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J G Bjaalie

Publications and source records attributed to J G Bjaalie.

At least 19 recordsLinked to original sources
PubMed2005

Three-dimensional chemoarchitecture of the basal forebrain: spatially specific association of cholinergic and calcium binding protein-containing neurons.

The basal forebrain refers to heterogeneous structures located close to the medial and ventral surfaces of the cerebral hemispheres. It contains diverse populations of neurons, including the cholinergic cortically projecting cells that show severe loss in Alzheimer's and related neurodegenerative diseases. The basal forebrain does not display any cytoarchitectural or other structural features that make it easy to demarcate functional boundaries, a problem that allowed different investigators to propose different organizational schemes. The present paper uses novel three-dimensional reconstructions and numerical analyses for studying the spatial organization of four major basal forebrain cell populations, the cholinergic, parvalbumin, calbindin and calretinin containing neurons in the rat. Our analyses suggest that the distribution of these four cell populations is not random but displays a general pattern of association. Within the cholinergic space (i.e. the volume occupied by the cortically projecting cholinergic cell bodies) the three other cell types form twisted bands along the longitudinal axis of a central dense core of cholinergic cells traversing the traditionally defined basal forebrain regions, (i.e. the medial septum, diagonal bands, the substantia innominata, pallidal regions and the bed nucleus of the stria terminalis). At a smaller scale, the different cell types within the cholinergic space occupy overlapping high-density cell clusters that are either chemically uniform or mixed. However, the cell composition of these high-density clusters is regionally specific. The proposed scheme of basal forebrain organization, using cell density or density relations as criteria, offers a new perspective on structure-function relationship, unconstrained by traditional region boundaries.

Acetylcholine↗
PubMed2005

Database and tools for analysis of topographic organization and map transformations in major projection systems of the brain.

Integration of dispersed and complicated information collected from the brain is needed to build new knowledge. But integration may be hampered by rigid presentation formats, diversity of data formats among laboratories, and lack of access to lower level data. We have addressed some of the fundamental issues related to this challenge at the level of anatomical data, by producing a coordinate based digital atlas and database application for a major projection system in the rat brain: the cerebro-ponto-cerebellar system. This application, Functional Anatomy of the Cerebro-Cerebellar System in rat (FACCS), is available via the Rodent Brain WorkBench (http://www.rbwb.org). The data included are x,y,z-coordinate lists describing exact distributions of tissue elements (axonal terminal fields of axons, or cell bodies) that are labeled with axonal tracing techniques. All data are translated to a common local coordinate system to facilitate across animal comparison. A search capability allows queries based on, e.g. location of tracer injection sites, tracer category, size of the injection sites, and contributing author. A graphic search tool allows the user to move a volume cursor inside a coordinate system to detect particular injection sites having connections to a specific tissue volume at chosen density levels. Tools for visualization and analysis of selected data are included, as well as an option to download individual data sets for further analysis. With this application, data and metadata from different experiments are mapped into the same information structure and made available for re-use and re-analysis in novel combinations. The application is prepared for future handling of data from other projection systems as well as other data categories.

Anatomy, Artistic↗
PubMed2001

A dendrodendritic reciprocal synapse provides a recurrent excitatory connection in the olfactory bulb.

Neuronal synchronization in the olfactory bulb has been proposed to arise from a diffuse action of glutamate released from mitral cells (MC, olfactory bulb relay neurons). According to this hypothesis, glutamate spills over from dendrodendritic synapses formed between MC and granule cells (GC, olfactory bulb interneurons) to activate neighboring MC. The excitation of MC is balanced by a strong inhibition from GC. Here we show that MC excitation is caused by glutamate released from bulbar interneurons located in the GC layer. These reciprocal synapses depend on an unusual, 2-amino-5-phosphonovaleric acid-resistant, N-methyl-d-aspartate receptor. This type of feedback excitation onto relay neurons may strengthen the original sensory input signal and further extend the function of the dendritic microcircuit within the main olfactory bulb.

2-Amino-5-phosphonovalerate↗
PubMed2001

Three-dimensional computerised atlas of the rat brain stem precerebellar system: approaches for mapping, visualization, and comparison of spatial distribution data.

