Biomedical subjects

T Deller

Publications and source records attributed to T Deller.

At least 55 records · Page 3Linked to original sources

PubMed1997

Up-regulation of astrocyte-derived tenascin-C correlates with neurite outgrowth in the rat dentate gyrus after unilateral entorhinal cortex lesion.

The extracellular matrix protein tenascin-C has been implicated in the regulation of axonal growth. Using unilateral entorhinal cortex lesions, which induce a massive sprouting response in the denervated outer molecular layer of the rat fascia dentata, the role of tenascin-C for axonal growth was investigated in vivo. Monoclonal antibodies against the neurite outgrowth and anti-adhesive domains of the molecule were employed. Immunostaining was increased throughout the denervated outer molecular layer by day 2, reached a maximum around day 10, and was back to control levels by four weeks post lesion. Growth cone deflecting as well as neurite outgrowth promoting isoforms of tenascin-C were up-regulated after the lesion. Using electron microscopy, single intensely tenascin-C immunoreactive cells were identified as reactive astrocytes that phagocytose degenerated terminals. In situ hybridization histochemistry for tenascin-C messenger RNA revealed numerous cellular profiles in the denervated outer molecular layer of the ipsilateral and contralateral dentate gyrus two days post lesion. Tenascin-C messenger RNA-positive cells in the outer molecular layer were identified as astrocytes using double-labelling for tenascin-C messenger RNA and glial fibrillary acidic protein immunohistochemistry. Thus, a tenascin-C-rich substrate is present in the outer molecular layer during the time of sprouting and a sharp boundary is formed against the inner molecular layer. This pattern may contribute to the layer-specific sprouting response of surviving afferents after entorhinal lesion. Neurite outgrowth may be promoted within the denervated zone, whereas axons trying to grow into the denervated outer molecular layer, for example from the inner molecular layer, would be deflected by a tenascin-C-rich barrier.

Animals↗

PubMed1997

The anatomy of the rat fascia dentata--new vistas.

The rat fascia dentata is frequently used as a model system to analyze normal as well as pathological processes of the brain. The normal anatomy of the fascia dentata is the basis for a meaningful interpretation of experimentally induced changes in this brain region. Using anterograde tracing with Phaseolus vulgaris-leucoagglutinin (PHAL) previously unknown commissural as well as entorhinal fiber systems to the fascia dentata were described. These fiber systems need to be incorporated into current concepts of the hippocampal network since they have profound implications for studies of lesion effects in this brain region.

Animals↗

PubMed1997

192 IgG-saporin-induced loss of cholinergic neurons in the septum abolishes cholinergic sprouting after unilateral entorhinal lesion in the rat.

After unilateral lesion of the entorhinal cortex, cholinergic septohippocampal fibres are believed to sprout in the denervated outer molecular layer of the rat dentate gyrus. This cholinergic sprouting has been demonstrated by acetylcholinesterase (AChE) histochemistry, a method said selectively to label cholinergic septohippocampal fibres in the hippocampus. However, a recent report has questioned this concept, suggesting that AChE may not be an adequate marker to monitor cholinergic sprouting and that other, non-cholinergic axons sprouting after entorhinal cortex lesion cause the dense AChE-positive band in the denervated outer molecular layer. In order to determine the contribution of cholinergic septohippocampal fibres to the dense AChE band appearing after entorhinal cortex lesion, the neurotoxin 192 IgG-saporin, known to destroy cholinergic neurons in the basal forebrain selectively, was used. Rats received bilateral injections of 192 IgG-saporin into the lateral ventricles 3 weeks before entorhinal cortex lesion, simultaneously with entorhinal cortex lesion, or 8 weeks after entorhinal cortex lesion. Immunocytochemistry for choline acetyltransferase (ChAT) and in situ hybridization for ChAT mRNA demonstrated the loss of cholinergic neurons in the medial septum and diagonal band after 192 IgG-saporin treatment. The cholinergic sprouting response in the molecular layer, as visualized with AChE histochemistry, was abolished in all animals treated with immunotoxin. These data indicate that the dense AChE band forming after entorhinal cortex lesion represents the sprouting of cholinergic septohippocampal fibres.

