Biomedical subjects

Trygve B Leergaard

Publications and source records attributed to Trygve B Leergaard.

7 recordsLinked to original sources

PubMed2006

Expression mapping of tetracycline-responsive prion protein promoter: digital atlasing for generating cell-specific disease models.

We present a digital atlas system that allows mapping of molecular expression patterns at cellular resolution through large series of histological sections. Using this system, we have mapped the distribution of a distinct marker, encoded by the LacZ reporter gene driven by the tetracycline-responsive prion protein promoter in double transgenic mice. The purpose is to evaluate the suitability of this promoter mouse line for targeting genes of interest to specific brain regions, essential for construction of inducible transgenic disease models. Following processing to visualize the promoter expression, sections were counterstained to simultaneously display cytoarchitectonics. High-resolution mosaic images covering entire coronal sections were collected through the mouse brain at intervals of 200 microm. A web-based application provides access to a customized virtual microscopy tool for viewing and navigation within and across the section images. For each section image, the nearest section in a standard atlas is defined, and annotations of key structures and regions inserted. Putative categorization of labeled cells was performed with use of distribution patterns, followed by cell size and shape, as parameters that were compared to legacy data. Among the ensuing results were expression of this promoter in putative glial cells in the cerebellum (and not in Purkinje cells), in putative glial cells in the substantia nigra, in pallidal glial cells or interneurons, and in distinct cell layers and regions of the hippocampus. The study serves as a precursor for a database resource allowing evaluation of the suitability of different promoter mouse lines for generating disease models.

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PubMed2006

Micro3D: computer program for three-dimensional reconstruction visualization, and analysis of neuronal populations and barin regions.

This article presents a computer program, Micro3D, designed for 3-D reconstruction, visualization, and analysis of coordinate-data (points and lines) recorded from serial sections. The software has primarily been used for studying shapes and dimension of brain regions (contour line data) and distributions of cellular elements such as neuronal cell bodies or axonal terminal fields labeled with tract-tracing techniques (point data). The tissue elements recorded could equally well be labeled with use of other techniques, the only requirement being that the data collected are saved as x,y,z coordinates. Data are typically imported from image-combining computerized microscopy systems or image analysis systems, such as Neurolucida (MicroBrightField, Colchester, VT) or analySIS (Soft Imaging System, Gmbh, Münster, Germany). System requirements are a PC running LINUX. Reconstructions in Micro3D may be rotated and zoomed in real-time, and submitted to perspective viewing and stereo-imaging. Surfaces are re-synthesized on the basis of stacks of contour lines. Clipping is used for defining section-independent subdivisions of the reconstruction. Flattening of curved sheets of points layers (e.g., neurons in a layer) facilitates inspection of complicated distribution patterns. Micro3D computes color-coded density maps. Opportunities for translation of data from different reconstructions into common coordinate systems are also provided. This article demonstrates the use of Micro3D for visualization of complex neuronal distribution patterns in somatosensory and auditory systems. The software is available for download on conditions posted at the NeSys home pages (http://www.nesys.uio.no/) and at The Rodent Brain Workbench (http://www.rbwb.org/).

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PubMed2006

Topographical organization of pathways from somatosensory cortex through the pontine nuclei to tactile regions of the rat cerebellar hemispheres.

The granule cell layer of the cerebellar hemispheres contains a patchy and noncontinuous map of the body surface, consisting of a complex mosaic of multiple perioral tactile representations. Previous physiological studies have shown that cerebrocerebellar mossy fibre projections, conveyed through the pontine nuclei, are mapped in registration with peripheral tactile projections to the cerebellum. In contrast to the fractured cerebellar map, the primary somatosensory cortex (SI) is somatotopically organized. To understand better the map transformation occurring in cerebrocerebellar pathways, we injected axonal tracers in electrophysiologically defined locations in Sprague-Dawley rat folium crus IIa, and mapped the distribution of retrogradely labelled neurons within the pontine nuclei using three-dimensional (3-D) reconstructions. Tracer injections within the large central upper lip patch in crus IIa-labelled neurons located centrally in the pontine nuclei, primarily contralateral to the injected side. Larger injections (covering multiple crus IIa perioral representations) resulted in labelling extending only slightly beyond this region, with a higher density and more ipsilaterally labelled neurons. Combined axonal tracer injections in upper lip representations in SI and crus IIa, revealed a close spatial correspondence between the cerebropontine terminal fields and the crus IIa projecting neurons. Finally, comparisons with previously published three-dimensional distributions of pontine neurons labelled following tracer injections in face receiving regions in the paramedian lobule (downloaded from http://www.rbwb.org) revealed similar correspondence. The present data support the coherent topographical organization of cerebro-ponto-cerebellar networks previously suggested from physiological studies. We discuss the present findings in the context of transformations from cerebral somatotopic to cerebellar fractured tactile representations.

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PubMed2004

Three-dimensional topography of corticopontine projections from rat sensorimotor cortex: comparisons with corticostriatal projections reveal diverse integrative organization.

