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Michael Frotscher - One of the best experts on this subject based on the ideXlab platform.

  • Organization of identified Fiber tracts in the rat fimbria-fornix: an anterograde tracing and electron microscopic study.
    Anatomy and embryology, 1996
    Co-Authors: G. Adelmann, Thomas Deller, Michael Frotscher
    Abstract:

    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.

  • Heterogeneity of the Commissural projection to the rat dentate gyrus: a Phaseolus vulgaris leucoagglutinin tracing study
    Neuroscience, 1996
    Co-Authors: Thomas Deller, Robert Nitsch, Michael Frotscher
    Abstract:

    Abstract 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.

  • Morphological evidence for the sprouting of inhibitory Commissural Fibers in response to the lesion of the excitatory entorhinal input to the rat dentate gyrus.
    The Journal of neuroscience : the official journal of the Society for Neuroscience, 1995
    Co-Authors: Thomas Deller, Michael Frotscher, R Nitsch
    Abstract:

    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.

  • Phaseolus vulgaris –leucoagglutinin tracing of Commissural Fibers to the rat dentate gyrus: Evidence for a previously unknown Commissural projection to the outer molecular layer
    The Journal of comparative neurology, 1995
    Co-Authors: Thomas Deller, Robert Nitsch, Michael Frotscher
    Abstract:

    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.

Thomas Deller - One of the best experts on this subject based on the ideXlab platform.

  • Organization of identified Fiber tracts in the rat fimbria-fornix: an anterograde tracing and electron microscopic study.
    Anatomy and embryology, 1996
    Co-Authors: G. Adelmann, Thomas Deller, Michael Frotscher
    Abstract:

    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.

  • Heterogeneity of the Commissural projection to the rat dentate gyrus: a Phaseolus vulgaris leucoagglutinin tracing study
    Neuroscience, 1996
    Co-Authors: Thomas Deller, Robert Nitsch, Michael Frotscher
    Abstract:

    Abstract 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.

  • Morphological evidence for the sprouting of inhibitory Commissural Fibers in response to the lesion of the excitatory entorhinal input to the rat dentate gyrus.
    The Journal of neuroscience : the official journal of the Society for Neuroscience, 1995
    Co-Authors: Thomas Deller, Michael Frotscher, R Nitsch
    Abstract:

    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.

  • Phaseolus vulgaris –leucoagglutinin tracing of Commissural Fibers to the rat dentate gyrus: Evidence for a previously unknown Commissural projection to the outer molecular layer
    The Journal of comparative neurology, 1995
    Co-Authors: Thomas Deller, Robert Nitsch, Michael Frotscher
    Abstract:

    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.

Robert Nitsch - One of the best experts on this subject based on the ideXlab platform.

  • Heterogeneity of the Commissural projection to the rat dentate gyrus: a Phaseolus vulgaris leucoagglutinin tracing study
    Neuroscience, 1996
    Co-Authors: Thomas Deller, Robert Nitsch, Michael Frotscher
    Abstract:

    Abstract 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.

  • Phaseolus vulgaris –leucoagglutinin tracing of Commissural Fibers to the rat dentate gyrus: Evidence for a previously unknown Commissural projection to the outer molecular layer
    The Journal of comparative neurology, 1995
    Co-Authors: Thomas Deller, Robert Nitsch, Michael Frotscher
    Abstract:

    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.

Nicola De Stefano - One of the best experts on this subject based on the ideXlab platform.

