Emergence in the central nervous system

“Emergence” is an idea that has received much attention in consciousness literature, but it is difficult to find characterizations of that concept which are both specific and useful. I will precisely define and characterize a type of epistemic (“weak”) emergence and show that it is a property of some neural circuits throughout the CNS, on micro-, meso- and macroscopic levels. I will argue that possession of this property can result in profoundly altered neural dynamics on multiple levels in cortex and other systems. I will first describe emergent neural entities (ENEs) abstractly. I will then show how ENEs function specifically and concretely, and demonstrate some implications of this type of emergence for the CNS.     

How do plant growth substances work?

Abstract. Despite intensive research effort, the role of growth substances in the life of the intact growing plant is far from clear. Two reasons are suggested which may account for the lack of progress. The first is the failure to recognize the unique aspects of plant development. These which are expressed by the regenerative, organizational and developmental plasticity of the meristem probably result from the possession of growth substances. The second is the concept of growth substances as hormones. This represents the main conceptual thrust of research and is considered critically, starting with the historical system, the coleoptile and dealing with other major growth substance systems in turn. It is concluded that a hormonal concept which includes control by changes in growth substance concentration fails to explain the developmental phenomena under examination. A role for growth substances as integrating agents is suggested and the notion of quantitative tissue sensitivity variation is developed to explain the major growth patterns of developing shoots.     

Imperfect eggs and oviform nymphs: a history of ideas about the origins of insect metamorphosis

The problem of insect metamorphosis has inspired naturalistsfor centuries. One question that often arises is why some insects,such as butterflies and bees, undergo a fairly radical metamorphosiswhile others, such as crickets and lice, do not. Even beforethe concept of homology emerged scientists speculated whichstage found in more direct-developing insects would correspondwith the pupal stage of metamorphosing insects. William Harvey(1651) considered the pupal stage to be a continuation of embryonicevents, calling it a "second egg." Since then variations ofthis idea have emerged over the centuries of scientific researchand have been supported by a wide variety of methods and rationales.This review will follow those ideas and the ideas that emergedin opposition to them to the present state of the field.     

Evolution and progress

The concept of progress is one which makes evolutionists feel very uneasy, yet it is also a concept to which they are forever returning. It is useful to make a distinction between 'comparative progress' which involves competition between groups, and 'absolute progress' which involves the climb up some objective scale. Both kinds of progress have been the subject of much debate in recent years, leading one to turn from expectations that the controversy will ever be resolved to queries about why it continues to obsess so many people.     

Local sensitivity of per-recruit fishing mortality reference points

We study the sensitivity of fishery management per-recruit harvest rates which may be part of a quantitative harvest strategy designed to achieve some objective for catch or population size. We use a local influence sensitivity analysis to derive equations that describe how these reference harvest rates are affected by perturbations to productivity processes. These equations give a basic theoretical understanding of sensitivity that can be used to predict what the likely impacts of future changes in productivity will be. Our results indicate that per-recruit reference harvest rates are more sensitive to perturbations when the equilibrium catch or population size per recruit, as functions of the harvest rate, have less curvature near the reference point. Overall our results suggest that per recruit reference points will, with some exceptions, usually increase if (1) growth rates increase, (2) natural mortality rates increase, or (3) fishery selectivity increases to an older age.     

The distribution and abundance of animal populations in a climate of uncertainty

Current predictions regarding the ecological consequences of climate change on animal populations are generally autecological and species-specific, and/or non-mechanistic extrapolations of recent short-term patterns. To better understand and predict the effects of climate change on the distribution of species and the abundance of populations we offer a novel, broad theoretical framework. Climate-induced changes in trophic structure may actually be more predictable than effects on individual species. The logic is that there are general differences in climatic sensitivity among trophic levels – specifically, that as one moves up trophic levels, there is an increase in the temperature sensitivity of vital rates. More precisely, we provide: (1) a formal mathematical definition of distribution limits that is both operational and conceptual, introducing the concept DL₅₀, defined as the geographic and climatic isoline representing an equilibrium occupancy of half of the suitable habitats; (2) a matrix of the possible changes in trophic structure from climate change and the general theoretical consequences; and (3) a new idea that predicts broad effects of climatic warming on trophic systems. Our intention is to help meet the challenge of developing and testing general theoretical models that can predict which species will be winners and losers in ecological time, which evolutionary traits will be favoured or selected against, and what will be consequences for ecosystem structure and function.     

