Eva B. Krammer

Somatotopic organization of the hypoglossal nucleus: a HRP study in the rat

Our present knowledge of the motor pool pattern in the hypoglossal nucleus is based mainly on cytoarchitectonic descriptions and is derived from a truly extraordinary miscellany of animals (see refs. 2, 4, 12). Therefore, it is not surprising that the hypoglossal complex of mammals is variously described as consisting of three 9 (see also ref. 4), four (see ref. 4), five 2, and even nine 12 subdivisions. Using retrograde degeneration methods, a somatotopic interpretation of the cell grouping in the hypoglossal nucleus was advanced with some confidenceZ, 5, 9,14. Since discrepancies and uncertainties still exist in these experimental results, with respect to individual muscle representation and/or functional grouping, we investigated the somatotopic organization of the hypoglossal nucleus by means of the retrograde transport of HRP 6 which has been previously adopted for the identification of motoneurons in a wide range of situations (see refs. 1, 7, 8, 10, 13, 15). Seventy male Sprague-Dawley rats weighing from 150-250 g were anesthetized with Nembutal (40 mg/kg, i.p.). A single nerve, either the hypoglossal nerve or one of its branches was cut and crystals of horseradish peroxidase (HRP) grade I (Boehringer-Mannheim) were applied to the proximal nerve stump*. HRP was applied to the cut end of (1) the hypoglossal nerve proximal to its ramification, (2) the main medial and (3) the main lateral branch of the hypoglossal nerve proximal to their ramifications. HRP was further applied to the cut muscular branches of the main medial branch, i.e. (4) the geniohyoidal and (5) the genioglossal nerves; and to the muscular branches of the main lateral branch, i.e. (6) the hyoglossal and (7) the styloglossal nerves. Following a 24-48 h postoperation survival time, the animals were perfused with 1.5-2.5 ~ glutaraldehyde n in 0.1 M cacodylate buffer (pH. 7.2). The brain stems were removed and fixed by immersion in the same fixative for 4 h at 4 °C before they were

The motoneuronal organization of the spinal accessory nuclear complex.

1 Introduction.- 2 Materials and Methods.- 3 Results.- 4 Discussion.- Summary.- References.

The human thyrocervical trunk: configuration and variability reinvestigated.

SummaryReinvestigation of the configuration of the human thyrocervical trunk revealed, that in the presently investigated specimens the dorsal scapular artery is a direct branch of the subclavian artery in approximately 75% of the cases, whereas in the remaining 25% it is derived from the thyrocervical trunk, either directly or via the transverse cervical artery (Nomina anatomica 1977). The internal thoracic artery participates in the thyrocervical trunk in more than 10% of the observed cases. Thus, both dorsal scapular and internal thoracic artery have to be considered as facultative branches of the thyrocervical trunk. According to our results, the subclavian artery must be considered as the most common site of origin of the dorsal scapular artery. This vessel may be replaced by another artery in about one fourth of the cases. A survey of studies on the origin of the dorsal scapular artery clearly demonstrates that it is not warranted to give an overall numerical proportion for the main modes of branching. As yet no satisfactory explanation for the high degree of variability of these subclavian branches has been given. Especially the widely held notion of differences related to race, which is based on Adachis (1928) work, has turned out to be invalid. Interpretation of variability may rather be based, as a general concept, on the late acquisition of a thyrocervical trunk in phylogeny as well as in ontogeny.

Neurotoxicity of kainic acid: Evidence against an interaction with excitatory glutamate receptors in rat olfactory bulbs

The hypothetical interaction of kainic acid (KA) at excitatory glutamate (GLU) receptors was tested by injecting this neurotoxin into the olfactory bulb (OB), since the putatively GLUergic output neurons of the OB are among the few neurons in the CNS that are not excited by GLU. However, the mitral (and tufted) cells are found to be highly and preferentially destroyed by KA, whereas the GLUreceptive interneurons of the OB appear to be relatively resistant to the neurotoxin. These findings suggest that the toxic effect of KA on OB neurons may be mediated by mechanisms other than by action on GLUreceptors.

Gross anatomy and evolutionary significance of the human peroneus III.

SummaryBecause our practical experience concerning the characteristic features of the peroneus III muscle disagreed with the usual statements and illustrations in anatomical text-books, we reexamined the gross anatomy of this muscle.A total of 157 peroneus III muscles was present in 169 lower limbs. Thus, the absence of this muscle (in 7.1% of our specimens) should be considered the variation rather than its presence. Moreover, the peroneus III has an identity separate from that of the extensor digitorum longus, and frequently is as large as or even larger than the extensor digitorum longus. Thus, the origin of the peroneus III extends much more proximally than stated in most text-books. It is a semipennate muscle with a tibially sited tendon, and therefore resembles the fibular and distal part of the extensor digitorum. This part of the extensor digitorum overlaps the extensor hallucis longus and is in turn overlapped by the peroneus III. The more proximal and tibial part of the extensor digitorum is arranged in a slender belly with its fasciculi converging towards a centrally sited tendon of considerable length. The proximal part of the extensor digitorum longus gives rise to slips to the medial toes, and the distal part to the lateral toes. The attachment of the peroneus III tendon is usually trifurcate, with one projection towards the tubercle and the dorsolateral aspect of the fifth metatarsal bone, another to the dorsomedial border of the same metatarsal bone, and a third projection to the base of the fourth metatarsal bone. An accessory slip to the dorsal aponeurosis of the fifth toe was found to occur only rarely.The usual description that the peroneus III is only a part of the extensor digitorum longus, or even its fifth tendon, should therefore be revised. The functional and evolutionary significance of this muscle is discussed, because the peroneus III occurs only in man, and in the gorilla alone of the anthropoid apes as well as of all other primates.

