| 1. |
- Coulson, S. J., et al.
(författare)
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Introduction of invertebrates into the High Arctic via imported soils: the case of Barentsburg in the Svalbard
- 2013
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Ingår i: Biological Invasions. - : Springer Science and Business Media LLC. - 1387-3547 .- 1573-1464. ; 15:1, s. 1-5
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Tidskriftsartikel (refereegranskat)abstract
- Forty six species of invertebrate were collected from the manure enriched imported soils below the abandoned cow sheds in the Russian mining town of Barentsburg, Svalbard. Of these, 11 (24 %) were new records for Svalbard, including Collembola, gamasid mites, Enchytraeidae and the first identified Lumbricidae. Many of the new records are species not frequently observed in the Arctic. It is hypothesized that these species arrived with the chernozem soils imported to Barentsburg for the greenhouses from central or southern European Russia, or with livestock. The observations presented here are the first records of human invertebrate introductions establishing in Svalbard outside of dwellings. It is not believed that the majority of new species records described present an immediate threat to the ecology of Svalbard but they may, especially Deuteraphorura variabilis, establish in the nutrient enriched floral communities beneath bird cliffs characteristic of Svalbard.
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| 2. |
- Coulson, S. J., et al.
(författare)
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The invertebrate fauna of anthropogenic soils in the High-Arctic settlement of Barentsburg, Svalbard
- 2013
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Ingår i: Polar Research. - : Norwegian Polar Institute. - 0800-0395 .- 1751-8369. ; 32
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Tidskriftsartikel (refereegranskat)abstract
- The terrestrial environment of the High Arctic consists of a mosaic of habitat types. In addition to the natural habitat diversity, various human-influenced types may occur. For the resident invertebrate fauna, these anthropogenic habitats may be either unusually favourable or detrimental. In the town of Barentsburg, Svalbard, soils were imported for the greenhouses from southern Russia. These soils were subsequently discarded outside the greenhouses and have become augmented with manure from the cowsheds. Both the greenhouse and the cowsheds are now derelict. This site represents an unusually nutrient-rich location with considerable development of organic soils, in stark contrast to the naturally forming organic soils in Svalbard, which are typically thin and nutrient poor. Few previous studies have examined the soil invertebrate communities of human-disturbed or -created habitats in the Arctic. In an often nutrient-poor terrestrial environment, it is unclear how the invertebrate fauna will react to such nutrient enhancement. In these soils, 46 species of invertebrates were determined. Eleven species have not been recorded from other habitats in Svalbard and are hence likely to have been introduced. The native species assemblage in the anthropogenic soils was not atypical for many natural sites in Svalbard. Despite the enriched organic soils and highly ameliorated winter temperature conditions, the soil invertebrate fauna biodiversity does not appear to be enhanced beyond the presence of certain probably introduced species.
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| 3. |
- Fransén, Erik, 1962-, et al.
(författare)
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Computational modeling of activity dependent velocity changes in peripheral C-fibers
- 2011
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Konferensbidrag (refereegranskat)abstract
- Initiation and propagation of action potentials along unmyelinated C-fibers are the first steps of the pain pathway. Propagation velocity and its fiber class-specific activity-dependent slowing (ADS) is intimately linked to fibre excitability. In chronic pain patients, ADS alterations have been suggested to reflect increased excitability, possibly underlying clinical pain. Due to their small diameter, peripheral axons of nociceptors in patients are not accessible for intraaxonal recordings of their ion channel properties. We have therefore constructed a model of a C-fibre to study the relationship between ion channel composition and velocity changes as well as excitability. Ion channels are modeled from data of DRG somata using a Hodgkin-Huxley formalism (Na currents: TTX-sensitive, Nav1.8, Nav1.9, K currents: Kdr, A-type, Kv7.3, non-specific cationic: HCN). Moreover, ion pumps (Na/K-ATPase) and concentrations of intra and extraaxonal sodium and potassium are also included. The geometry and temperature of the fibre represents a section of the superficial branch and the deeper parent and is represented by a multicompartmental structure where each compartment contains passive as well as ion channel and pump elements. Using parameter estimation techniques, we optimized ion channel and pump expression pattern such that basic electrophysiological characteristics of the action potential and its velocity matched the experimental data. Moreover, we have also replicated activity dependent slowing. In ongoing work, we extend optimization to also include recovery cycles. The model will be used to study hypothesis of the relationship between individual ion channel subtypes and axonal excitability related to pain, generating independent information on impact of selective neuronal targets.
