Changes in intra- and interlimb reflexes from hindlimb cutaneous afferents after staggered thoracic lateral hemisections during locomotion in cats.

When the foot dorsum contacts an obstacle during locomotion, cutaneous afferents signal central circuits to coordinate muscle activity in the four limbs. Spinal cord injury disrupts these interactions, impairing balance and interlimb coordination. We evoked cutaneous reflexes by electrically stimulating left and right superficial peroneal nerves before and after two thoracic lateral hemisections placed on opposite sides of the cord at 9- to 13-week interval in seven adult cats (4 males and 3 females). We recorded reflex responses in ten hindlimb and five forelimb muscles bilaterally. After the first (right T5-T6) and second (left T10-T11) hemisections, coordination of the fore- and hindlimbs was altered and/or became less consistent. After the second hemisection, cats required balance assistance to perform quadrupedal locomotion. Short-latency reflex responses in homonymous and crossed hindlimb muscles largely remained unaffected after staggered hemisections. However, mid- and long-latency homonymous and crossed responses in both hindlimbs occurred less frequently after staggered hemisections. In forelimb muscles, homolateral and diagonal mid- and long-latency response occurrence significantly decreased after the first and second hemisections. In all four limbs, however, when present, short-, mid- and long-latency responses maintained their phase-dependent modulation. We also observed reduced durations of short-latency inhibitory homonymous responses in left hindlimb extensors early after the first hemisection and delayed short-latency responses in the right ipsilesional hindlimb after the first hemisection. Therefore, changes in cutaneous reflex responses correlated with impaired balance/stability and interlimb coordination during locomotion after spinal cord injury. Restoring reflex transmission could be used as a biomarker to facilitate locomotor recovery. KEY POINTS: Cutaneous afferent inputs coordinate muscle activity in the four limbs during locomotion when the foot dorsum contacts an obstacle. Thoracic spinal cord injury disrupts communication between spinal locomotor centres located at cervical and lumbar levels, impairing balance and limb coordination. We investigated cutaneous reflexes during quadrupedal locomotion by electrically stimulating the superficial peroneal nerve bilaterally, before and after staggered lateral thoracic hemisections of the spinal cord in cats. We showed a loss/reduction of mid- and long-latency responses in all four limbs after staggered hemisections, which correlated with altered coordination of the fore- and hindlimbs and impaired balance. Targeting cutaneous reflex pathways projecting to the four limbs could help develop therapeutic approaches aimed at restoring transmission in ascending and descending spinal pathways.

Shrew's venom quickly causes circulation disorder, analgesia and hypokinesia.

Multiple representatives of eulipotyphlan mammals such as shrews have oral venom systems. Venom facilitates shrews to hunt and/or hoard preys. However, little is known about their venom composition, and especially the mechanism to hoard prey in comatose states for meeting their extremely high metabolic rates. A toxin (BQTX) was identified from venomous submaxillary glands of the shrew Blarinella quadraticauda. BQTX is specifically distributed and highly concentrated (~ 1% total protein) in the organs. BQTX shares structural and functional similarities to toxins from snakes, wasps and snails, suggesting an evolutional relevancy of venoms from mammalians and non-mammalians. By potentiating thrombin and factor-XIIa and inhibiting plasmin, BQTX induces acute hypertension, blood coagulation and hypokinesia. It also shows strong analgesic function by inhibiting elastase. Notably, the toxin keeps high plasma stability with a 16-h half-life in-vivo, which likely extends intoxication to paralyze or immobilize prey hoarded fresh for later consumption and maximize foraging profit.

Long-term, multidomain analyses to identify the breed and allelic effects in MSTN-edited pigs to overcome lameness and sustainably improve nutritional meat production.

