Biomedical subjects

M Frotscher

Publications and source records attributed to M Frotscher.

At least 37 records · Page 2Linked to original sources

PubMed2000

Ultrastructural localization of activated NF-kappaB in granule cells of the rat fascia dentata.

The distribution of activated NF-kappaB (p65) was studied in granule cells of the rat fascia dentata using confocal laser scanning microscopy and preembedding immunogold electron microscopy. Activated NF-kappaB, detected with a monoclonal antibody specific for the nuclear localization signal-epitope, was found in proximal dendrites, somata, and nuclei but not in axon terminals of granule cells. Within the nuclei of granule cells, clusters of NF-kappaB immunoreactivity were detected. These data are in line with the proposed function of NF-kappaB as a retrograde signal transducer which transports information from synaptic sites to the nucleus to initiate gene expression.

Animals↗

PubMed2000

Actin-associated protein synaptopodin in the rat hippocampal formation: localization in the spine neck and close association with the spine apparatus of principal neurons.

Dendritic spines are sites of synaptic plasticity in the brain and are capable of remodeling their shape and size. However, little is known about the cellular mechanisms that regulate spine morphology and motility. Synaptopodin is a recently described actin-associated protein found in renal podocytes and dendritic spines (Mundel et al. J Cell Biol. [1997] 139:193-204), which is believed to play a role in spine plasticity. The present study analyzed the distribution of synaptopodin in the hippocampal formation. In situ hybridization histochemistry revealed a high constitutive expression of synaptopodin mRNA in the principal cell layers. Light microscopic immunohistochemistry showed that the protein is distributed throughout the hippocampal formation in a region- and lamina-specific manner. Postembedding immunogold histochemistry demonstrated that synaptopodin is exclusively present in dendrites and spines, specifically in the spine neck in close association with the spine apparatus. Spines lacking a spine apparatus are not immunoreactive for synaptopodin. These data suggest that synaptopodin links the spine apparatus to actin and may thus be involved in the actin-based plasticity of spines.

Actins↗

PubMed2000

A hippocampal interneuron associated with the mossy fiber system.

Network properties of the hippocampus emerge from the interaction of principal cells and a heterogeneous population of interneurons expressing gamma-aminobutyric acid (GABA). To understand these interactions, the synaptic connections of different types of interneurons need to be elucidated. Here we describe a type of inhibitory interneuron of the hippocampal CA3 region that has an axon coaligned with the mossy fibers. Whole-cell patch-clamp recordings, in combination with intracellular biocytin filling, were made from nonpyramidal cells of the stratum lucidum under visual control. Mossy fiber-associated (MFA) interneurons generated brief action potentials followed by a prominent after-hyperpolarization. Subsequent visualization revealed an extensive axonal arbor which was preferentially located in the stratum lucidum of CA3 and often invaded the hilus. The dendrites of MFA interneurons were mainly located in the strata radiatum and oriens, suggesting that these cells are primarily activated by associational and commissural fibers. Electron microscopic analysis showed that axon terminals of MFA interneurons established symmetric synaptic contacts predominantly on proximal apical dendritic shafts, and to a lesser degree, on somata of pyramidal cells. Synaptic contacts were also found on GABAergic interneurons of the CA3 region and putative mossy cells of the hilus. Inhibitory postsynaptic currents (IPSCs) elicited by MFA interneurons in simultaneously recorded pyramidal cells had fast kinetics (half duration, 3.6 ms) and were blocked by the GABA(A) receptor antagonist bicuculline. Thus, MFA interneurons are GABAergic cells in a position to selectively suppress the mossy fiber input, an important requirement for the recall of memory traces from the CA3 network.

Action Potentials↗

PubMed2000

Potential role of synaptopodin in spine motility by coupling actin to the spine apparatus.

Dendritic spines are dynamic structures that rapidly remodel their shape and size. These morphological adaptations are regulated by changes in synaptic activity, and result from rearrangements of the postsynaptic cytoskeleton. A cytoskeletal molecule preferentially found in mature spines is the actin-associated protein synaptopodin. It is strongly expressed by spine-bearing neurons in the olfactory bulb, striatum, cerebral cortex, and hippocampus. In the hippocampus, principal cells express synaptopodin mRNA and sort the protein to the spine compartment. Within the spine microdomain, synaptopodin is preferentially located in the spine neck and is closely associated with the spine apparatus. On the basis of these data we hypothesize that synaptopodin could affect spine motility by bundling actin filaments in the spine neck. In addition, it could link the actin cytoskeleton of spines to intracellular calcium stores, i.e., the spine apparatus and the smooth endoplasmic reticulum.

