Axial Nuclei Research Articles

Ultrastructure of spermatozoa of a hairworm Gordionus alpestris (Villot, 1885) (Nematomorpha, Chordodidae)

ABSTRACT Sperm ultrastructure of the hairworm Gordionus alpestris (Nematomorpha, Chordodidae) has been studied. Spermatozoa are elongated aflagellate cells of clavate shape. Their dilated anterior part consists of an acrosomal complex comprising an apical acrosomal vesicle and axial acrosomal tube enveloped by an acrosomal sheath of four membrane-bound compartments. The basal part of the tube contains a cluster of vesicles. The slender posterior part of the spermatozoa includes an axial nucleus without a nuclear envelope surrounded by a halo and multivesicular complex composed of cisternae arranged into three layers. Spermatozoa of G. alpestris are nearly identical in size, proportion and internal structure to those of other gordiid spermatozoa. This uniformity makes spermatozoa useless for taxon descriptions and differentiation of Gordiida. The basic pattern of spermatozoon structure in Gordiida is not fully understood and requires more detailed studies. Controversies include absence or presence of the nuclear envelope and mitochondria, together with interpretation of the halo surrounding nuclei and membranous compartments of the acrosomal and multivesicular complexes. Detailed study of sperm development together with cytochemical analysis of components such as mitochondria, acrosome, perforatorium and halo might be helpful for understanding sperm relationships of Gordiida and Nematoda.

Collagenic architecture and morphotraits in a marine basal metazoan as a model for bioinspired applied research.

In some Porifera (Demospongiae: Keratosa), prototypes of the connective system are almost exclusively based on collagenic networks. We studied the topographic distribution, spatial layout, microtraits, and/or morphogenesis of these collagenic structures in Ircinia retidermata (Dictyoceratida: Irciniidae). Analyses were carried out on a clonal strain from sustainable experimental mariculture by using light and scanning electron microscopy. Histology revealed new insights on the widely diversified and complex hierarchical assemblage of collagenic structures. Key evolutionary novelties in the organization of sponge connective system were found out. The aquiferous canals are shaped as corrugate‐like pipelines conferring plasticity to the water circulation system. Compact clusters of elongated cells are putatively involved in a nutrient transferring system. Knob‐ended filaments are characterized by a banding pattern and micro‐components. Ectosome and outer endosome districts are the active fibrogenetic areas, where exogenous material constitutes an axial condensation nucleus for the ensuing morphogenesis. The new data can be useful to understand not only the evolutionary novelties occurring in the target taxon but also the morpho‐functional significance of its adaptive collagenic anatomical traits. In addition, data may give insights on both marine collagen sustainable applied researches along with evolutionary and phylogenetic analyses, thus highlighting sponges as a key renewable source for inspired biomaterials. Therefore, we also promote bioresources sustainable exploitation with the aim to provide new donors of marine collagen, thereby supporting conservation of wild populations/species.

Histology of Muscle Development in Pigs, Epigenetics from Myotubes to Tapered Fibres

Pre-natal muscle development in pigs starts with myotubes (axial nuclei in a tube of myofibrils) and secondary fibres (peripheral nuclei on an axial strand of myofibrils). By the time of birth, the nuclei of myotubes move to a peripheral position like secondary fibres. As pre-natal secondary fibres grow in length, the number of fibres in a transverse section may appear to increase. This stereology may also occur in post-natal muscles that have tapered fibres anchored in endomysial connective tissue around adjacent fibres and with one or both ends not reaching the end of their fasciculus. Up to 100 days gestation, Peroneus longus (no tapered fibres) had larger (P < 0.001) diameter secondary fibres than Longissimus thoracis (with tapered fibres). Up to 100 days gestation, no radial growth of secondary fibres was detected, but myotubes decreased in diameter (P < 0.001). From a curve showing the relative numbers of myotubes and secondary fibres, it was deduced that approximately 80% of muscle fibres in pigs are derived from secondary fibres. In post-natal Sartorius muscle there was an increase (P < 0.005) in the apparent number of muscle fibres attributed to longitudinal growth of tapered fibres. Myotubes located centrally within their fasciculi had the same position as slow-contracting fibres with a high myoglobin content in adult muscle. Post-natal changes in muscle fibre histochemistry were achieved through transitional types, probably neurally regulated rather than by differential longitudinal growth of tapered endings. Secondary fibres are important – they give rise to both the majority of muscle fibres in adult pigs and affect subsurface optical pathways and pork colourimetry.

