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M Rickmann

Publications and source records attributed to M Rickmann.

12 recordsLinked to original sources
PubMed1990

An unbiased estimation of the total number of synapses in the superior cervical ganglion of adult rats established by the disector method. Lack of change after long-lasting sodium bromide administration.

Previous physiological and morphological studies suggested that sodium bromide promotes synaptogenesis of implanted cholinergic nerves in the superior cervical ganglion of adult rats. To check whether sodium bromide also modifies synaptic numbers in the intact ganglion, quantitative electron microscopy was used to determine the total number of synaptic junctions in the superior cervical ganglion of adult rats. Untreated controls were compared with animals which drank water containing 280 mg ml-1 sodium bromide for 7 days. The disector method, an unbiased estimator of volume density of certain particles, has been adapted to this particular case. To accomplish the task, an on-line counting procedure was developed, which permitted the efficient adaptation of the disector method for the superior cervical ganglion, in which the synapses are known to be distributed sparsely. Three pairs of (control and treated) ganglia have been completely processed by three independent examiners. The estimated number of synapses in the ganglia ranged from 4 to 8 million while the volumes of the ganglia varied from 0.65 to 0.90 mm3. Evaluation of the results showed that variations in the total number of synapses were in each case proportional to differences in ganglionic volumes. This suggests that: (1) sodium bromide does not lead to changes in density of intrinsic synapses; and (2) the morphogenetic action of sodium bromide on principal ganglion cells previously described is essentially postsynaptic and requires additional presynaptic elements to increase the number of synapses.

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PubMed1990

x-y-recording in transmission electron microscopy. A versatile and inexpensive interface to personal computers with application to stereology.

An interface for IBM XT/AT-compatible computers is described which has been designed to read the actual specimen stage position of electron microscopes. The complete system consists of (i) optical incremental encoders attached to the x- and y-stage drivers of the microscope, (ii) two keypads for operator input, (iii) an interface card fitted to the bus of the personal computer, (iv) a standard configuration IBM XT (or compatible) personal computer optionally equipped with a (v) HP Graphic Language controllable colour plotter. The small size of the encoders and their connection to the stage drivers by simple ribbed belts allows an easy adaptation of the system to most electron microscopes. Operation of the interface card itself is supported by any high-level language available for personal computers. By the modular concept of these languages, the system can be customized to various applications, and no computer expertise is needed for actual operation. The present configuration offers an inexpensive attachment, which covers a wide range of applications from a simple notebook to high-resolution (200-nm) mapping of tissue. Since section coordinates can be processed in real-time, stereological estimations can be derived directly "on microscope". This is exemplified by an application in which particle numbers were determined by the disector method.

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PubMed1989

The anatomical substrate for telencephalic function.

The basic thesis for this study was that the telencephalon is needed to make decisions in new situations. Subsidiary hypotheses were that the telencephalon consists of: (a) a sensorimotor system which generates motor activity from sensory input and (b) a selection system which makes choices from possible motor programs. It was postulated that the selection system should fulfil the following requirements: be accessible for past and present events, have the capacity to process this information in a nondetermined way with a possibility for ordering, and have access to motor-affecting systems (the sensorimotor system). The ability of the selection system to correlate information in a nonpredetermined way was considered most important. In short: The selection system should be able to associate any information in any combination, and have the capability for internal control of neuronal activity and external selection of motor programs (see Fig. 1A.) Xenopus laevis was chosen as a subject, since it has a relatively simple telencephalon, with characteristics that it shares with "primitive" species of different vertebrate classes, and because it is easy to maintain as a laboratory animal. The main method used was the determination of connections with HRP. The pallium was in the focus of attention, since it was considered to be the core of the selection system. Immunohistochemistry was used as an additional parameter to compare Xenopus laevis forebrain with those of other vertebrates. The results showed that the pallium can be subdivided into a rostral (third) and a caudal (two-thirds) entity. The rostral third is the main recipient for thalamic and olfactory input. The caudal two-thirds are linked up to the rostral third and have a refined microcircuitry. Efferents from the pallium remain restricted to the forebrain. The entire pallium consists of a network of intrinsic reciprocal connections and can be considered to be positioned between the medial pallium (hippocampus), septum, and amygdaloid complex (amygdala). As a whole this system targets the hypothalamus. The hypothalamus in turn projects into the striatum complex (striatum with anterior entopeduncular nucleus). The rostral dorsal pallium and the amygdaloid complex also project into the striatum complex. The striatum is positioned between the sensory input from the thalamus and olfactory bulbs, and the motor output to the medulla. It is concluded, on the basis of its straightforward input-output relations and uniform appearance, that the striatum complex fulfils the requirements for a sensorimotor system. The pallium together with the septum, amygdaloid complex, and hypothalamus fulfils the requirements for a selection system.(ABSTRACT TRUNCATED AT 400 WORDS)

