Composition of the antennal nerve of Homarus americanus at different points along the flagellum

The antennal flagellum nerve of Homarus americanus was investigated as to structure, number and size of axons, and propagation velocity. Frequency distributions of axon diameters, evaluated at four equidistant levels on the flagellum, ranged with continuity between 0.25 and 14.7 µm, with maximum at 0.5-1.5 µm. Axons 0.5-1.5 µm in diameter were more abundant at the distal level, indicating sensory specialization near the tip. The total axon numbers increased from about 9000 at the distal level to about 45 000 at the base. Axons of different size followed different patterns of increase in number from tip to base; these patterns were examined in relation to structural features of the flagellum, and to hypotheses of association with known or unidentified receptors. Propagation velocities were distributed with continuity, in the range between 3.39 and 0.24 m/s; velocity-diameter correspondences were outlined.     

Motion of the Longitudinal Flagellum in Ceratium tripos (Dinoflagellida): A Retractile Flagellar Motion1

The longitudinal flagellum of Ceratium tripos moves in two dissimilar ways: undulation and retraction. The undulatory wave is planar and has a wavelength of 74.3 ± 9.6 μm and an amplitude of 14.2 ± 2.3 μm in sea water. The beat frequency is 30 Hz at 20°C, pH 8.0. The retractile motion is unique to Ceratium and is triggered by mechanical stimulation on the cell body, especially at the tip of the apical horn. When it retracts, the longitudinal flagellum folds every 4–5 μm along the flagellum. Cinematographic study showed that the flagellum folded from tip to base and was finally installed into the sulcus, a groove on the ventral side of the cell. This motion is completed in sea water within 28 msec. The retracted flagellum then re-extends and restores the undulation within a few seconds. The flagellum unfolds in the proximal portion first, then the distal, and finally the middle portion. Fixation always triggers the retraction. Scanning electron microscopy showed that the flagellum is folded and secondarily twisted in a helix. A new fiber in addition to the flagellar axoneme was found in the retracted flagellum by phase microscopy. This fiber (R-fiber) seems to contract during the retraction to fold the flagellum.     

Observations on the ultrastructure of the flagella and periplast in the Cryptophyceae

The flagella in Cryptomonas ovata Ehrenberg and two other un-named strains of Cryptomonas both bear stiff hairs with fine distal filaments of the same type as those found in the Xanthophyceae, the Chrysophyceae sensu stricto, the Phaeophyceae, the Bacillariophyceae, the Eustigmatophyceae and the Oomycetes. On the longer of the two flagella the hairs are 2·5 µm long and in two opposite rows whereas on the shorter flagellum they measure only 1 µm, are arranged in a single row and are more closely spaced. The long flagellum also bears a characteristic lateral swelling with a tuft of hairs of the same type as on the remainder of the flagellum, at approximately the level at which it emerges from the gullet. The hairs on the flagella of Hemiselmis rufescens Parke are distributed in a similar manner to those in Cryptomonas but they are more flexible and the swelling and tuft of hairs appear to be absent from the long flagellum. Hairs are apparently absent from the short flagellum of Chroomonas sp. The periplast in Cryptomonas ovata shows a hexagonal pattern in surface view and in sections of all three Cryptomonas strains appears as a typical plasmalemma underlain by a discontinuous layer of electron-dense material with variable substructure. The distribution of flagellar hairs and the structure of the periplast appear to be characters unique to the Cryptophyceae and these features emphasise the isolated position of this class of algae.     

Novel peripheral motor neurons in the posterior tentacles of the snail responsible for local tentacle movements

Three flexor muscles of the posterior tentacles of the snail Helix pomatia have recently been described. Here, we identify their local motor neurons by following the retrograde transport of neurobiotin injected into these muscles. The mostly unipolar motor neurons (15–35 µm) are confined to the tentacle digits and send motor axons to the M2 and M3 muscles. Electron microscopy revealed small dark neurons (5–7 µm diameter) and light neurons with 12–18 (T1 type) and 18–30 µm diameters (T2 type) in the digits. The diameters of the neurobiotin-labeled neurons corresponded to the T1 type light neurons. The neuronal processes of T1 type motor neurons arborize extensively in the neuropil area of the digits and receive synaptic inputs from local neuronal elements involved in peripheral olfactory information processing. These findings support the existence of a peripheral stimulus–response pathway, consisting of olfactory stimulus—local motor neuron—motor response components, to generate local lateral movements of the tentacle tip (“quiver”). In addition, physiological results showed that each flexor muscle receives distinct central motor commands via different peritentacular nerves and common central motor commands via tentacle digits, respectively. The distal axonal segments of the common pathway can receive inputs from local interneurons in the digits modulating the motor axon activity peripherally without soma excitation. These elements constitute a local microcircuit consisting of olfactory stimulus—distal segments of central motor axons—motor response components, to induce patterned contraction movements of the tentacle. The two local microcircuits described above provide a comprehensive neuroanatomical basis of tentacle movements without the involvement of the CNS.     

