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

Direct measurement of antiferromagnetic domain fluctuations

Measurements of magnetic noise emanating from ferromagnets due to domain motion were first carried out nearly 100 years ago and have underpinned much science and technology. Antiferromagnets, which carry no net external magnetic dipole moment, yet have a periodic arrangement of the electron spins extending over macroscopic distances, should also display magnetic noise, but this must be sampled at spatial wavelengths of order several interatomic spacings, rather than the macroscopic scales characteristic of ferromagnets. Here we present the first direct measurement of the fluctuations in the nanometre-scale spin- (charge-) density wave superstructure associated with antiferromagnetism in elemental Chromium. The technique used is X-ray Photon Correlation Spectroscopy, where coherent x-ray diffraction produces a speckle pattern that serves as a "fingerprint" of a particular magnetic domain configuration. The temporal evolution of the patterns corresponds to domain walls advancing and retreating over micron distances. While the domain wall motion is thermally activated at temperatures above 100K, it is not so at lower temperatures, and indeed has a rate which saturates at a finite value - consistent with quantum fluctuations - on cooling below 40K. Our work is important because it provides an important new measurement tool for antiferromagnetic domain engineering as well as revealing a fundamental new fact about spin dynamics in the simplest antiferromagnet.Comment: 19 pages, 4 figure

The rise and fall of the king : the correlation between FO Aquarii's low states and the White Dwarf's Spindown

The intermediate polar FO Aquarii experienced its first-reported low-accretion states in 2016, 2017, and 2018. We establish that these low states occurred shortly after the system's white dwarf (WD) began spinning down, after having spent a quarter-century spinning up. FO Aquarii is the only intermediate polar whose period derivative has undergone a sign change, and it has now done so twice. By combining our spin-pulse timings with previous data, we determine that the WD's spin period has varied quasi-sinusoidally since the system's discovery, and an extrapolation predicts that the white dwarf was spinning down during newly discovered low states in photographic plates from 1964, 1965, and 1974. Thus, FO Aquarii's low states appear to occur exclusively during epochs of spindown. Additionally, our time-series photometry of the 2016-18 low states reveals that the mode of accretion is extremely sensitive to the accretion rate; when the system is fainter than V~14.0, the accretion onto the WD is largely stream-fed, but when it is brighter, it is almost exclusively disk-fed. The system's grazing eclipse remained detectable throughout all observations, confirming the uninterrupted presence of a disk-like structure, regardless of the accretion state. Our observations are consistent with theoretical predictions that during the low states, the accretion disk dissipates into a ring of diamagnetic blobs. Finally, a new XMM-Newton observation from 2017 indicates that the system's anomalously soft X-ray spectrum and diminished X-ray luminosity in the wake of the 2016 low state appear to be long-lasting changes compared to pre-2016 observations.peer-reviewe

Modularity of Endpoint Force Patterns Evoked Using Intraspinal Microstimulation in Treadmill Trained and/or Neurotrophin-Treated Chronic Spinal Cats

Chronic spinal cats with neurotrophin-secreting fibroblasts (NTF) transplants recover locomotor function. To ascertain possible mechanisms, intraspinal microstimulation was used to examine the lumbar spinal cord motor output of four groups of chronic spinal cats: untrained cats with unmodified-fibroblasts graft (Op-control) or NTF graft and locomotor-trained cats with unmodified-fibroblasts graft (Trained) or NTF graft (Combination). Forces generated via intraspinal microstimulation at different hindlimb positions were recorded and interpolated, generating representations of force patterns at the paw. Electromyographs (EMGs) of hindlimb muscles, medial gastrocnemius, tibialis anterior, vastus lateralis, and biceps femoris posterior, were also collected to examine relationships between activated muscles and force pattern types. The same four force pattern types obtained in spinal-intact cats were found in chronic spinal cats. Proportions of force patterns in spinal cats differed significantly from those in intact cats, but no significant differences in proportions were observed among individual spinal groups (Op-control, NTF, Trained, and Combination). However, the proportions of force patterns differed significantly between trained (Trained and Combination) and untrained groups (Op-control and NTF). Thus the frequency of expression of some response types was modified by injury and to a lesser extent by training. Force pattern laminar distribution differed in spinal cats compared with intact, with more responses obtained dorsally (0–1,000 μm) and fewer ventrally (3,200–5,200 μm). EMG analysis demonstrated that muscle activity highly predicted some force pattern types and was independent of hindlimb position. We conclude that spinal motor output modularity is preserved after injury