A two-channel hypothesis for regulation of cell division and differentiation

We propose the hypothesis that extracellular regulation of cell division and differentiation acts through just two communications channels. These channels consist of a series of redundant components: extracellular messenger hormones; these hormones' receptors; cytoplasmic proteins activated by the hormone-receptor complex; and trans-activating nuclear regulatory proteins. One channel, here labeled "D" ("differentiate"), includes transforming growth factor-beta as one of its hormones; the other, labeled "G" ("growth") includes epidermal growth factor. We postulate that signal reception occurs as a result of competition between different actuating proteins for equilibrium-controlled binding to critical DNA sites. Stem cells commit to mitosis when some high proportion of critical sites is occupied by actuating proteins of the G class, and to terminal differentiation when a high proportion is occupied by "D" actuators. Intermediate occupancy can either lead to division into one differentiated and one stem cell, or to maintenance of cells in the reference state, quiescence. Equilibrium control of binding implies that critical site occupancy will be proportional to the relative concentrations of "D" and "G" actuating proteins in the nuclear fluid. These concentrations depend on the external hormone concentrations, the numbers of receptors on the cell membrane, and the coefficients of the rate-determining steps between internalization of the hormone-receptor complexes and activation of the actuating proteins. All of these quantities can be affected by various factors, including endocrine hormones. This model is consistent with most reported behavior of various growth factors, interferons, etc, toward a variety of cells in culture. It predicts that under otherwise constant conditions, high relative concentrations of a D-hormone (e.g. transforming growth factor-beta) will induce commitment to terminal differentiation, while high relative concentrations of a "G" hormone (e.g. epidermal growth factor) will induce mitosis. We have seen no report of an experiment which adequately tests this prediction. The model implies that cancer causing mutations are those which increase the relative intensity of the "G" signal; this can occur via changes in components of either channel. Such mutant cells should be both more likely to divide and less likely to differentiate than normal stem cells. Conversely, mutations which increase relative sensitivity to the "D" signal during embryonal development can lead to premature differentiation, cessation of growth, and structural abnormalities (terata).     

Glial cell inclusions and the pathogenesis of neurodegenerative diseases

In this review, we discuss examples that show how glial-cell pathology is increasingly recognized in several neurodegenerative diseases. We also discuss the more provocative idea that some of the disorders that are currently considered to be neurodegenerative diseases might, in fact, be due to primary abnormalities in glia. Although the mechanism of glial pathology (i.e. modulating glutamate excitotoxicity) might be better established for amyotrophic lateral sclerosis (ALS), a role for neuronal-glial interactions in the pathogenesis of most neurodegenerative diseases is plausible. This burgeoning area of neuroscience will receive much attention in the future and it is expected that further understanding of basic neuronal-glial interactions will have a significant impact on the understanding of the fundamental nature of human neurodegenerative disorders.     

The randomness of life: A philosophical approach inspired by the Enlightenment

Did the Enlightenment anticipate modern reflections about the role of chance within cells or in living beings? No, especially if one pays attention to the very different scientific context of that periods and takes care to distrust the concept of "precursors". Nonetheless, several thinkers of the Enlightenment, scientists or philosophers, have constructed an opposition between the random and order that shares some links with modern concerns. More precisely, philosophers like Diderot and some physicians, chemists or naturalists, have articulated the necessity and contingency in opposition to the idea of an absolute natural order and to any preformed "germ" explaining the development of animals. But I will argue that this subtle concept also diverges from the idea of a universal determinism developed by Laplace. There is a way to deal with natural necessity and the universal interdependence of phenomena without excluding the random, going beyond the classical - though posterior to the eighteenth century - opposition between determinism and indeterminism. Particularly with Diderot, the Enlightenment presents an epistemology of the random loosely attached to the natural sciences, producing a philosophical reflection that can be linked with some modern issues of biology. I examine two examples: the criticism of the explanation of order by order, and the thesis that probability can tell us something about natural productions through the idea of randomized "expression," e.g., stochastic expression of genes for modern molecular biology and expressions of natural forms for Diderot.     