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| 4. |
- Fransén, Erik, 1962-, et al.
(författare)
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Differences in action potential propagation in mechanosensitive and insensitive C-nociceptors - a modeling approach
- 2012
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Konferensbidrag (refereegranskat)abstract
- C-fibers, unmyelinated afferent axons, convey information from the periphery of the nervous system to the spinal cord. They transmit signals originating from noxious stimulation evoking the sensations of itch and pain in the central nervous system. Different classes of C-fibers are characterized by functional, morphological and biochemical characteristics. In pain studies, a classification into mechano-insensitive (CMi) and mechano responsive fibers (CM) has proven useful as changes in proportions and response characteristics of these fibers have been observed in neuropathy patients (Weidner et al. 1999, 2000; Orstavik 2003, 2010). In this study, using computational modeling of a C-fiber, we have studied the possible contribution of different ion channel subtypes (Na-TTXs, Nav1.8, Nav1.9, Kdr, KA, KM, K(Na), h) as well as the Na/K-ATPase pump to conductive properties of C-fibers. In particular we investigated mechanisms that could generate the fiber-specific differences between CM and CMi fibers with regard to activity dependent slowing (ADS) and recovery cycles (RC). In our study we represent the axon by three cylindrical sections, one representing the peripheral thin end (branch, 2.5 cm), one the central part (parent, 10 cm) and a conical section between these (0.5 cm). In total 730 compartments are used. Temperature is set to 32 degrees C in branch and 37 degrees in parent sections. We represent variable ion concentrations of Na and K intra axonally, periaxonally and extracellularly, from which reversal potentials are calculated. We use ion channel models based on Hodgkin Huxley formalism. An ion pump (Na/K-ATPase) is included. We find that TTX-sensitive Na and Nav1.8 have the strongest influence on action potential conduction velocity as is expected since these are the major components of the rising phase of the action potential. Preliminary observations indicate that a small subset of Na and K currents play a key role in determining differences in activity dependent velocity changes (ADS) in the two fiber classes. We plan to also study contributions from morphological characteristics (superficial branch lengths) to activity dependent differences between the fiber classes (Schmidt et al. 2002). We further intend to investigate candidate ion channels which could play a role in changing the functional characteristics of a CMi fiber to that of a CM fiber. Our studies may provide insights into ionic changes underlying changes in the excitability of C-fibers associated with pain.
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| 5. |
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| 6. |
- Schmelz, M., et al.
(författare)
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Microneurographic single-unit recordings to assess receptive properties of afferent human C-fibers
- 2010
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Ingår i: Neuroscience Letters. - : Elsevier BV. - 0304-3940 .- 1872-7972. ; 470:3, s. 158-161
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Forskningsöversikt (refereegranskat)abstract
- Action potentials in unmyelinated peripheral axons can be recorded in awake humans by microneurography with small electrodes placed in a peripheral nerve. This technique provides extracellular recordings of single C-fibers and thus enables characterization of their sensory and axonal properties. By using microneurographical basic properties of afferent C-fibers such as conduction velocities, innervation territories, sensory thresholds and chemical responsiveness were measured. Moreover, axonal excitability changes induced by repetitive activation were assessed. Sensory and axonal properties of the different fiber classes cluster. Based on those specific properties, unitary functional classes of nociceptors (such as polymodal nociceptors and mechano-insensitive nociceptors) and non-nociceptors (such as tactile afferents and warm fibers) were classified. With normal data available, sensitization and desensitization of afferent fibers have been found in pathophysiologic states as detected in chronic pain patients. As subjects and patients are awake during the recording, microneurography provides a unique tool to correlate the discharge behaviour of afferent nerve fibers with the sensation evoked by certain stimuli.
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