Actins↗

PubMed2000

Entorhinal cortex lesion does not alter reelin messenger RNA expression in the dentate gyrus of young and adult rats.

The extracellular matrix protein reelin plays an important role in neuronal pattern formation and axonal collateralization during the development of the central nervous system. With the concept that reelin might also be important for axonal growth in the injured nervous system we investigated whether reelin is re-expressed in areas of collateral sprouting after brain injury. The expression of reelin messenger RNA was studied in the denervated fascia dentata of adult rats one, four, seven and 14 days following entorhinal cortex lesion. In adult control animals, in situ hybridization histochemistry with digoxigenin-labeled reelin riboprobes revealed reelin messenger RNA expression in neurons located in the outer molecular layer and beneath the granule cell layer of the dentate gyrus. After entorhinal cortex lesion, this expression pattern did not change during the whole post-lesional time period investigated despite a strong glial activation and reactive sprouting in the outer molecular layer of the dentate gyrus as visualized by immunohistochemistry for glial fibrillary acidic protein and acetylcholinesterase histochemistry, respectively. The expression of reelin messenger RNA was also unaffected by entorhinal cortex lesion in the dentate gyrus of young animals (postnatal day seven), where an even stronger sprouting response occurs.

Age Factors↗

PubMed2000

Species-specific expression of parvalbumin in the entorhinal cortex of the Mongolian gerbil: dependence on local activity but not extrinsic afferents.

Mongolian gerbils are genetically predisposed to develop epileptic seizures in limbic structures. A species-specific property of the Mongolian gerbil is the expression of the calcium-binding protein parvalbumin in the perforant path where it is predominantly concentrated in nerve terminals. To test the hypothesis that this atypical expression of parvalbumin is induced by seizure-correlated hyperactivity in the entorhinohippocampal loop, we investigated whether it is dependent on extrinsic afferents to the entorhinal cortex. We cultivated organotypic slice cultures of neonate gerbil entorhinal cortex, isolated from all regions it is normally connected with in vivo. In these cultures, parvalbumin-expressing neurons demonstrated their characteristic features like in vivo. Blockade of spontaneous local activity with the sodium-channel blocker tetrodotoxin, however, considerably reduced the number of parvalbumin-expressing neurons in culture. These results indicate that spontaneous local activity, but not activity mediated by extrinsic afferents, is an essential factor for the expression of parvalbumin in the entorhinal cortex of the Mongolian gerbil.

Afferent Pathways↗

PubMed2000

Evidence for the existence of non-GABAergic, cholinergic interneurons in the rodent hippocampus.

Previous studies have revealed a small number of hippocampal interneurons immunoreactive for choline acetyltransferase, the acetylcholine-synthesizing enzyme. It remained an open question, however, whether these neurons represented a subgroup of inhibitory GABAergic neurons co-localizing acetylcholine. In this study, we have combined immunocytochemistry for choline acetyltransferase and in situ hybridization for glutamate decarboxylase messenger RNA, the GABA-synthesizing enzyme. None of the choline acetyltransferase-immunoreactive neurons in the various layers of the hippocampus proper and fascia dentata were found to co-localize glutamate decarboxylase messenger RNA. The lack of an in situ hybridization signal in these neurons is unlikely to result from the combination of the two labeling techniques. When combining in situ hybridization for glutamate decarboxylase messenger RNA with immunostaining for parvalbumin, a calcium-binding protein expressed by many GABAergic hippocampal interneurons, numerous double-labeled cells were observed. These data provide neurochemical evidence for the existence of non-GABAergic, supposedly cholinergic non-principal cells in the hippocampus.

Animals↗

PubMed2000

Up-regulation of growth-associated protein 43 mRNA in rat medial septum neurons axotomized by fimbria-fornix transection.