Physical and physiological properties of the crayfish antennal flagellum

• (1) Mechanoreceptors in the crayfish antennae are divided into four functional categories: vibration (13%), bidirectional displacement (19%), unidirectional displacement (45%), and position (23%) receptors. The distribution of receptors along the length of the flagellum follows a logarithmic progression, decreasing from about 40% at the base to less than 5% at the tip.
• (2) Vibratory stimulation of the antennae was found to induce a traveling wave. Because of an impedance gradient along the length of the flagellum, the traveling wave moves most efficiently from base to tip. The wave was observed to travel at an average velocity of 6.0 m/sec.
• (3) Large deflections of the tip are not uniformly transferred to the base, but decrease logarithmically. This is due to the existence of the impedance gradient.
• (4) Receptor output probability was found to be greatest when low frequency/high intensity stimulation was applied to the flagellar base.
• (5) Characteristics of large (2 cm) posterior-going deflections of the flagellar tip that are effective in producing response differences are displacement: (a) amplitude, (b) velocity, and (c) acceleration.

     

Fine structure of the spermatozoon of the viviparous teleost, Cymatogaster aggregata

The approximately 50 μm long sperm of Cymatoguster aggregata is composed of an elongate head (4 μm), an elongate mitochondria1 midpiece (3.5 μm) and a tail flagellum (roughly 40 μm). The sperm lacks an acrosome. Contained within depressions on one surface of the compressed head are a proximal centriole and a distal centriole separated by an electron dense, intercentriolar body. The anterior portion of the tail flagellum originates at the basal body (distal centriole) and is contained within an extracellular, flagellar tunnel within the mitochondria1 midpiece. The morphological similarity of C. uggregutu sperm to sperm of other internally fertilizing fishes supports the hypothesis that spermatozoan morphology is related to the mode of fertilization and that an elongate head and midpiece are specializations for internal fertilization.     

Spermiogenesis and spermatozoa ultrastructure of Aonides oxycephala (Annelida: Spionidae) from the Sea of Japan

Adults of Aonides oxycephala, common inhabitants of shallow boreal waters in the Atlantic and Pacific Oceans, release gametes into the water where fertilization and lecithotrophic larval development occur. During spermiogenesis, the acrosomal vesicle migrates from the posterior to the anterior end of the spermatid and the number of mitochondria reduces from six in early spermatids to four in mature spermatozoa. Each spermatozoon has an ovoid head with the acrosome 1.4?±?0.1?µm long and 1.6?±?0.1?µm wide and the nucleus 1.7?±?0.1?µm long and 2.3?±?0.1?µm in diameter, four spherical mitochondria, two centrioles oriented perpendicular to each other, putative glycogen in the shape of dense granules in the midpiece, and a flagellum with 9?×?2?+?2 organization of microtubules. The acrosome is a complex heterogeneous structure with five ordered layers of different electron densities, lying in a shallow depression on the anterior end of the nucleus. The nucleus is barrel-shaped (truncated ovoid) with the centriolar fossa housing the distal and proximal centrioles. Spermiogenesis and ultrastructure of spermatozoa of A. oxycephala are similar to those of another free spawning spionid, Marenzelleria viridis. Aonides and Marenzelleria have not, however, been considered as closely related taxa; thus, similarity in the morphology of their sperm might result from convergence or parallelism.     