Comparisons of microscopical neuroanatomic data from different experiments and investigators are typically hampered by the use of different section planes and dissimilar techniques for data documentation. We have developed a framework for visualization and comparison of section-based, spatial distribution data, in brain stem nuclei. This framework provides opportunities for harmonized data presentation in neuroinformatics databases. Three-dimensional computerized reconstructions of the rat brain stem and precerebellar nuclei served as a basis for establishing internal coordinate systems for the pontine nuclei and the precerebellar divisions of the sensory trigeminal nuclei. Coordinate based diagrams were used for presentation of experimental data (spatial distribution of labelled neurons and axonal plexuses) from standard angles of view. Each nuclear coordinate system was based on a cuboid bounding box with a defined orientation. The bounding box was size-adjusted to touch cyto- and myeloarchitectonically defined boundaries of the individual nuclei, or easily identifiable nearby landmarks. We exemplify the use of these internal coordinate systems with dual retrograde neural tracing data from pontocerebellar and trigeminocerebellar systems. The new experimental data were combined, in the same coordinate based diagrams, with previously published data made available via a neuroinformatics data repository (www.nesys.uio.no/Database, see also www.cerebellum.org). Three-dimensional atlasing, internal nuclear coordinate systems, and consistent formats for presentation of neuroanatomic data in web-based data repositories, offer new opportunities for efficient analysis and re-analysis of neuroanatomic data.

Animals↗
PubMed2000

Three-dimensional topography of corticopontine projections from rat barrel cortex: correlations with corticostriatal organization.

Subcortical re-entrant projection systems connecting cerebral cortical areas with the basal ganglia and cerebellum are topographically specific and therefore considered to be parallel circuits or "closed loops." The precision of projections within these circuits, however, has not been characterized sufficiently to indicate whether cortical signals are integrated within or among presumed compartments. To address this issue, we studied the first link of the rat cortico-ponto-cerebellar pathway with anterograde axonal tracing from physiologically defined, individual whisker "barrels" of the primary somatosensory cortex (SI). The labeled axons in the pontine nuclei formed several, sharply delineated clusters. Dual tracer injections into different SI whisker barrels gave rise to partly overlapping, paired clusters, indicating somatotopic specificity. Three-dimensional reconstructions revealed that the clusters were components of concentrically organized lamellar subspaces. Whisker barrels in the same row projected to different pontine lamellae (side by side), the somatotopic representation of which followed an inside-out sequence. By contrast, whisker barrels from separate rows projected to clusters located within the same lamellar subspace (end to end). In the neostriatum, this lamellar topography was the opposite, with barrels in the same row contacting different parts of the same lamellar subspace (end to end). The degree of overlap among pontine clusters varied as a function of the proximity of the cortical injections. Furthermore, corticopontine overlap was higher among projections from barrels in the same row than among projections from different whisker barrel rows. This anisotropy was the same in the corticostriatal projection. These findings have important implications for understanding convergence and local integration in somatosensory-related subcortical circuits.

Animals↗
PubMed2000

Rat somatosensory cerebropontocerebellar pathways: spatial relationships of the somatotopic map of the primary somatosensory cortex are preserved in a three-dimensional clustered pontine map.

In the primary somatosensory cortex (SI), the body surface is mapped in a relatively continuous fashion, with adjacent body regions represented in adjacent cortical domains. In contrast, somatosensory maps found in regions of the cerebellar hemispheres, which are influenced by the SI through a monosynaptic link in the pontine nuclei, are discontinuous ("fractured") in organization. To elucidate this map transformation, the authors studied the organization of the first link in the SI-cerebellar pathway, the SI-pontine projection. After injecting anterograde axonal tracers into electrophysiologically defined parts of the SI, three-dimensional reconstruction and computer-graphic visualization techniques were used to analyze the spatial distribution of labeled fibers. Several target regions in the pontine nuclei were identified for each major body representation. The labeled axons formed sharply delineated clusters that were distributed in an inside-out, shell-like fashion. Upper lip and other perioral representations were located in a central core, whereas extremity and trunk representations were found more externally. The multiple clusters suggest that the pontine nuclei contain several representations of the SI map. Within each representation, the spatial relationships of the SI map are largely preserved. This corticopontine projection pattern is compatible with recently proposed principles for the establishment of subcortical topographic patterns during development. The largely preserved spatial relationships in the pontine somatotopic map also suggest that the transformation from an organized topography in SI to a fractured map in the cerebellum takes place primarily in the mossy fiber pontocerebellar projection.

