Fluorescence and ultrastructural localization of aminergic neurons in the nerve cord of Eisenia foetida (Annelida—Oligochaeta)

Summary The aminergic nature of the CV neurons present in the genital segments of the nerve cord of Eisenia foetida is demonstrated by fluorescence microscopy and by the chromaffin reaction modified for electron microscopy.     

The fine structure of polychaete septate junctions

Summary Epidermal septate junctions of Nereis sp. and Cirriformia sp. fixed with OsO₄ or glutaraldehyde/OsO₄ display variable structure in electron micrographs. In transverse section the septa are often indistinct and obscured by opaque material that fills the junctional cleft. Septa (spaced at 180–280 Å) are more clearly defined in slightly oblique transverse section; they exhibit an electron lucent center and appear to be linked by arms. En face views of the junction show a honeycomb pattern. Cytoplasmic faces of junctional membranes are backed with plaques opposite the septa. Lanthanum used as a tracer delineates junctional structure in negative contrast. In transverse section a chain-like lattice is present in the junctional cleft. En face views show parallel rows of pleated elements often linked by arms into honeycomb arrays. Oblique sections demonstrate that these pleated elements are continuous with the chain-like lattice seen in transverse sections. Lanthanum does not pass entirely through the junction. Lanthanum reveals that the septa have a very intricate substructure, but it is difficult to visualize the architecture that could generate the various images presented by these junctions when seen in different orientations. However, it is clear that these junctions possess some features that are diagnostic of several supposedly different types of septate junctions in invertebrates.Supported by USPHS grants NIH 5 P01 NS-07512, NIH 2701 GM-00102, and NB-00840, and by a grant from the Pomona College Research CommitteeI thank Sarah Wurzelmann, Stanley Brown, Nancy Kelly, and Gerhard Ott for excellent technical assistance. Portions of this study were carried out while I was a Postdoctoral Fellow in the Department of Anatomy, Albert Einstein College of Medicine. I dedicate this article to Berta Scharrer as a token of appreciation and affection for her guidance, encouragement, inspiration, and example of excellence     

An ion-site interaction model for sodium currents in the giant axon

The time and voltage dependence of sodium currents in the Myxicola giant axon were examined as functions of the external sodium concentration. The results were incompatible with a model of free diffusion through a gated channel, but lent themselves to analysis in terms of a model involving a positive cooperative homotropic reaction in which Na⁺ interacts with two allosteric sites - a regulatory site and a transfer site - at the ‘sodium channel’. The time-dependent solution of the rate equations describing the kinetics of the transfer reaction was derived as an expression describing the sodium current as a function of time membrane potential and external sodium concentration. This function was used to test the validity of the model by its ability to predict the nerve excitability properties. The predicted i-v and i-t curves fitted the experimental results (p < 0.005 and p < 0.05, respectively). The computed parameters of these functions are consistent with other experimental results. The possibility of a noncooperative reaction was rejected.     

Riesenmitochondrien im Übergangsepithel der Harnblase des Maulwurfs

Zusammenfassung Das Harnblasenepithel des Maulwurfs wurde elektronenmikroskopisch untersucht. Bei bestimmten Tieren finden sich in den Intermediärzellen matrixreiche Riesenmitochondrien. Diese Riesenmitochondrien scheinen aus normalen Mitochondrien hervorzugehen und enthalten verschieden geformte Einschlüsse. Andere Organe und Zellen bei Maulwürfen mit Riesenmitochondrien in den Intermediärzellen des Harnblasenepithels weisen normale Mitochondrien auf. Es handelt sich demnach hier um eine sog. Mitochondriose der Intermediärzellen. Bedeutung, Bildung und Abbau der Riesenmitochondrien werden diskutiert.

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Giant mitochondria in urinary bladder transitional epithelium of the mole

Summary Giant mitochondria containing an enormous matrix volume were found in the intermediary cells of the urinary bladder transitional epithelium of the mole. Regularly shaped mitochondria develop club-like protrusions forming giant mitochondria that contain several types of inclusions. Various other tissues were examined, but we could state that giant mitochondria exist only in the intermediary cells of the urinary bladder epithelium. Thus a peculiar intermediary cell mitochondriosis is described in this paper, not regularly occurring in the mole. The functional significance of the giant mitochondria is discussed.

     

“Axonal spheroids” in the spinal cord of normal rabbits

Summary Within the gray matter and the white matter of the spinal cord of apparently healthy rabbits, myelinated and unmyelinated axonal swellings, so called axonal spheroids, occur. Most of the spheroids contain mitochondria, dense bodies, vesicles and fragments of the tubular or smooth endoplasmic reticulum. In myelinated spheroids the process of swelling is effected by slippage of the myelin leaflets. At the periphery of the unmyelinated parts of the spheroids, synapses are regularly found. The presynaptic terminal bouton is formed by the spheroid. A few myelinated and unmyelinated spheroids are packed with fine granular material while mitochondria are lacking. The axonal spheroids may represent a physiological, perhaps age dependent phenomenon.Dedicated to Prof. Dr. Berta Scharrer on the occasion of her 70^th birthdayThe author wishes to thank Mrs. Helga Zuther-Witzsch, Mrs. Elisabeth Schöngarth and Miss Hildegard Schöning for excellent technical assistance. Supported by the Deutsche Forschungsgemeinschaft, Projekt Le 69/7-13     

