The inability of axons to regenerate after a spinal cord injury in the adult mammalian central nervous system (CNS) can lead to permanent paralysis. At sites of CNS injury, a glial scar develops, containing extracellular matrix molecules including chondroitin sulphate proteoglycans (CSPGs). CSPGs are inhibitory to axon growth in vitro, and regenerating axons stop at CSPG-rich regions in vivo. Removing CSPG glycosaminoglycan (GAG) chains attenuates CSPG inhibitory activity. To test the functional effects of degrading chondroitin sulphate (CS)-GAG after spinal cord injury, we delivered chondroitinase ABC (ChABC) to the lesioned dorsal columns of adult rats. We show that intrathecal treatment with ChABC degraded CS-GAG at the injury site, upregulated a regeneration-associated protein in injured neurons, and promoted regeneration of both ascending sensory projections and descending corticospinal tract axons. ChABC treatment also restored post-synaptic activity below the lesion after electrical stimulation of corticospinal neurons, and promoted functional recovery of locomotor and proprioceptive behaviours. Our results demonstrate that CSPGs are important inhibitory molecules in vivo and suggest that their manipulation will be useful for treatment of human spinal injuries.

Chondroitinase ABC promotes functional recovery after spinal cord injury

Muscle fatigue encompasses a class of acute effects that impair motor performance. The mechanisms that can produce fatigue involve all elements of the motor system, from a failure of the formulation of the descending drive provided by suprasegmental centers to a reduction in the activity of the contractile proteins. We propose four themes that provide a basis for the systematic evaluation of the neural and neuromuscular fatigue mechanisms: 1) task dependency to identify the conditions that activate the various mechanisms; 2) force-fatigability relationship to explore the interaction between the mechanisms that results in a hyperbolic relationship between force and endurance time; 3) muscle wisdom to examine the association among a concurrent decline in force, relaxation rate, and motor neuron discharge that results in an optimization of force; and 4) sense of effort to determine the role of effort in the impairment of performance. On the basis of this perspective with an emphasis on neural mechanisms, we suggest a number of experiments to advance our understanding of the neurobiology of muscle fatigue.

Neurobiology of muscle fatigue.

SUMMARY Available literature on the ecological and toxicological aspects of mercury (Hg) in the environment, with special reference to fish and wildlife resources, is reviewed and summarized. Subdivisions include sources, chemical properties, background concentrations, acute and chronic toxicity, sublethal effects, and proposed criteria to protect sensitive resources. Mercury has been used by man for at least 2,300 years, most recently as a fungicide in agriculture, in the manufacture of chlorine and sodium hydroxide, as a slime control agent in the pulp and paper industry, in the production of plastics and electrical apparatus, and in mining and smelting operations. Mercury burdens in some environmental compartments are estimated to have increased up to 5X precultural levels, primarily as a result of man's activities. The construction of artificial reservoirs, for example, which releases Hg from flooded soils, has contributed to the observed elevation of Hg concentrations in fish tissues from these localities. Elevated levels of Hg in living organisms in Hg-contaminated areas may persist for as long as 100 years after the source of pollution has been discontinued. One major consequence of increased mercury use, coupled with careless waste disposal practices, has been a sharp increase in the number of epidemics of fatal mercury poisonings in humans, wildlife, and aquatic organisms. Most authorities agree on six points: (1) mercury and its compounds have no known biological function, and the presence of the metal in the cells of living organisms is undesirable and potentially hazardous; (2) forms of mercury with relatively low toxicity can be transformed into forms of very high toxicity, such as methylmercury, through biological and other processes; (3) mercury can be bioconcentrated in organisms and biomagnified through food chains; (4) mercury is a mutagen, teratogen, and carcinogen, and causes embryocidal, cytochemical, and histopathological effects; (5) some species of fish and wildlife contain high concentrations of Hg that are not attributable to human activities; (6) anthropogenic use of Hg should be curtailed, as the difference between tolerable natural background levels of Hg and harmful effects in the environment is exceptionally small. Concentrations of total Hg lethal to sensitive, representative, nonhuman species range from 0.1 to 2.0 ug/l (ppb) of medium for aquatic organisms; from 2,200 to 31,000 ug/kg body weight (acute oral) and 4,000 to 40,000 ug/kg (dietary) for birds; and from 100 to 500 ug/kg body weight (daily dose) and 1,000 to 5,000 ug/kg diet for mammals. Organomercury compounds, especially methylmercury, …

