Institute for Structural Neurobiology

Hamburg, Germany

Institute for Structural Neurobiology

Hamburg, Germany
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Zhao S.,Institute for Structural Neurobiology | Studer D.,University of Bern | Chai X.,Institute for Structural Neurobiology | Graber W.,University of Bern | And 6 more authors.
Frontiers in Neural Circuits | Year: 2012

The granule cells of the dentate gyrus give rise to thin unmyelinated axons, the mossy fibers. They form giant presynaptic boutons impinging on large complex spines on the proximal dendritic portions of hilar mossy cells and CA3 pyramidal neurons. While these anatomical characteristics have been known for some time, it remained unclear whether functional changes at mossy fiber synapses such as long-term potentiation (LTP) are associated with structural changes. Since subtle structural changes may escape a fine-structural analysis when the tissue is fixed by using aldehydes and is dehydrated in ethanol, rapid high-pressure freezing (HPF) of the tissue was applied. Slice cultures of hippocampus were prepared and incubated in vitro for 2 weeks. Then, chemical LTP (cLTP) was induced by the application of 25 mM tetraethylammonium (TEA) for 10 min. Whole-cell patch-clamp recordings from CA3 pyramidal neurons revealed a highly significant potentiation of mossy fiber synapses when compared to control conditions before the application of TEA. Next, the slice cultures were subjected to HPF, cryosubstitution, and embedding in Epon for a fine-structural analysis. When compared to control tissue, we noticed a significant decrease of synaptic vesicles in mossy fiber boutons and a concomitant increase in the length of the presynaptic membrane. On the postsynaptic side, we observed the formation of small, finger-like protrusions, emanating from the large complex spines. These short protrusions gave rise to active zones that were shorter than those normally found on the thorny excrescences. However, the total number of active zones was significantly increased. Of note, none of these cLTP-induced structural changes was observed in slice cultures from Munc13-1 deficient mouse mutants showing severely impaired vesicle priming and docking. In conclusion, application of HPF allowed us to monitor cLTP-induced structural reorganization of mossy fiber synapses. © 2012 Zhao, Studer, Chai, Graber, Brose, Nestel, Young, Rodriguez, Saetzler and Frotscher.


Sibbe M.,Albert Ludwigs University of Freiburg | Haussler U.,Albert Ludwigs University of Freiburg | Dieni S.,Albert Ludwigs University of Freiburg | Althof D.,Albert Ludwigs University of Freiburg | And 3 more authors.
European Journal of Neuroscience | Year: 2012

Temporal lobe epilepsy (TLE) is the most frequent form of epilepsy in adults. In addition to recurrent focal seizures, patients suffer from memory loss and depression. The factors contributing to these symptoms are unknown. In recent years, adult hippocampal neurogenesis has been implicated in certain aspects of learning and memory, as well as in depression and anhedonia. Here we investigated whether the adult hippocampal stem cell niche is affected by status epilepticus in a mouse model of TLE using unilateral intrahippocampal kainic acid injection. Eight days after status epilepticus, we found a strong diminution in Notch signalling, a key pathway involved in stem cell maintenance, as assayed by hes5 reporter gene activity. In particular, hes5-GFP expression in the subgranular zone of the dentate gyrus was diminished. Furthermore, Sox2-positive cells as well as stem cell proliferation were reduced, thus pointing to a disruption of the stem cell niche in epilepsy under the present experimental conditions. © 2012 Federation of European Neuroscience Societies and Blackwell Publishing Ltd.


Gunn B.G.,University of California at Irvine | Cox C.D.,University of California at Irvine | Chen Y.,University of California at Irvine | Frotscher M.,Institute for Structural Neurobiology | And 3 more authors.
Cerebral Cortex | Year: 2017

Memory is strongly influenced by stress but underlying mechanisms are unknown. Here, we used electrophysiology, neuroanatomy, and network simulations to probe the role of the endogenous, stress-related neuropeptide corticotropinreleasing hormone (CRH) in modulating hippocampal function. We focused on neuronal excitability and the incidence of sharp waves (SPWs), a form of intrinsic network activity associated with memory consolidation. Specifically, we blocked endogenous CRH using 2 chemically distinct antagonists of the principal hippocampal CRH receptor, CRHR1. The antagonists caused a modest reduction of spontaneous excitatory transmission onto CA3 pyramidal cells, mediated, in part by effects on IAHP. This was accompanied by a decrease in the incidence but not amplitude of SPWs, indicating that the synaptic actions of CRH are sufficient to alter the output of a complex hippocampal network. A biophysical model of CA3 described how local actions of CRH produce macroscopic consequences including the observed changes in SPWs. Collectively, the results provide a first demonstration of the manner in which subtle synaptic effects of an endogenously released neuropeptide influence hippocampal network level operations and, in the case of CRH, may contribute to the effects of acute stress on memory. © The Author 2016. Published by Oxford University Press. All rights reserved.


