The morphology and physiological properties of nereid giant fibres

• 1.1. The three sets of giant fibres in the nerve cord of Nereis virens are connected by both electrotonic and chemically transmitting junctions.
• 2.2. The paired laterals and paramedials are connected to their partners by electronic junctions. The laterals are also electrically coupled to the median giant fibre.
• 3.3. The laterals are connected to the paramedials by an excitatory chemical synapse, while in the anterior segments the paramedials provide an inhibitory input to the median giant fibre.
• 4.4. Afferent input to the giant fibres through the segmental nerves two and four is excitatory, except that to the median fibre in the caudal segments.
• 5.5. There is no evidence of the segmental origin of the lateral giant fibres, either in the form of macrosynapses or segmental cell bodies.
• 6.6. The median giant fibre originates from two groups of cell bodies in the sub-oesophageal ganglia.

     

Zur Feinstruktur des dorsalen Riesenfasersystems im Bauchmark des Regenwurms

Zusammenfassung Die proximalen Kollateralen der dorsalen Riesenfasern des Regenwurms wurden in Serienschnitten vom Soma bis zum Eintritt in die Riesenfaser verfolgt und im Hinblick auf ihre Feinstruktur und ihre synaptischen Kontakte Untersucht. Es finden sich sowohl chemische als auch elektrische Synapsen. Ihre Feinstruktur wird mit der bekannter Synapsen anderer Wirbellosen und Wirbeltiere verglichen. In beiden Riesenfasersystemen kommen efferente chemische Synapsen mit feinen postsynaptischen Verzweigungen vor, die anscheinend von Bauchmark-Motoneuronen stammen. Das Axon der medianen Riesenfaser weist darüber hinaus nur noch eine elektrische Synapse mit den Rieseninterneuronen auf. Demgegenüber erhalten die Kollateralen der lateralen Riesenfasern zahlreiche Afferenzen, die zum Teil als sensorische Fasern der Epidermis, multisegmentale Fasern der Hauptfaserzüge und Rieseninterneurone identifiziert werden konnten. Weitere Afferenzen stammen vermutlich von unisegmentalen Interneuronen her. Beide lateralen Riesenzellaxone bilden außerdem miteinander eine elektrische Chiasma-Synapse mit besonderen Membraneinfaltungen.

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Ultrastructure of the dorsal giant fibre system in the ventral nerve cord of the earthwormII. Synaptic connections of the proximal collaterals of the giant fibres

Summary The proximal collaterals of the dorsal giant fibres of the earthworm were traced through serial sections from the cell bodies to the giant axons. Their structure and synaptic connections were examined. There are chemical as well as electrical synapses. Their fine structure is compared to that of other known invertebrate and vertebrate synapses. Both giant fibre systems have efferent chemical connections with thin postsynaptic arborizations which probably belong to ventral cord motoneurons. Moreover the median giant axon is connected by an electrical synapse with the giant interneurons. The lateral giant collaterals on the contrary receive many afferences through chemical synapses which were partly identified as sensory fibers from the epidermis, multisegmental axons from the main fibre bundles or giant interneurones. Other afferences probably come from unisegmental interneurones. In addition both lateral giant axons form an electrical chiasma synapse with special membrane folds.

Mit Unterstützung durch die Deutsche Forschungsgemeinschaft Gu 117/1.     

Multisegmental cobalt filling of the dorsal giant fibers in the nervous system of the earthworm,Lumbricus terrestris