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Mercury Hazards to Fish, Wildlife, and Invertebrates: A Synoptic Review

Preface (1999) Preface (1990) 1. Subjects of Sex/Gender/Desire I. 'Women' as the Subject of Feminism II. The Compulsory Order of Sex/Gender/Desire III. Gender: The Circular Ruins of Contemporary Debate IV. Theorizing the Binary, the Unitary and Beyond V. Identity, Sex and the Metaphysics of Substance VI. Language, Power and the Strategies of Displacement 2. Prohibition, Psychoanalysis, and the Production of the Heterosexual Matrix I. Structuralism's Critical Exchange II. Lacan, Riviere, and the Strategies of Masquerade III. Freud and the Melancholia of Gender IV. Gender Complexity and the Limits of Identification V. Reformulating Prohibition as Power 3. Subversive Bodily Acts I. The Body Politics of Julia Kristeva II. Foucault, Herculine, and the Politics of Sexual Discontinuity III. Monique Wittig - Bodily Disintegration and Fictive Sex IV. Bodily Inscriptions, Performative Subversions Conclusion - From Parody to Politics

Postmodern Subjects, Postmodern BodiesThinking Fragments: Psychoanalysis, Feminism, and Postmodernism in the Contemporary WestYearning: Race, Gender, and Cultural PoliticsGender Trouble: Feminism and the Subversion of Identity

Variability of the North Atlantic Oscillation and the Tropical Atlantic dominate the climate of the North Atlantic sector, the underlying ocean and surrounding continents on interannual to decadal time scales. Here we review these phenomena, their climatic impacts and our present state of understanding of their underlying cause. Copyright © 2001 Royal Meteorological Society.

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North atlantic climate variability: Phenomena, impacts and mechanisms

Buku ini merupakan satu eksplorasi inter-disipliner yang tidak hanya dipandang dari berbagai pokok persoalan tetapi juga berdasarkan barmacam metodologi. Lewat buku ini para pembaca akan digiring untuk mempergunakan pengetahuan bahasanya terhadap manifestasi dan konteks tertentu sebagai cara mengeksplorasi bidang-bidang kajian lainnya di dalam kehidupan masyarakat. Singkatnya, pembaca dilibatkan untuk aktif di dalam proses dialektika antara pengetahuan terhadap wacana teks tertentu dan subjektivitas mereka sendiri. Bahasa dalam penerapan sedemikian lebih dari sekedar refleksi-hidup. Pokok yang jadi kajian antara lain tentang ideologi, wacana dan fiksi narasi; posisi pembaca dan subjek di dalam cerita fiksi anak-anak; dan juga, Words of power.

Language and ideology in children's fiction

The physical processes determining the path of the Gulf Stream as it leaves the continental shelf of the USA are complex and involved. Understanding these processes is important to global climate studies because the Gulf Stream plays a major role in the distribution of heat in the northern hemisphere. Here we show that during the last 3 decades, the latitude of the Gulf Stream has been clearly correlated with the North Atlantic Oscillation (NAO); high values of the NAO index, which correspond to stronger westerly and trade winds, favouring more northerly paths of the Stream about 2 years later. The time-delay may be associated with the adjustment time of this part of the ocean circulation. If allowance is made for persistence of the Gulf Stream position from one year to the next, more than half the interannual variation in the position can be predicted.