Acetylcholinesterase↗

PubMed1996

Multiple projections are unlikely to account for the survival of rat medial septal neurons after axotomy.

Previous studies have demonstrated that numerous septohippocampal neurons survive axotomy disconnecting them from target-derived neurotrophins. One reason for survival could be that these neurons have additional projections to other targets supplying them with neurotrophic factor(s). We show that anterograde tracing indeed labeled additional targets of the medial septum (MS) in controls as well as in experimental animals. However, only very few MS neurons could be double-labeled by retrograde tracer injections into the hippocampus and these targets. Thus, for the majority of septohippocampal neurons multiple projections cannot account for their survival following axotomy.

Animals↗

PubMed1996

A novel entorhinal projection to the rat dentate gyrus: direct innervation of proximal dendrites and cell bodies of granule cells and GABAergic neurons.

Entorhinal fibers to the fascia dentata originating from layer II stellate neurons are known to terminate exclusively in the outer two thirds of the molecular layer, where they innervate distal dendritic portions of dentate neurons. Using anterograde tracing with Phaseolus vulgaris leucoagglutinin, we unraveled a previously unknown entorhinal projection that directly innervates proximal dendritic portions and somata of granule cells and GABAergic neurons. This projection originates from neurons located in entorhinal layers IV-VI of the medial entorhinal area. These fibers enter the outer two thirds of the molecular layer, traverse the inner molecular layer (IML) and granule cell layer, where they form numerous boutons, and finally arborize subjacent to the granule cells. Correlated light and electron microscopy revealed that the boutons formed by these fibers establish asymmetric synapses on dendrites in the IML, on spines and somata of granule cells, and on spineless dendrites subjacent to the granule cell layer. Postembedding immunogold staining indicates that this entorhino-dentate projection is not GABAergic and that it also terminates on GABAergic inhibitory neurons. These data demonstrate that not all entorhino-dentate fibers display a similar high laminar specificity for the outer molecular layer (OML). Although fibers from the superficial layers of the entorhinal cortex terminate exclusively in the OML, entorhinal fibers arising from deeper layers are not confined to laminar boundaries. Finally, the possibility that these supposedly excitatory entorhinal afferents may monosynaptically activate proximal dendrites and somata of dentate neurons needs to be incorporated into contemporary concepts of the hippocampal network.

Animals↗

PubMed1996

Selective expression of the immediate early gene c-jun in axotomized rat medial septal neurons is not related to neuronal degeneration.

In the present study, we use the anatomically well defined septohippocampal projection to study the molecular events involved in the reaction of neurons to axotomy. The expression of three immediate early genes (c-fos, c-jun, and jun B) was investigated in rat septohippocampal neurons after axotomy by bilateral fimbria-fornix transection (FFT). Moreover, the extent of retrograde degeneration in the septal complex was assessed by analyzing DNA fragmentation. In a postoperative time course analysis, a strong increase of c-jun immunoreactivity (IR) was observed in the nuclei of neurons in the medial septum/diagonal band complex (MSDB) 2 and 6 d postaxotomy, which was followed by a decline after 12 d and 3 weeks, respectively. Nine weeks after FFT, c-jun IR had disappeared. The c-jun-positive MS neurons were identified as former septohippocampal projection cells by double-labeling with the retrogradely transported tracer Fluoro-Gold injected into the hippocampus before axotomy. In line with the immunocytochemical data, there was a massive induction of c-jun mRNA in the axotomized MS neurons as visualized by in situ hybridization histochemistry. c-fos mRNA and c-fos or jun B IR were not detectable in either unoperated or lesioned medial septal neurons. Experiments using the TdT-mediated deoxyuridine triphosphate nick-end-labeling technique, designed to detect nuclear DNA fragmentation in degenerating neurons, complemented this study. During the postoperative time range studied, MS neurons did not exhibit DNA fragmentation. We conclude that MSDB neurons survive axotomy by FFT and display characteristic changes in gene expression.