Transection of septohippocampal fibres is widely used to study the response of CNS neurons to axotomy. Septohippocampal projection neurons survive axotomy and selectively up-regulate the transcription factor c-Jun. In the present study we investigated whether these cells concomitantly up-regulate the growth-associated protein-43 (GAP-43), a potential target gene of c-Jun implicated in axonal growth and regeneration. Using in situ hybridization histochemistry (ISHH) it was demonstrated that postlesional c-jun mRNA expression is accompanied by an increased expression of GAP-43 mRNA in the medial septum 3 days following fimbria-fornix transection (FFT). The increase reached a maximum at 7 days and gradually declined thereafter (17 days, 3 weeks). Retrograde prelabeling with Fluoro-Gold followed by axotomy and ISHH revealed that GAP-43 mRNA was up-regulated in septohippocampal projection neurons. Colocalization of GAP-43 mRNA and choline acetyltransferase protein showed that GAP-43 mRNA was expressed by cholinergic medial septal neurons after axotomy. Selective immunolesioning of the cholinergic component of the septohippocampal projection with 192 IgG-saporin followed by FFT demonstrated that GAP-43 mRNA was also synthesized by axotomized GABAergic neurons. These results demonstrate an up-regulation of GAP-43 mRNA in axotomized septohippocampal projection neurons independent of their transmitter phenotype which is closely correlated with c-Jun expression. Because the GAP-43 gene contains an AP-1 site, we hypothesize a c-Jun-driven up-regulation of GAP-43 in lesioned medial septal neurons that may contribute to their survival and regenerative potential following axotomy.

Animals↗

PubMed2000

The chondroitin sulphate proteoglycan brevican is upregulated by astrocytes after entorhinal cortex lesions in adult rats.

The chondroitin sulphate proteoglycan brevican is one of the most abundant extracellular matrix molecules in the adult rat brain. It is primarily synthesized by astrocytes and is believed to influence astroglial motility during development and under certain pathological conditions. In order to study a potential role of brevican in the glial reaction after brain injury, its expression was analysed following entorhinal cortex lesion in rats (12 h, 1, 2, 4, 10, 14 and 28 days and 6 months post lesion). In situ hybridization and immunohistochemistry were employed to study brevican mRNA and protein, respectively, in the denervated outer molecular layer of the fascia dentata and at the lesion site. In both regions brevican mRNA was upregulated between 1 and 4 days post lesion. The combination of in situ hybridization with immunohistochemistry for glial fibrillary acidic protein demonstrated that many brevican mRNA-expressing cells are astrocytes. In the denervated zone of the fascia dentata, immunostaining for brevican was increased by 4 days, reached a maximum by 4 weeks and remained detectable up to 6 months post lesion. Electron microscopic immunocytochemistry showed that brevican is a component of the extracellular matrix compartment. At the lesion site a similar time course of brevican upregulation was observed. These data demonstrate that brevican is upregulated in areas of brain damage as well as in areas denervated by a lesion. They suggest a role of brevican in reactive gliosis and are compatible with the hypothesis that brevican is involved in the synaptic reorganization of denervated brain areas.

Acetylcholinesterase↗

PubMed2000

Role of afferent innervation and neuronal activity in dendritic development and spine maturation of fascia dentata granule cells.

By using slice cultures of hippocampus as a model, we have studied the development of dendritic spines in fascia dentata granule cells. We raised the question as to what extent spine development is dependent on a major afferent input to these neurons, the fibers from the entorhinal cortex and neuronal activity mediated by these axons. Our results can be summarized as follows: (i) the entorhino-hippocampal projection develops in an organotypic manner in co-cultures of entorhinal cortex and hippocampus. Like in vivo, entorhinal fibers, labeled by anterograde tracing with biocytin, terminate in the outer molecular layer of the fascia dentata. (ii) The layer-specific termination of entorhinal fibers is not altered by the blockade of neuronal activity with tetrodotoxin. Likewise, the differentiation of the dendritic arbor of postsynaptic granule cells does not require neuronal activity. Blockade of neuronal activity did not affect the mean spine number of granule cell dendrites in entorhino-hippocampal co-cultures, but led to a relative increase in thin, long filiform spines that are characteristic of immature neurons. (iii) The maturation of the granule cell dendritic arbor is, however, controlled by the afferent fibers from the entorhinal cortex in an activity-independent manner. In single slice cultures of hippocampus lacking entorhinal input, Golgi-impregnated granule cells have much shorter, less branched dendrites when compared with granule cells in entorhino-hippocampal co-cultures. This reduction in dendritic length in granule cells lacking entorhinal input results in a lower mean total number of spines per neuron, but the mean number of spines per microm is not reduced in the absence of entorhinal innervation. These results indicate that innervation by fibers from the entorhinal cortex, but not neuronal activity mediated via these axons, is essential for the normal development of the granule cell dendritic arbor. Neuronal activity is required, however, for the maturation of dendritic spines.

Animals↗

PubMed2000

Development of the entorhino-hippocampal projection: guidance by Cajal-Retzius cell axons.