Beef and mutton production has been aided by breeding to integrate allelic diversity for myostatin (MSTN), but a lack of diversity in the MSTN germplasm has limited similar advances in pig farming. Moreover, insurmountable challenges with congenital lameness and a dearth of data about the impacts of feed conversion, reproduction, and meat quality in MSTN-edited pigs have also currently blocked progress. Here, in a largest-to-date evaluation of multiple MSTN-edited pig populations, we demonstrated a practical alternative edit-site-based solution that overcomes the major production obstacle of hindlimb weakness. We also provide long-term and multidomain datasets for multiple breeds that illustrate how MSTN-editing can sustainably increase the yields of breed-specific lean meat and the levels of desirable lipids without deleteriously affecting feed-conversion rates or litter size. Apart from establishing a new benchmark for the data scale and quality of genome-edited animal production, our study specifically illustrates how gene-editing site selection profoundly impacts the phenotypic outcomes in diverse genetic backgrounds.

Ischemic-Trained Monocytes Improve Arteriogenesis in a Mouse Model of Hindlimb Ischemia.

OBJECTIVE: Monocytes, which play an important role in arteriogenesis, can build immunologic memory by a functional reprogramming that modifies their response to a second challenge. This process, called trained immunity, is evoked by insults that shift monocyte metabolism, increasing HIF (hypoxia-inducible factor)-1α levels. Since ischemia enhances HIF-1α, we evaluate whether ischemia can lead to a functional reprogramming of monocytes, which would contribute to arteriogenesis after hindlimb ischemia. METHODS AND RESULTS: Mice exposed to ischemia by 24 hours (24h) of femoral artery occlusion (24h trained) or sham were subjected to hindlimb ischemia one week later; the 24h trained mice showed significant improvement in blood flow recovery and arteriogenesis after hindlimb ischemia. Adoptive transfer using bone marrow-derived monocytes (BM-Mono) from 24h trained or sham donor mice, demonstrated that recipients subjected to hindlimb ischemia who received 24h ischemic-trained monocytes had remarkable blood flow recovery and arteriogenesis. Further, ischemic-trained BM-Mono had increased HIF-1α and GLUT-1 (glucose transporter-1) gene expression during femoral artery occlusion. Circulating cytokines and GLUT-1 were also upregulated during femoral artery occlusion.Transcriptomic analysis and confirmatory qPCR performed in 24h trained and sham BM-Mono revealed that among the 15 top differentially expressed genes, 4 were involved in lipid metabolism in the ischemic-trained monocytes. Lipidomic analysis confirmed that ischemia training altered the cholesterol metabolism of these monocytes. Further, several histone-modifying epigenetic enzymes measured by qPCR were altered in mouse BM-Mono exposed to 24h hypoxia. CONCLUSIONS: Ischemia training in BM-Mono leads to a unique gene profile and improves blood flow and arteriogenesis after hindlimb ischemia.

Single-cell and ensemble activity of lumbar intermediate and ventral horn interneurons in the spinal air-stepping cat.

We explored the relationship between population interneuronal network activation and motor output in the adult, in vivo, air-stepping, spinal cat. By simultaneously measuring the activity of large numbers of spinal interneurons, we explored ensembles of coherently firing interneurons and their relation to motor output. In addition, the networks were analyzed in relation to their spatial distribution along the lumbar enlargement for evidence of localized groups driving particular phases of the locomotor step cycle. We simultaneously recorded hindlimb EMG activity during stepping and extracellular signals from 128 channels across two polytrodes inserted within lamina V-VII of two separate lumbar segments. Results indicated that spinal interneurons participate in one of two ensembles that are highly correlated with the flexor or the extensor muscle bursts during stepping. Interestingly, less than half of the isolated single units were significantly unimodally tuned during the step cycle whereas >97% of the single units of the ensembles were significantly correlated with muscle activity. These results show the importance of population scale analysis in neural studies of behavior as there is a much greater correlation between muscle activity and ensemble firing than between muscle activity and individual neurons. Finally, we show that there is no correlation between interneurons' rostrocaudal locations within the lumbar enlargement and their preferred phase of firing or ensemble participation. These findings indicate that spinal interneurons of lamina V-VII encoding for different phases of the locomotor cycle are spread throughout the lumbar enlargement in the adult spinal cord.NEW & NOTEWORTHY We report on the ensemble organization of interneuronal activity in the spinal cord during locomotor movements and show that lumbar intermediate zone interneurons organize in two groups related to the two major phases of walking: stance and swing. Ensemble organization is also shown to better correlate with muscular output than single-cell activity, although ensemble membership does not appear to be somatotopically organized within the spinal cord.