Acetylcholine↗

PubMed1996

Sprouting of crossed entorhinodentate fibers after a unilateral entorhinal lesion: anterograde tracing of fiber reorganization with Phaseolus vulgaris-leucoagglutinin (PHAL).

Fibers from the contralateral entorhinal cortex (EC) to the dentate gyrus partially replace the input lost after an ipsilateral EC lesion. To study the morphology and course of single sprouted crossed entorhinodentate fibers, the anterograde tracer Phaseolus vulgaris-leucoagglutinin (PHAL) was used. Rats that survived for 4 to 8 weeks after a unilateral entorhinal lesion received PHAL deposits into the entorhinal cortex contralateral to the lesion. Control animals received a similar PHAL deposit. Single PHAL-labeled fibers in the molecular layer of the contralateral (EC lesion) fascia dentata were drawn with a camera lucida, and an axon-branching index (branch points/100 microns axon length) was calculated for these crossed entorhinodentate fibers in controls and operated animals. In animals with EC lesions, the density of PHAL-labeled crossed entorhinodentate fibers had increased remarkably. Single crossed entorhinodentate axons showed significantly more axon branch points in experimental than in control animals. In addition, some axon segments displayed high densities of small axonal extensions. Frequently, tanglelike structures were observed in the denervated outer molecular layer. These tangles consisted of one or more PHAL-labeled axons that intertwined and formed an axon tangle filled completely with branches, extensions, and boutons. Our data indicate that crossed EC fibers sprout by forming additional collaterals, axonal extensions, and tangles. Abnormal neurite formations are a characteristic feature of plaques in Alzheimer's disease. Future studies must be done to show whether or not there is a close relationship between axonal tangles and plaques in Alzheimer's disease, which, like the present lesion paradigm, severely affects entorhinal projection neurons.

Acetylcholinesterase↗

PubMed1996

Organization of identified fiber tracts in the rat fimbria-fornix: an anterograde tracing and electron microscopic study.

The fimbria is a major route for afferent and efferent fibers of the hippocampal formation. However, little is known about the intrinsic organization of the fimbria-fornix complex. In this study, the anterograde tracer Phaseolus vulgaris-leucoagglutinin (PHAL) was used to analyze the ultrastructure and topography of identified fiber tracts within the fimbria-fornix. Septo-hippocampal fibers are loosely distributed throughout the fimbria-fornix. Commissural fibers cross the midline in the ventral hippocampal commissure and form a tight fiber bundle in the fimbria. Crossed entorhino-hippocampal fibers cross the midline in the ventral hippocampal commissure rostral to the commissural fiber bundle, and crossed entorhino-entorhinal fibers pass through the dorsal hippocampal commissure. This suggests a topographical organization of fiber tracts within the fimbria-fornix that reflects the laminar organization of the hippocampal target structure: fibers of the diffusely terminating septohippocampal projection are loosely distributed throughout the fimbria-fornix, while those projections that are known to terminate in specific laminae of the hippocampal formation (commissural projection, crossed entorhino-hippocampal projection) form fiber bundles within the fimbria and the ventral hippocampal commissure.

Animals↗

PubMed1996

The alvear pathway of the rat hippocampus.