Recovery of Serotonergic Innervation in Spinal Motor Nuclei below Cervical Spinal Injury: Effects of Intermittent Hypoxia

Cervical spinal cord injury (cSCI) disrupts serotonergic innervation below the injury. Since serotonin underlies motor functional recovery following cSCI, it is important to know the extent of serotonergic reinnervation after incomplete cSCI and to understand factors that accelerate that process. Repetitive acute intermittent hypoxia (rAIH) is one treatment known to elicit serotonin‐dependent respiratory and limb motor plasticity, partially restoring breathing and limb functions after chronic cSCI. Chronic intermittent hypoxia (CIH) similar to that experienced during sleep apnea elicits neuropathology, and potentially undermines the capacity for AIH‐induced motor plasticity. Although rAIH was previously reported to increase serotonergic innervation of the phrenic motor nucleus in intact rats, the impact of different intermittent hypoxia (IH) protocols on serotonergic innervation of respiratory motor nuclei in rats with or without chronic cSCI has not been investigated. Further, the impact of IH on serotonergic innervation of non‐respiratory motor nuclei has never been investigated. Thus, we tested the hypotheses that rAIH and CIH exert differential effects on serotonergic innervation of phrenic, intercostal, forelimb and axial motor nuclei motor nuclei post‐cSCI. Serotonergic innervation was assessed via immunofluorescence in male Sprague Dawley rats with and without C2 spinal hemisection (C2Hx; 12 wks post‐injury) exposed to 28 days of: 1) normoxia; 2) daily AIH (10, 5min 10.5% O2 episodes per day; 5min normoxic intervals); 3) mild CIH (5‐min 10.5% O2 episodes; 5min intervals; 8 hrs/day); and 4) moderate CIH (2min 10.5% O2 episodes; 2min intervals; 8 hrs/day). Rats received intrapleural injections of Cholera toxin B subunit 14 days before C2Hx to label phrenic and intercostal motor neurons. Forelimb and axial motor nuclei regions were determined using anatomical landmarks. In all regions investigated, no IH protocol impacted serotonergic innervation in intact or injured rats, contrary to previous reports. All areas had significant reductions in the number of serotonergic structures ipsilateral to C2Hx (p<0.001). Serotonergic structures innervating ipsilateral phrenic nuclei were larger (p<0.001), resulting in an overall increase in total innervation (p<0.001). Serotonergic structures innervating ipsilateral intercostal nuclei were also larger (p<0.001), but total innervation was reduced (p<0.001) due to larger reductions in number. In forelimb and axial nuclei, the size of serotonergic structures was unaffected by C2Hx (p<0.001), resulting in less total innervation ipsilateral to C2Hx (p<0.0001). Thus, C2Hx deferentially impacts serotonin reinnervation in spinal motor nuclei ipsilateral to C2Hx. The functional impact of increased serotonergic structure size in phrenic and intercostal motor nuclei is unclear. Our results indicate substantial serotonergic reinnervation below cSCI at this time point, potentially enabling serotonin‐dependent, AIH‐induced plasticity with chronic cSCI.Support or Funding InformationSPARC OT2OD023854 NIH T32 HD043730 NIH K12 HD055929 and UF McKnight Brain Institute

Toroidal Modes in Nuclei by Inelastic Electron Scattering

Electron scattering is a tool that can provide relatively clean view of the nuclear structure in both ground and excited states, as it depends on the well-known electromagnetic interaction. But since the common expressions for its cross section were derived with certain assumptions, in this paper we describe several nontrivial steps necessary for a proper theoretical calculation within the current density-functional framework, namely with Skyrme QRPA for axial nuclei, with aim to enable comparison of the theoretically predicted low-lying $1^-$ toroidal modes with future (e,e') experiments.

Individual Low-Energy Toroidal Dipole State in ^{24}Mg.