Limited changes in locomotor recovery and unaffected white matter sparing after spinal cord contusion at different times of day.

The circadian gene expression rhythmicity drives diurnal oscillations of physiological processes that may determine the injury response. While outcomes of various acute injuries are affected by the time of day at which the original insult occurred, such influences on recovery after spinal cord injury (SCI) are unknown. We report that mice receiving moderate, T9 contusive SCI at ZT0 (zeitgeber time 0, time of lights on) and ZT12 (time of lights off) showed similar hindlimb function recovery in the Basso mouse scale (BMS) over a 6 week post-injury period. In an independent study, no significant differences in BMS were observed after SCI at ZT18 vs. ZT6. However, the ladder walking test revealed modestly improved performance for ZT18 vs. ZT6 mice at week 6 after injury. Consistent with those minor effects on functional recovery, terminal histological analysis revealed no significant differences in white matter sparing at the injury epicenter. Likewise, blood-spinal cord barrier disruption and neuroinflammation appeared similar when analyzed at 1 week post injury at ZT6 or ZT18. Therefore, locomotor recovery after thoracic contusive SCI is not substantively modulated by the time of day at which the neurotrauma occurred.

D-Serine produces antidepressant-like effects in mice through suppression of BDNF signaling pathway and regulation of synaptic adaptations in the nucleus accumbens.

OBJECTIVE: D-Serine is a crucial endogenous co-agonist of N-methyl-D-aspartate receptors (NMDARs) in the central nervous system and can affect the function of the brain derived neurotrophic factor (BDNF) system, which plays an essential role in modulating synaptic plasticity. The current study aimed to systematically evaluate the role and mechanisms of D-serine in depressive behavior in nucleus accumbens (NAc). METHODS: D-Serine concentration in the chronic social defeat stress (CSDS) model in NAc was measured using high-performance liquid chromatography (HPLC). The antidepressant-like effects of D-serine were identified using forced swim test (FST) and tail suspension test (TST) in control mice and then assessed in CSDS model. We applied social interaction and sucrose preference tests to identify the susceptibility of CSDS model. Western blotting was further performed to assess the changes of BDNF signaling cascade in NAc after CSDS and D-serine treatment. The BDNF signaling inhibitor (K252a) was also used to clarify the antidepressant-like mechanism of D-serine. Moreover, D-serine effects on synaptic plasticity in NAc were investigated using electrophysiological methods. RESULTS: D-Serine concentration was decreased in depression susceptible mice in NAc. D-Serine injections into NAc exhibited antidepressant-like effects in FST and TST without affecting the locomotor activity of mice. D-Serine was also effective in CSDS model of depression. Moreover, D-serine down-regulated the BDNF signaling pathway in NAc during CSDS procedure. Furthermore, BDNF signaling inhibitor (K252a) enhanced the antidepressant effects of D-serine. We also found that D-serine was essential for NMDARs-dependent long-term depression (LTD). CONCLUSION: D-Serine exerts antidepressant-like effects in mice mediated through restraining the BDNF signaling pathway and regulating synaptic plasticity in NAc.

Weight bearing as a measure of disease progression in experimental autoimmune encephalomyelitis.

Motor disability in multiple sclerosis is often modeled using experimental autoimmune encephalomyelitis (EAE) and assessed using the clinical score (CS), an observer-dependent tool that can lead to potential bias. The Advanced Dynamic Weight Bearing (ADWB) system was evaluated as an observer-independent measurement of EAE symptoms. ADWB detected weight shifts onto the front paws as mice develop hindlimb motor disability. CS and ADWB were strongly correlated, indicated that these measures are comparable and suggesting that ADWB may be an appropriate observer-independent tool for the assessment of EAE progression.

Regenerative effect of platelet-rich plasma in the murine ischemic limbs.

