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M Rydmark

Publications and source records attributed to M Rydmark.

18 recordsLinked to original sources
PubMed1995

Axonal constriction at Ranvier's node increases during development.

We have studied the ratio between the nodal and the internodal diameter (the dn/d(in) ratio) of large myelinated axons in the L7 ventral spinal root of the cat during pre- and postnatal development using light and electron microscopy. A substantial nodal constriction, dn/d(in) = 0.6, was found at the beginning of myelination, about 2 weeks before birth. The ratio decreased during the subsequent 10 weeks and approached the adult value of 0.47 (SE 0.01, N = 45) in the 8 weeks old kitten. The observations are discussed with respect to the maturation of the nodal region and to our earlier idea that the constricted nodal axon segments of large peripheral myelinated nerve fibres of adult cats and kittens 2 months and more of age are sites capable of interacting with and perhaps even controlling the passage of axonally transported materials.

Age Factors↗
PubMed1995

Automated correction of linear deformation due to sectioning in serial micrographs.

This paper describes an objective and automatic method for detection and correction of sectioning deformations in digitized micrographs, as well as an evaluation of the method applied to light and electron microscopic images of semi-thin and ultra-thin serial sections from brain cortex. The detection is based on matching of image subregions and the deformation model is bi-linear, i.e. two first-order polynomials are used for modelling compression/expansion in perpendicular directions. The procedure is applicable to prealigned serial two-dimensional sections and is primarily aimed at three-dimensional reconstruction of tissue samples consisting of a large number of cells with random distribution and morphology.

Animals↗
PubMed1994

Dimensions of individual alpha and gamma motor fibres in the ventral funiculus of the cat spinal cord.

Using light and electron microscopy, axon diameter, myelin sheath thickness (measured as number of myelin lamellae) and internodal length of alpha and gamma motor axons of the L7 ventral root and spinal cord segment were investigated in serial cross-sections. The CNS internodes of the alpha motor fibres had, on average, an axon diameter of 8.6 microns, 105 myelin lamellae and a length of about 560 microns. The CNS internodes of the gamma motor fibres had, on average, an axon diameter of 3.4 microns, 66 myelin lamellae and a length of about 440 microns. Axon diameter at the nodes of Ranvier was 30-40% of the internodal axon diameter. Axon diameter, number of myelin lamellae and internodal length varied considerably between consecutive internodes. Statistical analysis showed no systematic increases or decreases. Regression analyses of the scatter plots of the number of myelin lamellae and internodal length against axon diameter showed large variations and correlation coefficients of r < 0.50. In conformity with ventral root (PNS) internodes (Nilsson & Berthold, 1988) the plotting of intrafunicular (CNS) internodal myelin volume against internodal axon mantle area showed linear correlations with correlation coefficients of r > 0.90. The mean axon diameter of the investigated CNS internodes was similar to, the mean number of myelin lamellae somewhat lower than, and the mean internodal length considerably shorter than that of internodes of axons of the L7 ventral root (Nilsson & Berthold, 1988). In contrast to the ventral root, the intrafunicular alpha motor fibres had higher g values (axon diameter/fibre diameter value) and lower il/d ratios (internodal length/axon diameter ratio) than is considered optimal for conduction. We consider that these deviations from the theoretical optimum are not large enough to impair the conduction properties of the CNS parts of the motor axons in a significant way.

Animals↗
PubMed1993

Axoplasmic organelles at nodes of Ranvier. I. Occurrence and distribution in large myelinated spinal root axons of the adult cat.

Using light microscopy (LM) and electron microscopy (EM) we have examined the occurrence and distribution of axoplasmic organelles in large myelinated nerve fibres of the L7 ventral and dorsal spinal roots of the cat with special reference to the paranode-node-paranode (pnp)-regions. Ninety-eight percent of the 550 Toluidine Blue-stained paranode-node-paranode-regions examined in the light microscope contained dark-blue bodies accumulated distal to the midlevel of the paranode-node-paranode-region. Further, a veil of Toluidine Blue positive material was observed in about 50% of the paranode-node paranode-regions. In about 25% of these paranode-node-paranode-regions the veil lay distal to the midlevel of the paranode-node-paranode-region and in the remainder it lay proximally. Electron microscopy suggested that the ultrastructural equivalents of the dark-blue bodies and of the veil were dense lamellar bodies and a diffuse granular material, respectively. Our calculations indicate that from 70% to more than 90% of some organelles (dense lamellar bodies, multivesicular bodies and vesiculo-tubular membranous organelles) present in an axon are accumulated in the paranode-node-paranode-regions. The occurrence of these organelles in the individual paranode-node-paranode-regions varied within wide limits also in adjacent fibres. The dense lamellar and multivesicular bodies dominated the distal part of the paranode-node-paranode-regions while the vesiculo-tubular membranous organelles dominated the proximal part, i.e. the organelles showed a mutual proximo-distal segregation with reference to the midlevel of the paranode-node-paranode-region. Of seventeen paranode-node-paranode-regions analyzed ultrastructurally, seven were classified as 'fully segregated', that is 67% or more of the lamellar and multivescular bodies, present in the whole paranode-node-paranode-region, lay distal to the mid-level, and 67% or more of the vesiculo-tubular membranous organelles lay proximal to it.