Role of moving growth cone–like “wave” structures in the outgrowth of cultured hippocampal axons and dendrites

Hippocampal neurons exhibit periodically recurring growth cone–like structures, referred to as “waves,” that emerge at the base of neurites and travel distally to the tip. As a wave nears the tip, the neurite undergoes retraction, and when it reaches the tip, the neurite undergoes a burst of growth. At 1 day in culture, during early axon outgrowth, axons undergo an average 7.5‐μm retraction immediately preceding wave arrival at the tip followed by 12‐μm growth immediately after arrival (an average net growth of 4.5 μm). In branched axons, waves often selectively travel down one branch or the other. Growth selectively occurs in the branch chosen by the wave. In dendrites, which grow much slower on average, wave‐associated retractions are much greater, resulting in less net growth. In the presence of Brefeldin A, which disrupts membrane traffic through the Golgi apparatus and leads to retraction of the axon, axonal waves continue to be associated with both growth spurts and retractions. The magnitude of the growth spurts is not significantly different from untreated axons, but wave‐associated retractions are significantly increased. The close association between waves and cyclical elongation suggests that waves may act to bring about this pattern of growth. Our results also show that modulation of regularly occurring retraction phases plays a prominent role in determining average outgrowth rates. © 1999 John Wiley & Sons, Inc. J Neurobiol 39: 97–106, 1999     

Association of actin filaments with axonal microtubule tracts

Axoplasmic organelles move on actin as well as microtubules in vitro and axons contain a large amount of actin, but little is known about the organization and distribution of actin filaments within the axon. Here we undertake to define the relationship of the microtubule bundles typically found in axons to actin filaments by applying three microscopic techniques: laser-scanning confocal microscopy of immuno-labeled squid axoplasm; electronmicroscopy of conventionally prepared thin sections; and electronmicroscopy of touch preparations-a thin layer of axoplasm transferred to a specimen grid and negatively stained. Light microscopy shows that longitudinal actin filaments are abundant and usually coincide with longitudinal microtubule bundles. Electron microscopy shows that microfilaments are interwoven with the longitudinal bundles of microtubules. These bundles maintain their integrity when neurofilaments are extracted. Some, though not all microfilaments decorate with the S1 fragment of myosin, and some also act as nucleation sites for polymerization of exogenous actin, and hence are definitively identified as actin filaments. These actin filaments range in minimum length from 0.5 to 1.5 µm with some at least as long as 3.5 µm. We conclude that the microtubule-based tracks for fast organelle transport also include actin filaments. These actin filaments are sufficiently long and abundant to be ancillary or supportive of fast transport along microtubules within bundles, or to extend transport outside of the bundle. These actin filaments could also be essential for maintaining the structural integrity of the microtubule bundles.     

The Relationship Between Cell Size and Cell Number and the Distance from the Root Tip to the Region of Phloem Initiation in Groundnuts (Arachis hypogea. L. var. Bukene Red)

The effects of cell size and number on the distance from theroot tip to phloem inception in groundnuts have been investigated.The roots were treated with a number of plant growth regulatorshaving a wide range of effects on the growth rate. Increasing the growth rate of roots increased the distance ofphloem initiation and lignification from the apex. In all treatments,the average distance to phloem inception varied from about 590to 885 µm behind the root apex. The average lengths of the cortical and epidermal cells, whichwere 16 and 20 µm respectively, remained constant regardlessof the distance from the root tip.     

Structure and ultrastructure of the spermatozoa of Trichogramma pretiosum Riley and Trichogramma atopovirilia Oatman and Platner (Hymenoptera: Trichogrammatidae)

Lino‐Neto, J., Báo, S. N. and Dolder, H. 2000. Structure and Ultrastructure of the Spermatozoa of Trichogramma pretiosum Riley and Trichogramma atopovirilia Oatman and Platner (Hymenoptera: Trichogrammatidae). —Acta Zoologica (Stockholm) 81 : 205–211 Spermatozoa of the Trichogramma pretiosum and T. atopovirilia are very slender and long, about 0.35 µm in diameter and 283 µm and 106 µm in length, respectively. Under light microscopy, they appear wavy along their entire length. The head contains a small acrosome which, together with the initial nuclear region is surrounded by an ‘extracellular sheath’, from which innumerable filaments irradiate. The nucleus is filled with homogeneous, compact chromatin and is attached to the flagellum by an electron dense centriolar adjunct, which extends anteriorly from the nuclear base. The flagellum consists of an axoneme with the 9 + 9 + 2 microtubule arrangement pitched in a long helix, as well as a pair of spiralling mitochondrial derivatives which coil around the axoneme. Based on these characteristics, the sperm of these Trichogramma are very similar to the chalcidoids studied to date and differ from non‐chalcidoid Hymenoptera. They differ widely from the sperm of T. dendrolimi and T. ostriniae studied, where no helically twisted structure is shown. However, based on these results we argue that the spiralling of the flagellar structures is a synapomorphy for Trichogrammatidae as well as for Eulophidae + Eurytomidae + Pteromalidae.     