Neurons of the entorhinal cortex project to the hippocampus proper and dentate gyrus. This projection is called the "perforant pathway" because it perforates the subiculum; current usage applies this term to all entorhino-hippocampal fibers. However, entorhinal fibers also reach Ammon's horn via the alveus ("alvear pathway"), an alternative route first described by Cajal. The anterograde tracer Phaseolus vulgaris leucoagglutinin (PHAL) was used in order to analyze the contribution of this pathway to the temporo-ammonic projection. In the temporal portion of the rat hippocampus, most of the entorhinal fibers reach Ammon's horn after perforating the subiculum (classical perforant pathway). At more septal levels, the number of entorhinal fibers that take the alvear pathway increases; in the septal portion of the hippocampal formation, most of the entorhinal fibers to hippocampal subfield CA1 reach this subfield via the alveus. These fibers make sharp right-angle turns in the alveus, perforate the pyramidal cell layer, and finally terminate in the stratum lacunosum-moleculare. The crossed temporo-ammonic fibers reach their termination area in the stratum lacunosum-moleculare of CA1 almost exclusively via the alveus. These data indicate that the alveus is a major route by which entorhinal fibers reach their targets in CA1.

Animals↗

PubMed1996

Layer-specific sprouting of commissural fibres to the rat fascia dentata after unilateral entorhinal cortex lesion: a Phaseolus vulgaris leucoagglutinin tracing study.

After unilateral entorhinal cortex lesion commissural fibres to the inner molecular layer of the rat fascia dentata are said to sprout into the former termination zone of entorhinal afferents. This sprouting process has not yet been demonstrated at the level of individual fibres. In the present study, Phaseolus vulgaris leucoagglutinin tracing was used to analyse the commissural projection to the inner molecular layer in rats with longstanding entorhinal cortex lesions. In comparison with controls, the commissural fibre plexus in the inner molecular layer had expanded by 20-45 microns outwards on the side of the entorhinal lesion. Unexpectedly, only a small number of axons arising from the bulk of commissural fibres in the inner molecular layer left the main fibre plexus and entered the outer molecular layer. Thus, there was still a clearly recognizable border between the Phaseolus vulgaris leucoagglutinin-labelled commissural fibre plexus in the inner molecular layer and the unstained outer molecular layer. The few commissural axons invading the outer molecular layer rarely branched but formed multiple en passant boutons, and occasionally exhibited growth cones. The data indicate that only few commissural fibres appear to be able to sprout beyond the border of their appropriate layer suggesting that the characteristic laminar specificity of hippocampal afferents is largely retained following deafferentation.

Animals↗

PubMed1996

Heterogeneity of the commissural projection to the rat dentate gyrus: a Phaseolus vulgaris leucoagglutinin tracing study.

The commissural and associational projections to the rat dentate gyrus are believed to be anatomically homologous fiber systems. They are often referred to as the so-called commissural/ associational system of the dentate gyrus. However, whereas characteristic laminar termination patterns within the molecular layer of the dentate gyrus have been described for the different cells of origin of the associational projection, the axons of the different cell types of commissural neurons have long been believed to terminate exclusively within the inner molecular layer. Only recently, a previously unknown commissural projection to the outer molecular layer of the dentate gyrus was described and the question was raised whether the commissural fibers could exhibit a heterogeneity similar to that of the associational projections. Using the anterograde tracer Phaseolus vulgaris leucoagglutinin, which labels individual axons and their collaterals, we have studied the termination pattern of commissural axons in the dentate gyrus of the septal hippocampus. At least four different commissural fiber types could be revealed on the basis of their laminar termination pattern: fibers to the inner molecular layer (type 1), fibers to the outer molecular layer (type 2), fibers terminating throughout the molecular layer (type 3), and fibers terminating in both the granule cell layer and the molecular layer (type 4). These observations demonstrate a previously underestimated heterogeneity of the commissural projection. In addition, there is a great deal of parallelism between the different commissural and associational fibers, pointing to a coordinated action of the two systems in the two hippocampi.

Afferent Pathways↗

PubMed1996

Survival, regeneration and sprouting of central neurons: the rat septohippocampal projection as a model.