Animals↗
PubMed1993

Axoplasmic organelles at nodes of Ranvier. II. Occurrence and distribution in large myelinated spinal cord axons of the adult cat.

The occurrence and distribution of axoplasmic organelles in large myelinated axons of the ventral, the lateral and the dorsal funiculi of L7 spinal cord segments of the cat have been studied using electron microscopy (EM). Most organelles were found to be concentrated to the paranode-node-paranode (pnp)-regions and they showed their highest relative concentration in the constricted part of these regions, i.e. at the nodes of Ranvier. In the paranode-node-paranode-regions of the lateral and dorsal funiculi, large dense bodies predominated distal to the nodal mid-level and vesiculo-tubular membranous organelles proximal to it. This pattern of organelle distribution, a proximo-distal (with reference to the neuron soma) segregation of the organelles, was only faintly indicated in the paranode-node-paranode-regions of the alpha motor axons of the ventral funiculus. These paranode-node-paranode-regions were, apart from a weak proximo-distal segregation of a few organelles, characterized by deposits of electron dense granules and clusters of large round mitochondria. We conclude that there are two types of organelle accumulation and distribution in the paranode-node-paranode-regions of large spinal cord nerve fibres of the cat. One type is found in the lateral and dorsal funiculi, i.e. in axons with terminal (synaptic) fields inside the blood-brain-barrier. The other type is found in the alpha motor axons of the ventral funiculus, i.e. in axons with their terminal field in the PNS and thus outside the blood-brain barrier. It should be noted that retrogradely transported material in the alpha motor axons has passed through a long sequence of paranode-node-paranode-regions equipped with Schwann cells before it reaches the CNS, while material transported retrogradely in the axons of the dorsal and lateral funiculi has not. The following discussion includes a comparison of the organelle accumulation and distribution in these two types of CNS paranode-node-paranode-regions with the organelle accumulation and distribution observed in the paranode-node-paranode-regions of PNS axons.

Animals↗
PubMed1992

Metabolic relationships between proteins of myelin and paranodally shedded, partially degraded myelin fragments in the rabbit CNS.

The "close-to-node" regions of myelinated nerve fibres, i.e., the paranodal end segments, are generally thought to be sites of high metabolic activity and myelin sheath turnover. Data on turnover rates of individual myelin constituents are conflicting but there exists a common belief that myelin is metabolized as independent molecules rather than as a unit. The occurrence of paranodal Marchi-positive bodies, with morphological and biochemical properties consistent with partially degraded myelin, prompted us to examine the temporal dynamics of the incorporation of radioactive precursor label in the major proteins of myelin and the Marchi-positive bodies. 3H-leucine was administered intrathecally in adult rabbits. After various survival times, the spinal cord was subfractionated by ultracentrifugation in a discontinuous two-step 0.32 M/0.85 M sucrose gradient. Myelin was collected from the interface and a floating fraction, heavily enriched in Marchi-positive bodies, was recovered on top of the 0.32 M sucrose. By scintillation counting and by gel fluorography combined with immunoblotting, a gradual appearance with time of partially degraded peptides of myelin-associated protein and 2',3'-cyclic nucleotide 3'-phosphodiesterase was seen in the floating fraction but not in myelin. The temporal dynamics of the specific activities of these two proteins and myelin-basic protein and proteolipid protein were consistent with a typical source-product relationship between myelin and the material in the floating fraction. In conjunction with earlier morphological and biochemical findings, these data may suggest that Marchi-positive bodies appear as a consequence of myelin catabolism.

Animals↗
PubMed1992

Computer-assisted realignment of light micrograph images from consecutive section series of cat cerebral cortex.