The North Atlantic Oscillation and the latitude of the Gulf Stream

Retelling Stories, Framing Culture: Traditional Story and Metanarratives in Children's Literature

It is shown that there is a marked tendency for long, strongly tidal estuaries to have greater suspended particulate matter (SPM) concentrations within their high-turbidity regions than shorter estuaries with comparable tidal ranges at their mouths, or weakly tidal estuaries. Using consistently derived data from 44 estuaries in Europe and the Americas, contours of the logarithm of maximum estuarine SPM concentration are shown to be reasonably smooth when plotted against the logarithm of mean spring tidal range (at the estuary mouth) and the logarithm of estuarine tidal length. Predictions from the plot are compared with published observations made in the Delaware, Scheldt, Rio de la Plata, Gironde, Bay of Fundy, Changjiang (Yangtze), Amazon, Patos Lagoon and the Hawkesbury Estuary and it is shown that, qualitatively, there are no serious discrepancies. Short, weakly tidal estuaries are predicted to have very low ‘intrinsic’ SPM concentrations. High SPM concentrations in these estuaries would most likely be the result of either locally generated wave resuspension, high freshwater sediment loads due to freshets, or intruding seawater carrying suspended sediments derived from wave activity in the coastal zone. Application of a generic tidal model demonstrates that longer estuaries possess faster tidal currents for a given tidal range at their mouth and, in the presence of a supply of erodable fine sediment, therefore (by implication) produce greater concentrations of SPM that can be accumulated within a turbidity maximum. The same is true if the tidal range is increased for estuaries of a given length. These features are illustrated by comparing surveys of SPM data from two large estuaries possessing greatly different tidal ranges (the microtidal, medium turbidity Potomac and the macrotidal, highly turbid Humber-Ouse) and a third, much smaller but strongly tidal estuary (the low-turbidity Tweed). It is demonstrated that longer estuaries tend to have longer flushing times for solutes than shorter systems and that larger tides tend to reduce flushing times, although the tidal influence is secondary. Short, rapidly flushed estuaries quickly lose their erodable fine sediment to the coastal zone during freshets and during the ebbing currents of spring tides. Turbidity is therefore small during low runoff, low wave activity conditions. Very long, very slowly flushed estuaries are unlikely to lose a significant fraction of their resuspended sediments during freshets or individual ebb tides and are therefore able to accumulate large and increasing amounts of fine sediment in the long-term. Turbidity within them is therefore high during the fast currents of large spring tides.

The dependence of estuarine turbidity on tidal intrusion length, tidal range and residence time

The effects of changing muscle length on the mechanical properties of 89 motor units from adult cat medial gastrocnemius have been studied in eight experiments. Few differences were found between the effects of length on tetanic tension, twitch tension, twitch-tetanus ratio, twitch contraction time, twitch half relaxation time, rate of force development and electrical activity for fast contracting (twitch contraction time less than or equal to 45 msec) and slowly contracting (greater than 45 msec) units. Those differences that did appear did not persist when these two groups were matched by tetanic tension. It is concluded that the biophysical mechanisms responsible for the changes in mechanical and electrical properties with length must be similar for fast and slow twitch units and not related to potential differences in their muscle fiber type. The effects of changing muscle length on the mechanical properties of the eight whole muscles suggest that changes in force output with length are of minor importance during normal movements as the muscle is found to be electrically active over a relatively narrow range of lengths close to the optimum length for tetanus of the whole muscle. The very shortest muscle lengths at which there is only minimal force development are not used in natural movements, while the declining limb of the length tension curve is at muscle lengths beyond the maximum in situ length.

John Stephens

Papers

Language and ideology in children's fiction

The North Atlantic Oscillation and the latitude of the Gulf Stream

Retelling Stories, Framing Culture: Traditional Story and Metanarratives in Children's Literature

The dependence of estuarine turbidity on tidal intrusion length, tidal range and residence time

The motor units of cat medial gastrocnemius: Electrical and mechanical properties as a function of muscle length