  • relevance of brain lesion location to cognition in relapsing multiple sclerosis
    PLOS ONE, 2012
    Co-Authors: Francesca De Rossi, Antonio Giorgio, Marco Battaglini, Maria Laura Stromillo, Emilio Portaccio, Benedetta Goretti, Antonio Federico, Bahia Hakiki, Maria Pia Amato, Nicola De Stefano
    Abstract:

    Objective To assess the relationship between cognition and brain white matter (WM) lesion distribution and frequency in patients with relapsing-remitting multiple sclerosis (RR MS). Methods MRI-based T2 lesion probability map (LPM) was used to assess the relevance of brain lesion location for cognitive impairment in a group of 142 consecutive patients with RRMS. Significance of voxelwise analyses was p<0.05, cluster-corrected for multiple comparisons. The Rao Brief Repeatable Battery was administered at the time of brain MRI to categorize the MS population into cognitively preserved (CP) and cognitively impaired (CI). Results Out of 142 RRMS, 106 were classified as CP and 36 as CI. Although the CI group had greater WM lesion volume than the CP group (p = 0.001), T2 lesions tended to be less widespread across the WM. The peak of lesion frequency was almost twice higher in CI (61% in the forceps major) than in CP patients (37% in the posterior corona radiata). The voxelwise analysis confirmed that lesion frequency was higher in CI than in CP patients with significant bilateral clusters in the forceps major and in the splenium of the corpus callosum (p<0.05, corrected). Low scores of the Symbol Digit Modalities Test correlated with higher lesion frequency in these WM regions. Conclusions Overall these results suggest that in MS patients, areas relevant for cognition lie mostly in the Commissural Fiber tracts. This supports the notion of a functional (multiple) disconnection between grey matter structures, secondary to damage located in specific WM areas, as one of the most important mechanisms leading to cognitive impairment in MS.

  • Relevance of brain lesion location to cognition in relapsing multiple sclerosis
    2012
    Co-Authors: Francesca De Rossi, Antonio Giorgio, Marco Battaglini, Maria Laura Stromillo, Emilio Portaccio, Benedetta Goretti, Antonio Federico, Bahia Hakiki, Maria Pia Amato, Nicola De Stefano
    Abstract:

    Objective: To assess the relationship between cognition and brain white matter (WM) lesion distribution and frequency in patients with relapsing-remitting multiple sclerosis (RR MS). Methods: MRI-based T2 lesion probability map (LPM) was used to assess the relevance of brain lesion location for cognitive impairment in a group of 142 consecutive patients with RRMS. Significance of voxelwise analyses was p,0.05, cluster-corrected for multiple comparisons. The Rao Brief Repeatable Battery was administered at the time of brain MRI to categorize the MS population into cognitively preserved (CP) and cognitively impaired (CI). Results: Out of 142 RRMS, 106 were classified as CP and 36 as CI. Although the CI group had greater WM lesion volume than the CP group (p = 0.001), T2 lesions tended to be less widespread across the WM. The peak of lesion frequency was almost twice higher in CI (61 % in the forceps major) than in CP patients (37 % in the posterior corona radiata). The voxelwise analysis confirmed that lesion frequency was higher in CI than in CP patients with significant bilateral clusters in the forceps major and in the splenium of the corpus callosum (p,0.05, corrected). Low scores of the Symbol Digit Modalities Test correlated with higher lesion frequency in these WM regions. Conclusions: Overall these results suggest that in MS patients, areas relevant for cognition lie mostly in the Commissural Fiber tracts. This supports the notion of a functional (multiple) disconnection between grey matter structures, secondary t

Thomas Meier - One of the best experts on this subject based on the ideXlab platform.

  • Organization of the Commissural Fibers in the adult brain of the locust.
    The Journal of comparative neurology, 1993
    Co-Authors: George Boyan, Leslie Williams, Thomas Meier
    Abstract:

    The brain (supraoesophageal ganglion) is the most complex of the segmental ganglia composing the nerve cord of the locusts Schistocerca gregaria and Locusta migratoria. In this paper, we describe the ground plan of the commissures crossing the midline of the brain and propose a nomenclature with the aim of making a complex neuropil more understandable at the level of individual neurons. For developmental and comparative reasons the neuroarchitecture of the brain is related to the neural axis, not to the body axis. We have identified 73 Commissural Fiber bundles belonging to the adult brain, and these are named according to their location (ventral, dorsal, anterior, posterior, medial) with respect to the central complex as reference point. Reconstructions of identified neurons from intracellular stainings, cobalt backfills, or immunohistochemical studies demonstrate the various configurations in which Fibers cross the brain.