Animals↗
PubMed1999

Topographic organization of the dorsal nucleus of the lateral lemniscus in the cat.

The dorsal nucleus of the lateral lemniscus (DNLL) is an auditory structure of the brainstem. It plays an important role in binaural processing and sound localization and it provides the inferior colliculus with an inhibitory projection. The DNLL is a highly conserved auditory structure across mammals, but differences among species in its detailed organization have been reported. The main goal of this study was to analyze the topographic organization of the cat DNLL. Single, small iontophoretic injections of biotinylated dextran amine were made at different loci in the central nucleus of the inferior colliculus (CNIC). The distribution of the labeled structures in the ipsi- and contralateral DNLL was computer reconstructed in three dimensions. In individual sections, a band of labeling is seen in the DNLL on both sides. These two labeled bands occupy symmetric locations and are made of retrogradely labeled neurons with flattened dendritic arbors oriented parallel to each other. Moreover, the ipsilateral labeled band contains labeled terminal fibers parallel to the labeled dendrites. With three-dimensional reconstructions, it becomes evident that the labeled band seen in each individual DNLL section represents a slice through a rostrocaudally oriented lamina. The shape, size, orientation, and location of this lamina change as the injection site is shifted along the tonotopic axis of the CNIC. An injection in the low-frequency region of the CNIC, produces a lamina that resembles a flattened tube located in the dorsolateral corner of the DNLL. An injection in the high-frequency region of the CNIC, by contrast, results in a lamina that is an elongated sheet located at the ventromedial surface of the DNLL. The laminae of the DNLL might constitute the structural basis for its tonotopical organization. Previous studies (Merchan MA, et al. 1994. J Comp Neurol 342:259-278) in conjunction with our current results suggest that the laminar organization in the DNLL might be common among mammals.

Animals↗
PubMed1999

Monkey somatosensory cerebrocerebellar pathways: uneven densities of corticopontine neurons in different body representations of areas 3b, 1, and 2.

We have studied the anatomic organization of corticopontine neurons in the monkey cytoarchitectonic areas 3a, 3b, 1, and 2. The purpose was to provide information about the composition of somatosensory cortical influence on cerebellar operations. Large tracer injections were made in the pontine nuclei. Retrogradely labeled neurons were confined to cortical layer 5, with the largest cell bodies located in area 3a and the smallest in area 3b. The distribution of labeled cells was quantitatively recorded and displayed in three-dimensional reconstructions and in flat maps. We have: (1) compared the average densities of labeled cells among the cytoarchitectonic areas, and (2) outlined the distribution of labeled cells within the cortical map of the body surface representation. The average density of labeled cells was considerably higher in areas 3a, 1, and 2, compared to area 3b. This finding suggests that areas 3a, 1, and 2 are more engaged in cerebellar operations than area 3b. We found marked density gradients of labeled cells within areas 3b, 1, and 2, but not within area 3a. When the density maps from areas 3b, 1, and 2 were superimposed on previously published somatotopic maps, we found higher average densities of corticopontine neurons in regions representing the trunk and proximal limbs, than in regions representing the distal forelimb. Thus, the distal forelimb representation, which is known to be strongly emphasized in terms of cortical volume, appears not to be correspondingly emphasized in the corticopontine projection.

Animals↗
PubMed1999

Spatial correspondence between tactile projection patterns and the distribution of the antigenic Purkinje cell markers anti-zebrin I and anti-zebrin II in the cerebellar folium crus IIA of the rat.