Growth and cellular organization of Arabidopsis pollen tubes in vitro

Tricellular pollen tubes of Arabidopsis thaliana were cultured in vitro on solid media and studied with respect to growth, cellular organization and ultrastructure, cytoskeletal organization, organelle movement, deposition and structure of the wall and the occurrence of coated pits, all elements assumed to be relevant for tip growth. For our ultrastructural studies we used freeze fixation and freeze substitution. Although Arabidopsis pollen tubes are broadly similar to those of bicellular species such as Nicotiana tabacum and Lilium spec. and in vivo grown pollen tubes of Arabidopsis, some differences occurred. The density of the equally distributed, relatively small (85 nm) secretory vesicles (SV) in the tip is low (five/µm ²). In between the SV of the tip, membranous material, possibly smooth endoplasmic reticulum, fragments of rough endoplasmic reticulum and loose ribosomes are present. The wall in the tip is not amorphous but layered and a secondary wall is formed already in the flanks of the tip. The general pattern of organelle motion is reverse fountain-like, but individual organelles move in distinct lanes at speeds of up to 2 µm/s, and about half of the organelle population shows a moderate velocity or Brownian movement. These properties are discussed in relation to the low growth rate (10 µm/h) of Arabidopsis pollen grown in vitro. The two similar sperm cells are closely attached and are always found near the vegetative nucleus. No surrounding wall and no cytoskeletal elements were obvious in the sperm cells. The preferential location of the mitochondria at the wall and the large (up to 400 nm) coated pits are unique for angiosperm pollen tubes. The size of the coated pits may allow not only membrane retrieval but also pinocytosis.     

Morphology and fine structure of Acipenser persicus (Acipenseridae, Chondrostei) spermatozoon: Inter-species comparison in Acipenseriformes

This study describes morphology and fine structure of the Persian sturgeon (Acipenser persicus) (Acipenseridae, Chondrostei) spermatozoon. The results show that the spermatozoon of A. persicus is differentiated into an elongated head (length: mean±SD: 7.1±0.5μm) with an acrosome (length: 1.2±0.2μm), a cylindrical midpiece (length: 1.8±0.5μm), a flagellum (length: 50.3±5.9μm) and a total length of 59.2±6.2μm. Ten posterolateral projections (PLPs) arise from the posterior edge of the acrosome and there were 3 endonuclear canals that traversed the nucleus from the acrosomal end to the basal nuclear fossa region. Three to six mitochondria were in peripheral midpiece and the proximal and distal centrioles were located near to "implantation fossa" and basement of the flagellum. The axoneme has a typical eukaryotic structure composed of 9 peripheral microtubules and a central pair of single microtubule surrounded by the plasma membrane. Lateral fins were observed along the flagellum. The fins started and ended at 0.5-1μm from midpiece and at 4-6μm from the end of flagellum. There were significant differences in the size of almost all measured morphological parameters between males and flagellar, midpiece and nucleus characters were more isolated parameters that can be considered for detecting inter-individual variations. This study showed that sperm morphology and fine structure are similar among sturgeon species, but the dimensions of the parameters may differ.     

Fine structure of the statocyst sensilla of the mysid shrimp Neomysis integer (Leach, 1814) (Crustacea,Mysidacea)

The fine structure of the statocyst sensilla of Neomysis integer was investigated. The statocyst contains about 35 sensilla, which are composed of two bipolar sensory cells, nine enveloping cells, and a seta. The sensory cells consist of an axon, a perikaryon, and a dendrite. The dendrite contains a proximal segment with a ciliary rootlet and at least one basal body, and a distal segment with a ciliary axoneme (9 × 2 + 0) at its base. The distal segment extends along the peripheral wall of the seta and is in close contact with the wall of the hair shaft. The enveloping cells surround the proximal and distal segments of the dendrite. The innermost enveloping cell contains a scolopale rod. It surrounds the receptor lymph cavity and secretes flocculent material into this cavity. From the tip of the cell a dendritic sheath, which encloses the distal segment of the dendrite, emerges. A peculiar feature of the second enveloping cell is the presence of a scolopale-like rod, which is more slender and less pronounced than in the first enveloping cell. The seta consists of three parts: a socket, a tubular midpart, and a gutter-like apical part, the tip of which penetrates into the statolith. The seta shows over its full length a bilaterally symmetrical axis that is coplanar with the plane in which the seta is bent toward the statolith. The structure of the seta and the position of the distal segments provide morphological evidence for directional sensitivity of the sensilla and for the magnitude of shear on the setal wall being an adequate stimulus.     