The low-energy dipole excitations in ^{24}Mg are investigated within the Skyrme quasiparticle random phase approximation for axial nuclei. The calculations with the force SLy6 reveal a remarkable feature: the lowest I^{π}K=1^{-}1 excitation (E=7.92 MeV) in ^{24}Mg is a vortical toroidal state (TS) representing a specific vortex-antivortex realization of the well-known spherical Hill's vortex in a strongly deformed axial confinement. This is a striking example of an individual TS which can be much more easily discriminated in experiment than the toroidal dipole resonance embracing many states. The TS acquires the lowest energy due to the huge prolate axial deformation in ^{24}Mg. The result persists for different Skyrme parametrizations (SLy6, SVbas, SkM*). We analyze spectroscopic properties of the TS and its relation with the cluster structure of ^{24}Mg. Similar TSs could exist in other highly prolate light nuclei. They could serve as promising tests for various reactions to probe a vortical (toroidal) nuclear flow.

Individual low-energy E1 toroidal and compression states in light nuclei: deformation effect, spectroscopy and interpretation

The existence of individual low-energy E1 toroidal and compression states (TS and CS) in 24Mg was predicted recently in the framework of quasiparticle random phase approximation (QRPA) model with Skyrme forces. It was shown that the strong axial deformation of 24Mg is crucial to downshift the toroidal strength to the low-energy region and thus make the TS the lowest E1(K=1) dipole state. In this study, we explain this result by simple mean-field arguments. Comparing TS in two strongly axial nuclei, 24Mg and 20Ne, we show that the lowest TS is not a universal phenomenon but rather a peculiarity of 24Mg. The spectroscopy of TS and CS is analyzed and some additional interpretation of these states is suggested.

Ultrastructure of spermiogenesis and spermatozoa in Marchalina hellenica (Gennadius) (Hemiptera: Sternorrhyncha, Marchalinidae)

The spermiogenesis, the sperm structure and the sperm motility of Marchalina hellenica (Gennadius) were examined. In the early spermiogenesis a centriolar apparatus was identified, but this structure is not involved in the production of the sperm flagellum. As in other Coccoidea, the flagellar axoneme originates by the activity of the thickened tip of the numerous microtubules surrounding the nuclear anterior region close to the periphery of the cell. This region pushes against a narrow cytoplasmic layer, giving rise to a papilla. In this region a novel structure, consisting of a regular network of thin filaments, arranged orthogonally to the bundle of microtubules, is visible. The sperm flagellum consists of a series of about 260 microtubules, regularly arranged in rings around the axial nucleus. This latter extends in the middle part of the sperm length. As usual in scale insects, sperm form a bundle, which in M. hellenica is composed of 64 sperm cells, surrounded by somatic cyst cells. The sperm bundle has an helicoidal array, with a cap of dense material at its apex, lending the anterior and the posterior region of the sperm bundle with a different structural organization. This difference is responsible of the different speed gradient observed in the helical wave propagating along the sperm bundle.

The ultrastructure of spermiogenesis in four species of Coccoidea (Insecta, Homoptera)

The ultrastructure of spermiogenesis in four species of Coccoidea, namely Quadraspidiotus perniciosus and Pseudaulacaspis pentagona (Diaspididae), as well as Planococcus citri and Planococcus ficus (Pseudococcidae), is described. Similarly to other coccids, during spermiogenesis sperm nuclei elongate towards the plasma membrane, forming a conical papilla. The microtubule bundles surrounding the nucleus subsequently elongate and a mature sperm is formed. At the end of spermiogenesis, the motile sperm of all the species consists of a cylindrical axial nucleus surrounded by a spiral (Q. perniciosus) or by concentric rings of microtubules (P. pentagona, P. citri and P. ficus) forming a peculiar flagellum. Other features common to all these species are the lack of centrioles, acrosome and mitochondria in the spermatid and mature sperm. Differences arise in the number of spermatid cells per cyst (32 in Q. perniciosus and 16 in the other three species) and in the number and arrangement of microtubules forming the flagellum. Details on the origin of the flagellum and on the formation of the secondary sheath of the sperm bundle are provided. Lastly, the evolution of the Coccid group is discussed from a phylogenetic perspective based on sperm ultrastructure.

Signature and parity splitting in rotational bands and chiral bands. Double minimum potential model

The effects of the signature and parity splitting in nuclear spectra and the properties of the chiral bands are analyzed basing on a one-dimensional Schrödinger equation with a double-minimum potential. Rotational bands in odd axial nuclei, alternating parity bands in even-even nuclei and the chiral bands in odd-odd nuclei are considered. The results obtained are discussed.

