Overview of periodontal clinical trials utilizing anti-infective or host modulating agents

In ants, antennal movements support the stimulus perception of olfactory and mechanosensory sensilla, most of which are located on the distal part of the antenna. In addition, sensory hair plates, campaniform sensilla, and Janet's organ provide the ant with proprioceptive information about the position, velocity, and acceleration of their antennae. We describe the morphology of these proprioceptors and their afferent neurons with special reference to the trap-jaw ant genus Odontomachus. All these sensory neurons terminate in the dorsal lobe, the part of the brain that also contains antennal motor neurons and that controls antennal movements. Neurons originating from campaniform sensilla and Janet's organ send additional collaterals into the subesophageal ganglion. Particularly fast antennal movements occur during protective withdrawal of the antenna. Under natural conditions, antennal retraction in Odontomachus always precedes the rapid mandible strike. We have found no indication of monosynaptic coupling between the antennal proprioceptive afferents and the trigger motor neurons that release the mandible strike. Instead, complex neuronal interactions in the involved neuromeres are more likely to control the timing of the two reflexes. The normal behavioral sequence of antennal retraction can be reversed by artificially releasing the mandible strike earlier than normal. The significance of fast antennal reflexes and of proprioceptive control is discussed.     

Peripheral synapses at identified mechanosensory neurons in spiders: three-dimensional reconstruction and GABA immunocytochemistry

The mechanosensory organs of arachnids receive diverse peripheral inputs. Little is known about the origin, distribution, and function of these chemical synapses, which we examined in lyriform slit sense organ VS-3 of the spider Cupiennius salei. The cuticular slits of this organ are each associated with two large bipolar mechanosensory neurons with different adaptation rates. With intracellular recording, we have now been able to correlate directly the staining intensity of a neuron for acetylcholinesterase with its adaptation rate, thus allowing us simply to stain a neuron to identify its functional type. All rapidly adapting neurons stain more heavily than slowly adapting neurons. Immunostaining of whole-mount preparations reveals GABA-like immunoreactive fibers forming numerous varicosities at the surface of all sensory neurons in VS-3; peripheral GABA-like immunoreactive somata are lacking. Sectioning the leg nerve procures rapid degeneration of most fiber profiles, confirming that the fibers are efferent. Punctate synapsin-like immunoreactivity colocalizes to these varicosities, although some synapsin-like immunoreactive puncta are GABA-immunonegative. Fibers with similar immunoreactivities are also associated with trichobothria, tactile hairs, internal joint receptors, i.e. other types of spider mechanosensory organs. In organ VS-3, immunoreactivity is most dense across the initial axon segment. The exact distribution of peripheral synapses was reconstructed from a 10-microm-long electron micrograph series of the dendritic, somatic, and initial axon regions of acetylcholinesterase-stained VS-3 neurons. These reveal a pattern similar to that of the synapsin-like immunoreactivity. Two different types of synapse were distinguished on the basis of their presynaptic vesicle populations. Many peripheral synapses thus appear to derive from efferent GABA-like immunoreactive fibers and probably provide centrifugal inhibitory control of primary mechanosensory activities.     

Haltere afferents provide direct, electrotonic input to a steering motor neuron in the blowfly, Calliphora

The first basalar muscle (b1) is one of 17 small muscles in flies that control changes in wing stroke kinematics during steering maneuvers. The b1 is unique, however, in that it fires a single phase-locked spike during each wingbeat cycle. The phaselocked firing of the b1's motor neuron (mnb1) is thought to result from wingbeat-synchronous mechanosensory input, such as that originating from the campaniform sensilla at the base of the halteres. Halteres are sophisticated equilibrium organs of flies that function to detect angular rotations of the body during flight. We have developed a new preparation to determine whether the campaniform sensilla at the base of the halteres are responsible for the phasic activity of b1. Using intracellular recording and mechanical stimulation, we have found one identified haltere campaniform field (dF2) that provides strong synaptic input to the mnb1. This haltere to mnb1 connection consists of a fast and a slow component. The fast component is monosynaptic, mediated by an electrical synapse, and thus can follow haltere stimulation at high frequencies. The slow component is possibly polysynaptic, mediated by a chemical synapse, and fatigues at high stimulus frequencies. Thus, the fast monosynaptic electrical pathway between haltere afferents and mnb1 may be responsible in part for the phase-locked firing of b1 during flight.     