Summary The anatomical organization of the two dorsal giant fiber systems of the earthworm Lumbricus terrestris is demonstrated in whole mounts and serial-section reconstructions based on backfillings of the ventral nerve cord with cobalt chloride. Both the medial and lateral fiber systems can be labeled selectively over more than ten body segments. They show a characteristic segmental pattern of collaterals with some modification in tail segments and of dorsal plasma protrusions in the unpaired medial giant fiber presumably representing openings in the myelin sheath. We found no multisegmental cobalt transport in other large neurons of the nerve cord. Cobalt passes through the segmentai septa between consecutive axonal elements of the metameric giant fibers and presumably also through commissural contacts between specific collaterals of the lateral giant fibers. Since these sites of contact are known to represent electrical synapses, cobalt coupling may, in L. terrestris, correlate with functional electrotonic coupling.Abbreviations CL collateral of lateral giant fiber - CM collateral of medial giant fiber - GIN giant interneuron - LGF lateral giant fiber - MGF medial giant fiber - SN segmental nerve     

Pathological changes in the microstructure of longissimus lumborum muscle from five breeds of pigs

The aim of the study was to determine the extent of histopathological changes in m. longissimus lumborum of PL, PLW, Duroc, Pietrain, and Pu?awska pigs (N = 30 per breed) aged 210 days. Changes in fibre size (atrophy, hypertrophy - giant fibres), changes in fibre shape (angular fibres), degenerative lesions (necrosis with phagocytosis) and connective tissue hypertrophy were evaluated. The percentage of individual pathological changes in m. longissimus lumborum of the analysed pig breeds was relatively low. Significantly more normal fibres were found in the muscles of Pu?awska compared to Pietrain pigs. Muscle fibre atrophy was the most frequent and extensive histopathological change. The muscles of Pu?awska pigs had significantly fewer atrophic, giant and angular fibres, significantly less necrosis with phagocytosis, and less animals with connective tissue hypertrophy compared to the other pig breeds. On the other hand, Pietrain pigs were characterized by a greater number of animals with giant fibres and a significantly higher proportion of giant fibres compared to the other breeds. Also the diameter of giant fibres was the largest in Pietrain, intermediate in PL and PLW, and the smallest in Duroc and Pulawska pigs. Moreover, current findings indicate that giant fibres may arise from each muscle fibre type (I, IIA and IIB). It is concluded that selection of pigs for increased leanness contributes to the incidence of histopathological changes, which may decrease pork quality.     

The innervation of the wind-sensitive head hairs of the locust, Schistocerca gregaria

ABSTRACT. The innervation of the locust head hairs was investigated by filling the sub-cuticular neurones with cobalt and by recording antidromic spikes at individual hairs when the circumoesophageal and cervical connectives were stimulated. The central projections from most head hairs ( c. 80%) terminate in the suboesophageal ganglion, whereas about 20% extend into the thoracic ganglia. Sensilla with projections to the thoracic ganglia are structurally no different from those whose fibres terminate in the suboesophageal ganglion and they are scattered throughout the hair fields with no consistent positions in different individuals. We have re-investigated the 'accessory response' (Camhi, 1969) and conclude that it is not indicative of a separate afferent or efferent system but is simply cross-talk from adjacent axons. We relate our findings to the fibre composition of the dorsal tegumentary nerve.     

Distribution of glutamate decarboxylase-like immunoreactivity in the sixth abdominal ganglion of the cockroach Periplaneta americana

Summary An antiserum against glutamate decarboxylase (GAD) of the rat brain was used to locate GAD activity in sections of the nervous system of the cockroach, Periplaneta americana. The sixth abdominal ganglion was chosen because electrophysiological evidence suggests the presence of GABAergic inhibitory synapses in the cereal-giant interneuron system. Groups of somata and numerous fibres and tracts were positively labelled by the GAD antiserum. A posterior group of labelled somata could be identified close to the entry of the cereal nerves. A line of somata clusters lay along a ventro-lateral furrow. Another discrete row of GAD-like cells was located dorso-laterally. Some small cells among the dorsal unpaired neurons were labelled. A small central group appeared under these cells. An abundance of GAD-like processes and transversal tracts were found within the neuropile. The different systems of GABAergic inhibitors in the ganglion are discussed; in particular we show that the fibres of cereal nerve X are not labelled. This demonstrates that the latter act on the giant fibres via interneurons. We suggest that the group that sends axons into the overlapping region between the cereal nerve and the giant fibre could be the inhibitory interneurons involved in this system.     