Signature and parity splitting in the rotational bands and the chiral bands. Double-minimum potential model

The effects of signature and parity splitting in nuclear spectra and the properties of the chiral bands are analyzed basing on a one-dimensional Schrodinger equation with a double-minimum potential. Rotational bands in odd axial and triaxial nuclei, alternating parity bands in even-even nuclei and the chiral bands in odd-odd nuclei are considered. The results obtained are discussed.

Trigeminal Nucleus Caudalis Anatomy: Guidance for Radiofrequency Dorsal Root Entry Zone Lesioning

Object: This study seeks to improve the accuracy of trigeminal nucleus caudalis dorsal root entry zone (DREZ) radiofrequency lesioning by quantifying the size and orientation of the nucleus caudalis. Methods: Using serial axial photographs of 6 formalin-fixed cadaver brainstems, digital nucleus caudalis measurements were taken at 1-mm intervals from the level of the obex to the C₂ dorsal nerve roots. Results: From the obex to the C₂ dorsal nerve roots, the nucleus caudalis decreases in width (from 2.6 ± 0.2 to 1.0 ± 0.3 mm) and, excluding superficial tract thickness, decreases in axial nucleus depth (from 2.4 ± 0.3 to 1.7 ± 0.2 mm). At levels between the obex and 10 mm caudal to the obex, the accessory nerve rootlets exit the brainstem at the junction of the spinal trigeminal tract and the dorsal spinocerebellar tract. Conclusion: This study details the anatomic dimensions and orientation of the nucleus caudalis for surgeons who perform DREZ lesioning.

Fundamental Deformations in Asymmetric Continuum

Abstract The complexity of processes in a seismic source zone has inspired us to reconsider a class of basic motions and deformations in an asymmetric continuum, including simple motions (translation and rotation, named spin) and simple deformations. Simple deformations include the axial nuclei, that is, point extension/compression, and the shear nuclei related to string-string point deformations. The point deformation is further redefined as another kind of rotational motion, called twist, representing oscillations of the main shear axes and their amplitudes. Some remarks are added on the recording systems used to measure these motions and deformations.

Effect of Mechanical Loading on Electrical Conductivity in Human Intervertebral Disk

The intervertebral disk (IVD), characterized as a charged, hydrated soft tissue, is the largest avascular structure in the body. Mechanical loading to the disk results in electromechanical transduction phenomenon as well as altered transport properties. Electrical conductivity is a material property of tissue depending on ion concentrations and diffusivities, which are in turn functions of tissue composition and structure. The aim of this study was to investigate the effect of mechanical loading on electrical behavior in human IVD tissues. We hypothesized that electrical conductivity in human IVD is strain-dependent, due to change in tissue composition caused by compression, and inhomogeneous, due to tissue structure and composition. We also hypothesized that conductivity in human annulus fibrosus (AF) is anisotropic, due to the layered structure of the tissue. Three lumbar IVDs were harvested from three human spines. From each disk, four AF specimens were prepared in each of the three principal directions (axial, circumferential, and radial), and four axial nucleus pulposus (NP) specimens were prepared. Conductivity was determined using a four-wire sense-current method and a custom-designed apparatus by measuring the resistance across the sample. Resistance measurements were taken at three levels of compression (0%, 10%, and 20%). Scanning electron microscopy (SEM) images of the human AF tissue were obtained in order to correlate tissue structure with conductivity results. Increasing compressive strain significantly decreased conductivity for all groups (p<0.05, analysis of variance (ANOVA)). Additionally, specimen orientation significantly affected electrical conductivity in the AF tissue, with conductivity in the radial direction being significantly lower than that in the axial or circumferential directions at all levels of compressive strain (p<0.05, ANOVA). Finally, conductivity in the NP tissue was significantly higher than that in the AF tissue (p<0.05, ANOVA). SEM images of the AF tissues showed evidence of microtubes orientated in the axial and circumferential directions, but not in the radial direction. This may suggest a relationship between tissue morphology and the anisotropic behavior of conductivity in the AF. The results of this investigation demonstrate that electrical conductivity in human IVD is strain-dependent and inhomogeneous, and that conductivity in the human AF tissue is anisotropic (i.e., direction-dependent). This anisotropic behavior is correlated with tissue structure shown in SEM images. This study provides important information regarding the effects of mechanical loading on solute transport and electrical behavior in IVD tissues.