Dendritic integration in olfactory sensory neurons: a steady-state analysis of how the neuron structure and neuron environment influence the coding of odor intensity

Response properties of the receptor potential at steady state were analyzed in a biophysical model of an olfactory sensory neuron embedded in a multicell environment. The neuron structure was described as a set of several identical dendrites (or cilia) bearing the transduction mechanisms, joined to a nonsensory part--dendritic knob, soma, and axon. The different ionic compositions of the media surrounding the neuron sensory and nonsensory parts and the extraneuronal voltage sources, which both result from the presence of auxiliary cells, were also taken into account. Analytical solutions were found to describe how the receptor potential at the nonsensory part responds to a uniform change in the odorant-dependent conductance resulting from odorant stimulation of the sensory dendrites. We investigated the influence of various geometrical and electrical parameters on the receptor-potential response in the classical model neuron within a homogeneous environment and in the model neuron surrounded with auxiliary cells. First, it was found that the maximum amplitude of the receptor potential is independent of the neuron structure in the absence of auxiliary cells but not in their presence. In the latter case, the amplitude decreases with the length and number of sensory dendrites and with the input resistance of the nonsensory part. Second, the sensitivity (as measured by the increase in membrane conductance at half-maximum response) of the neuron model in the absence of auxiliary cells is higher, but its dynamic range is narrower than in their presence. The dynamic range is wide and the sensitivity low when the input resistance of the nonsensory part is small and the sensory dendrite is unbranched. Both sensitivity and dynamic range are higher for a longer dendrite. These results help understand the morphology of insect olfactory sensilla and can be generalized to other neuron types.     

Motility of the vestibular hair cell of the guinea pig and bull frog

The motile response of the isolated vestibular hair cell induced by a neurotransmitter was studied. After application of both physostigmine and acetylcholine (Ach) as well as glutamic acid, shortening or tilting of the neck of the guinea pig hair cell was observed. These findings suggest that the effect of a neurotransmitter in the neck region as well as the efferent neuron is involved in the motile response. The location of F-action in isolated vestibular hair cells was investigated by using FITC-labeled phalloidin. In freeze-fixed vestibular hair cells, marked labeling was noted in the hair bundle, cuticular plate and throughout the cytoplasm. After application of both physostigmine and Ach, the labeling in the cuticular plate and the cytoplasm became more intense than that in the hair bundle. Alteration of this phalloidin-labeling pattern suggests that actin could play an important role in the self movement of vestibular sensory cells. The shape of the bull frog hair cell also changed after application of Ach. At the same time, spontaneous discharge and the time constant of the posterior semicircular canal nerve activity decreased. These results suggest that an adaptation mechanism induced by change in the cell shape and membrane potential inhibits the activity of the afferent neuron. Furthermore, these active events could be closely related to the active regulation of vestibular hair cell transmission.     

The role of 18-methyleicosanoic acid in the structure and formation of mammalian hair fibres