Fine-structural and morphometrical studies on the segmental septa of the giant fibers in the earthworm,Eisenia foetida

Summary The fine structure of junctional specializations on the segmental septa in the median and lateral giant fibers of the earthworm (Eisenia foetida) was examined. Eight morphologically different septal domains were identified; a gap junction, a junction with hemispherical hollow structures, a chemical synapse-like junction, intermediate type and punctum adherens type junctions, a junction with adjoining vesicular layers, an area flanked by flattened membranous sacs, a non specialized area, and an area consisting of widely separated membranes with interposed glial processes. The area of each domain was measured by a cytometrical technique using quasi-serial sections. The gap junction occupied 3% and 0.2% of the septal area of the median and lateral giant fibers, respectively. Junctions with hemisperical hollow structures, characteristic of the earthworm giant fibers, occupied 2.5% and 13.9% of the median and lateral giant fibers, respectively. Various membrane domains except the gap junction, the junction with hemispherical hollow structures, and the chemical synapse-like junction accounted for similar proportional areas in both median and lateral giant fibers.The functional implications of these junctional specializations, especially the gap junction, are discussed.     

Dorsal giant fibre septum of earthworm. Fine structural details and further evidence for gap junctions

The fine structure of the dorsal giant fibre septa of earthworm (Lumbricus terrestris and Eisenia foetida) was studied by thin sectioning. E-PTA, BIUL and ZIO impregnation were carried out to characterize the various membrane specializations found. A septum, which is formed by two axon membranes only ca. 7 nm apart, is a heterogeneous structure showing a number of different specializations (intermediate junctions, dense projection-like humps, septate regions, vesicles quite often associated with a widened intercellular gap and membrane thickening). Septal areas referred to as septal complexes are of particular interest. They comprise up to 20% of septal cross-sections and are characterized by membrane appositions (diameter ca. 25 nm) which bridge the septal gap, protrude 16-25 nm into the respective axoplasms, and form a more or less hexagonal array with a centre-to-centre spacing of ca. 33 nm (ca. 29 nm after E-EPTA treatment) in en face sections. We interpret the septal complexes as gap junctions, i.e. sites of electronic coupling, and emphasize their unusually large dimension. The vesicles found at the septum could not be stained by ZIO treatment.     

Wool Fibres: Sectioning and Staining, Differentiation of Ortho and Paracortex

A double embedding technique for tangential sectioning of hair and wool fibres is as follows: The cleaned fibre bundle is attached to a U-shaped, 16 gauge, tinned-copper wire frame with collodion adhesive, soaked in 6% nitrocellulose for 1 hr, and treated with chloroform for 2 hr. The hardened bundle is then cut fom the wire support and embedded in paraffin-beeswax, 95:5. Sectioning is at 6-8 μ. The use of 2% orange G or saturated aqueous picric acid for quantitative study of the fibres, and the demonstration of wool fibre cortical fractions by staining with polychrome methylene blue after oxidation of the sectioned fibres in a solution of formic acid (98/100 w/v) 25 ml; distilled water, 65 ml; and H₂O₂ (30% w/v), 10 ml, for 1 hr, is recommended.     

Pattern formation of the sensible nerves in the hand of mouse embryos with special reference to the posterior-anterior developmental gradient

The development of the sensible innervation of the hand was investigated. For this reason normal forelimbs and limb bud cultures from 12- to 14-day-old mouse embryos were stained in toto using the cholinesterase technique. The dorsal side of the hand is mainly innervated by sensible branches of the radial and the musculocutaneous nerve, which penetrate the fascia in the region of the elbow. From here they grow in a distal direction forming the dorsal digital nerves. On the ventral side the median nerve grows in a subfascial compartment towards the palmar side of the hand. While passing the wrist the median nerve exhibits a frayed appearance. A net of branching and anastomosing small nerve fibre bundles is visible. This implies that on the palmar side of the metacarpal region of the hand-plate no specific highways for the growing nerve fibres exist. From late day 12 to early day 14 of embryonic development this diffuse nerve net is organized. In a posterior-anterior (ulnoradial) developmental gradient the common palmar digital nerves were formed, and these nerves divide at their tip into the proper digital nerves. However, the proper digital nerves again follow special pathways during their outgrowth.     

