Conduction in demyelinated axons—A simplified model

This paper is concerned with conduction of the nervous impulse in a myelinated axon and the effect of demyelination on conduction characteristics. A model of nerve conduction called the “gunpowder fuse” model is presented which accurately predicts conduction velocities in both myelinated and unmyelinated nerves. The effect on conduction velocity in this model by reducing myelin thickness is examined by utilizing basic data and building and equivalent circuit. The result is a curve relating reduced conduction velocity to reduced myelin thickness. A similar analysis and resultant curve is derived from a saltatory conduction model. Supported in part by National Multiple Sclerosis Society Research Grant No. 516 and Air Force Grant AFOSR 669-67.     

Distinguished words in data sequences: Analysis and applications to neural coding and other fields

This paper concerns sequences of letters in which certain “distinguished” words are of interest. Such sequences arise as data in numerous fields including genetics and neuroscience. A probability distribution is given for the number of occurrences of a chosen word in a randomized sequence of letters. Such words are considered “favored” if they occur more than expected at random. Favored words have been discovered in nerve impulse trains and may reflect a neural coding scheme. This article is dedicated to my mother, Margaret Oakley Dayhoff, whose enthusiasm encouraged me to pursue research in mathematical biology.     

Mycobacterium leprae — The outer lipoidal surface

There is now a considerable body of evidence to suggest that the phthiocerol-containing lipids, including the phenolic glycolipids, comprise the so-called “peribacillary substance”, “spherical droplets”, “foamy structures” and “capsular materials” ofMycobacterium leprae. Thus, the phthiocerol-containing lipid capsule may be directly responsible for the intracellular survival ofMycobacterium leprae.     

Physico-chemical model of a voltage-gated sodium channel

A permeant ion is known to create in the channel pore a local electrical field, the intensity of which exceeds the intensity of an electrical field produced by the membrane potential. In our study, we consider a sodium channel model, in which the effects of a permeant ion, an inactivating particle, and pharmacological agents on mobile charged groups of the channel are semi-phenomenologically taken into account by using motion equations for a generalized structural variable. Stationary solutions for the equation correspond to “open,” “closed,” and “inactivated” channel states. Because of this, the channel free energy profile, as a function of the structural variable, has three local minima. The three energy values of these states depend both on the electrical field applied externally and on the near-membrane concentrations of permeant ions and acting pharmacological agents. Sodium channel activation and inactivation kinetics are considered resulting from relative changes of the free energy typical of the above three states of the channel. The results we obtained in the course of channel activation and inactivation modeling and their voltage dependence are qualitatively consistent with the commonly known experimental data. The proposed model allows one to qualitatively predict the dependence of the sodium channel kinetic characteristics on the concentrations of permeant ions and pharmacological agents.     

Source-sink landscape theory and its ecological significance

Exploring the relationships between landscape pattern and ecological processes is the key topic of landscape ecology, for which, a large number of indices as well as landscape pattern analysis model were developed. However, one problem faced by landscape ecologists is that it is hard to link the landscape indices with a specific ecological process. Linking landscape pattern and ecological processes has become a challenge for landscape ecologists. “Source” and “sink” are common concepts used in air pollution research, by which the movement direction and pattern of different pollutants in air can be clearly identified. In fact, for any ecological process, the research can be considered as a balance between the source and the sink in space. Thus, the concepts of “source” and “sink” could be implemented to the research of landscape pattern and ecological processes. In this paper, a theory of sourcesink landscape was proposed, which include: (1) In the research of landscape pattern and ecological process, all landscape types can be divided into two groups, “source” landscape and “sink” landscape. “Source” landscape contributes positively to the ecological process, while “sink” landscape is unhelpful to the ecological process. (2) Both landscapes are recognized with regard to the specific ecological process. “Source” landscape in a target ecological process may change into a “sink” landscape as in another ecological process. Therefore, the ecological process should be determined before “source” or “sink” landscape were defined. (3) The key point to distinguish “source” landscape from “sink” landscape is to quantify the effect of landscape on ecological process. The positive effect is made by “source” landscape, and the negative effect by “sink” landscape. (4) For the same ecological process, the contribution of “source” landscapes may vary, and it is the same to the “sink” landscapes. It is required to determine the weight of each landscape type on ecological processes. (5) The sourcesink principle can be applied to non-point source pollution control, biologic diversity protection, urban heat island effect mitigation, etc. However, the landscape evaluation models need to be calibrated respectively, because different ecological processes correspond with different source-sink landscapes and evaluation models for the different study areas. This theory is helpful to further study landscape pattern and ecological process, and offers a basis for new landscape index design. __________ Translated from Acta Ecologica Sinica, 2006, 26(5): 1444–1449 [译自: 生态学报]     