Although branched chain fatty acids perform many functions in biological systems, the importance of the anteiso 18 methyleicosanoic acid (MEA) has only recently been recognized. In this first review on MEA its role and distribution is explored. MEA has been found in minor amounts in the fatty acid components of a wide range of biological materials, but the current interest results from it being the major covalently bound fatty acid in mammalian hair fibres, a finding which is unusual because protein-bound fatty acids are typically straight-chain, even-numbered acids (C14-C18). MEA is released by surface restricted reagents indicating that it is located exclusively in or on the surface of the cuticle cells, a conclusion that has been verified by analysis of isolated cuticle cells, X-ray photoelectron spectroscopy (XPS) and secondary-ion mass spectroscopy (SIMS) studies support these results in that they show the surface of the cuticle to be predominantly hydrocarbon. When either neutral hydroxylamine or acidic chlorine solutions are applied to hair and wool fibres fatty acids are liberated, indicating the presence of thioester bonds. Calculations, based on fatty acid and amino acid analysis, indicate that approximately one residue in 10 of the cuticular membrane protein is a fatty acid thioester of cysteine. Removal of this covalently linked fatty acid renders the fibre hydrophilic, thus offering a chemical explanation for many technological and cosmetic treatments of mammalian fibres. Examination of the fibre surface and that of isolated cuticle cells by transmission electron microscopy (TEM) confirms the presence of a thin non-staining continuous layer surrounding the cuticle cells. Alkaline treatments which remove the bound fatty acids were found to disrupt this layer. TEM examination of developing hair fibres has indicated that the fatty acid layer on the upper surface and scale edges of the cuticle cell differs from that of the underside of the cell. Similar structural studies of hair from patients with maple syrup urine disease (MSUD) support the findings that thioester-bound MEA is limited to the upper surface of fibre cuticle cells. The current model proposed for the boundary layer consists of crosslinked protein with surface thioester-linked fatty acids, forming a continuous hydrophobic layer on the upper surface and scale edges of the cells.     

Ultrastructure and blood-nerve barrier of chordotonal organs in the Drosophila embryo

Chordotonal organs of Drosophila embryos have become models for studies of developmental biology and molecular genetics due to their consistent segmental placement and mutability. Our first goal was to find the origin and anatomical correlate of the blood-nerve barrier of this PNS proprioreceptor in wild type embryos. The concept of a blood-nerve barrier for the PNS of the Drosophila embryo is new, and the present data are the first in this regard. A second goal was to reveal the ultrastructure of these four-celled stretch receptors, focusing particularly on the 'core' of this organ: the bipolar neuron enclosed by a scolopale cell. These latter data have resulted in a graphic reconstruction of the chordotonal organ which reveals how the four consistent cells fit together. At Stage 13 we first observed a clearly recognizable scolopale cell with an enclosed neuron. Surprisingly, an operative blood-nerve barrier, comprised of occlusive pleated-sheet septate junctions, exists at this relatively early stage. A blood-brain barrier is not yet functioning in the CNS during this same stage, as the perineurium is not present until Stage 17. Cross-sectional views of a more mature chordotonal organ show that the neuron's inner segment has a 'tongue-in-groove' formation which fits the dendrite into the scolopale cell. Other newly discovered fine structural features are: hemidesmosomes linking individual scolopale rod bundles to the inner dendrite, and a cap cell matrix bonding with the tip of the ciliary dendrite. Functional aspects of these findings are discussed.     

Orientation Dependence of Columnar Dendritic Growth with Sidebranching Behaviors in Directional Solidification: Insights from Phase-Field Simulations

In this study, a thin-interface phase-field model was employed to study the orientation dependence of the columnar dendritic growth with sidebranching behaviors in directional solidification. It was found that the dimensionless tip undercooling increases with the increase of misorientation angle for three pulling velocities. The primary spacing is found to be a function of misorientation angle, and the dimensionless primary spacing with respect to the misorientation angle follows the orientation correction given by Gandin and Rappaz (Acta. Metall. 42:2233–2246, 1994). For the analysis of the dendritic tip, the two-dimensional (2-D) form of the nonaxisymmetric needle crystal was used to determine the radius of the tilted columnar dendrite. Based on the definitions of open side and constrained side of the dendrite, the analysis of the width active sidebranches and the dendritic area in 2-D with respect to the distance from the dendritic tip was carried out to investigate the asymmetrical dendrite envelop and sidebranching behaviors on the two sides in directional solidification. The obtained prefactor and exponent with respect to misorientation angle are discussed, showing that the sidebranching behaviors of a tilted columnar dendritic array obey a similar power-law relationship with that of a free dendritic growth.     