AIMS: The purpose of this study was to investigate the effect of PPRP (pure PRP) and LPRP (PRP with leukocytes) on recovery from limb ischemia and on expression of growth factors involved in angiogenesis, myogenesis and fibrogenesis. MATERIAL AND METHODS: PPRP and LPRP prepared by centrifugation were added to cultures of C2C12 and NIH3T3 cells (1 or 10% PRPs) to evaluate alterations in cell metabolism and expression of growth factors by MTT, ELISA and RT-qPCR, respectively. To evaluate in vivo regenerative effects, PRPs were injected into the ischemic limbs of BALB/c mice and muscle mass/strength and histomorphometry were evaluated after 30 days. KEY FINDINGS: Mice treated with PRPs after limb ischemia showed an increase in the size of myofibers and muscle strength, reduced fibrosis and adipocytes, and decreased capillary density and necrosis scores compared to untreated mice. In cell culture, serum deprivation reduced the viability of C2C12 and NIH3T3 cells to about 50%, but the addition of 1% PRPs completely recovered this loss. Both PRPs, downregulated most of the tested genes; however, angiogenic gene Vegfa in C2C12 and the fibrogenic genes Col1a1 and Col3a1 in NIH3T3 cells were upregulated by LPRP. SIGNIFICANCE: PPRP and LPRP had similar effects in regulation of genes involved in angiogenesis, myogenesis and fibrogenesis. However, the presence of leucocytes did not significantly affect regenerative activities of PRP in the ischemic limb.

Effect of spinal cord injury on neural encoding of spontaneous postural perturbations in the hindlimb sensorimotor cortex.

Supraspinal signals play a significant role in compensatory responses to postural perturbations. Although the cortex is not necessary for basic postural tasks in intact animals, its role in responding to unexpected postural perturbations after spinal cord injury (SCI) has not been studied. To better understand how SCI impacts cortical encoding of postural perturbations, the activity of single neurons in the hindlimb sensorimotor cortex (HLSMC) was recorded in the rat during unexpected tilts before and after a complete midthoracic spinal transection. In a subset of animals, limb ground reaction forces were also collected. HLSMC activity was strongly modulated in response to different tilt profiles. As the velocity of the tilt increased, more information was conveyed by the HLSMC neurons about the perturbation due to increases in both the number of recruited neurons and the magnitude of their responses. SCI led to attenuated and delayed hindlimb ground reaction forces. However, HLSMC neurons remained responsive to tilts after injury but with increased latencies and decreased tuning to slower tilts. Information conveyed by cortical neurons about the tilts was therefore reduced after SCI, requiring more cells to convey the same amount of information as before the transection. Given that reorganization of the hindlimb sensorimotor cortex in response to therapy after complete midthoracic SCI is necessary for behavioral recovery, this sustained encoding of information after SCI could be a substrate for the reorganization that uses sensory information from above the lesion to control trunk muscles that permit weight-supported stepping and postural control.NEW & NOTEWORTHY The role of cortical circuits in the encoding of posture and balance is of interest for developing therapies for spinal cord injury. This work demonstrated that unexpected postural perturbations are encoded in the hindlimb sensorimotor cortex even in the absence of hindlimb sensory feedback. In fact, the hindlimb sensorimotor cortex continues to encode for postural perturbations after complete spinal transection.

Formation of a novel supraspinal-spinal connectome that relearns the same motor task after complete paralysis.

Having observed that electrical spinal cord stimulation and training enabled four patients with paraplegia with motor complete paralysis to regain voluntary leg movement, the underlying mechanisms involved in forming the newly established supraspinal-spinal functional connectivity have become of great interest. van den Brand et al. (Science 336: 1182-1185, 2012) subsequently, demonstrated the recovery, in response to spinal electro-neuromodulation and locomotor training, of voluntary stepping of the lower limbs in rats that received a lesion that is assumed to eliminate all long-descending cortical axons that project to lumbosacral segments. Here, we used a similar spinal lesion in rats to eliminate long-descending axons to determine whether a novel, trained motor behavior triggered by a unique auditory cue learned before a spinal lesion, could recover after the lesion. Hindlimb stepping recovered 1 mo after the spinal injury, but only after 2 mo, the novel and unique audio-triggered behavior was recovered, meaning that not only was a novel connectivity formed but also further evidence suggested that this highly unique behavioral response was independent of the recovery of the circuitry that generated stepping. The unique features of the newly formed supraspinal-spinal connections that mediated the recovery of the trained behavior is consistent with a guidance mechanism(s) that are highly use dependent.NEW & NOTEWORTHY Electrical spinal cord stimulation has enabled patients with paraplegia to regain voluntary leg movement, and so the underlying mechanisms involved in this recovery are of great interest. Here, we demonstrate in rodents the recovery of trained motor behavior after a spinal lesion. Rodents were trained to kick their right hindlimb in response to an auditory cue. This behavior recovered 2 mo after the paralyzing spinal cord injury but only with the assistance of electrical spinal cord stimulation.