The fine structural localization of acetylcholinesterase in the muscle spindle of the rat

Summary Muscle spindles from lumbricalis muscles of the rat were incubated for acetylcholinesterase with a modified thiocholine-method of Lewis and Shute and examined by light and electron microscopy.All types of motor nerve ending showed heavy deposits of reaction product in the synaptic cleft. The underlying sarcoplasmic reticulum, transverse tubular system, and, when present, the envelope of sole plate nuclei were also stained.In the sensory region, the reaction was negative in the interface between the plasma membranes of the primary sensory terminal and muscle. One of two secondary sensory endings identified showed distinct reaction product in the cleft; the other secondary sensory ending showed no such reaction.Precipitates were present on the sarcolemma of the intrafusal muscle fibers in the polar and adjacent myotube regions, but not at the spindle equator. Extrafusal and intrafusal myelinated -nerve fibers and preterminal motor axons showed staining of the axolemma. Fibers with thick myelin sheaths and preterminal sensory axons were free of acetylcholinesterase activity, as were the unmyelinated nerve fibers.We wish to thank Mrs. D. Schilling and Mrs. Ch. Beyer for technical assistanc     

Ultrastructural studies on euspermatozoa and paraspermatozoa in Mantispidae (Insecta, Neuroptera)

Previous studies have demonstrated the presence of sperm dimorphism in the Mantispidae Perlamantispa perla. We extended the study on several other mantidflies. In all the examined species the occurrence of euspermatozoa (typical) and paraspermatozoa (atypical) was established. The euspermatozoa are characterized by the presence of a cylindrical nucleus surrounded by an envelope that fans out laterally into two thin wings of different length. The acrosome seems to be missing. The nucleus is surrounded by extracellular material. The flagellum is provided with a 9 + 9 + 2 axonemal pattern; the accessory tubules contain 16 protofilaments and the intertubular material has the distribution typical of the taxon. Two elongated accessory bodies flank partially the axoneme and connect this structure with the mitochondrial derivatives. The flagellar axoneme of paraspermatozoa consists of an axoneme and two giant mitochondrial derivatives filled with large globular units. The axoneme exhibits a 9 + 9 + 2 pattern, in which the central 9 + 2 units have a normal structure, in that the microtubular doublets are provided with both dynein arms and radial links. On the contrary, the nine accessory microtubules have a large diameter and their tubular wall consists of 40 protofilaments. This comparative study provided evidences about the uniformity of sperm ultrastructure in Mantispidae. The function of non-fertilizing giant sperm in mantidflies is discussed.     

Morphology of regenerated spinal cord in Sternarchus albifrons

Summary The tail of the gymnotid Sternarchus albifrons, including the spinal cord, regenerates following amputation. Regenerated spinal cord shows a rostro-caudal gradient of differentiation. Cross sections of the most distal regenerated cord show radially enlarged ependymal cells, relatively undifferentiated cells, and numerous blood vessels. More anterior sections contain well differentiated electromotor neurons, glial cells, and myelinated axons. The number of electromotor-neuron cell bodies in cross sections of regenerated spinal cord is three to six times the number in nonregenerated cord. Distinct tracts of axons, easily identifiable in normal cord, are not distinguishable in cross sections of regenerated cord. Some reorganization of the spinal cord also appears to take place anterior to the site of transection.Individual electromotor neurons in the regenerated spinal cord have morphologies largely similar to those of normal electrocytes, i.e., cell bodies are rounded, lack dendrites, have synapses characterized by gap junctions with presynaptic axons, and lack an unmyelinated initial segment. The presence of electromotor neurons with normal morphology in regenerated spinal cord correlates with the re-establishment of relatively normal electrocyte axonSchwann cell relationships in the regenerating electric organ of this sternarchid.Supported in part by the Medical Research Service, Veterans Administration and by a grant from the National Institutes of Health. We also thank the Paralyzed Veterans of America for their support. We thank Mary E. Smith and Susan Cameron for excellent technical support     

Microanatomy of the subumbrellar motor innervation inAglantha digitale (Hydromedusae: Trachylina)

Summary The hydrozoan medusaAglantha digitale (Müller 1776) has eight syncytical giant motor axons, up to 40 m in diameter, running from the margin, up the inside of the bell towards the apex. Giant motor axons injected with Lucifer Yellow CH are connected with lateral neurons running circumferentially across the subumbrellar muscle. These processes fill with the dye. Bundles of 20 to 50 small dye-coupled neurons extend circumferentially along the margin for up to 0.85mm. Giant motor axons injected with horseradish peroxidase divide into a few short branches on entering the inner nerve ring. Here the giant motor axon forms both chemical synapses and gap junctions with neurons that also send their axons into the inner nerve ring. In this region the inner and outer nerve ringe are connected by axons passing through openings in the intervening mesoglea.     