Dendrite characteristics in directionally solidified Pb-8 Pct Au and Pb-3 Pct Pd alloys

Pb-8 pct Au and Pb-3 pct Pd alloy specimens partially directionally solidified and then quenched have been examined in order to characterize their dendritic microstructural details and solute composition profiles. Dendrite tip radii have been measured by a controlled sectioning technique. Dendrite tip radius, solute content of quenched liquid at the dendrite tip, solute profile within the interdendritic region and ahead of the dendrite tip, cell length, and the primary arm spacing values obtained experimentally have been compared with the theoretical predictions. Two groups of models, one based on the minimum undercooled dendrite tip criterion and the other based on the marginal stability at the dendrite tip, have been examined. The Burden and Hunt model, based on the “minimum undercooling” approach, does not predict the observed behavior. However, a modification of the Burden and Hunt's model recently proposed by Laxmanan shows a good fit to the experimentally observed parameters. The models based on the marginal stability approach also predict most of the observed behavior well. It is concluded that quantitative comparison of the primary arm spacing measurements can not form the basis of distinguishing among the various dendrite growth models in a positive temperature gradient. There is a critical need to carry out carefully controlled directional solidification experiments in a well characterized metallic alloy system to help distinguish between the minium dendrite tip undercooling and the marginal stability approaches. New experiments based on simultaneous measurements of (a) dendrite tip radius, (b) dendrite tip temperature, and (c) the solute profile ahead of the dendrite tip—all in a convection free atmosphere—are required.     

Target neuron specification of short-term synaptic facilitation and depression in the cricket CNS

We investigated the role of retrograde signals in the regulation of short-term synaptic depression and facilitation by characterizing the form of plasticity expressed at novel synapses on four giant interneurons in the cricket cercal sensory system. We induced the formation of novel synapses by transplanting a mesothoracic leg and its associated sensory neurons to the cricket terminal abdominal segment. Axons of ectopic leg sensory neurons regenerated and innervated the host terminal abdominal ganglion forming monosynaptic connections with the medial giant interneuron (MGI), lateral giant interneuron (LGI), and interneurons 7-1a and 9-2a. The plasticity expressed by these synapses was characterized by stimulating a sensory neuron with pairs of stimuli at various frequencies or with trains of 10 stimuli delivered at 100 Hz and measuring the change in excitatory postsynaptic potential amplitude recorded in the postsynaptic neuron. Novel synapses of a leg tactile hair on 7-1a depressed, as did control synapses of cercal sensory neurons on this interneuron. Novel synapses of leg campaniform sensilla (CS) sensory neurons on MGI, like MGI's control synapses, always facilitated. The form of plasticity expressed by novel synapses is thus consistent with that observed at control synapses. Leg CS synapses with 9-2a also facilitated; however, the plasticity expressed by these sensory neurons is dependent on the identity of the postsynaptic cell since the synapses these same sensory neurons formed with LGI always depressed. We conclude that the form of plasticity expressed at these synaptic connections is determined retrogradely by the postsynaptic cell.     

Compartmentalized vesicular traffic around the hair cell cuticular plate

Through thin-section and freeze-fracture electron microscopy, we identify structural correlates of an intense vesicular traffic in a narrow band of cytoplasm around the cuticular plate of the bullfrog vestibular hair cells. Myriads of coated and uncoated vesicles associated with longitudinally oriented microtubules populate the narrow cytoplasmic region between the cuticular plate and the actin network of the apical junctional belt. If microtubules in the sensory hair cells, like those in axons, are pathways for organelle transport, then the characteristic distribution of microtubules around the cuticular plate represents transport pathways across the apical region of the hair cells. This compartmentalized membrane traffic system appears to support an intense vesicular release and uptake along a band of apical plasma membrane near the cell border. Functions of this transport system may include membrane recycling as well as exocytotic and endocytotic exchange between the hair cell cytoplasm and the endolymphatic compartment.     