Interaction of cycles

We discuss under the McCulloch and Pitts assumptions for neural nets a circuit consisting ofk cycles such that one cycle is activated by an outside stimulus and sends an impulse to a second cycle which in its turn sends an impulse to the next cycle, etc., up to thekth cycle, which sends an impulse to a response. We thus have a “series” ofk cycles “interacting”. We give several theorems regarding the response patterns of such circuits under the additional constraint that the stimulus acts but once, and at the time it acts the circuit is at rest.     

Energy efficiency of electron plasma emitters

Electron emission influence from gas-discharge plasma on plasma emitter energy parameters is considered. It is shown, that electron emission from plasma is accompanied by energy contribution redistribution in the gas-discharge from plasma emitter supplies sources—the gas-discharge power supply and the accelerating voltage power supply. Some modes of electron emission as a result can be realized: “a probe measurements mode,” “a transitive mode,” and “a full switching mode.”     

Nerves in the endodermal canals of hydromedusae and their role in swimming inhibition

N eoturris breviconis (Anthomedusae) has a nerve plexus in the walls of its endodermal canals. The plexus is distinct from the ectodermal nerve plexuses supplying the radial and circular muscles in the ectoderm and no connections have been observed between them. Stimulation of the endodermal plexus evokes electrical events recorded extracellularly as “E” potentials. These propagate through all areas where the plexus has been shown by immunohistology to exist and nowhere else. When Neoturris is ingesting food, trains of “E” potentials propagate down the radial canals to the margin and cause inhibition of swimming. This response is distinct from the inhibition of swimming associated with contractions of the radial muscles but both may play a part in feeding and involve chemoreceptors. Preliminary observations suggest that the “E” system occurs in other medusae including Aglantha digitale (Trachymedusae) where the conduction pathway was previously thought to be an excitable epithelium.     

A membrane filter direct count technique for enumeratingBdellovibrio

A membrane filter direct count method was devised for enumeratingBdellovibrio cells in “clean” suspensions. The procedure involves filtering a specified volume of a diluted, Trisbuffered suspension ofBdellovibrio cells through a known area of a 100-nm-pore-size Millipore brand membrane filter. A clarification solvent was used to render the filter transparent, so that the bdeloyvibrios on the filter could be photomicrographed and counted either visually or by means of a Quantimet 720 Image Analyzing Computer. The number ofBdellovibrio cells per milliliter in the undituted suspension could be calculated from the mean number of cells per unit area of the filter, the dilution factor, and the volume of diluted suspension filtered. TheBdellovibrio cells were distributed on the filters in a Poisson manner when there were not more than about 3.5 cells per 100 μm² of filter surface. The membrane filter direct counts correlated well with direct counts obtained by the Petroff-Hausser method. The correlation of direct counts with plaque (“viable”) counts showed that 80 to 95% of the direct-countedBdellovibrio cells in the clean suspensions were capable of forming plaques on lawns of suitable substrate bacteria. *** DIRECT SUPPORT *** A01R4002 00007     

Electrical Concepts in the Surface Electromyographic Signal

There are frequently used electrical terms in the biofeedback literature. Often it is assumed that the reader has detailed knowledge of these terms. The difficulty begins when seemingly familiar terms are used as a basis for an in-depth explanation of the process of electromyography. For example, the concept of impedance is based on three building blocks of electricity: current, voltage and resistance. The term “impedance” is found in every manual for biofeedback equipment with the suggestion that the electrode site be kept “low” and the encoder input “high”. A little electrical knowledge can explain why this is so and in the process formulate a more thorough understanding of the equipment used everyday with a client.     