Self-consistent separable random-phase approximation for Skyrme forces: Giant resonances in axial nuclei

We formulate the self-consistent separable random-phase-approximation (SRPA) method and specify it for Skyrme forces with pairing for the case of axially symmetric deformed nuclei. The factorization of the residual interaction allows to avoid diagonalization of high-rank RPA matrices, which dramatically reduces the computational expense. This advantage is crucial for the systems with a huge configuration space, first of all for deformed nuclei. SRPA takes self-consistently into account the contributions of both time-even and time-odd Skyrme terms as well as of the Coulomb force and pairing. The method is implemented to description of isovector E1 and isoscalar E2 giant resonances in a representative set of deformed nuclei: $^{154}$Sm, $^{238}$U, and $^{254}$No. Four different Skyrme parameterizations (SkT6, SkM*, SLy6, and SkI3) are employed to explore dependence of the strength distributions on some basic characteristics of the Skyrme functional and nuclear matter. In particular, we discuss the role of isoscalar and isovector effective masses and their relation to time-odd contributions. High sensitivity of the right flank of E1 resonance to different Skyrme forces and the related artificial structure effects are analyzed.

Anisotropic Ion Diffusivity in Intervertebral Disc: An Electrical Conductivity Approach

Investigation of the transport behavior of ions in intervertebral disc using an electrical conductivity method. To determine the electrical conductivity and ion diffusivity of nucleus pulposus and anulus fibrosus in 3 major directions (axial, circumferential, and radial). Knowledge of diffusivity of small molecules is important for understanding nutrition supply in intervertebral disc and disc degeneration. However, little is known on the anisotropic behaviors of ion diffusivity and of electrical conductivity in intervertebral disc. Electrical conductivity measurement was performed on 24 axial, circumferential, and radial anulus fibrosus specimens and 24 axial nucleus pulposus specimens from bovine coccygeal discs. The diffusivity of Na and Cl were estimated by the analysis of conductivity data. The electrical conductivity (mean +/- standard deviation; n = 24) of the bovine anulus fibrosus was 4.70 +/- 1.08 mS/cm in the axial, 2.86 +/- 0.83 mS/cm in the radial, and 4.38 +/- 1.25 mS/cm in the circumferential direction. For nucleus pulposus, the electrical conductivity (mean +/- standard deviation; n = 24) was 8.95 +/- 0.89 mS/cm. The mean value for nucleus pulposus was significantly higher than that of anulus fibrosus (t test, P < 0.05). For anulus fibrosus, the conductivity in the radial direction was significantly lower than in axial or circumferential directions. Similar trends were found for both Na and Cl diffusivities. Both electrical conductivity and ion diffusivity were highly sensitive to water content. Electrical conductivity and ion diffusivity of anulus fibrosus are anisotropic.

Pulsed EPR and NMR spectroscopy of paramagnetic iron porphyrinates and related iron macrocycles: how to understand patterns of spin delocalization and recognize macrocycle radicals.

