Plasticity in ascending long propriospinal and descending supraspinal pathways in chronic cervical spinal cord injured rats

The high clinical relevance of models of incomplete cervical spinal cord injury (SCI) creates a need to address the spontaneous neuroplasticity that underlies changes in functional activity that occur over time after SCI. There is accumulating evidence supporting long projecting propriospinal neurons as suitable targets for therapeutic intervention after SCI, but focus has remained primarily oriented toward study of descending pathways. Long ascending axons from propriospinal neurons at lower thoracic and lumbar levels that form inter-enlargement pathways are involved in forelimb-hindlimb coordination during locomotion and are capable of modulating cervical motor output. We used non-invasive magnetic stimulation to assess how a unilateral cervical (C5) spinal contusion might affect transmission in intact, long ascending propriospinal pathways, and influence spinal cord plasticity. Our results show that transmission is facilitated in this pathway on the ipsilesional side as early as 1 week post-SCI. We also probed for descending magnetic motor evoked potentials (MMEPs) and found them absent or greatly reduced on the ipsilesional side as expected. The frequency-dependent depression (FDD) of the H-reflex recorded from the forelimb triceps brachii was bilaterally decreased although H(max)/M(max) was increased only on the ipsilesional side. Behaviorally, stepping recovered, but there were deficits in forelimb–hindlimb coordination as detected by BBB and CatWalk measures. Importantly, epicenter sparing correlated to the amplitude of the MMEPs and locomotor recovery but it was not significantly associated with the inter-enlargement or segmental H-reflex. In summary, our results indicate that complex plasticity occurs after a C5 hemicontusion injury, leading to differential changes in ascending vs. descending pathways, ipsi- vs. contralesional sides even though the lesion was unilateral as well as cervical vs. lumbar local spinal networks

Nickel isotope fractionation in komatiites and associated sulfides in the hart deposit, Late Archean Abitibi Greenstone Belt, Canada

Extremely light and highly variable δ60Ni values have been observed in komatiite-associated magmatic sulfides in recent studies. In this study, we examine the mechanisms of Ni isotope fractionation between silicate and sulfide liquids in the Hart komatiite-associated Fe-Ni-Cu-sulfide system. We assess the petrogenetic significance of these mechanisms using Ni isotope and concentration data. The concentration of Ni in bulk rock varies from 774 to 2690 ppm in komatiite samples with no sulfide minerals to 8380–39,300 ppm in samples almost entirely consisting of sulfide minerals. The δ60Ni values vary from +0.14‰ in komatiite samples with no sulfide minerals to −1.06‰ in samples dominantly consisting of sulfide minerals. A theoretical model of fractionation between the komatiitic lava and sulfide xenomelt with nickel isotope exchange followed by fractional crystallization during crystallization of the sulfide melt can produce a range of δ60Ni values from +0.17‰ to −1.02‰ in sulfide-rich rocks depending on the extent of fractional crystallization and the amount of trapped melt between the sulfide mineral grains, which corresponds well with the range of values observed in these rocks. This proposed model requires fractionation of Ni isotopes between sulfide liquid and the earliest formed sulfide crystals during crystallization. Effects of later crystallization during peritectic reactions and subsolidus exsolution could be tested by in situ measurements of Ni isotopes in different textural varieties of pentlandite that formed over a large range of temperatures during cooling

Activity-Dependent Increase in Neurotrophic Factors Is Associated with an Enhanced Modulation of Spinal Reflexes after Spinal Cord Injury

Activity-based therapies such as passive bicycling and step-training on a treadmill contribute to motor recovery after spinal cord injury (SCI), leading to a greater number of steps performed, improved gait kinematics, recovery of phase-dependent modulation of spinal reflexes, and prevention of decrease in muscle mass. Both tasks consist of alternating movements that rhythmically stretch and shorten hindlimb muscles. However, the paralyzed hindlimbs are passively moved by a motorized apparatus during bike-training, whereas locomotor movements during step-training are generated by spinal networks triggered by afferent feedback. Our objective was to compare the task-dependent effect of bike- and step-training after SCI on physiological measures of spinal cord plasticity in relation to changes in levels of neurotrophic factors. Thirty adult female Sprague-Dawley rats underwent complete spinal transection at a low thoracic level (T12). The rats were assigned to one of three groups: bike-training, step-training, or no training. The exercise regimen consisted of 15 min/d, 5 days/week, for 4 weeks, beginning 5 days after SCI. During a terminal experiment, H-reflexes were recorded from interosseus foot muscles following stimulation of the tibial nerve at 0.3, 5, or 10 Hz. The animals were sacrificed and the spinal cords were harvested for Western blot analysis of the expression of neurotrophic factors in the lumbar spinal cord. We provide evidence that bike- and step-training significantly increase the levels of brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and NT-4 in the lumbar enlargement of SCI rats, whereas only step-training increased glial cell-derived neurotrophic factor (GDNF) levels. An increase in neurotrophic factor protein levels that positively correlated with the recovery of H-reflex frequency-dependent depression suggests a role for neurotrophic factors in reflex normalization