Über Bindungsstellen zweiwertiger Schwermetallionen am Ranvierschen Schnürring

SummaryThe effects of extraction of lipids, of denaturation of protein by high temperature and of some enzymes on the copper-binding at the node of Ranvier were investigated. Copper sulfide staining of the node was totally prevented by extraction of lipids with chloroform/methanol. Denaturing of proteins showed no effect. The reduced copper-binding after pronase probably is due to the severe structural alterations caused by this enzyme. The reaction was markedly reduced by Neuraminidase and by Hyaluronidase too. It is concluded that carboxyl groups of a sialoglycolipid or of sialic acid containing lipopolysaccharides are responsible for the copper-binding at the node.ZusammenfassungDer Effekt von Lipidextraktion, Hitzedenaturierung, Pronase, Hyaluronidase und Neuraminidase auf die Kupferbindung am Ranvierschen Schnürring wurde untersucht. Die Metallophilie wird durch Lipidextraktion vollkommen verhindert, durch Neuraminidase stark reduziert und auch durch Hyaluronidase beeinträchtigt. Hitzedenaturierung zeigt keinen Effekt. Die Abschwächung der Reaktion nach Pronase ist wohl auf die starke Strukturzerstörung zurückzuführen. Diese Befunde legen den Schluß nahe, daß möglicherweise die Carboxylgruppen eines Sialoglykolipids oder eines neuraminsäurehaltigen Lipopolysaccharides für die Bindung metallischer Kationen am Schnürring verantwortlich sind.

Effekt von Zinkionen auf Struktur und Verteilung der Neurotubuli

SummaryBeing interested in factors stabilizing neurotubules (NTs)in situ, we decided to immerse short segments of fresh rat peripheral nerves in buffered solutions containing ZnCl2 in final concentrations up to 10−2m prior to fixation with buffered osmium or glutaraldehyde, both containing ZnCl2. Zinc treatment resulted in a remarkable structural preservation of NTs after fixation with osmium, though they are not preserved by osmium fixation alone. Cross sections of myelinated nerve fibres show NTs arranged predominantly in compact groups. Within the groups NTs are surrounded or embedded in an electron dense fine granular material. The occurrence of incomplete C-shaped NTs and NT-like densities can be seen. NTs exhibit relatively constant distances and sometimes geometric patterns of arrangement. A lot of intertubule cross bridges and NTs with arms could be observed. In longitidinal section the bridge and arm spacing is seen to be periodic along the tubule axis at about 500 Å. Zinc treatment of nerves fixed in glutaraldehyde resulted in the same ultrastructural alterations described above. The resistance of zinc-stabilized NTs to degradation by osmium and the ultrastructural changes induced by zinc are discussed. The results suggest that in the presence of zinc ions osmium-labile NTs are transformed — by disassembly and reassembly — to osmium-stabile microtubules that are not identical with preexisting ones.

Horseradish peroxidase histochemistry on mounted sections from embedded specimen: a simple method for serial reconstruction of neuronal projections

A combination of two procedures, embedding of specimens and horseradish peroxidase (HRP) histochemistry on mounted serial sections, is proposed for three-dimensional reconstruction of neuronal projections. To clarify the intrinsic organization of the peripheral nervous system, this simple method is more adequate than previously used techniques.

Schwermetallaffine Strukturen des peripheren Nerven

SummaryThe ultrastructural localisations of copper in ventral and dorsal roots of the rat were studied by varying fixation and converting medium. Precipitated copper was deposited in axonal membranes (axolemma, membranes of axonal organelles) and Schwann cell membranes (inner and outer plasmalemma, major and minor dense lines in the region of the splitting myelin sheath, terminal loops and Schwann cell interdigitations). Copper obviously was bound within and attached to inner and outer leaflet of these membranes. If there was little or less electron-dense precipitate membranes appeared three-layered, dimensions corresponding to those of the unit membrane. If there was electron-dense or plenty of precipitate only the middle electron-lucent layer of approximately 30 Å was revealed. The predominant deposition on nodal and paranodal membranes may be explained either by facilitated access to this region or by specific metal ion binding sites at those specialised membranes. Metal ion binding is discussed in relation to cytochemical demonstration of AChE activity, because these methods use incubation media containing heavy metal cations and copper binding sites partly correspond with the localisation of AChE activity. The appearance of unit membranes in unstained sections probably could be a hint at unspecific heavy metal ion binding ocouring in demonstration of specific AChE. Therefore control-incubation in the heavy-metal solution with subsequent conversion is suggested.ZusammenfassungKonvertiertes Kupfer wurde an axonalen und Schwannschen Zellmembranen, vor allem im nodalen und paranodalen Bereich beobachtet. Kupfer wird offenbar in “inner” und “outer leaflet” der “unit membrane” ein- und an diese angelagert. Denn bei wenig Präzipitat oder geringer Elektronendichte des Niederschlags stellten sich die Membranen als dreischichtiger Komplex dar, der in den Dimensionen der “unit membrane” entsprach. Bei großen Präzipitatmengen oder bei hoher Elektronendichte des Niederschlags blieb nur die helle Mittelschicht von ca. 30 Å frei. Diese Metallaffinität wird im Zusammenhang mit den cytochemischen AChE-Nachweisverfahren diskutiert, weil bei diesen Methoden Schwermetallionen im Inkubationsmedium verwendet werden, und die Kupferbindungsstellen zum Teil mit den Lokalisationen der AChE identisch sind. Möglicherweise gibt beim cytochemischen AChE-Nachweis schon die Darstellung von “unit membranes” in unkontrastierten Präparaten Aufschluß auf erfolgte unspezifische Schwermetallbindung. Als weitere Kontrolle wird Inkubation in der verwendeten Schwermetallösung mit nachfolgender Konversion vorgeschlagen.