Species as family resemblance concepts: The (dis‐)solution of the species problem?

The so-called "species problem" has plagued evolutionary biology since before Darwin's publication of the aptly titled Origin of Species. Many biologists think the problem is just a matter of semantics; others complain that it will not be solved until we have more empirical data. Yet, we don't seem to be able to escape discussing it and teaching seminars about it. In this paper, I briefly examine the main themes of the biological and philosophical literatures on the species problem, focusing on identifying common threads as well as relevant differences. I then argue two fundamental points. First, the species problem is not primarily an empirical one, but it is rather fraught with philosophical questions that require-but cannot be settled by-empirical evidence. Second, the (dis-)solution lies in explicitly adopting Wittgenstein's idea of "family resemblance" or cluster concepts, and to consider species as an example of such concepts. This solution has several attractive features, including bringing together apparently diverging themes of discussion among biologists and philosophers. The current proposal is conceptually independent (though not incompatible) with the pluralist approach to the species problem advocated by Mishler, Donoghue, Kitcher and Dupré, which implies that distinct aspects of the species question need to be emphasized depending on the goals of the researcher. From the biological literature, the concept of species that most closely matches the philosophical discussion presented here is Templeton's cohesion idea.     

Embryonic recapitulation, coenogenesis and heterochrony. An attempt at a comparative analysis of the relationships between embryogenesis and evolution.

The relationships between embryogenesis and the scale of living beings have been the subject of long-dated observations. It is well known that Haeckel, going back and codifying this data, has divided it into two large groups called palingenesis and coenogenesis. He has only mentioned the concept of heterochrony to which we give much more importance nowadays. We will look over these questions and link them up with some aspects of modern genetics.     

Estudio de la vulnerabilidad neuronal selectiva en el sistema nervioso central humano

Introduction

The concept of ‘selective neuronal vulnerability’ refers to the differential sensitivity of neuronal populations in the nervous system to stresses that cause cell damage and lead to neurodegeneration. Because oxidative stress play a causal role in the physiological aging process, and it is often invoked as an aetiopathogenic and/or pathophysiological mechanism for neurodegeneration, in the present work we propose that the molecular bases of selective neuronal vulnerability is linked with cell adaptations related to oxidative stress.

Material and methods

The grey substance of 5 different regions from healthy human subjects (n = 7) were selected: i) to evaluate their membrane fatty acid profile by chromatographic methods, ii) to determine their membrane susceptibility to peroxidation, and iii) to recognise potential mechanisms involved in its regulation.

Results

The results showed significant inter-regional differences in the fatty acid profile, basically due to the content of mono- and highly polyunsaturated fatty acids; changes that, in turn, induce significant differences in theirs susceptibilities to peroxidation, as well as differences that can be ascribed to the desaturase activity.

Conclusion

Thus, the cross-regional comparative approach seems to confirm the idea that the level of cell membrane unsaturation may be a key trait associated with selective neuronal vulnerability.     