THE SYNTHESIS OF CHOLINE PHOSPHOGLYCERIDES IN THE GIANT FIBRE SYSTEM OF THE SQUID

The mechanisms and pathways of synthesis of phosphatidylcholine in the giant fibre system of the squid (Loligo vulgaris) have been examined by incubating the stellate ganglion-nerve preparation or its separated compartments in an artificial bathing solution with labelled choline. Other experiments were done by dissecting the whole stellate ganglion into axoplasm, axon sheath, giant fibre lobe, small fibres and ganglion residue, after incubation. The initial rate of choline incorporation into choline phosphoglycerides was severalfold higher in the lobe than in the axon. Higher lipid radioactivity was recovered in the axon sheath as compared to the axoplasm, and in the small fibres as compared to the ganglion residue which contains its cell bodies. The production of phosphorylcholine and CDP-choline in the intact ganglion-nerve preparation during incubation with choline points to the occurrence of the net synthesis pathway for phosphatidylcholine in this material. Base-exchange activity was also observed in the axon and giant fibre lobe preparations in vitro, but no indication can yet be given whether it also takes place in intact preparations. Electrical stimulation and‘depolarizing’conditions enhance choline phosphorylation in the squid axon and lobe, but decrease phosphatidylcholine labelling.     

The vasopressin-like immunoreactive (VPLI) neurons of the locust,Locusta migratoria. I. Anatomy

Summary Antiserum to arginine-vasopressin has been used to characterise the pair of vasopressin-like immunoreactive (VPLI) neurons in the locust. These neurons have cell bodies in the suboesophageal ganglion, each with a bifurcating dorsal lateral axon which gives rise to predominantly dorsal neuropilar branching in every ganglion of the ventral nerve cord. There are extensive beaded fibre plexuses in most peripheral nerves of thoracic and abdominal ganglia, but in the brain, the peripheral plexuses are reduced while neuropilar branching is more extensive, although it generally remains superficial. An array of fibres runs centripetally through the laminamedulla chiasma in the optic lobes. Lucifer Yellow or cobalt intracellular staining of single VPLI cells in the adult suboesophageal ganglion shows that all immunoreactive processes emanate from these two neurons, but an additional midline arborisation (that was only partially revealed by immunostaining) was also observed. Intracellularly staining VPLI cells in smaller larval instars, which permits dye to reach the thoracic ganglia, confirms that there is no similar region of poorly-immunoreactive midline arborisation in these ganglia. It has been previously suggested that the immunoreactive superficial fibres and peripheral plexuses in ventral cord ganglia serve a neurohaemal function, releasing the locust vasopressin-like diuretic hormone, F₂. We suggest that the other major region of VPLI arborisation, the poorly immunoreactive midline fibres in the suboesophageal ganglion, could be a region where VPLI cells receive synaptic input. The function of the centripetal array of fibres within the optic lobe is still unclear.Abbreviations AVP arginine vasopressin - DIT dorsal intermediate tract - FLRF Phe-Leu-Arg-Phe - FMRF-amide Phe-Met-Arg-Phe-amide - LDT lateral dorsal tract - LVP lysine vasopressin - MDT median dorsal tract - MVT median ventral tract - SEM scanning electron microscopy - SOG suboesophageal ganglion - VIT ventral intermediate tract - VNC ventral nerve cord - VPLI vasopressin-like immunoreactive     

Some observations on the fine structure of the giant synapse in the stellate ganglk of the squid,Doryteuphis bleekeri