Myelinated nerve cell perikaryon in mouse spinal cord

Summary In the thoracic cord (posterior horn region) of a wild mouse, we have observed a small nerve cell soma completely enveloped by a myelin sheath. The number of myelin lamellae varied between 7 and 12. In one place, the existence of an inner mesoperikaryon could also be shown. The significance of this fortuitous finding has not yet been explained.

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Zusammenfassung Im Thorakalmark (Hinterhornbereich) einer Wildmaus wurde ein kleines Nervenzellperikaryon beobachtet, das vollständig von einer Markscheide umhüllt war. Die Zahl der Markscheidenlamellen variierte zwischen 7 und 12. An einer Stelle konnte ein sogenanntes inneres Mesoperikaryon nachgewiesen werden. Die Bedeutung dieses zufällig erhobenen Befundes ist vorerst noch offen.

     

Fine structure of nerve-melanophore contacts in the angelfish Pterophyllum scalare

Contacts between small unmyelinated nerve fibres and dermal melanophores of the angelfish, Pterophyllum scalare, exhibit several features characteristic of synapses, including small synaptic vesicles and dense core vesicles, a narrow synaptic cleft, electron-dense material at the postsynaptic membrane (cell membrane of the melanophore) and, occasionally, presynaptic densities. An analysis of serial thin sections shows that the synapses described here represent varicosities of an otherwise more or less straight nerve fibre. A single axon thereby may form several en passant synapses with a single melanophore. It is suggested that the synaptic contacts described here not only represent sites of transmitter release but also play a role as sites of firm attachment between nerves and melanophores which guarantee a stable arrangement of nerve fibres and melanophores.Supported by the Deutsche Forschungsgemeinschaft     

Muscle cells in a nerve trunk of a frog muscle

Summary Three muscle fibers were identified by electron microscopy within a nerve of a frog muscle. They resembled extrafusal muscle fibers but were located in an endoneurial rather than in an endomysial compartment. To call these endoneurial muscle fibers the obvious continuation of extrafusal fibers of a muscle spindle is certainly unwarranted; to label these fibers ectopic and to let the matter rest there is probably an understatement of sorts.     

Marginal bundles of axoplasmic microtubules at nodes of Ranvier within muscle

Summary Using a special albumin technique, nodes of Ranvier have been examined within frog skeletal muscle, sciatic nerve and rat and frog cerebrum. Initial segments have been examined in cerebrum of frog and rat. Microtubules usually run longitudinally through these regions, but within the bare area of the intramuscular node of Ranvier, annular or helical bundles of microtubules run in a marginal band at right angles to the more centrally placed longitudinal microtubules. These nodal bare areas show a pronounced convexity and it is suggested that the annular microtubules serve to maintain this convexity during muscle contraction.Dr. Westrum is an affiliate of the CDMRC, University of Washington and a recipient of a Wellcome Trust (U.K.) Burroughs Wellcome Fund (U.SA.) Research Travel Grant. This research was also supported, in part, by NIH research Grants NS 09678 and NS 04053 from the NINCDS and DE 04942 from the NIDR, USPHS/DHEW. The authors also wish to thank Julie Barron for excellent technical assistance     

Nerve-purkinje fiber relationship in the moderator band of bovine and caprine heart

Summary The moderator band in the heart of the ox and goat contains bundles of Purkinje fibers and nerve fibers separated by connective tissue. The axons are mostly unmyelinated and embedded in the cytoplasm of Schwann cells.Small bundles of axons run close to the Purkinje fibers. The axons dilate into varicosities 0.5 to 1.6 in diameter (mean 0.95 ), containing three types of vesicles: 1) agranular vesicles with a diameter of 400–500 Å, 2) large dense-cored vesicles with a diameter of 800–1200 Å, 3) small dense-cored vesicles with a diameter of 500 Å. Most varicosities contain agranular vesicles together with a few large dense-cored vesicles.The gap between the varicosities and the nearest Purkinje fiber is unusually wide and normally varies between 0.3 and 0.8 . No intimate nerve-Purkinje fiber contacts, with a cleft of 200 Å, were observed.     

Block of sodium conductance by n-octanol in crayfish giant axons

The block of the Na⁺ current by $\text{n-}\text{octanol}$ was studied in crayfish giant axons under axial wire voltage-clamp conditions. Standard kinetic analysis of the Na⁺ currents was undertaken to test the hypothesis that the $\text{n-}\text{octanol-induced}$ block of the Na⁺ current could be accounted for on the basis of changes in the voltage dependence of the kinetic parameters. Alterations in the membrane dipolar potential arising from rearrangement of membrane lipids would be the anticipated source of changes in the voltage dependence. Although some changes in voltage dependence did evolve with the block by $\text{n-}\text{octanol}$, the changes were not of sufficient magnitude to account for the block. In conclusion, although higher concentrations of $\text{n-}\text{octanol}$ produced shifts along the voltage axis of the kinetic parameters, direct blocking action of $\text{n-}\text{octanol}$ on the channel appears to be the most important mechanism of the block.