The entorhinal cortex gives rise to a massive projection to the hippocampus and fascia dentata. In the rat, this projection forms early in development with first entorhinal axons reaching the hippocampus around embryonic day (E) 17. From the very beginning, the entorhinal axons recognize their appropriate termination zones in the hippocampus proper and fascia dentata, i.e., stratum lacunosum-moleculare and the outer molecular layer of the dentate. This is remarkable, because at the time of entorhinal fiber ingrowth, the definitive target cells of entorhinal axons, pyramidal cells and granule cells, are not yet fully developed, and the majority of their distal dendritic tips have not yet reached these layers. This raises the question as to the cellular and molecular signals guiding the entorhinal axons to and keeping them in their target layers. Here we hypothesize that early generated Cajal-Retzius (CR) cells located in stratum lacunosum-moleculare and the outer molecular layer of the dentate, and in particular their axons projecting to the entorhinal cortex, provide a template that is used by the entorhinal axons to find their target layers in the hippocampus.

Aging↗

PubMed2000

Reorganization of the rat fascia dentata after a unilateral entorhinal cortex lesion. Role of the extracellular matrix.

Entorhinal cortex lesion (ECL) partially denervates the fascia dentata of the hippocampus. This is said to induce the sprouting of intact fibers from neighboring layers that invade the zone of the degenerating axons. However, recent studies using anterograde tracing failed to demonstrate sprouting across laminar boundaries. Sprouting does occur, but it mainly involves unlesioned fiber systems terminating within the layer of fiber degeneration. It is now of interest to identify the cues that could underlie this layer-specific sprouting response. Since extracellular matrix (ECM) molecules delineate boundaries of axonal growth during development, it was tested whether these molecules play a similar role during the sprouting process following ECL. After ECL, reactive astrocytes rapidly synthesize and secrete growth-inhibiting ECM molecules, such as tenascin-C and the chondroitin sulfate proteoglycan neurocan, into the ECM of the outer molecular layer. These molecules form a sharp border against the nondenervated inner molecular layer. This pattern of ECM molecule expression may contribute to the layer-specific sprouting response of surviving afferents after ECL: axons trying to grow into the denervated outer molecular layer, for example, from the inner molecular layer, would be deflected by a growth-inhibiting ECM barrier.

Animals↗

PubMed1999

Cerebral amyloid induces aberrant axonal sprouting and ectopic terminal formation in amyloid precursor protein transgenic mice.

A characteristic feature of Alzheimer's disease (AD) is the formation of amyloid plaques in the brain. Although this hallmark pathology has been well described, the biological effects of plaques are poorly understood. To study the effect of amyloid plaques on axons and neuronal connectivity, we have examined the axonal projections from the entorhinal cortex in aged amyloid precursor protein (APP) transgenic mice that exhibit cerebral amyloid deposition in plaques and vessels (APP23 mice). Here we report that entorhinal axons form dystrophic boutons around amyloid plaques in the entorhinal termination zone of the hippocampus. More importantly, entorhinal boutons were found associated with amyloid in ectopic locations within the hippocampus, the thalamus, white matter tracts, as well as surrounding vascular amyloid. Many of these ectopic entorhinal boutons were immunopositive for the growth-associated protein GAP-43 and showed light and electron microscopic characteristics of axonal terminals. Our findings suggest that (1) cerebral amyloid deposition has neurotropic effects and is the main cause of aberrant sprouting in AD brain; (2) the magnitude and significance of sprouting in AD have been underestimated; and (3) cerebral amyloid leads to the disruption of neuronal connectivity which, in turn, may significantly contribute to AD dementia.

Amyloid beta-Protein Precursor↗

PubMed1999

Importance of AMPA receptors for hippocampal synaptic plasticity but not for spatial learning.

Gene-targeted mice lacking the L-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptor subunit GluR-A exhibited normal development, life expectancy, and fine structure of neuronal dendrites and synapses. In hippocampal CA1 pyramidal neurons, GluR-A-/- mice showed a reduction in functional AMPA receptors, with the remaining receptors preferentially targeted to synapses. Thus, the CA1 soma-patch currents were strongly reduced, but glutamatergic synaptic currents were unaltered; and evoked dendritic and spinous Ca2+ transients, Ca2+-dependent gene activation, and hippocampal field potentials were as in the wild type. In adult GluR-A-/- mice, associative long-term potentiation (LTP) was absent in CA3 to CA1 synapses, but spatial learning in the water maze was not impaired. The results suggest that CA1 hippocampal LTP is controlled by the number or subunit composition of AMPA receptors and show a dichotomy between LTP in CA1 and acquisition of spatial memory.

Action Potentials↗

PubMed1999

Cholinergic innervation of mossy cells in the rat fascia dentata.