Flagellar elongation as a moving boundary problem

Movement of a proposed controlling factor along the growing flagellum is considered as a special case of one-dimensional diffusion with a moving boundary. Flagellar elongation, which involves polymerization of the building units at the distal tip, is viewed as taking place in a series of steps. The concentration of the controlling factor at the tip is computed as a function of the distance of the tip from the base, and the time between polymerization reactions. It is proposed that the concentration of this factor at the tip is responsible for regulating the flagellar growth rate and final length.     

ULTRASTRUCTURAL OBSERVATIONS ON THE SPERMATOZOA OF PLEUROTOMARIA AFRICANA TOMLIN (GASTROPODA)

Spermatozoa from formalin/alcohol preserved testes of Pleuotomariaafricana Tomlin are examined using transmission electron microscopy.These spermatozoa possess the following features: (1) an acro-somalvesicle (acrosomal cone), 1 µm long and deeply invaginated;(2) an axial rod occupying the inva-gination of the acrosomalvesicle; (3) a cylindrical nucleus (length 4 µm, maximumdiameter 1.5 µm) exhibiting occasional irregular cavities;(4) shallow imaginations at anterior and posterior extremitiesof the nucleus; (5) four or five spherical mitochondria pressedinto posterior indentations of the nucleus, and clustered aroundthe proximal and distal centrioles; (6) a single flagellum continuouswith the distal cen-triole and (7) a satellite fibre—densering complex associated with the distal centriole and attachedflagellum. Substructure of the centrioles could not be determined,but presumably both are composed of triplets. Spermatozoa ofP. africana are simple in structure (as expected of an externallyfertilizing species) and, among the Gastropoda, resemble spermatozoaof some trochids more so than those of other pleurotomaroideans(Haliotidae, Scissurellidae) or the Fissurelloidea. The primitiveposition of the Ple-urotomariidae within the Prosobranchia issupported by sperm morphology ^*Present address: Department of Zoology, University of Queensland,St. Lucia, 4067 Queensland, Australia (Received 30 December 1987; accepted 11 January 1988)     

Vessel-element dimensions and frequency within the most current growth increment along the length of Eucalyptus globulus stems

The mean number of vessels per unit area in the outer most growth increment at six percentage heights in individual trees, viewed in transverse section, showed an increasing trend from basal to apical regions. The highest frequency of vessels occurred at 90% of total tree height (23.58 mm^-2) while the lowest frequency (9.99 mm^-2) was recorded at 15% of total tree height from the base. Vessel elements were largest at 15% of total tree height and proceeded to decrease in size with increased stem height. Average radial measurements ranged between 111.27 µm and 160.0 µm while average tangential measurements ranged between 76.30 µm and 112.80 µm. There was variation seen at each percentage height between collection dates (i.e. individual trees); however, the trend of increasing vessel frequency from basal to apical regions existed regardless of between-tree variation in dimensions. Vessel-element dimensions showed a similar, but inverse trend to vessel-element frequency with the largest vessel elements located at 15% of total tree height and the smallest vessel elements located at 90% of total tree height.     

Understanding the Reactivity of a Thin Li1.5Al0.5Ge1.5(PO4)3 Solid‐State Electrolyte toward Metallic Lithium Anode

The thickness of solid‐state electrolytes (SSEs) significantly affects the energy density and safety performance of all‐solid‐state lithium batteries. However, a sufficient understanding of the reactivity toward lithium metal of ultrathin SSEs (<100 µm) based on NASICON remains lacking. Herein, for the first time, a self‐standing and ultrathin (70 µm) NASICON‐type Li_1.5Al_0.5Ge_1.5(PO₄)₃ (LAGP) electrolyte via a scalable solution process is developed, and X‐ray photoelectron spectroscopy reveals that changes in LAGP at the metastable Li–LAGP interface during battery operation is temperature dependent. Severe germanium reduction and decrease in LAGP particle size are detected at the Li–LAGP interface at elevated temperature. Oriented plating of lithium metal on its preferred (110) face occurs during in situ X‐ray diffraction cycling.