Summary The fine structure of the synapse between the second-order giant fibre and the third order-giant fibre of the squid Doryteuphis bleekeri was studied by means of electron microscope. In the synaptic region, the two giant fibres are arranged side by side. Many small processes from the third-order giant fibre penetrate the common sheath which separats the adjacent giant axons making synaptic contact with the second order giant axon.The contact surface consists of opposing two plasma membranes of adjacent axons separated by a narrow space of 20–30 m in width. The synaptic membranes are more electron dense and thicker than the other part of the axon membrane. The synaptic vesicles are concentrated exclusively in the presynaptic axon.The fine structural differences between giant synapse in the stellate ganglion of the squid and the giant-to-motor giant synapse of the crayfish were discussed.This work was supported by Grant Number B-3348 from the National Institutes of Health, United States Public Health Service, Department of Health, Education and Welfare.     

Contributions to Physiology of the Antenna-Heart in Periplaneta americana (L.) (Blattodea: Blattidae)

An accessory pulsatile organ of an open circulatory system in insects supplying the antennae with haemolymph was investigated. The rhythm of this so-called antenna-heart is generated by a myogenic automatism and can be neuronally influenced via the nervus cardioantennalis.The action potentials of the muscle fibres show typical pre-depolarization and mostly no overshoot. A specific membrane resistance (R(m)) of about 660Omegacm(-2) was calculated for the fibres. Some electrical coupling between the muscle fibres is presumed for synchronization of any myogenically triggered heart beat which could actually be proved experimentally by current injection in the antenna-heart. However, intercalated disks or gap junctions could not be found. Nevertheless, a good coupling factor (U(2)/U(1)) between all fibres was demonstrated by parallel recordings and can be well described by a conductance model according to fibre topology.     

The fin musculature of cuttlefish and squid (Mollusca, Cephalopoda): morphology and mechanics

The lateral fins of cuttlefish and squid consist of a tightly packed three-dimensional array of musculature that lacks bony skeletal support or fluid-filled cavities for hydrostatic skeletal support. During swimming and manoeuvring, the fins are bent upward and downward in undulatory waves. The fin musculature is arranged in three mutually perpendicular planes. Transverse muscle bundles extend parallel to the fin surface from the base of the fin to the fin margin. Dorso-ventral muscle bundles extend from dorsal and ventral connective tissue fasciae to a median connective tissue fascia. A layer of longitudinal muscle bundles is situated adjacent to both the dorsal and ventral surface of the median fascia. The muscle fibres are obliquely striated and include a core of mitochondria. A zone of muscle fibres with a more extensive core of mitochondria is present in both the dorsal and the ventral transverse muscle bundles. It is hypothesized that these muscle masses include two fibre types with different aerobic capacity. A network of connective tissue fibres is present in the transverse and dorso-ventral muscle masses. These fibres, probably collagen, are oriented at 45 to the long axes of the transverse and dorsoventral muscle fibres in transverse planes.
A biomechanicayl analysis of the morphology suggests that support for fin movements is provided by simultaneous contractile activity of muscles of specific orientations in a manner similar to that proposed for other 'muscular-hydrostats'. The musculature therefore provides both the force and support for movement. Connective tissue fibres may aid in providing support and may also serve for elastic energy storage.     

The overlapping in the striatum of the projection areas of corticofugal fibers from the somatosensory and motor regions of the rat cerebral cortex]

The Fink-Heimer techniques were used to determine the neostriatal projections from cortical M1 and S1 physiologically identified representations of the forepaw. While corticostriatal fibres from S1 enter dorso-lateral parts of the neostriatum fibres from M1 penetrate the dorsal part of the neostriatum more rostrally. Both fibre groups pass in rostrocaudal direction to the globus pallidum, forming terminals on their way. Most of the fibre terminals of M1 projection are located laterally overlapping the zone of distribution of S1 fibre terminals in the neostriatum. Overlapping terminals of the corticofugal fibres of S1 and M1 in the lateral neostriatum can form a basis for interaction of somatosensory and motor impulses. It may be suggested that the role of the neostriatum in sensory integration is associated with certain features of the corticofugal fibre terminals distribution in it at all levels of development of the central nervous system.     