We have compared the band-like distribution of the Purkinje cell-specific polypeptides zebrin I and zebrin II with the spatial organization of tactile projections to crus IIa in the cerebellar hemisphere of the rat. Maps of tactile responses in the granular layer of the cerebellar hemispheres are fractured into discontinuous regions, termed "patches". High-density micromapping was used to identify specific patches and their boundaries within this fractured somatotopic map. In one series of experiments, medial and lateral boundaries of the large central ipsilateral upper lip-related patch were identified and labeled with either Fast Blue or India Ink. Following immunocytochemical processing, the band-like distribution of immunostained Purkinje cells (zebrin-positive bands) and the identified patch boundaries were digitized and reconstructed in three dimensions. Comparisons between these two features demonstrate a spatial correspondence between zebrin transitions and the boundaries of the electrophysiologically defined upper lip-related patch. In another series of experiments, we outlined the boundaries or centers of several smaller patches consistently located in the medial portion of the folium. Again, we found a correspondence between the distribution of granule cell layer tactile patches and the zebrin staining pattern. The correspondence between tactile projection patterns and molecular features demonstrated in the present study implies that there is a distinct and largely fixed spatial pattern of organization in the cerebellar hemispheres. We discuss possible causal connections and developmental determinates, as well as the physiological significance of the correspondence between the two features.

Afferent Pathways↗
PubMed1998

Anatomic evidence of a three-dimensional mosaic pattern of tonotopic organization in the ventral complex of the lateral lemniscus in cat.

The ventral complex of the lateral lemniscus (VCLL, i.e., the ventral and intermediate nuclei) is composed of cells embedded in the fibers of the lateral lemniscus. These cells are involved in the processing of monaural information and receive input from the collaterals of the fibers ascending to the inferior colliculus. Whereas tonotopic organization is a feature of all other nuclei of the auditory system, this functional principle is debated in the VCLL. We have made focal injections of the tracer biotinylated dextran amine into different frequency band representations of the inferior colliculus in cat. Retrogradely labeled cells and terminal fibers (collaterals of efferent local axons and other ascending lemniscal fibers) were found in the ipsilateral VCLL. The spatial distribution of the labeling was analyzed using three-dimensional (3-D) reconstruction and computer graphical visualization techniques. A complex topographic organization was found. In all cases, labeled fibers and cells were distributed in multiple clusters throughout the dorsoventral extent of the VCLL. The shape, size, and location of the labeled clusters suggest an interdigitation of clusters assigned to different frequency-band representations. But an overall mediolateral distribution gradient was observed, with high frequencies represented medially and lower frequencies progressively more laterally. We conclude that the clusters may represent discontinuous frequency-band compartments as a counterpart to the continuous laminar compartments in the remaining auditory nuclei. The 3-D orderly mosaic pattern indicates that the VCLL preserves the spectral decomposition originated in the cochlea in a way that facilitates across-frequency integration.

Animals↗
PubMed1998

Synaptic vesicular localization and exocytosis of L-aspartate in excitatory nerve terminals: a quantitative immunogold analysis in rat hippocampus.

To elucidate the role of aspartate as a signal molecule in the brain, its localization and those of related amino acids were examined by light and electron microscopic quantitative immunocytochemistry using antibodies specifically recognizing the aldehyde-fixed amino acids. Rat hippocampal slices were incubated at physiological and depolarizing [K+] before glutaraldehyde fixation. At normal [K+], aspartate-like and glutamate-like immunoreactivities were colocalized in nerve terminals forming asymmetrical synapses on spines in stratum radiatum of CA1 and the inner molecular layer of fascia dentata (i.e., excitatory afferents from CA3 and hilus, respectively). During K+ depolarization there was a loss of aspartate and glutamate from these terminals. Simultaneously the immunoreactivities strongly increased in glial cells. These changes were Ca2+-dependent and tetanus toxin-sensitive and did not comprise taurine-like immunoreactivity. Adding glutamine at CSF concentration prevented the loss of aspartate and glutamate and revealed an enhancement of aspartate in the terminals at moderate depolarization. In hippocampi from animals perfused with glutaraldehyde during insulin-induced hypoglycemia (to combine a strong aspartate signal with good ultrastructure) aspartate was colocalized with glutamate in excitatory terminals in stratum radiatum of CA1. The synaptic vesicle-to-cytoplasmic matrix ratios of immunogold particle density were similar for aspartate and glutamate, significantly higher than those observed for glutamine or taurine. Similar results were obtained in normoglycemic animals, although the nerve terminal contents of aspartate were lower. The results indicate that aspartate can be concentrated in synaptic vesicles and subject to sustained exocytotic release from the same nerve endings that contain and release glutamate.