Hilar mossy cells are the main cells of origin of the commissural/associational projection to the inner molecular layer of the rat fascia dentata. In order to analyze the cholinergic innervation of hilar mossy cells, a light and electron microscopic double-labeling technique was used. Immunolabeling for calcitonin gene-related peptide (CGRP) was employed to identify mossy cells and immunocytochemistry for choline acetyltransferase (ChAT) was used to label cholinergic septohippocampal fibers. Cholinergic boutons were abundant around mossy cell somata and on their proximal dendrites. Electron microscopy confirmed that many of these boutons formed synapses with the CGRP-positive mossy cells. These data demonstrate a direct innervation of hilar mossy cells by cholinergic septohippocampal afferents. This connectivity could contribute to the electrophysiological behavior of mossy cells during theta oscillations.

Animals↗

PubMed1999

1-Imidazolylcarbonyloxy-substituted tetrahydroquinolines and pyridines: synthesis and evaluation of P450 TxA2 inhibition.

The title compounds are derived from our model describing structural requirements for strong P450 TxA2 inhibition. In the present paper the syntheses of the 1-imidazolylcarbonyloxy-substituted tetrahydroquinolines 1, 3, and 4, tetrahydro-naphthalene 2 and 3-ethylpyridines 5 and 6 are described. Using our P450 TxA2 inhibition assay, 1-6 were tested for enzyme inhibitory activity. Compound 1 (5-(1-imidazolylcarbonyloxy)-5,6,7,8-tetrahydroquinoline) turned out to be the most active derivative showing a potency similar to the reference compound dazoxiben (IC50 values 1.6 and 1.1 microM).

Humans↗

PubMed1999

Different primary target cells are important for fiber lamination in the fascia dentata: a lesson from reeler mutant mice.

The factors determining the lamina-specific termination of entorhinal and commissural afferents to the fascia dentata are poorly understood. Recently it was shown that early generated Cajal-Retzius (CR) cells in the outer molecular layer and reelin, synthesized by CR cells, play a role in the lamina-specific termination of entorhinal fibers which form transient synapses with CR cells before establishing their definite contacts with granule cell dendrites (J. A. del Rio et al., 1997, Nature 385, 70-74). By using anterograde tracing with Phaseolus vulgaris leukoagglutinin we show that the normal, sharply delineated entorhinal projection to the outer molecular layer is retained in reeler mutant mice lacking reelin. This coincides with the regular presence of CR cells, the primary, transient target cells of entorhinal fibers. In contrast, the commissural fibers were found to terminate in an abnormal broad, not clearly defined area. This widespread projection coincides with the distribution of granule cells which in the mutant do not form a dense cell layer but are scattered all over the hilus due to a migration defect. Unlike the entorhinal fibers, the commissural fibers arrive in their target layer late in development, when granule cell dendrites are already there. We hypothesize from these results that the presence of the adequate postsynaptic element at the time of fiber ingrowth, CR cells for the early ingrowing entorhinal fibers and granule cells for the late-arriving commissural fibers, is crucial for the normal formation of these layer-specific projections.

Afferent Pathways↗

PubMed1999

The hippocampus of the reeler mutant mouse: fiber segregation in area CA1 depends on the position of the postsynaptic target cells.

Area CA1 of the rodent hippocampus is characterized by a highly lamina-specific and nonoverlapping termination of afferent fiber tracts. Entorhinal fibers terminate in stratum lacunosum-moleculare and commissural/associational fibers terminate in strata radiatum and oriens. It has been hypothesized that this fiber lamination depends on specific signals for the different afferent fiber tracts that are located on distinct dendritic segments of the postsynaptic neuron. In order to test this hypothesis, entorhinal and commissural/associational afferents to Ammon's horn were investigated in the adult reeler mutant mouse, in which developmental cell migration defects have disrupted the normal array of cells. Golgi staining revealed a deep and a superficial principal cell layer in the mutant. The morphology of the cells located in the deep pyramidal cell layer was considerably abnormal, whereas most cells located in the superficial pyramidal cell layer showed an almost normal cellular and dendritic morphology. Anterograde tracing with Phaseolus vulgaris leukoagglutinin revealed that the duplication and disorganization of the pyramidal cell layer in area CA1 are mirrored by the duplication and disruption of afferent fiber termination zones. In the zone above the abnormal deep pyramidal cell layer, i.e., between the two cell layers, entorhinal fibers as well as commissural/associational fibers terminate and intermingle. In contrast, in the zone above the fairly normal superficial pyramidal cell layer, entorhinal and commissural/associational fibers retain their normal fiber segregation. These data suggest that the normal laminar organization of the murine hippocampus depends on positional cues presented by their target cells.

Afferent Pathways↗