Further analysis of dendritic growth data for succinonitrile

Data reported by Glicksman, Schaefer and Ayers¹ on dendritic growth kinetics in undercooled succinotrile have been reanalyzed using the Trivedi model of dendritic growth, after relaxation of the arbitrary requirement that the dendrite grows with a tip radius, ρ max, that gives the maximum velocity, V_max The experimental results, for both tip radius and growth velocity, fit the Trivedi model with a tip radius some 2 to 4 times greater than ρ_max. The tip radius adopted by a dendrite growing in liquid at a given undercooling, appears to correspond to the radius which gives relative instability of a sphere growing in liquid with the same undercooling. The experimental results also give qualitative support to the model recently proposed by Cantor and Vogel for the influence of fluid flow on dendritic growth.     

Evolution of Specific Surface Area with Solid Volume Fraction During Coalescence with Parabolic Shape Assumption for Dendrite

Coalescence of secondary dendrite arms in terms of the evolution of specific surface area for a dendritic envelope with respect to the fraction solid during directional solidification is studied analytically in 2-D and 3-D frame of reference. For 2D case study, the dendritic growth has been captured by gradual penetration of a parabola with fixed tip radius (??) inside a square domain, while for 3D case study, we replace the parabola and square domain for 2-D case with a paraboloid of revolution and cubic domain, respectively. The dimensions of the enclosing volumes are characterized by the secondary dendrite arm-spacing. Coalescence obtained by the analytical solution is compared with existing dendrite growth simulation results obtained by phase-field method.     

Quantitative study of primitive pyramidal cells in rat anterior cingular cortex

In the present paper the primitive pyramidal cells of the Vthlayer of the anterior cingulate cortex in adult male white rats were analyzed quantitatively and compared statisticaly with large pyramidal cells of the same region. The number of dendrites, the total lengths of dendrites, the number of spines and the density of spines -- according to the order of dendrites -- show similarity between the primitive pyramidal cells and the large pyramidal cells the latter one exhibit the higher values. The curves of distribution of the various density of spines along the apical main dendrite of both cell types are similar in shape, too. The lengths of the dendritic fields and their basal spines-values are without significant distinction for both cell types, however there are more dendritic fields in large pyramidal cells. Refered to a complete pyramidal neuron they can say: there are significantly higher values in large pyramidal cells for the number of dendrites and their total lengths, the total number of spines, the number of branching sites sites and free endings. However the density of spines of the complete neuron has no significant differences between primitive and large pyramidal cells.     

Comparative ultrastructure of the cuticle of trichostrongyle nematodes

The ultrastructure of the cuticle was examined in Austrostrongylus victoriensis, Patricialina birdi and Woolleya monodelphis (Herpetostrongylidae) from marsupials, Paraustrostrongylus ratti (Herpetostrongylidae) from rodents, Nippostrongylus magnus and Odilia bainae (Heligmonellidae) from rodents, Cooperia oncophora and Camelostrongylus mentulatus (Trichostrongylidae) from ruminants, and Nematodirus spathiger (Molineidae) from ruminants. The principal cuticular layers described previously were present in all species investigated. Major differences in the shape and composition of cuticular struts were observed as well as differences in components of the median zone of the cuticle, including the fluid-filled regions present in several species. Several different types of strut were observed. Although strut structure within the Heligmonellidae appeared to be constant, there were variations within both the Herpetostrongylidae and Trichostrongylidae. In Nem. spathiger the cuticular ridges lacked struts. The diversity of structures found in the species examined suggests that more extensive comparative studies of the trichostrongyle cuticle are warranted.     