Pulsed EPR spectroscopic techniques, including ESEEM (electron spin echo envelope modulation) and pulsed ENDOR (electron-nuclear double resonance), are extremely useful for determining the magnitudes of the hyperfine couplings of macrocycle and axial ligand nuclei to the unpaired electron(s) on the metal as a function of magnetic field orientation relative to the complex. These data can frequently be used to determine the orientation of the g-tensor and the distribution of spin density over the macrocycle, and to determine the metal orbital(s) containing unpaired electrons and the macrocycle orbital(s) involved in spin delocalization. However, these studies cannot be carried out on metal complexes that do not have resolved EPR signals, as in the case of paramagnetic even-electron metal complexes. In addition, the signs of the hyperfine couplings, which are not determined directly in either ESEEM or pulsed ENDOR experiments, are often needed in order to translate hyperfine couplings into spin densities. In these cases, NMR isotropic (hyperfine) shifts are extremely useful in determining the amount and sign of the spin density at each nucleus probed. For metal complexes of aromatic macrocycles such as porphyrins, chlorins, or corroles, simple rules allow prediction of whether spin delocalization occurs through sigma or pi bonds, and whether spin density on the ligands is of the same or opposite sign as that on the metal. In cases where the amount of spin density on the macrocycle and axial ligands is found to be too large for simple metal-ligand spin delocalization, a macrocycle radical may be suspected. Large spin density on the macrocycle that is of the same sign as that on the metal provides clear evidence of either no coupling or weak ferromagnetic coupling of a macrocycle radical to the unpaired electron(s) on the metal, while large spin density on the macrocycle that is of opposite sign to that on the metal provides clear evidence of antiferromagnetic coupling. The latter is found in a few iron porphyrinates and in most iron corrolates that have been reported thus far. It is now clear that iron corrolates are remarkably noninnocent complexes, with both negative and positive spin density on the macrocycle: for all chloroiron corrolates reported thus far, the balance of positive and negative spin density yields -0.65 to -0.79 spin on the macrocycle. On the other hand, for phenyliron corrolates, the balance of spin density on the macrocycle is zero, to within the accuracy of the calculations (Zakharieva, O.; Schünemann, V.; Gerdan, M.; Licoccia, S.; Cai, S.; Walker, F. A.; Trautwein, A. X. J. Am. Chem. Soc. 2002, 124, 6636-6648), although both negative and positive spin densities are found on the individual atoms. DFT calculations are invaluable in providing calculated spin densities at positions that can be probed by (1)H NMR spectroscopy, and the good agreement between calculated spin densities and measured hyperfine shifts at these positions leads to increased confidence in the calculated spin densities at positions that cannot be directly probed by (1)H NMR spectroscopy. (13)C NMR spectroscopic investigations of these complexes should be carried out to probe experimentally the nonprotonated carbon spin densities.

Calculated paramagnetic resonance parameters of a gallium arsenide cluster: Ga2As3

Dirac molecular-orbital calculations are reported for the trigonal bipyramid gallium arsenide Ga2As3 cluster, and comparisons are made to electron spin resonance spectra. The calculations show good agreement with the observed Δg and 71Ga hyperfine tensors. This theoretical study predicts both parallel and perpendicular components of the 75As hyperfine tensors, while experimentally only the perpendicular component was assigned. Furthermore, the calculated isotropic and anisotropic spin distributions show some discrepancy with the empirically deduced spin distributions. The discrepancy between the calculated and empirically deduced values may be traced back to the methodology used in the empirical treatment. The calculations predict that the single unpaired electron spin spend 31.4% of its time on each axial 71Ga nuclei, and, 12.4% of its time on each equatorial 75As nuclei.

EPR AND ENDOR INVESTIGATION OF SINGLE CRYSTALLINE AND POWDERED NaCl:Rh2+ and AgCl:Rh2+

Single crystalline NaCl doped with Rh2+ was investigated with electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR). An orthorhombic Rh2+ centre was found similar to that observed previously in AgCl, where Rh2+ substitutes for Na+ forming an [RhCl6]4− complex elongated along a [001] axis with a charge compensating Na+ vacancy in a second nearest Na+ position in the equatorial plane. In addition, two further axial Rh2+ centres were found, where the Na+ vacancy is not in the nearby equatorial plane. In the powder ENDOR spectra of NaCl:Rh2+ the interactions with axial second nearest 23Na and axial 103Rh nuclei could be resolved. Powder ENDOR spectra of AgCl:Rh2+ precipitated from aqueous solution showed that the Rh2+ defect is different from that generated in Rh2+ -doped AgCl grown from the melt. The limitations and possibilities of powder ENDOR are discussed. © 1997 Elsevier Science Ltd

Nonadiabatic mean field effects in theΔI=2staggering of superdeformed bands

It is shown that the {Delta}I=2 staggering in the isolated rotational band of axial nuclei may be explained by the nonaxial distortion of a self-consistent field under rotation. The method for obtaining the effective rotational Hamiltonian from the microscopic Routhian has been developed by using the mean field approach with the exact diagonalization in the space of intruder orbitals and the perturbation theory for low-j ones. The rotational dynamics of the simplest effective Hamiltonian, resulting in staggering, has been analyzed in its parameter space. The parameters are estimated in the axially deformed oscillator potential with and without pairing. The close connection of the phenomenon with the single-particle configurations of the superdeformed bands is discussed. {copyright} {ital 1997} {ital The American Physical Society}