The major cortical-subcortical re-entrant pathways through the basal ganglia and cerebellum are considered to represent anatomically segregated channels for information originating in different cortical areas. A capacity for integrating unique combinations of cortical inputs has been well documented in the basal ganglia circuits but is largely undefined in the precerebellar circuits. To compare and quantify the amount of overlap that occurs in the first link of the cortico-ponto-cerebellar pathway, a dual tracing approach was used to map the spatial relationship between projections originating from the primary somatosensory cortex (SI), the secondary somatosensory cortex (SII), and the primary motor cortex (MI). The anterograde tracers biotinylated dextran amine and Fluoro-Ruby were injected into homologous whisker representations of either SI and SII, or SI and MI. The ensuing pontine labeling patterns were analyzed using a computerized three-dimensional reconstruction approach. The results demonstrate that whisker-related projections from SI and MI are largely segregated. At some locations, the two projections are adjoining and partly overlapping. Furthermore, SI contributes significantly more corticopontine projections than MI. By comparison, projections from corresponding representations in SI and SII terminate in similar parts of the pontine nuclei and display considerable amounts of spatial overlap. Finally, comparison of corticopontine and corticostriatal projections in the same experimental animals reveals that SI-SII overlap is significantly larger in the pontine nuclei than in the neostriatum. These structural differences indicate a larger capacity for integration of information within the same sensory modality in the pontocerebellar system compared to the basal ganglia.

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PubMed2003

In vivo tracing of major rat brain pathways using manganese-enhanced magnetic resonance imaging and three-dimensional digital atlasing.

The magnetic resonance imaging (MRI)-detectable T1 contrast agent manganese (Mn2+) has recently been introduced as a neural tracer in rodents, birds, and monkeys. We have tested to what extent this in vivo method is useful for three-dimensional (3-D) survey of connectivity patterns in the rat somatosensory system. A commonly available 3 T human clinical MRI scanner was used to trace neural pathways following focal injection of manganese chloride (MnCl2) in the somatosensory cortex. Six to 10 h after MnCl2 injection, we found significant signal enhancement in major projection systems, including corticocortical, corticostriatal, corticothalamic, corticotectal, corticopontine, and corticospinal pathways. To facilitate the assignment of anatomic localization to the observed Mn2+ signal enhancement, we registered the MRI data with a 3-D digital reconstruction of a stereotaxic rat brain atlas. Across-animal comparison using the digital model allowed demonstration of a corticothalamic 3-D topographic organization in agreement with previously published two-dimensional topographic schemes based on classical neural tracing data. We conclude that anterograde MnCl2/MRI tracing allows rapid analysis of topographic organization across multiple brain regions. The method allows a higher data throughput for 3-D studies of large-scale brain connectivity than conventional methods based on tissue sectioning.

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PubMed2002

Clustered and laminar topographic patterns in rat cerebro-pontine pathways.

Novel neuroanatomic approaches for investigating topographic maps at a systems level include combined use of sensitive neural tracing techniques and computerized methods for three-dimensional reconstruction from serial sections. Application of these methods have allowed discovery of new principles of topographic organization in the rat pontine nuclei. The pontine nuclei are intercalated in the large pathways connecting the cerebral cortex to the cerebellum. In rat, cerebropontine projections are characterized by multiple delineated terminal fields. It is generally accepted that these projections are topographically organized. The presence of widespread axonal clusters in the pontine nuclei is typically interpreted to represent a complex scheme of organization. In recent anatomic investigations of somatosensory corticopontine projections in young and adult rats, a somatotopic distribution of axonal clusters, concentrically organized in an inside-out fashion, has been reported. This review summarizes the topographic principles of organization proposed for somatosensory corticopontine projections, and discusses the possibility that widely segregated corticopontine terminal fields are located inside lamellar volumes. This organizational pattern may be explained by mechanisms operative during development, and resembles the patterns of organization previously described in cat and monkey. Possible implications of this architecture are discussed in relation to map transformations from the cerebral cortex to the cerebellum.

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PubMed2002

Comparison of semi-automatic and automatic data acquisition methods for studying three-dimensional distributions of large neuronal populations and axonal plexuses.

Neuroanatomy is in need of high throughput methods for reliably recording the distribution of tissue elements across large brain regions. We compared two methods for recording the spatial distribution of identified neuronal elements such as tracer labelled cell bodies or axonal plexuses. The methods compared were computerized image-combining microscopy (semi-automatic method), which is a user controlled method providing feedback during digitization, and digital camera technology with image analysis software (automatic method). Both methods were applied to biotinylated dextran amine labelled axonal plexuses and FluoroRuby labelled neuronal cell bodies, in the pontine nuclei of the rat. Coordinates were assigned to the labelled elements using both methods. The ensuing distribution patterns were compared, section by section, and in three-dimensional reconstruction. The experienced investigator, using the semi-automatic method, could detect individual axons, fragments of axons, weakly labelled elements, and overlapping cell bodies, better than the automatic system. Nevertheless, both methods detected the overall distribution of the labelled axons and cells investigated. Automatic methods provide opportunities for efficient large-scale data acquisition of labelled neuronal elements.

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