Thermodynamic-kinetic simulation of constrained dendrite growth in steels

A model of constrained dendritic growth for steels, based on thermodynamic and kinetic theory, is presented. The model links thermodynamic chemical potential-equality equations to an existing, approximate treatment of constrained dendritic growth in multicomponent steels, taking into account the deviation from the local thermodynamic equilibrium of the phase interface caused by interface friction, capillarity, and solute trapping. Due to the thermodynamic approach, with a thermodynamic model and recently assessed data, the present treatment yields a more accurate determination of phase stabilities than the earlier methods. Depending on the steel composition and the growth conditions (growth rate and temperature gradient), the model determines the dendrite tip undercooling, the primary solid phase (ferrite or austenite), the stability of that phase, certain dimensions of the microstructure, and the solute accumulation ahead of the dendrite tip. A special optional calculation is that of the equally probable formation of ferrite and austenite in stainless steels. Calculations for testing the model and for validating it with experimental data are presented.     

Identification of mycotoxins produced by species of Fusarium and Stachybotrys obtained from Eastern Europe

Sense organs that lie just posterior to the lips on the sides of the body of Heterakis gallinarum have been examined by scanning and transmission electron microscopy. The sense organs appear externally as a short peg surrounded by a collarlike elevation of cuticle. Each sense organ contains the endings of 2 sensory dendrites; 1 extending to the tip of the peg is probably chemosensitive, while the other ending just within the cuticular cylinder that projects internally from the peg, is probably mechanosensitive.     

Fine needle aspiration cytology of mycetoma

Models for the surface of cuticle cells in hair fibers consist of a monolayer of fatty acids covalently bound to the underlying protein membrane by thioester linkages. The most prominent of these fatty acids is 18-methyleicosanoic acid (C21a), the synthesis of which requires the oxidative decarboxylation of isoleucine. Maple syrup urine disease (MSUD) is caused by an inherited deficiency in the enzyme branched chain 2-oxo acid dehydrogenase, which leads to the accumulation of branched chain alpha-keto-acids derived from the amino acids, leucine, isoleucine, and valine. Transmission electron microscopy studies of developing hair fibers show a structural defect in the fiber shaft in hair from patients with MSUD. This defect is confined to the cuticle of the fiber, where the cuticle membrane directly apposes the intercellular material. Thus, the defect indicates that C21a is located exclusively on the upper surface of fiber cuticle cells. Lipid analysis of MSUD hairs has demonstrated significant changes in the relative abundance of the covalently bound fatty acids and an almost complete absence of C21a, whereas there was little difference in the amino acid composition compared with normal hair. These results provide further evidence for the existence of the surface lipid monolayer and its crucial role in cellular adhesion.     

Analysis of solidification microstructures in Fe-Ni-Cr single-crystal welds

A geometric analysis technique for the evaluation of the microstructures in autogenous single-crystal electron beam welds has been previously developed. In the present work, these analytical methods are further extended, and a general procedure for predicting the solidification microstructure of single-crystal welds with any arbitrary orientation is established. Examples of this general analysis are given for several welding orientations. It is shown that a nonsymmetric cell structure is expected in transverse micrographs for most welding geometries. The development of steady-state conditions in the weld pool is also examined in terms of the weld pool size, its shape (as revealed by the dendritic growth pattern), and the size of the dendritic cells. It is found that steady state is established within a few millimeters of the beginning of the weld. Furthermore, steady state is achieved faster in welds made at higher welding speeds. A general analysis of the three-dimensional (3-D) weld pool shape based on the dendritic structure as revealed in the two-dimensional (2-D) transverse micrographs is also developed. It is shown that in combination with information on the preferred growth direction as a function of the solidification front orientation, the entire dendritic growth pattern in single-crystal welds can be predicted. A comparison with the actual weld micrographs shows a reasonable agreement between the theory and experiment. Finally, the theoretical analysis of the dendrite tip radius is extended from binary systems to include the case of ternary systems. The theoretical dendrite trunk spacing in a ternary Fe-Ni-Cr alloy is calculated from the dendrite tip radius and is compared with the experimental values for several weld conditions. Good agreement between experiment and theory is found. Formerly Visiting Scientist, Solid State Division, Oak Ridge National Laboratory.