcitabine and axitinib to be highly cytotoxic, requiring only low picomolar concentrations when used in combination. In the orthotopic model, gemcitabine and axitinib showed efficacy in terms of tumor control and survival. In both models, gemcitabine and axitinib were better tolerated than the standard regimen comprising of cisplatin and etoposide phosphate. 3D light-sheet-fluorescence-microscopy of intact tumors revealed thinning and rarefication of tumor vessels, providing one explanation for reduced tumor growth. Thus, the combination of the two drugs gemcitabine and axitinib has favorable effects on preventing tumor progression in an orthotopic group 3 medulloblastoma xenograft model while exhibiting a favorable toxicity profile. The combination merits further exploration as a new approach to treat high-risk group 3 medulloblastoma.
Aneurysmal subarachnoid hemorrhage (aSAH) remains a disease with high mortality and morbidity. Since treating vasospasm has not inevitably led to an improvement in outcome, the actual emphasis is on finding neuroprotective therapies in the early phase following aSAH to prevent secondary brain injury in the later phase of disease. Within the early phase, neuroinflammation, thromboinflammation, disturbances in brain metabolism and early neuroprotective therapies directed against delayed cerebral ischemia (DCI) came into focus. Herein, the role of neuroinflammation, thromboinflammation and metabolism in aSAH is depicted. Potential neuroprotective strategies regarding neuroinflammation target microglia activation, metalloproteases, autophagy and the pathway via Toll-like receptor 4 (TLR4), high mobility group box 1 (HMGB1), NF-κB and finally the release of cytokines like TNFα or IL-1. Following the link to thromboinflammation, potential neuroprotective therapies try to target microthrombus formation, platelets and platelet receptors as well as clot clearance and immune cell infiltration. Potential neuroprotective strategies regarding metabolism try to re-balance the mismatch of energy need and supply following aSAH, for example, in restoring fuel to the TCA cycle or bypassing distinct energy pathways. Overall, this review addresses current neuroprotective strategies in aSAH, hopefully leading to future translational therapy options to prevent secondary brain injury.
Revealing the molecular organization of anatomically precisely defined brain regions is necessary for refined understanding of synaptic plasticity. Although three-dimensional (3D) single-molecule localization microscopy can provide the required resolution, imaging more than a few micrometers deep into tissue remains challenging. To quantify presynaptic active zones (AZ) of entire, large, conditional detonator hippocampal mossy fiber (MF) boutons with diameters as large as 10 mu m, we developed a method for targeted volumetric direct stochastic optical reconstruction microscopy (dSTORM). An optimized protocol for fast repeated axial scanning and efficient sequential labeling of the AZ scaffold Bassoon and membrane bound GFP with Alexa Fluor 647 enabled 3D-dSTORM imaging of 25 mu m thick mouse brain sections and assignment of AZs to specific neuronal substructures. Quantitative data analysis revealed large differences in Bassoon cluster size and density for distinct hippocampal regions with largest clusters in MF boutons. Pauli et al. develop targeted volumetric dSTORM in order to image large hippocampal mossy fiber boutons (MFBs) in brain slices. They can identify synaptic targets of individual MFBs and measured size and density of Bassoon clusters within individual untruncated MFBs at nanoscopic resolution.
Objective:
Traumatic brain injury is a major global public health problem for which specific therapeutic interventions are lacking. There is, therefore, a pressing need to identify innovative pathomechanism-based effective therapies for this condition. Thrombus formation in the cerebral microcirculation has been proposed to contribute to secondary brain damage by causing pericontusional ischemia, but previous studies have failed to harness this finding for therapeutic use. The aim of this study was to obtain preclinical evidence supporting the hypothesis that targeting factor XII prevents thrombus formation and has a beneficial effect on outcome after traumatic brain injury.
Methods:
We investigated the impact of genetic deficiency of factor XII and acute inhibition of activated factor XII with a single bolus injection of recombinant human albumin-fused infestin-4 (rHA-Infestin-4) on trauma-induced microvascular thrombus formation and the subsequent outcome in 2 mouse models of traumatic brain injury.
Results:
Our study showed that both genetic deficiency of factor XII and an inhibition of activated factor XII in mice minimize trauma-induced microvascular thrombus formation and improve outcome, as reflected by better motor function, reduced brain lesion volume, and diminished neurodegeneration. Administration of human factor XII in factor XII-deficient mice fully restored injury-induced microvascular thrombus formation and brain damage.
Interpretation:
The robust protective effect of rHA-Infestin-4 points to a novel treatment option that can decrease ischemic injury after traumatic brain injury without increasing bleeding tendencies.