Genetic and biochemical studies on the suppression of and a recovery from the tumorous state in higher plants

Four neoplastic diseases of plants: crown gall, which is caused by Ti plasmid DNA; Black's wound tumor disease by an RNA virus; the Kostoff genetic tumors by chromosomal imbalance; and habituation, which results from a spontaneous activation of select biosynthetic systems, have been analyzed and compared. It has been found that both the development of a capacity for autonomous growth and the nature of the heritable cellular change that underlies tumorigenesis are similar in the four instances. All develop a capacity for autonomous growth as a result of the persistent activation of select biosynthetic systems, the products of which are concerned with cell growth and division. That the persistent activation of these biosynthetic systems does not involve heritable changes of an irreversible type is indicated by the finding that a reversal of the neoplastic state occurred in three of the test systems. Since the tumor cells in these instances were found to remain totipotent the results suggest that whether the normal or tumor phenotype is expressed is determined by how the genetic information is regulated in a cell. Regulation appears to be accomplished in part through positive feedback control mechanisms. Foreign genetic information could act either in a regulatory manner to persistently activate normal biosynthetic systems or it could code for one or more essential but normally limiting substance(s) and thus replace a substance(s) that in the case of the Kostoff tumors or habituation is specified by host cell genes, or it could do both. In either case, the foreign genetic information can be regulated in much the same manner as are the host cell genes to give rise to either the normal or tumor phenotype.     

Testing the mutagenic potency of chemical substances in a linear host-mediated assay (LIHMA).

Instead of comparing "mutation frequencies" as used in the conventional host-mediated assay (HMA), a modified concept of measuring mutagenic potency is introduced by using a number of time intervals for taking samples. Regression analysis methods can then be applied to the numbers of mutant bacteria (reversions). Not only the mutagenic but also an additional antibacterial potency of a compound can be detected and estimated in the sam assay. It is demonstrated that interference of (undetected) antibacterial activity with the mutagenic activity may lead to misclassification of a substance concening its mutagenicity in the conventional HMA. This kind of erroneous assessment will be avoided by the LIHMA. Another advantage of the LIHMA over the conventiona HMA is that regression analysis also allows estimation of the sensitivity and reliability of the assay. The calculative procedure may be programmed on desk computers and is then most suitable for laboratories where large numbers of substances have to be examined routinely. A numerical is given using results obtained with nitrosoguanidine.     

Consequences of the widespread use of antibiotics

The cancer problem is increasing as life expectancy increases and greater portions of the populace live to the age at which cancer is more likely. Early diagnosis still is difficult. Even with modern methods and with considerable public education with regard to cancer, the disease is often not diagnosed until it is beyond the stage at which cure might be effected. The need for a serodiagnostic test for general screening purposes for cancer detection is tremendous. The major objective of cancer serodiagnostic test methods is to discover a general test that will detect cancer in a high percentage of cases while it is in an early stage; that will give few "false positive" results; that can be done in any laboratory; and that is simple and inexpensive. Many serodiagnostic tests for cancer have been published but none has proven worthy of being a good general test to detect cancer. Yet unless some serodiagnostic test which will be suitable for general screening purposes is developed, it is difficult to see how there can be much improvement in the early diagnosis of cancer, particularly internal cancer. It is hoped that an open-minded attitude will be maintained by physicians on this subject. Recent reports of such a test being developed are encouraging and it is hoped that continued investigations will be confirmatory.     

Cod Gadus morhua and climate change: processes, productivity and prediction

Environmental factors act on individual fishes directly and indirectly. The direct effects on rates and behaviour can be studied experimentally and in the field, particularly with the advent of ever smarter tags for tracking fishes and their environment. Indirect effects due to changes in food, predators, parasites and diseases are much more difficult to estimate and predict. Climate can affect all life-history stages through direct and indirect processes and although the consequences in terms of growth, survival and reproductive output can be monitored, it is often difficult to determine the causes. Investigation of cod Gadus morhua populations across the whole North Atlantic Ocean has shown large-scale patterns of change in productivity due to lower individual growth and condition, caused by large-scale climate forcing. If a population is being heavily exploited then a drop in productivity can push it into decline unless the level of fishing is reduced: the idea of a stable carrying capacity is a dangerous myth. Overexploitation can be avoided by keeping fishing mortality low and by monitoring and responding rapidly to changes in productivity. There are signs that this lesson has been learned and that G. morhua will continue to be a mainstay of the human diet.     