The septohippocampal projection was used to study the survival following axotomy, axonal regeneration, and sprouting of a defined group of central neurons. Septohippocampal projection neurons in adult rats were axotomized by bilateral lesions of the fimbria-fornix. Using prelabeling prior to axotomy, intracellular staining, electron microscopy, and immunocytochemical and in situ hybridization techniques, we were able to demonstrate that the majority of septohippocampal neurons survived after axotomy. At least in young postnatal rats, these axotomized neurons have the capacity to regenerate an axonal process that reinnervates its appropriate target tissue, the hippocampus. We demonstrated this by axotomizing young septohippocampal neurons and co-culturing them with sections of hippocampus. Septohippocampal neurons appear to retain their capacity for axonal growth in adulthood, since they are able to sprout within hippocampal layers partially denervated by removing entorhinal afferents. In this paradigm the terminals of septohippocampal neurons themselves were not lesioned. Our results point to a previously underestimated capacity of septohippocampal neurons for survival following axotomy, regeneration, and sprouting.

Acetylcholinesterase↗

PubMed1995

Phaseolus vulgaris-leucoagglutinin tracing of commissural fibers to the rat dentate gyrus: evidence for a previously unknown commissural projection to the outer molecular layer.

Numerous studies have shown a lamina-specific termination of commissural fibers to the dentate gyrus in the inner molecular layer. However, the exact course and arborization pattern of individual fibers remained unknown. In this study, the commissural fiber tract to the dentate gyrus of the rat has been studied using the anterograde tracer Phaseolus vulgaris-leucoagglutinin (PHA-L), which labels individual axons and their collaterals. Following iontophoretic application of the tracer, anterogradely labeled fibers were followed through the posterior basal fornix and medial fimbria where they formed a dense fiber bundle. Labeled fibers then entered the dentate gyrus close to the medial blade of the granule cell layer where they separated and traversed the hilus. Only in those cases where the injection also involved CA3 pyramidal cells could axons arborizing in the hilus be observed. Typically, fibers that continued into the molecular layer did not arborize in the hilus. Upon their entrance into the molecular layer, these fibers changed direction, gave off several collaterals, and followed a new path parallel to the granule cell layer where they preferentially formed en passant contacts. These commissural fibers to the inner molecular layer terminated in a wide septotemporal (longitudinal) extension. However, a considerable number of fibers reached the outer molecular layer where some of them formed extensive arborizations. Moreover, these commissural fibers to the outer molecular layer appeared to be restricted to the hippocampal lamella, corresponding to the level of the contralateral injection site. These data suggest the existence of three commissural projections to the rat dentate gyrus: (1) commissural fibers to the hilus arising from CA3 neurons, (2) commissural fibers to the inner molecular layer, and, (3) commissural fibers to the outer molecular layer.

Animals↗

PubMed1995

Selective rostral transection of the fornix spares the hippocampal commissural pathway in the rat: a Phaseolus vulgaris leucoagglutinin tracing study.

This study describes an approach for disconnecting the septal region from the hippocampus by fimbria-fornix lesions while sparing the commissural projections. After a frontal cut through the rostral fornix, commissural fibres were labelled with the anterograde tracer Phaseolus vulgaris leucoagglutinin. The commissural fibre bundle located in the posterior-basal fornix (ventral hippocampal commissure) remained unaffected by the rostral fornix transection, whereas the absence of septal fibres in the hippocampus could be verified using AChE histochemistry. Thus, using this approach, selective studies of the septo-hippocampal projection can be performed while leaving the overwhelming portion of the commissural fibre system intact.

Acetylcholinesterase↗

PubMed1995

Morphological evidence for the sprouting of inhibitory commissural fibers in response to the lesion of the excitatory entorhinal input to the rat dentate gyrus.