Unusual Quadrupedal Locomotion in Rat during Recovery from Lumbar Spinal Blockade of 5-HT7 Receptors.

Coordination of four-limb movements during quadrupedal locomotion is controlled by supraspinal monoaminergic descending pathways, among which serotoninergic ones play a crucial role. Here we investigated the locomotor pattern during recovery from blockade of 5-HT7 or 5-HT2A receptors after intrathecal application of SB269970 or cyproheptadine in adult rats with chronic intrathecal cannula implanted in the lumbar spinal cord. The interlimb coordination was investigated based on electromyographic activity recorded from selected fore- and hindlimb muscles during rat locomotion on a treadmill. In the time of recovery after hindlimb transient paralysis, we noticed a presence of an unusual pattern of quadrupedal locomotion characterized by a doubling of forelimb stepping in relation to unaffected hindlimb stepping (2FL-1HL) after blockade of 5-HT7 receptors but not after blockade of 5-HT2A receptors. The 2FL-1HL pattern, although transient, was observed as a stable form of fore-hindlimb coupling during quadrupedal locomotion. We suggest that modulation of the 5-HT7 receptors on interneurons located in lamina VII with ascending projections to the forelimb spinal network can be responsible for the 2FL-1HL locomotor pattern. In support, our immunohistochemical analysis of the lumbar spinal cord demonstrated the presence of the 5-HT7 immunoreactive cells in the lamina VII, which were rarely 5-HT2A immunoreactive.

Chronic ablation of TRPV1-sensitive skeletal muscle afferents attenuates the muscle metaboreflex.

Exercise intolerance is a hallmark symptom of cardiovascular disease and likely occurs via enhanced activation of muscle metaboreflex-induced vasoconstriction of the heart and active skeletal muscle which, thereby limits cardiac output and peripheral blood flow. Muscle metaboreflex vasoconstrictor responses occur via activation of metabolite-sensitive afferent fibers located in ischemic active skeletal muscle, some of which express transient receptor potential vanilloid 1 (TRPV1) cation channels. Local cardiac and intrathecal administration of an ultrapotent noncompetitive, dominant negative agonist resiniferatoxin (RTX) can ablate these TRPV1-sensitive afferents. This technique has been used to attenuate cardiac sympathetic afferents and nociceptive pain. We investigated whether intrathecal administration (L4-L6) of RTX (2 µg/kg) could chronically attenuate subsequent muscle metaboreflex responses elicited by reductions in hindlimb blood flow during mild exercise (3.2 km/h) in chronically instrumented conscious canines. RTX significantly attenuated metaboreflex-induced increases in mean arterial pressure (27 ± 5.0 mmHg vs. 6 ± 8.2 mmHg), cardiac output (1.40 ± 0.2 L/min vs. 0.28 ± 0.1 L/min), and stroke work (2.27 ± 0.2 L·mmHg vs. 1.01 ± 0.2 L·mmHg). Effects were maintained until 78 ± 14 days post-RTX at which point the efficacy of RTX injection was tested by intra-arterial administration of capsaicin (20 µg/kg). A significant reduction in the mean arterial pressure response (+45.7 ± 6.5 mmHg pre-RTX vs. +19.7 ± 3.1 mmHg post-RTX) was observed. We conclude that intrathecal administration of RTX can chronically attenuate the muscle metaboreflex and could potentially alleviate enhanced sympatho-activation observed in cardiovascular disease states.