Characterization and validation of a split belt treadmill for measuring hindlimb ground-reaction forces in able-bodied and spinalized felines.

BACKGROUND: The measurement of ground reaction forces (GRFs) in animals trained to locomote on a treadmill after spinal cord injury (SCI) could prove valuable for evaluating training outcomes; however, quantitative measures of the GRFs in spinal felines are limited. NEW METHOD: A split belt treadmill was designed and constructed to measure the GRFs of feline hindlimbs during stepping. The treadmill consists of two independent treadmill assemblies, each mounted on a force plate. The design allows measurements of the vertical (F RESULTS: Static and dynamic noise tests revealed little to no noise at frequencies below 6Hz. Validation of the force plate measurements with a hand-held force sensor force showed good agreement between the two force readings. Peak normalized (to body mass) vertical GRFs for intact cats were 4.89±0.85N/kg for the left hindlimb and 4.79±0.97N/kg for the right. In comparison, trained spinalized cats peak normalized vertical GRFs were 2.20±0.94N/kg for the left hindlimb and 2.85±0.99N/kg for the right. COMPARISON WITH OTHER EXISTING METHODS: Previous methods of measuring GRFs used stationary single force plates or treadmill mounted to single force plate. Using independent treadmills for each hindlimb allows measurement of the individual hindlimb\u27s GRFs in spinalized cats following body-weight supported treadmill training. CONCLUSIONS: The split belt force treadmill enables the simultaneous recording of ground-reaction forces for both hindlimbs in cats prior to spinalization, and following spinalization and body-weight-supported treadmill training (BWST)

Identification of biRFSA languages ⋆

The task of identifying a language from a set of its words is not an easy one. For instance, it is not feasible to identify regular languages in the general case. Therefore, looking for subclasses of regular languages that can be identified in this framework is an interesting problem. One of the most classical identifiable classes is the class of reversible languages, introduced by D. Angluin, also called bideterministic languages as they can be represented by deterministic automata (DFA) whose reverse is also deterministic. Residual Finite State Automata (RFSA) on the other hand is a class of non deterministic automata that shares some properties with DFA. In particular, DFA are RFSA and RFSA can be much smaller. We study here learnability of the class of languages that can be represented by biRFSA: RFSA whose reverse are RFSA. We prove that this class is not identifiable in general but we present two subclasses that are learnable, the second one being identifiable in polynomial time.

Neuromuscular transmission failure and muscle fatigue in ankle muscles of the adult rat after spinal cord injury

Current evidence suggests that significant morphological changes occur in nerve-muscle connections caudal to spinal cord injury (SCI). To determine whether neuromuscular junction (NMJ) function is compromised after SCI, we investigated the contribution of NMJ failure to hindlimb muscle fatigue in control and spinalized adult rats. Repetitive supramaximal nerve stimulation was applied to two muscle-nerve preparations: medial gastrocnemius (MG)-tibial and tibialis anterior (TA)-peroneal. NMJ transmission failure was evident in control and SCI animals after repetitive stimulation. At 2 wk post-SCI, NMJ transmission failure was greater in SCI animals compared with controls, but the difference was not significant (P = 0.205 for the MG and P = 0.053 for the TA). At 6 wk post-SCI, there was a significant but small difference in NMJ transmission failure for the TA between control and spinal animals. These results demonstrate that, although there may be a mild decrement in NMJ function, NMJ transmission remains largely intact for supramaximal nerve stimulation