Correlations between the psychological peculiarities of an individual and the efficacy of a single neurofeedback session (by the EEG characteristics)

Modifications of different EEG rhythms induced by a single neurofeedback session (by the EEG characteristics) directed toward an increase in the ratio of the spectral powers (SPs) of the α vs θ oscillations were compared with the psychological characteristics of the tested subjects (the group included 30 persons). A generally accepted neurofeedback technique was used; the intensity of acoustic white noise served as the feedback signal. EEG potentials were recorded from the C3 and C4 leads. Psychological testing was carried out using Eysenck’s (EPQ), Rusalov’s (OST), and (16 PF) questionnaires. The directions of changes in the SPs of EEG frequency components were found to significantly correlate with some individuality-related peculiarities of the tested subjects. The SP of the δ rhythm correlated with the EPQ scale “neuroticism,” OST scale “social plasticity,” and 16 PF factors H (“parmia”), I (“premsia”), and Q₃ (“self-control of behavior”). The SP of the θ component demonstrated correlations with the OST scales “ergisity,” “plasticity,” and “social temp” and with 16 PF factors M (“autia”), Q₄ (“frustration”), and Q1 (“exvia”). The SP of the α rhythm correlated with 16 PF factors Q₃ (“self-control of behavior”), G (“strength of superEgo”), O (“hypothymia”), L (“protension”), and N (“shrewdness”). The SP of the β rhythm correlated with the OST scale “emotionality,” while that of the γ rhythm showed correlations with the 16 PF indices L (“protension”) and M (“autia”). Changes in the ratio of the α vs θ SPs correlated with the EPQ scale “neuroticism.” Thus, our data confirm the statement that a high individual variability of the results of a single (first in the series) neurofeedback session is to a great extent related to peculiarities of the individual psychological pattern of the subject. Neirofiziologiya/Neurophysiology, Vol. 38, No. 3, pp. 239–247, May–June, 2006.     

Reflex responses of the spinal cord under conditions of the spinal “superreflexia” evoked by pharmacological agents increasing its excitability

We studied monosynaptic reflex discharges (MRD) recorded from the ventral roots (VR) of rats subjected to systemic administration with thyroliberin, thyroxin, or 4-aminopyridine (4-AP). Under such conditions, in some of the experiments the MRD amplitude reached values sufficient to excite non-active VR fibers. In these cases, immediately after the MRD peak had been reached, abnormally increased responses (AIR) developed, whose amplitude was 2–2.5 times higher than the amplitude of highly facilitated MRD. Proofs are presented that AIR reflect excitation of “neighboring” VR fibers, which were not involved in the reflex response, and MRD plays the role of a “stimulus” exciting these fibers. Therefore, we demonstrate the possibility of transmission of excitation from “active” to “silent” fibers within a nerve trunk under conditions of the development of “superreflexia”. This state can be considered a model of excitation spreading via a non-synaptic pathway under conditions of hyperexcitability of the CNS structures, in seizure states in particular. neirofiziologiya/Neurophysiology, Vol. 32, No. 2, pp. 120–127, March–April, 2000.     

The most likely voltage path and large deviations approximations for integrate-and-fire neurons

We develop theory and numerical methods for computing the most likely subthreshold voltage path of a noisy integrate-and-fire (IF) neuron, given observations of the neuron’s superthreshold spiking activity. This optimal voltage path satisfies a second-order ordinary differential (Euler-Lagrange) equation which may be solved analytically in a number of special cases, and which may be solved numerically in general via a simple “shooting” algorithm. Our results are applicable for both linear and nonlinear subthreshold dynamics, and in certain cases may be extended to correlated subthreshold noise sources. We also show how this optimal voltage may be used to obtain approximations to (1) the likelihood that an IF cell with a given set of parameters was responsible for the observed spike train; and (2) the instantaneous firing rate and interspike interval distribution of a given noisy IF cell. The latter probability approximations are based on the classical Freidlin-Wentzell theory of large deviations principles for stochastic differential equations. We close by comparing this most likely voltage path to the true observed subthreshold voltage trace in a case when intracellular voltage recordings are available in vitro. Action Editor: Peter Latham     

Influence of initial substratum surface tension on marine micro- and macro-fouling in the Gulf of Thailand