Aminooxyacetic Acid↗
PubMed1997

Corticopontine terminal fibres form small scale clusters and large scale lamellae in the cat.

We investigated whether terminal fibres in the pontine nuclei are arranged in a lamellar pattern like that demonstrated earlier for pontocerebellar neurones. Following tracer injections in visual and parietal cortices and subsequent computer-based 3-D analysis, we found that labelled corticopontine terminal fibres form numerous sharply delimited aggregates of variable shape. Several of the aggregates are cylindroids (diameter 200-300 microns, length 1-3 mm). The aggregates are confined to a lamellar subspace, the position of which depends on the anteroposterior location of the cortical injections. These findings suggest that the cerebroponto-cerebellar system may be organized according to fairly simple, topographical rules. We discuss the implications of our results in relation to the development of corticopontine topographical organization.

Animals↗
PubMed1997

Salient anatomic features of the cortico-ponto-cerebellar pathway.

Recent studies of the primate corticopontine projection show that the neocerebellum--in addition to connections from motor and sensory areas--receives connections from various association areas of the cerebral cortex, some of which are thought to be primarily engaged in cognitive tasks. The quantities of such connections in relation to those from more clearly motor-related parts of the cortex need to be more precisely determined, however. Furthermore, the anatomic data on origin of corticopontine fibers needs to be supplemented with physiological experiments to clarify their functional properties at the single-cell level. For example, nothing is known of the functional role of the large input from the cingulate gyrus, nor is the input from the posterior parietal cortex physiologically characterized. Finally, the scarcity of corticopontine connections from the prefrontal cortex in the monkey (and probably also in man) may not seem readily compatible with a prominent role of the neocerebellum in certain cognitive tasks. We discuss data--in particular from three-dimensional reconstructions--indicating that both corticopontine projects and pontocerebellar neurons are arranged in a lamellar pattern. Corticopontine and pontocerebellar lamellae have similar shapes and orientations but appear to differ in other respects. Corticopontine terminal fields are sharply delimited, apparently without gradual overlap between projections from different sites in the cortex, whereas pontocerebellar lamellae are more fuzzy and exhibit gradual overlap of neuronal populations projecting to different targets. In spite of the sharpness of the corticopontine projection, there may be many opportunities for convergence of inputs from different parts of the cortex. Thus, the wide divergence of corticopontine projections produces many sites of overlap, and extensive interfaces between different terminal fields enabling convergence of inputs onto each neuron. We suggest that the lamellar arrangement of corticopontine terminal fields and of pontocerebellar neurons serve to create diversity of pontocerebellar neuronal properties. Thus, each small part of the cerebellar cortex would receive a specific combination of messages from many different sites in the cerebral cortex. The spatial arrangement of cerebrocerebellar connections have to be understood both in terms of fairly simple large-scale, gradual topographic relationships and an apparently highly complex pattern of divergence and convergence. Developmental studies of corticopontine and of pontocerebellar projections together with three-dimensional reconstructions in adults suggest that the highly complex adult connectional pattern may be created by simple rules operating during development.

Animals↗
PubMed1997

Cat pontocerebellar network: numerical capacity and axonal collateral branching of neurones in the pontine nuclei projecting to individual parafloccular folia.

We have studied the convergence and divergence in the pontocerebellar pathway. Two or three different fluorescent tracers were injected in separate folia of the parafloccular complex. Retrogradely labelled cells were quantitatively recorded. The estimated total number of labelled neurones in the pontine nuclei contralateral to the injection sites was 18000 (median; range 5000-46000; 14 cell populations, six animals). Using stereological principles, the total number of neurones on one side in the pontine nuclei was estimated to be 490000 (mean; n = 6). Thus, approximately 4% of the total number of neurones in the pontine nuclei would project to a single parafloccular folium. Assuming that the highest estimates of labelled cells are the most representative, the proportion would be 9%. Considering that the volume injected makes up a tiny fraction of the total cerebellar cortical volume, these figures reflect an extreme convergence. After injections in adjacent folia we observed 19-27% double labelling. The double labelling frequency dropped steeply with increasing distance between injections. The strong convergence and limited local axonal branching suggest the existence of extensive branching to widely separated cerebellar regions.

Animals↗