Parent-of-origin imprints have been implicated in the regulation of neural differentiation and brain development. Previously we have shown that, despite the lack of a paternal genome, human parthenogenetic (PG) embryonic stem cells (hESCs) can form proliferating neural stem cells (NSCs) that are capable of differentiation into physiologically functional neurons while maintaining allele-specific expression of imprinted genes. Since biparental ("normal") hESC-derived NSCs (N NSCs) are targeted by immune cells, we characterized the immunogenicity of PG NSCs. Flow cytometry and immunocytochemistry revealed that both N NSCs and PG NSCs exhibited surface expression of human leukocyte antigen (HLA) class I but not HLA-DR molecules. Functional analyses using an in vitro mixed lymphocyte reaction assay resulted in less proliferation of peripheral blood mononuclear cells (PBMC) with PG compared with N NSCs. In addition, natural killer (NK) cells cytolyzed PG less than N NSCs. At a molecular level, expression analyses of immune regulatory factors revealed higher HLA-G levels in PG compared with N NSCs. In line with this finding, MIR152, which represses HLA-G expression, is less transcribed in PG compared with N cells. Blockage of HLA-G receptors ILT2 and KIR2DL4 on natural killer cell leukemia (NKL) cells increased cytolysis of PG NSCs. Together this indicates that PG NSCs have unique immunological properties due to elevated HLA-G expression.
Background:
Traumatic brain injury (TBI) is a devastating neurological condition and a frequent cause of permanent disability. Posttraumatic inflammation and brain edema formation, two pathological key events contributing to secondary brain injury, are mediated by the contact-kinin system. Activation of this pathway in the plasma is triggered by activated factor XII. Hence, we set out to study in detail the influence of activated factor XII on the abovementioned pathophysiological features of TBI.
Methods:
Using a cortical cryogenic lesion model in mice, we investigated the impact of genetic deficiency of factor XII and inhibition of activated factor XII with a single bolus injection of recombinant human albumin-fused Infestin-4 on the release of bradykinin, the brain lesion size, and contact-kinin system-dependent pathological events. We determined protein levels of bradykinin, intracellular adhesion molecule-1, CC-chemokine ligand 2, and interleukin-1β by enzyme-linked immunosorbent assays and mRNA levels of genes related to inflammation by quantitative real-time PCR. Brain lesion size was determined by tetrazolium chloride staining. Furthermore, protein levels of the tight junction protein occludin, integrity of the blood-brain barrier, and brain water content were assessed by Western blot analysis, extravasated Evans Blue dye, and the wet weight-dry weight method, respectively. Infiltration of neutrophils and microglia/activated macrophages into the injured brain lesions was quantified by immunohistological stainings.
Results:
We show that both genetic deficiency of factor XII and inhibition of activated factor XII in mice diminish brain injury-induced bradykinin release by the contact-kinin system and minimize brain lesion size, blood-brain barrier leakage, brain edema formation, and inflammation in our brain injury model.
Conclusions:
Stimulation of bradykinin release by activated factor XII probably plays a prominent role in expanding secondary brain damage by promoting brain edema formation and inflammation. Pharmacological blocking of activated factor XII could be a useful therapeutic principle in the treatment of TBI-associated pathologic processes by alleviating posttraumatic inflammation and brain edema formation.
Background
Traumatic brain injury (TBI) is a major cause of death and disability. Neuroinflammation contributes to acute damage after TBI and modulates long-term evolution of degenerative and regenerative responses to injury. The aim of the present study was to evaluate the relationship of microglia activation to trauma severity, brain energy metabolism, and cellular reactions to injury in a mouse closed head injury model using combined in vivo PET imaging, ex vivo autoradiography, and immunohistochemistry.
Methods
A weight-drop closed head injury model was used to produce a mixed diffuse and focal TBI or a purely diffuse mild TBI (mTBI) in C57BL6 mice. Lesion severity was determined by evaluating histological damage and functional outcome using a standardized neuroscore (NSS), gliosis, and axonal injury by immunohistochemistry. Repeated intra-individual in vivo μPET imaging with the specific 18-kDa translocator protein (TSPO) radioligand [\(^{18}\)F]DPA-714 was performed on day 1, 7, and 16 and [\(^{18}\)F]FDG-μPET imaging for energy metabolism on days 2–5 after trauma using freshly synthesized radiotracers. Immediately after [\(^{18}\)F]DPA-714-μPET imaging on days 7 and 16, cellular identity of the [\(^{18}\)F]DPA-714 uptake was confirmed by exposing freshly cut cryosections to film autoradiography and successive immunostaining with antibodies against the microglia/macrophage marker IBA-1.