The density of five major groups of fouling organisms (bacteria, diatoms, choanoflagellates, ciliates, macroorganisms) on seven artificial substrata with surface tensions between 19.0 and 64.5 mN m⁻¹ was studied in the Gulf of Thailand. Two series of test panels of the different substrata were immersed into the sea between 3 hours and 64 days (macrofauna 128 days). The results show that surface tension has a limited impact on the density of the organisms. Only bacteria settled continuously in significantly lower numbers on materials within the minimum bioadhesive range (20–25 mN m⁻¹) than on other substrata. Significant differences between the substrata may disappear after long exposure, as in series 2 after 16 days. For diatoms and protozoa, a colonisation pattern similar to that of bacteria with a minimum of 20–25 mN m⁻¹ was detected after several exposure intervals. However, it was never recorded in more than 3 exposure intervals in a row. The colonisation pattern of macroorganisms could not be attributed to substratum surface tension. An index, called “colonisation degree” is introduced to give a general impression of the density of organisms on the materials tested. The colonisation degree did not show any significant difference at any exposure interval. The present results clearly suggest that substratum surface tension is easily overshadowed by other factors in colonisation processes under natural conditions. *** DIRECT SUPPORT *** A03B6037 00003     

New perspectives on the angiosperm female gametophyte

This review builds upon previous classifications of angiosperm female gametophytes but offers two new perspectives. Firstly, the course of development is compared to an algorithm: a predetermined set of rules that produces a mature female gametophyte. This analogy allows hypotheses to be developed as to what changes in the “developmental program” are responsible for variant forms of development. Secondly, the review recognizes that the four meiotic products of a megaspore mother cell have different genetic constitutions and may have conflicting interests. In most cases, only one member of a megaspore tetrad gives rise to a functional egg. This megaspore is called the germinal spore. The other members of the tetrad are called somatic spores. Somatic spores do not give rise to functional eggs and, therefore, cannot leave direct genetic descendants. Non-monosporic embryo sacs are genetic chimeras containing derivatives of more than one megaspore nucleus. Conflict may arise within such embryo sacs between the derivatives of the germinal megaspore nucleus and the derivatives of somatic megaspore nuclei. “Antipodal eggs” and chalazal “strike” are interpreted as evidence of this conflict. The behavior of somatic spores and their derivatives is often variable for different embryo sacs produced by the same sporophyte. This has created difficulties for existing classifications of embryo sac “types” because more than one type is sometimes recognized within a species. A new classification of developmental algorithms is presented that emphasizes the fate of the germinal spore and its derivatives.     

Physiological bases of oligotrophy of microorganisms and the concept of microbial community

Three groups of physiological processes in microorganisms are considered the physiological basis of oligotrophy: the greater substrate affinity of the oligotrophs' transport systems, efficient or “economical” metabolism, and existence of a “master reaction” or “rate-determining steps” controlling the rate of metabolism. Heterotrophic microorganisms are divided into three unequal groups according to “reaction norma.” Two groups representing the extremes are small groups with the “narrow” reaction norma, regarding the concentrations and structure of the assimilated organic compounds and variability limits of the physiological characteristics mentioned above. The third, intermediate group includes the majority of microorganisms with the “wide” reaction norma.     

Extra tarsal joints and abnormal cuticular polarities in various mutants ofDrosophila melanogaster

Summary The legs of flies from 16 different mutant strains ofDrosophila melanogaster were examined for abnormal cuticular polarities and extra joints. The strains were chosen for study because they manifest abnormal cuticular polarities in some parts of the body (10 strains) or because they have missing or defective tarsal joints (6 strains). All but three of the stocks were found to exhibit misorientations of either the bristles, hairs, or “bract-socket vectors” on the legs. The latter term denotes an imaginary vector pointing from a hairlike structure called a “bract” to the bristle socket with which it is associated. On the legs of wild-type flies nearly all such vectors point distally, as do the bristles and hairs. In the mutant flies, the most common vector misorientation is a 180° reversal. When the bract-socket vectors of adjacent bristle sites in the same bristle row point toward one another, the distance between the sites is frequently abnormally large, whereas when the vectors point in opposite directions, the interval is frequently abnormally small. This correlation is interpreted to mean that bristle cells actively repel one another via cytoplasmic extensions that are longer in the direction of the bract-socket vector than in the opposite direction. Repulsive forces of this kind may be responsible for “fine-tuning” the regularity of bristle spacing in wild-type flies. Extra tarsal joints were found in eight of the 16 strains. A ninth strain completely lacking tarsal joints appears in some cases to have an extra tibia-basitarsus joint in its tibia. Whereas the tarsi of wild-type flies contain four joints, the tarsi ofspiny legs mutant flies contain as many as eight joints. In this extreme extra-joint phenotype, four of the joints correspond to the normal wild-type joints, and there is an extra joint in every tarsal segment except the distal-most (fifth) segment. Nearly all such ectopic extra joints have inverted polarity. In other strains the extra tarsal joints are located mainly at the wild-type joint sites, and joints of this sort have wild-type polarity. The alternation of normal and inverted (extra) joints inspiny legs resembles the alternation of normal and inverted (extra) body segment boundaries in the embryonic-lethal mutantpatch, suggesting that tarsal and body segmentation may share a common patterning mechanism.     