Dieni S.,University Hospital Freiburg | Nestel S.,Albert Ludwigs University of Freiburg | Sibbe M.,Albert Ludwigs University of Freiburg | Frotscher M.,Institute for Structural Neurobiology | Hellwig S.,University Hospital Freiburg
Frontiers in Synaptic Neuroscience | Year: 2015

Proper synaptic function depends on a finely-tuned balance between events such as protein synthesis and structural organization. In particular, the functional loss of just one synaptic-related protein can have a profound impact on overall neuronal network function. To this end, we used a mutant mouse model harboring a mutated form of the presynaptic scaffolding protein Bassoon (Bsn), which is phenotypically characterized by: (i) spontaneous generalized epileptic seizure activity, representing a chronically-imbalanced neuronal network; and (ii) a dramatic increase in hippocampal brain-derived neurotrophic factor (BDNF) protein concentration, a key player in synaptic plasticity. Detailed morphological and neurochemical analyses revealed that the increased BDNF levels are associated with: (i) modified neuropeptide distribution; (ii) perturbed expression of selected markers of synaptic activation or plasticity; (iii) subtle changes to microglial structure; and (iv) morphological alterations to the mossy fiber (MF) synapse. These findings emphasize the important contribution of Bassoon protein to normal hippocampal function, and further characterize the Bsn-mutant as a useful model for studying the effects of chronic changes to network activity. © 2015 Dieni, Nestel, Sibbe, Frotscher and Hellwig.


Sibbe M.,Albert Ludwigs University of Freiburg | Kuner E.,Albert Ludwigs University of Freiburg | Althof D.,Albert Ludwigs University of Freiburg | Frotscher M.,Institute for Structural Neurobiology
PLoS ONE | Year: 2015

Adult hippocampal neurogenesis has been implicated in hippocampus-dependent learning and memory. Furthermore, the decline of neurogenesis accompanying aging could be involved in age-related cognitive deficits. It is believed that the neural stem cell niche comprises a specialized microenvironment regulating stem cell activation and maintenance. However, little is known about the significance of the extracellular matrix in controlling adult stem cells. Reelin is a large glycoprotein of the extracelluar matrix known to be of crucial importance for neuronal migration. Here, we examined the local interrelation between Reelin expressing interneurons and putative hippocampal stem cells and investigated the effects of Reelin deficiency on stem cell and progenitor cell proliferation. Reelin-positive cells are found in close vicinity to putative stem cell processes, which would allow for stem cell regulation by Reelin. We investigated the proliferation of stem cells in the Reelin-deficient reeler hippocampus by Ki67 labeling and found a strong reduction of mitotic cells. A detailed analysis of dividing Type 1, type 2 and type 3 cells indicated that once a stem cell is recruited for proliferation, the progression to the next progenitor stage as well as the number of mitotic cycles is not altered in reeler. Our data point to a role for Reelin in either regulating stem cell quiescence or maintenance. © 2015 Sibbe et al.


Pohlkamp T.,Albert Ludwigs University of Freiburg | Pohlkamp T.,University of Texas Southwestern Medical Center | David C.,Albert Ludwigs University of Freiburg | David C.,Semmelweis University | And 14 more authors.
Cerebral Cortex | Year: 2014

GABAergic inhibitory interneurons (IN) represent a heterogeneous population with different electrophysiological, morphological, and molecular properties. The correct balance between interneuronal subtypes is important for brain function and is impaired in several neurological and psychiatric disorders. Here we show the data of 123 molecularly and electrophysiologically characterized neurons of juvenile rat barrel cortex acute slices, 48 of which expressed Reelin (Reln). Reln mRNA was exclusively detected in Gad65/67-positive cells but was found in interneuronal subtypes in different proportions: all cells of the adapting-Somatostatin (SST) cluster expressed Reln, whereas 63% of the adapting-neuropeptide Y (NPY, 50% of the fast-spiking Parvalbumin (PVALB), and 27% of the adapting/bursting-Vasoactive Intestinal Peptide (VIP) cluster were Reln-positive. Silhouette analysis revealed a high impact of the parameter Reln on cluster quality. By analyzing the co-localization of RELN immunoreactivity with those of different IN-markers, we found that RELN is produced layer-independently in SST-, NPY-, and NOS1-expressing INs, whereas co-localization of RELN and VIP was mostly absent. Of note, RELN co-localized with PVALB, predominantly in INs of layers IV/V (>30%). Our findings emphasize RELN's role as an important IN-marker protein and provide a basis for the functional characterization of Reln-expressing INs and its role in the regulation of inhibitory IN networks. © The Author 2013.