The structure of the nerve fibre layer and neurocord in the enteropneusts

Summary The nerve fibre layer and the neurocord of the Enteropneusts Saccoglossus horsti, Harrimania kupfferi and Ptychodera flava have been examined with the electron microscope. The nerve fibres vary in diameter between 0.15 to 10 m. The majority of the fibres are of the smaller diameters. The nerve fibre layer is intraepidermal, and is divided by processes running radially from the epithelial cells to the basement membrane that separates the nerve fibre layer from the muscle cells.The cells of origin of these nerve fibres are situated mainly in the innermost layers of the epidermal cells. The nerve fibre profiles contain numerous vesicles of very varied diameter and contents, together with larger granular inclusions that are also found in the nerve cell bodies.Morphologically recognisable synapses are rare, but the majority of fibres are in intimate contact with one another. Sometimes the mass of fibres is divided into bundles by the epithelial cell processes. The majority of giant fibres are situated near to the basement membrane of the neurocord. The giant fibres also have a varied content of vesicles as well as neurofilaments and neurotubules.The central canal in Ptychodera flava and the remnants of the central canal in Saccoglossus horsti are both lined by columnar cells that bear microvilli as well as cilia with the typical 9 + 2 pattern of tubules. Scattered amongst these cells are mucus secreting cells which open into the cavity of the canal.I (P.N.D.) should like to thank Professor J. Z. Young, F. B. S. for much advice and encouragement. Dr. R. Bellairs generously provided the electron microscope facilities, and Dr. R. Newell kindly collected and identified the Saccoglossus specimens. Mr. R. Moss, Mrs. J. Hamilton and Mr. A. Aldrich gave excellent technical and photographic assistance.     

The ultrastructure of giant fibre and serial synapses in crayfish

Summary The ultrastructure of synapses between the cord giant fibres (lateral and medial) and the motor giant fibres in crayfish, Astacus pallipes, third abdominal ganglia have been examined. These electrotonic synapses are asymmetrical, they have synaptic vesicles only in the presynaptic fibre, and they have synaptic cleft widths normally of about 100 Å but narrowed to about 50 Å in restricted areas. Localized increases in density of the synaptic cleft and adjacent membranes also occur within a synapse, and synaptic vesicles are most tightly grouped at the membrane in such areas. Tight or gap junctions with 30 Å or narrower widths have not been found, but the junctions probably function in a similar way to gap junctions.Three small nerves are closely associated with the synapses between the giant fibres. One of these small nerves has round synaptic vesicles and is thought to be excitatory on morphological grounds; one has flattened vesicles and is thought to be inhibitory; and one is postsynaptic to the lateral giant and the two small presynaptic nerves. It is proposed that these small nerves modulate activity in the much larger giant fibre synapse.     

Functional differentiation of splanchnic A delta fibres in relation to viscerosomatic reflexes.

The splanchnic afferent signal in the myelinated fibre spectrum was analysed in cats and its relationship to viscerosomatic reflex activity was studied. In addition to Abeta and Adelta components, a further elevation was observed in the sympathetic chain neurogram. According to the conduction rate (15 plus or minus 4 m/sec), it was caused by myelinated fibres 2-3 mu in diameter. The presence of this component at thoracic dorsal root level, or in the sympathetic chain in stimulation of the postganglionic part of the nerve trunk, confirmed the afferent nature of the observed activity. The threshold stimulus for these fibres, which were termed group Adelta2, was four times higher than for Abeta fibres. Correlation of the neurogram with evoked activity in the intercostal nerves confirmed the different functional role of group Adelta2 fibres. Adelta2 fibre activity evokes the early component of the two-component viscerosomatic discharge and Adelta2 fibre activity its later component. The authors discuss the functional significance of Adelta2 fibres, which probably mediate nociceptive information from the viscera.