Submicroscopic structure of the membranous labyrinth

Summary Investigations were performed by light and electron microscope on the basilar membrane, limbus spiralis and spiral ligament.These different parts continue one into the other and make up a single morphological and functional structure which may be called the supporting structure of Corti's organ (s.s.C.o.).It is formed by a tissue the components of which are the cells and an intercellular substance in which are arranged the capillary vessels.The cells can be classed in two groups, the first consisting of the cells proper (basilar membrane, limbus spiralis and spiral ligament cells) which present structural changes parallel with the growth mechanism of the intercellular substance; the second of the cochlear duct covering cells (Corti's organ cells, inner and outer spiral sulcus cells, interdental cells, stria vascularis cells).The intercellular substance is organised in laminae, fibrolaminae, bundles and microscopic fibers composed of filaments with an intervening ground substance.The filaments have a diameter ranging from 85 to 105 Å. Topochemical tests with polarised light microscope, enzymatic tests, diffractographic and chemical analyses suggest that these filaments unquestionably consist of protein material which have nothing to do with collagen or elastic fibers. Perhaps it may be classed in the K.E.M.F. group.The ground substance generally appear anhistous and transparent but in some parts of the basilar membrane it presents a cottony appearance.The possible different hypotheses about the classification of the s.s.C.o. tissue are discussed.The quantity and architecture of the cells and the intercellular substance vary appreciably in the basilar membrane, limbus spiralis and spiral ligament, which are examined in detail one by one.The demonstration that the s.s.C.o. is formed of a tissue possessing an intercellular substance containing filamentous scleroproteins clearly corroborates the theory that is performs supporting activity in respect of Corti's organ. The term supporting structure of Corti's organ is based on this interpretation.Research financed by C.N.R. grant.     

冷冻电子断层扫描研究原代培养神经元中的线粒体膜动态变化（英文）

<正>Dear Editor,Mitochondria acts as a cellular organelle that produces ATP and buffers Ca²⁺, and plays an important role in neuronal growth, survival and function^[1]. Loss of mitochondria will make the ATP supply insufficient, resulting in synaptic transmission dysfunction^[2]. Further, presynaptic mitochondrial dysfunctions are often associated with severe neurological diseases^[3].     

Pitch the niche – taking responsibility for the concepts we use in ecology and species distribution modelling

In a discussion it is often easier to staunchly reject or offer resolute support for an idea. This third paper on the niche concept aims to develop a balanced argument by exploring general principles for determining an appropriate level for pitching the niche concept that will guide better use and less abuse of niche concepts. To do this we first have to accept that niche concepts are not necessarily essential for ecology. Rather than to improve niche concepts, our aim should then be to pitch the niche in terms of ecology. This aim helps us develop an ‘ultimate goal of the niche’ by which we can evaluate the concepts we use. For species distribution modelling, there has been a focus on the niche as an equilibrium outcome that perhaps has less relevance for disequilibrium situations (e.g. climate change projections). As is the case for much of ecology, more causal explanations of species' distributions use alternative terminologies and less frequently use the word ‘niche’. We suggest that niche concepts that are better aligned with the rest of ecology could arise from taking more responsibility for our own implementations, and by explaining our models with terms other than niche. A general, holistic niche concept promotes this view and promotes practical thinking about what we are modelling and how we interpret those models, which in turn should help inspire and support innovative modelling approaches in species distribution modelling.     

The stability of benthic ecosystems

Physicists have two conceptions of the stability of systems: global and neighbourhood stability. Global stability corresponds to the idea of successional changes leading to climax communities. Yet, neighbourhood stability is shown to be a more realistic model for changes in dominance of marine benthic sediment-living communities. The factors inducing state changes in dominance pattern were shown to be principally biological interactions. In order to model the stability of benthic ecosystems, much more attention must be given to natural history-type studies of biological interactions. Furthermore, mathematical models usually assume that the systems are globally stable. Should neighbourhood stability prove to be the rule for benthic systems then realistic models of such systems will be an order of magnitude more complex.