Komatiitic Sills and Multigenerational Peperite at Dundonald Beach, Abitibi Greenstone Belt, Ontario: Volcanic Architecture and Nickel Sulfide Distribution

International audienceThe density and the tectonic stresses in the deep crust and the physical properties of komatiitic magmas determine the level to which they will rise, but once in the near-surface environment, the density and rheology of the near-surface rocks (consolidated and dense lava flows and sedimentary rocks versus unconsolidated sedimentary or volcaniclastic deposits) govern whether they will be emplaced as lava flows, invasive flows, or sills. Where near-surface strata are competent (i.e., flow-dominated or consolidated sedimentary and/or volcaniclastic successions), komatiitic magma erupts as flows that form extensive lava shields (e.g., Kambalda). However, where near-surface strata are not competent (i.e., unconsolidated volcaniclastic- and/or sediment-dominated successions), komatiitic magmas typically are emplaced as high-level sills that increase the bulk density of the volcano-sedimentary pile and eventually allow the eruption of lava and the construction of complex sub-volcanic-volcanic lava shields (e.g., Dundonald and Shaw dome, Abitibi belt; Raglan, Cape Smith belt; Pechenga, Kola Peninsula; Thompson Ni belt, Manitoba). The latter environment is illustrated in the volcano-sedimentary succession in Dundonald Township, which is only weakly metamorphosed and deformed and superbly exposed in glacially polished outcrops. The volcano-sedimentary succession in this area comprises (from base to top) (1) the McIntosh formation, composed of a succession of pillowed and massive intermediate volcanic flows; (2) the Dundonald formation, composed of a lower section of komatiite sills, argillites, and felsic volcaniclastic deposits and an upper section of komatiite flows, komatiitic sills, and pillowed intermediate volcanic flows; and (3) the Frederick House Lake formation, composed of massive and pillowed mafic flows. The distribution and thickness of argillites and felsic volcaniclastic rocks define a synvolcanic graben in which the Dundonald South and Alexo Ni-Cu-(PGE) deposits occur within the center and the margin, respectively. Sills and peperites in the lower komatiitic succession at Dundonald Beach exhibit a multigenerational emplacement history recording progressive lithification and increases in the bulk density and rheological strength of the unconsolidated argillites, which ultimately permitted the eruption of lavas at Alexo. Importantly, the nature of the near-surface rocks also influences the localization of Ni-Cu-(PGE) deposits. In lava shields (e.g., Kambalda), the initial eruptions are typically most voluminous and, if erupted at sufficient flow rates, form channelized flows conducive to thermomechanical erosion of sulfur-rich footwall rocks. In sub-volcanic-volcanic lava shields, however, channelized units may occur within the subvolcanic plumbing system and/or within overlying lavas. Where only sills are channelized (e.g., Thompson), mineralization will occur only within the subvolcanic environment; where only the flows are channelized (e.g., Damba-Silwane, Zimbabwe), mineralization will occur only within the volcanic environment. Where both sills and lava flows are channelized (e.g., Dundonald, Shaw dome, Raglan), the distribution of the mineralization is more diverse and may occur as subsea- or sea-floor Ni-Cu-(PGE) deposits

Modes and rates of selfing and associated inbreeding depression in the self-incompatible plant Senecio squalidus (Asteraceae): a successful colonizing species in the British Isles

The strength of the self-incompatibility (SI) response in Senecio squalidus was measured across its British range. Geographic variation in SI was investigated and the extent and inheritance of pseudo-self-compatibility (PSC) and inbreeding depression were determined. Mean self-fruit-set per capitulum was calculated for individuals and sample populations. The heritability of PSC and the magnitude of inbreeding depression were assessed by comparing selfing rates and fitness trait values between SI and PSC parent-progeny lines. SI was found to be strongly expressed in S. squalidus throughout its British range, with only 3.1% of the individuals sampled showing PSC. This PSC had relatively low heritability with stronger expression of SI in selfed progeny relative to PSC parents. Inbreeding depression was shown to be great in S. squalidus, with mean life history stage values ranging from 0.18 to 0.25. The strength of SI in S. squalidus appears not to have weakened in response to its rapid colonization of Britain. The avoidance of inbreeding depression is likely to be the primary factor maintaining strong SI in this successful colonizing species