Recently a commissural fiber projection that terminates in the outer molecular layer of the fascia dentata was described in normal rats (Deller et al., 1995). In the present article, Phaseolus vulgaris leucoagglutinin (PHAL) tracing was used to analyze the contribution of this previously unknown projection to the commissural sprouting response after entorhinal cortex lesion. Rats 4-8 weeks after unilateral entorhinal lesion received a single PHAL deposit into the hilus of the fascia dentata contralateral to the lesion side. Unlesioned control animals received a similar PHAL deposit. The degree of axonal arborization and the bouton density per axon length were determined for individual PHAL-labeled commissural axons to the outer molecular layer of the dentate gyrus. A significant increase in both parameters was observed in the lesioned group. The PHAL-labeled commissural fibers established symmetric synapses in the denervated outer molecular layer. Postembedding immunocytochemistry indicated that some of these sprouting commissural fibers are GABAergic. Our findings provide morphological evidence for lamina-specific sprouting of an inhibitory commissural projection that normally terminates in the outer molecular layer. This suggests that inhibitory fibers participate in the replacement of the excitatory perforant pathway after entorhinal lesion.

Afferent Pathways↗

PubMed1995

Understanding the cortex through the hippocampus: lamina-specific connections of the rat hippocampal neurons.

A characteristic feature of hippocampal organisation is the lamina-specific termination of afferent fibres. The factors determining this characteristic fibre segregation are not known. By using slice cultures as a model, we have recently demonstrated that the laminated termination of hippocampal afferents does not result from the temporal sequence of ingrowth of the various afferent fibre systems during development. Moreover, the lack of extrinsic afferents in culture does not induce a substantial translaminar sprouting of the remaining (intrinsic) fibres or of a defined afferent system supplied by a coculture. These results contrast with previous reports on an expansion of intact fibre systems in the hippocampus in response to partial deafferentation, for instance by removal of entorhinal afferents. We therefore studied the sprouting of commissural fibres following an entorhinal lesion directly by labelling commissural axons in vivo with the anterogradely transported tracer Phaseolus vulgaris leucoagglutinin. Sprouting of commissural fibres following an entorhinal lesion was observed but, in accordance with our in vitro observations, this growth of commissural terminals took place within the appropriate termination zones of commissural fibres. These results point to a rigid laminar specificity of hippocampal afferents that is preserved after partial deafferentiation.

Animals↗

PubMed1994

Associational and commissural afferents of parvalbumin-immunoreactive neurons in the rat hippocampus: a combined immunocytochemical and PHA-L study.

Nonpyramidal neurons containing the calcium-binding protein parvalbumin (PV) are one of the inhibitory elements of the hippocampal network. Previous studies have indicated that they are involved in septohippocampal disinhibitory circuits. This study analyzes the commissural and ipsilateral associational afferents of parvalbumin neurons. Injections of the anterograde tracer Phaseolus vulgaris-leucoagglutinin (PHA-L) into the hilus of the fascia dentata labeled numerous axons in the molecular layer that established synaptic contacts with parvalbumin-immunoreactive neurons on both the injection and the contralateral side. Mossy fibers, labeled by injections into the granule cell layer, terminated on parvalbumin neurons in the hilus and in CA3. Injections of PHA-L into CA3 resulted in a dense labeling of fibers in the hilus and in CA3, CA2, and CA1 on both the injection and the contralateral side. In all these hippocampal fields, PHA-L-labeled fibers established asymmetric contacts with PV-immunoreactive, presumably GABAergic, inhibitory neurons. These observations indicate that parvalbumin-immunoreactive inhibitory neurons in the hippocampus are targets of presumably excitatory associational and commissural projections and suggest that they are involved in feed-forward and feed-back circuits.

Animals↗

PubMed1994

Reciprocal connections of lateral septal neurons and neurons in the lateral hypothalamus in the rat: a combined phaseolus vulgaris-leucoagglutinin and Fluoro-Gold immunocytochemical study.

Reciprocal connections between lateral septal neurons and neurons in the lateral hypothalamus/lateral preoptic area were studied in the rat. The anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L) and the retrograde tracer Fluoro-Gold (FG) were simultaneously injected into the lateral septum. After double-immunocytochemistry, PHA-L-labeled terminals were found in synaptic contact with dendrites of retrogradely FG-labeled neurons in the lateral hypothalamic/lateral preoptic area.

Afferent Pathways↗