Results
Functional outcome correlated with focal brain lesions, gliosis, and axonal injury. [\(^{18}\)F]DPA-714-μPET showed increased radiotracer uptake in focal brain lesions on days 7 and 16 after TBI and correlated with reduced cerebral [\(^{18}\)F]FDG uptake on days 2–5, with functional outcome and number of IBA-1 positive cells on day 7. In autoradiography, [\(^{18}\)F]DPA-714 uptake co-localized with areas of IBA1-positive staining and correlated strongly with both NSS and the number of IBA1-positive cells, gliosis, and axonal injury. After mTBI, numbers of IBA-1 positive cells with microglial morphology increased in both brain hemispheres; however, uptake of [\(^{18}\)F]DPA-714 was not increased in autoradiography or in μPET imaging.
Conclusions
[\(^{18}\)F]DPA-714 uptake in μPET/autoradiography correlates with trauma severity, brain metabolic deficits, and microglia activation after closed head TBI.
Parent of origin imprints on the genome have been implicated in the regulation of neural cell type differentiation. The ability of human parthenogenetic (PG) embryonic stem cells (hpESCs) to undergo neural lineage and cell type-specific differentiation is undefined. We determined the potential of hpESCs to differentiate into various neural subtypes. Concurrently, we examined DNA methylation and expression status of imprinted genes. Under culture conditions promoting neural differentiation, hpESC-derived neural stem cells (hpNSCs) gave rise to glia and neuron-like cells that expressed subtype-specific markers and generated action potentials. Analysis of imprinting in hpESCs and in hpNSCs revealed that maternal-specific gene expression patterns and imprinting marks were generally maintained in PG cells upon differentiation. Our results demonstrate that despite the lack of a paternal genome, hpESCs generate proliferating NSCs that are capable of differentiation into physiologically functional neuron-like cells and maintain allele-specific expression of imprinted genes. Thus, hpESCs can serve as a model to study the role of maternal and paternal genomes in neural development and to better understand imprinting-associated brain diseases.
The two bradykinin receptors B1R and B2R are central components of the kallikrein–kinin system with different expression kinetics and binding characteristics. Activation of these receptors by kinins triggers inflammatory responses in the target organ and in most situations enhances tissue damage. We could recently show that blocking of B1R, but not B2R, protects from cortical cryolesion by reducing inflammation and edema formation. In the present study, we investigated the role of B1R and B2R in a closed head model of focal traumatic brain injury (TBI; weight drop). Increased expression of B1R in the injured hemispheres of wild-type mice was restricted to the later stages after brain trauma, i.e. day 7 (P<0.05), whereas no significant induction could be observed for the B2R (P>0.05). Mice lacking the B1R, but not the B2R, showed less functional deficits on day 3 (P<0.001) and day 7 (P<0.001) compared with controls. Pharmacological blocking of B1R in wild-type mice had similar effects. Reduced axonal injury and astroglia activation could be identified as underlying mechanisms, while inhibition of B1R had only little influence on the local inflammatory response in this model. Inhibition of B1R may become a novel strategy to counteract trauma-induced neurodegeneration.
Traumatic brain injury (TBI) induces a strong inflammatory response which includes blood-brain barrier damage, edema formation and infiltration of different immune cell subsets. More recently, microvascular thrombosis has been identified as another pathophysiological feature of TBI. The contact-kinin system represents an interface between inflammatory and thrombotic circuits and is activated in different neurological diseases. C1-Inhibitor counteracts activation of the contact-kinin system at multiple levels. We investigated the therapeutic potential of C1-Inhibitor in a model of TBI. Male and female C57BL/6 mice were subjected to cortical cryolesion and treated with C1-Inhibitor after 1 h. Lesion volumes were assessed between day 1 and day 5 and blood-brain barrier damage, thrombus formation as well as the local inflammatory response were determined post TBI. Treatment of male mice with 15.0 IU C1-Inhibitor, but not 7.5 IU, 1 h after cryolesion reduced lesion volumes by ~75% on day 1. This protective effect was preserved in female mice and at later stages of trauma. Mechanistically, C1-Inhibitor stabilized the blood-brain barrier and decreased the invasion of immune cells into the brain parenchyma. Moreover, C1-Inhibitor had strong antithrombotic effects. C1-Inhibitor represents a multifaceted anti-inflammatory and antithrombotic compound that prevents traumatic neurodegeneration in clinically meaningful settings.