Two computer- and image-analysis-based procedures for realignment of images of consecutive light micrographs of nerve tissue (cat motor cortex) have been developed. One procedure (CENT) was interactive, employing the subjective overall 'best fit' of two images to each other and the other (AUTOCENT) was based on an automatic comparison of two images (image thresholding and binary comparison). Images of light micrographs of several hundred consecutive sections were realigned using the interactive and the automatic methods. The interactive procedure was easy to use; realignment of an image took only a few minutes in the hands of an experienced operator and should be easy to implement on commercially available smaller computers like PCs and workstations, but the realignment was possibly disturbed by the operator's subjective expectancy of regular forms. The automatic procedure realigned 1-4 images per hour, might be implemented on smaller computers if the programming is made more efficient, was probably objective and restored the 'true position of images'.

Animals↗
PubMed1991

Axon-Schwann cell networks are regular components of nodal regions in normal large nerve fibres of cat spinal roots.

The paranodal occurrence of axon-Schwann cell networks (ASNs), which are entities assumed to take part in the removal of degenerate axonal material, was examined quantitatively by electron microscopical serial section analysis in normal cat ventral and dorsal spinal roots. In nerve fibres greater than or equal to 10 microns in diameter 88% of the nodal regions in the ventral roots and 97% in the dorsal roots showed ASN complexes, which especially in the ventral roots often consisted of many segregated axoplasmic portions. The corresponding frequencies in fibres less than 10 microns were 28% and 62% in the ventral and the dorsal roots, respectively. ASN complexes were rare in fibres less than 5 microns. The results show that the ASN is a part of the normal paranodal architecture in large myelinated nerve fibres. The ASN occurrence seems to differ with neurone type.

Animals↗
PubMed1984

Ultrastructural morphometric studies on regeneration of the lateral sural cutaneous nerve in the white rat after transection of the sciatic nerve.

The lateral sural cutaneous nerves of 49 Sprague-Dawley rats 7-76 weeks of age were examined morphometrically in single transverse sections using electron microscopy. The following variables were estimated: the relative proportions of collagen-occupied and collagen-free areas of the extracellular compartment of the endoneurial space, the number and the diameters of axons, the number of myelin lamellae, and the number of different kinds of cell nuclei. The nerve contained on the average 2600 axons of which about 2200 (85%) were unmyelinated. The different variables were computed with regard to the animal-to-animal, side-to-side, and age variations. From these data normal reference diagrams based on the 95% prediction intervals for individual observations were constructed. Animal-to-animal and side-to-side variations were of about the same magnitude except in cases where the variation was age-dependent. Prediction intervals for individual observations that were +/- 50-70% of the mean value were found for the numbers of different types of Schwann cell nuclei. The intervals for the number and mean diameters of unmyelinated axons and myelinated fibres was +/- 20-30%. The g-value showed the narrowest interval +/- 10%. Age-related variation was found for the transverse section area of the nerve, axon diameters, and the number of myelin sheath lamellae. The application of normal values as a reference system to experimental data is discussed.

Aging↗
PubMed1983

Electron microscopic serial section analysis of nodes of Ranvier in lumbosacral spinal roots of the cat: ultrastructural organization of nodal compartments in fibres of different sizes.

The general ultrastructural organization of nodes of Ranvier in peripheral nerve fibres from 2 to 20 microns in diameter (D) was investigated in the adult cat using serially sectioned ventral and dorsal spinal roots. The study was performed in order to collect and systematize information considered necessary for a morphometric analysis of the node of Ranvier. In all cases a node of Ranvier could be divided into a central nodal axon segment and a surrounding nodal Schwann cell compartment. The latter included a nodal gap matrix substance, more or less overlapping nodal Schwann cell collars and, as a rule, also a Schwann cell brush-border emanating from the nodal Schwann cell collars and occupying the nodal gap. The relative size and the organization level of the nodal Schwann cell compartment increased with increasing fibre size up to a fibre diameter of 8-10 microns. At this fibre size the nodal gap was of a fairly even height (1 micron) all around the nodal axon and contained a thick brush-border of densely packed, more or less radially arranged Schwann cell microvilli. In very small fibres (D less than 3 microns) the nodal gap was low (less than 0.1 microns) and contained no or few microvilli. In fibres greater than 10 microns in diameter the relative size and the degree of structural order of the nodal Schwann cell compartment decreased with increasing fibre size. Drastic sectorial variations in nodal gap height and local thinning-out of the brush-border became prominent features in the largest fibres. The possible in vivo organization of the nodal Schwann cell compartment is discussed. Preliminary calculations indicate that the extracellular space directly surrounding the nodal axon might be quite small and that the area open for free communication between this extracellular space and the endoneurial space might be very much restricted, measuring as little as 2% of the area of the nodal axolemma. Algorithms for calculating various nodal structural parameters are discussed.

Animals↗
PubMed1983

Electron microscopic serial section analysis of nodes of Ranvier in lumbar spinal roots of the cat: a morphometric study of nodal compartments in fibres of different sizes.