Association between contrasting methane emissions of two rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) cultivars from the irrigated agroecosystem of northeast India and their growth and photosynthetic characteristics

Over two consecutive years in the North Bank Plain Zone of Assam, India, during the spring growing season (February–June) of- 2006 and 2007 we examined effects of morpho-physiological characteristics of rice (Oryza sativa L.) plants in relation to methane (CH₄) emission from paddy fields. Traditional cultivar “Agni” and modern improved cultivar “Ranjit” were grown in light textured loamy soil under irrigation. A higher seasonal integrated methane flux (E _sif) was recorded from “Agni” compared to “Ranjit”. Both cultivars exhibited an emission peak during active vegetative growth and a second peak at panicle initiation. Leaf and tiller number, leaf area, length, and volume of root were greater in “Agni”, but grain yield and yield-related parameters such as increased photosynthate partitioning to panicles at the expense of roots were greater in “Ranjit”. “Ranjit” also photosynthesed faster than “Agni” during panicle development but slower than “Agni” at tillering. In both the years, a higher soil organic carbon content was recorded in plots of “Agni”. Our results suggest that in “Agni” enhanced diversion of photosynthate to roots resulted in more substrate being available to methanogenic bacteria in the rhizosphere. Additionally, the more extensive vegetative growth of this cultivar may enhance methane transport from the soil to the above-ground atmosphere.     

Wavelet entropy in event-related potentials: a new method shows ordering of EEG oscillations

 In this work we show the application of a measure of entropy defined from the wavelet transform, namely the wavelet entropy (WS), to the study of event-related potentials (ERPs). WS was computed for ERPs recorded from nine healthy subjects with three different types of stimuli, among them target stimuli in a cognitive task. A significant decrease of entropy was correlated with the responses to target stimuli (P300), thus showing that these responses correspond to a more “ordered” state than the spontaneous EEG. Furthermore, we propose the WS as a quantitative measure for such transitions between EEG (“disordered state”) and ERP (“ordered state”). Received: 12 April 2000 / Accepted in revised form: 11 September 2000     

Morphological hemiplasies in cladistic studies of phylogeny,with examples from birds

Cladograms usually include many evolutionary reversions, parallelisms, and convergences united under the term homoplasy. Recently, it has become evident that molecular traits that look like homoplasy may be in fact true homologies. The processes of independent sorting of genes, which provide the basis of these events, were recently termed hemiplasy. The present study demonstrates theoretical possibility of independent manifestation of true homology (synapomorphy) in remote lineages of phylogenetic tree, as morphological characters are analyzed; this phenomenon is similar in manifestation (but not in nature) to hemiplasy. In the case of “morphological hemiplasy,” characters that appeared only once in evolution may formally be treated by a cladist as parallelisms, since they occur in remote lineages of phylogenetic tree. It is proposed that “morphological hemiplasy” is responsible for a number of uncertain cases in avian phylogeny. Examples are provided by the ducklike bill in Paleogene Presbyornithidae and extant Anatidae and Anseranatidae (Anseriformes), the apomorphic structure of the flying apparatus in Paleogene Jungornithidae (Apodiformes) and extant Trochilidae, and “independent” development of a highly-modified zygodactyl foot in Zygodactylidae and Pici.