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PubMed1987

Organization of radial glial cells during the development of the rat dentate gyrus.

The temporal and spatial patterns of development of radial glial processes in the rat dentate gyrus have been studied in immunohistochemical preparations stained for the presence of either the glial fibrillary acidic protein (GFAP) or the vimentin-associated antigen R4. Additional electron microscopic (EM) observations were made from material prepared either immunohistochemically or by the Golgi method. R4 immunoreactive radial fibers were observed in the incipient dentate gyrus as early as E13 and by E14 the density of stained fibers was clearly higher in the anlage of the dentate gyrus than in the adjacent hippocampus. By E15 it was possible to identify in the EM the endfeet of radial glial cells that contained numerous glycogen particles. GFAP-positive radial processes were first observed on E17; these processes tended to be of larger diameter than those stained with the R4 antibody, suggesting that they were among the more mature processes. The orientation of both the R4- and GFAP-positive glial processes changed throughout the last week of embryonic life and by the end of the first postnatal week they formed a complex meshwork of intertwined processes. The distribution of their cell bodies also changed with time; initially their perikarya were located in the neuroepithelium at the lateral margin of the hippocampal primordium; later they were found mainly beneath the granule cell layer. Dividing cells that contained GFAP were observed along the trajectory of the migrating granule cell precursors and in the hilus of the dentate gyrus; at later stages some GFAP-positive mitotic figures were seen within and immediately below the granule cell layer. On the basis of these observations, we have attempted to reconstruct the role that radial glial processes play in the morphogenesis of the dentate gyrus. First, radial processes extend from the neuroepithelium to the pial surface prior to the migration of neurons that will form the dentate gyrus. These early generated glia appear to form the boundaries of the developing dentate gyrus and provide an internal lattice that may guide the initial wave of migrating progenitor cells. As the dentate gyrus enlarges, these early formed processes maintain their contacts along the hippocampal fissure and along the pial surface of the dentate anlage. Thus, with time they become increasingly distorted and are ultimately compressed into two bundles; one lies deep to the hippocampal fissure parallel to the granule cell layer and the other is located at the fimbriodentate juncture.(ABSTRACT TRUNCATED AT 400 WORDS)

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PubMed1985

The migration of neural crest cells and the growth of motor axons through the rostral half of the chick somite.

We have studied the pathway of migration of neural crest cells through the somites of the developing chick embryo, using the monoclonal antibodies NC-1 and HNK-1 to stain them. Crest cells, as they migrate ventrally from the dorsal aspect of the neural tube, pass through the lateral part of the sclerotome, but only through that part of the sclerotome which lies in the rostral half of each somite. This migration pathway is almost identical to the path which presumptive motor axons take when they grow out from the neural tube shortly after the onset of neural crest migration. In order to see whether the ventral root axons are guided along this pathway by neural crest cells, we surgically excised the neural crest from a series of embryos, and examined the pattern of axon outgrowth approximately 24 h later. In somites which contained no neural crest cells, ventral root axons were still found only in the rostral half of the somite, although axonal growth was slightly delayed. These axons were surrounded by sheath cells, which had presumably migrated out of the neural tube, to a point about 50 micron proximal to the growth cones. With appropriate antibodies we found that the extracellular matrix components fibronectin and laminin are evenly distributed between the rostral and caudal halves of the somite. Neither of these molecules therefore plays a critical role in determining the specific pathway of neural crest cells or motor axons through the rostral half of the somite.

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