PubMed | Institute for Structural Neurobiology and Albert Ludwigs University of Freiburg
Type: Journal Article | Journal: PloS one | Year: 2015

Adult hippocampal neurogenesis has been implicated in hippocampus-dependent learning and memory. Furthermore, the decline of neurogenesis accompanying aging could be involved in age-related cognitive deficits. It is believed that the neural stem cell niche comprises a specialized microenvironment regulating stem cell activation and maintenance. However, little is known about the significance of the extracellular matrix in controlling adult stem cells. Reelin is a large glycoprotein of the extracelluar matrix known to be of crucial importance for neuronal migration. Here, we examined the local interrelation between Reelin expressing interneurons and putative hippocampal stem cells and investigated the effects of Reelin deficiency on stem cell and progenitor cell proliferation. Reelin-positive cells are found in close vicinity to putative stem cell processes, which would allow for stem cell regulation by Reelin. We investigated the proliferation of stem cells in the Reelin-deficient reeler hippocampus by Ki67 labeling and found a strong reduction of mitotic cells. A detailed analysis of dividing Type 1, type 2 and type 3 cells indicated that once a stem cell is recruited for proliferation, the progression to the next progenitor stage as well as the number of mitotic cycles is not altered in reeler. Our data point to a role for Reelin in either regulating stem cell quiescence or maintenance.


Nullmeier S.,Otto Von Guericke University of Magdeburg | Panther P.,University Hospital of Magdeburg | Frotscher M.,Institute for Structural Neurobiology | Zhao S.,Institute for Structural Neurobiology | Schwegler H.,Otto Von Guericke University of Magdeburg
Neuroscience | Year: 2014

The heterozygous reeler mouse (HRM), haploinsufficient for reelin, shares several neurochemical and behavioral similarities with patients suffering from schizophrenia. It has been shown that defective reelin signaling influences the mesolimbic dopaminergic pathways in a specific manner. However, there is only little information about the impact of reelin haploinsufficiency on the monoaminergic innervation of different brain areas, known to be involved in the pathophysiology of schizophrenia. In the present study using immunocytochemical procedures, we investigated HRM and wild-type mice (WT) for differences in the densities of tyrosine hydroxylase (TH)-immunoreactive (IR) and serotonin (5-HT)-IR fibers in prefrontal cortex, ventral and dorsal hippocampal formation, amygdala and ventral and dorsal striatum. We found that HRM, compared to WT, shows a significant increase in TH-IR fiber densities in dorsal hippocampal CA1, CA3 and ventral CA1. In contrast, HRM exhibits a significant decrease of TH-IR in the shell of the nucleus accumbens (AcbShell), but no differences in the other brain areas investigated. Overall, no genotype differences were found in the 5-HT-IR fiber densities. In conclusion, these results support the view that reelin haploinsufficiency differentially influences the catecholaminergic (esp. dopaminergic) systems in brain areas associated with schizophrenia. The reelin haploinsufficient mouse may provide a useful model for studying the role of reelin in hippocampal dysfunction and its effect on the dopaminergic system as related to schizophrenia. © 2014 IBRO.


Sapir T.,Weizmann Institute of Science | Frotscher M.,Institute for Structural Neurobiology | Levy T.,Weizmann Institute of Science | Mandelkow E.-M.,Research Center | Reiner O.,Weizmann Institute of Science
Human Molecular Genetics | Year: 2012

Microdeletions encompassing the MAPT (Tau) locus resulting in intellectual disability raised the hypothesis that Tau may regulate early functions in the developing brain. Our results indicate that neuronal migration was inhibited in mouse brains following Tau reduction. In addition, the leading edge of radially migrating neurons was aberrant in spite of normal morphology of radial glia. Furthermore, intracellular mitochondrial transport and morphology were affected. In early postnatal brains, a portion of Tau knocked down neurons reached the cortical plate. Nevertheless, they exhibited far less developed dendrites and a striking reduction in connectivity evident by the size of boutons. Our novel results strongly implicate MAPT as a dosage-sensitive gene in this locus involved in intellectual disability. Furthermore, our results are likely to impact our understanding of other diseases involving Tau. © The Author 2011. Published by Oxford University Press. All rights reserved.


PubMed | Institute for Structural Neurobiology and TU Braunschweig
Type: | Journal: Cerebral cortex (New York, N.Y. : 1991) | Year: 2017

The Fragile X syndrome (FXS) as the most common monogenetic cause of cognitive impairment and autism indicates how tightly the dysregulation of synapse development is linked to cognitive deficits. Symptoms of FXS include excessive adherence to patterns that point to compromised hippocampal network formation. Surprisingly, one of the most complex hippocampal synapses connecting the dentate gyrus (DG) to CA3 pyramidal neurons has not been analyzed in FXS yet. Intriguingly, we found altered synaptic function between DG and CA3 in a mouse model of FXS (fmr1 knockout [KO]) demonstrated by increased mossy fiber-dependent miniature excitatory postsynaptic current (mEPSC) frequency at CA3 pyramidal neurons together with increased connectivity between granule cells and CA3 neurons. This phenotype is accompanied by increased activity of fmr1 KO animals in the marble burying task, detecting repetitive and obsessive compulsive behavior. Spine apparatus development and insertion of AMPA receptors is enhanced at postsynaptic thorny excrescences (TEs) in fmr1 KO mice. We report age-dependent alterations in TE morphology and in the underlying actin dynamics possibly linked to a dysregulation in profilin1 expression. TEs form detonator synapses guiding CA3 network activity. Thus, alterations described here are likely to contribute substantially to the impairment in hippocampal function and therefore to the pathogenesis of FXS.

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