Serially sectioned nodes of Ranvier from nerve fibres 2-20 micron in diameter of feline ventral and dorsal spinal roots were examined electron microscopically, reconstructed to scale and analysed morphometrically. The assumed 'fresh-state' value of several structural variables, considered to be of functional significance, were calculated by the use of compensation factors. The compensated data were plotted against fibre and axon diameters. It was calculated that the membranous area of the 'fresh-state' nodal axon segment increased more or less exponentially from less than 5 micron2 to 30 micron2 with increasing fibre diameter (D). Most variables associated with the nodal gap and the Schwann cell initially increased rapidly with D and then levelled out or even decreased in fibres with a D value greater than 8-12 micron. The area open for communication between the nodal axolemma and the endoneurial space was 30-100 times smaller than the membrane area of the nodal axolemma. The volume of the extracellular space in the nodal gap, outside the nodal axolemma, increased linearly from less than 0.1 micron3 to about 0.6 micron3 with increasing fibre size. The Schwann cell membrane area facing the nodal gap outnumbered the membrane area of the nodal axon by 10-15 times in nerve fibres with a D value between 5 and 15 microns. Some functional implications of the 'fresh-state' nodal model are discussed.

Animals↗
PubMed1983

Axon diameter and myelin sheath thickness in nerve fibres of the ventral spinal root of the seventh lumbar nerve of the adult and developing cat.

The axon diameter (d) and the number of myelin sheath lamellae (nl) were estimated in electron micrographs of cross sectioned ventral spinal roots of the seventh lumbar nerve of adult cats, kittens and cat fetuses. Myelination started between the 40th and the 45th day after mating (about 3 weeks before birth). From birth onwards the calibre spectrum consisted of a group of small fibres and a group of large fibres. During the first two postnatal months the point distribution of the number of myelin lamellae plotted against the axon diameter appeared more or less linear. This point distribution pattern became curved from the 10th postnatal week onwards, and a function of the general expression: nl = C0 + C1d + C2 log(d) could be fitted to describe the regression. In adult cats, the mean number of myelin lamellae/axon diameter ratio was about 30 in the group of small and about 15 in the group of large fibres. Observations on immature animals indicated that the difference between the two fibre groups could have been established already during the third postnatal week. Considerable myelin production took place after the age of 1 year. The cross sectional area of the myelin sheath in the alpha fibre group increased about 10% after the age of 1 year, while in the gamma fibre group it increased as much as about 85%. The absolute amount of myelin per unit fibres. Differences and similarities between myelin production in the two fibre groups are discussed.

Animals↗
PubMed1981

Nodal axon diameter correlates linearly with internodal axon diameter in spinal roots of the cat.

Nodal and internodal axon diameters of individual myelinated nerve fibres were measured electron microscopically in fibre samples from serially sectioned L7 ventral and dorsal spinal root of young adult cats. Axon cross-sectional area at the node of Ranvier in axons more than 4 micrometer in diameter was reduced to less than 20% of its internodal value. Internodal and nodal axon diameters showed a rectilinear distribution and linear regression analysis gave coefficients of correlation between 0.93 and 0.99. An individual nodal diameter value could be fitted to an internodal axon diameter value in a 95% prediction interval of +/- 1.06-2.41 micrometer.

Animals↗
PubMedDate not supplied

Computer-assisted 3D analysis of cell distributions in the normal and epileptic cerebral cortex: description of a methodology in progress.

This paper describes software routines that (a) visualizes a stack of several thousands of aligned sequential photographic two-dimensional (2D) images stored in an image processing system; (b) creates a data base containing information about objects identified sequentially from the 2D images; (c) transfers the data base to a graphical terminal; (d) reconstructs a three-dimensional (3D) object space; and (e) supports on-line interaction between the image processing system and the graphical terminal. As an application example, the cell content of a prism of motor cerebral cortex of the cat is reconstructed. Preliminary results from reconstructing human epileptic temporal cortex (cortical microdysgenesia) are also reported.

Adult↗
PubMedDate not supplied

3D reconstruction of biological objects from sequential image planes--applied on cerebral cortex from cat.

A prism of cat cerebral cortex was reconstructed with a method for three-dimensional (3D) representation of biological objects. A series of 918 semithin sections were digitized into an image analysis system. The images were aligned and analyzed, and a data base with the coordinates and a classification of the cells was created. The data base (i.e., the cortical prism) was visualized in a 3D graphic terminal, and parameters such as columnar and lamellar organization, clustering, and cell density were analyzed. A neuronal perikaryon and its neurites was reconstructed and shown together with the cortical prism.

Algorithms↗