The intercellular adhesion of circulating leukocytes to vascular endothellum ls a prerequisite for leukocyte emigration from the blood to extravascular tlssues. This process is facllltated by adhesion molecules on the surfaces of both the vascular endothelial cells and the leukocytes. The experiments presented here demonstrate for the first time that the leukocyte adhesion receptor, intercellular adhesion molecule-1, is constitutively expressed on cultured cerebromicrovascular endothelial cell lines derived from both spontaneously hypertensive (SHR) rats and normotensive WistarKyoto (WKY) rats. Both cultures contained simliar numbers of cells constitutively expressing this adhesion molecule (31.4% and 29.6%, respectlvely). Adhesion molecule expression was up-regulated by interleukin-1 ß, tumor necrosis factor-a, interferon-y and lipopolysaccharide in a dose- and time-dependent manner. Both cultures exhibited similar maximum levels of adhesion molecule up-regulation to optimal concentrations of all three cytokines. However, SHR endothelial cells were moresensitive to all three cytokines; significantly higher levels of intercellular adhesion molecule-1 expresslon were seen on SHR as opposed to WKY endothelial cells cultured with sub-optimal cytokine concentrations. It was also observed that lipopolysaccharide up-regulated intercellular adhesion molecule-1 expression on SHR endothelial cells to a greater extent than on WKY endothelial cells.
The findings that intercellular adhesion molecule-1 can be up-regulated to a greater degree on SHR endothelial cells may have important implications for in vivo perivascular leukocyte accumulation under hypertensive conditions. These observations indicate a possible mechanism by which hypertension may predispose to the development of disorders such as atherosclerosis and stroke.
The numbers of monocytes and macrophages in the walls of cerebral blood vessels were counted on perfusion-fixed frozen brain sections (16 JLffi) of spontaneously hypertensive rats (SHR), stroke-prone SHR (SHR-SP), normotensive Wistar-Kyoto (WKY) rats, and young (16-week-old) and old (2-year-old) normotensive Sprague-Dawley rats (SD-l6w and SD-2y, respectively) using monoclonal antiborlies against rat macrophages (ED2). The staining was visualized with fluoresceinlabeled second antiborlies. The ED2-specific staining in brain sections was restricted to macrophages in a perivascular location. The number of perivascular cells per square millimeter of high-power field was significantly greater in SHR-SP (8.6 ± 2.1; n = 4) and SHR (6. 7 ± 0.9; n = 6) than in normotensive WKY (4.0 ± 0.5; n = 6; p <0.01). The number of perivascular macrophages was also greater in SD-2y (7.5 ± 2.7; n = 9) than in SD-l6w (2.9 ± 1.8; n = 8; p < 0.01). No ED2 staining was found in the resident microglia or in the endothelial cells, which were identified by double staining with rhodamine-labeled anti-factor VIII-related antigen antiborlies. The results suggest that the stroke risk factors hypertension and advanced age are associated with increased subendothelial accumulation of monocytes and macrophages. This accumulation could increase the tendency for the endothelium to convert from an anticoagulant to a procoagulant surface in response to mediators released from these subendothelial cells.
Thyrotropin releasing hormone (TRH), 10 pmol kg-1 injected in the region of locus coeruleus, caused a rapid (within 1 min) rise of mean arterial pressure in the urethane- naesthetized rat. No clear-cut effects in heart rate or ventilation were observed. When TRH was injected into the lateral ventricle, a dose more than 10-fold higher was required to achieve a comparable rise in arterial pressure. It is concluded that TRH may have a physiological rote in centrat cardiovascular regulation.
Introduction
Structural plasticity with synapse formation and elimination is a key component of memory capacity and may be critical for functional recovery after brain injury. Here we describe in detail two surgical techniques to create a cranial window in mice and show crucial points in the procedure for long-term repeated in vivo imaging of synaptic structural plasticity in the mouse neocortex.
Methods
Transgenic Thy1-YFP(H) mice expressing yellow-fluorescent protein (YFP) in layer-5 pyramidal neurons were prepared under anesthesia for in vivo imaging of dendritic spines in the parietal cortex either with an open-skull glass or thinned skull window. After a recovery period of 14 days, imaging sessions of 45–60 min in duration were started under fluothane anesthesia. To reduce respiration-induced movement artifacts, the skull was glued to a stainless steel plate fixed to metal base. The animals were set under a two-photon microscope with multifocal scanhead splitter (TriMScope, LaVision BioTec) and the Ti-sapphire laser was tuned to the optimal excitation wavelength for YFP (890 nm). Images were acquired by using a 20×, 0.95 NA, water-immersion objective (Olympus) in imaging depth of 100–200 μm from the pial surface. Two-dimensional projections of three-dimensional image stacks containing dendritic segments of interest were saved for further analysis. At the end of the last imaging session, the mice were decapitated and the brains removed for histological analysis.
Results
Repeated in vivo imaging of dendritic spines of the layer-5 pyramidal neurons was successful using both open-skull glass and thinned skull windows. Both window techniques were associated with low phototoxicity after repeated sessions of imaging.
Conclusions
Repeated imaging of dendritic spines in vivo allows monitoring of long-term structural dynamics of synapses. When carefully controlled for influence of repeated anesthesia and phototoxicity, the method will be suitable to study changes in synaptic structural plasticity after brain injury.