A novel imidazolinone metformin-methylglyoxal metabolite promotes endothelial cell angiogenesis via the eNOS/HIF-1α pathway.

Peripheral arterial disease (PAD) is one of the major complications of diabetes due to an impairment in angiogenesis. Since there is currently no drug with satisfactory efficacy to enhance blood vessel formation, discovering therapies to improve angiogenesis is critical. An imidazolinone metabolite of the metformin-methylglyoxal scavenging reaction, (E)-1,1-dimethyl-2-(5-methyl-4-oxo-4,5-dihydro-1H-imidazol-2-yl) guanidine (IMZ), was recently characterized and identified in the urine of type-2 diabetic patients. Here, we report the pro-angiogenesis effect of IMZ (increased aortic sprouting, cell migration, network formation, and upregulated multiple pro-angiogenic factors) in human umbilical vein endothelial cells. Using genetic and pharmacological approaches, we showed that IMZ augmented angiogenesis by activating the endothelial nitric oxide synthase (eNOS)/hypoxia-inducible factor-1 alpha (HIF-1α) pathway. Furthermore, IMZ significantly promoted capillary density in the in vivo Matrigel plug angiogenesis model. Finally, the role of IMZ in post-ischemic angiogenesis was examined in a chronic hyperglycemia mouse model subjected to hind limb ischemia. We observed improved blood perfusion, increased capillary density, and reduced tissue necrosis in mice receiving IMZ compared to control mice. Our data demonstrate the pro-angiogenic effects of IMZ, its underlying mechanism, and provides a structural basis for the development of potential pro-angiogenic agents for the treatment of PAD.

Chronic inactivation of the contralesional hindlimb motor cortex after thoracic spinal cord hemisection impedes locomotor recovery in the rat.

After incomplete spinal cord injury (SCI), cortical plasticity is involved in hindlimb locomotor recovery. Nevertheless, whether cortical activity is required for motor map plasticity and recovery remains unresolved. Here, we combined a unilateral thoracic spinal cord injury (SCI) with a cortical inactivation protocol that uncovered a functional role of contralesional cortical activity in hindlimb recovery and ipsilesional map plasticity. In adult rats, left hindlimb paralysis was induced by sectioning half of the spinal cord at the thoracic level (hemisection) and we used a continuous infusion of muscimol (GABAA agonist, 10 mM, 0.11 µl/h) delivered via implanted osmotic pump (n = 9) to chronically inactivate the contralesional hindlimb motor cortex. Hemisected rats with saline infusion served as a SCI control group (n = 8), and intact rats with muscimol infusion served as an inactivation control group (n = 6). Locomotion was assessed in an open field, on a horizontal ladder, and on a treadmill prior to and for three weeks after hemisection. Cortical inactivation after hemisection significantly impeded hindlimb locomotor recovery in all tasks and specifically disrupted the ability of rats to generate proper flexion of the affected hindlimb during stepping compared to SCI controls, with no significant effect of inactivation in intact rats. Chronic and acute (n = 4) cortical inactivation after hemisection also significantly reduced the representation of the affected hindlimb in the ipsilesional motor cortex derived with intracortical microsimulation (ICMS). Our results provide evidence that residual activity in the contralesional hindlimb motor cortex after thoracic hemisection contributes to spontaneous locomotor recovery and map plasticity.

Vascular permeability of skeletal muscle microvessels in rat arterial ligation model: in vivo analysis using two-photon laser scanning microscopy.

Peripheral artery disease (PAD) in the lower limb compromises oxygen supply due to arterial occlusion. Ischemic skeletal muscle is accompanied by capillary structural deformation. Therefore, using novel microscopy techniques, we tested the hypothesis that endothelial cell swelling temporally and quantitatively corresponds to enhanced microvascular permeability. Hindlimb ischemia was created in male Wistar rat's by iliac artery ligation (AL). The tibialis anterior (TA) muscle microcirculation was imaged using intravenously infused rhodamine B isothiocyanate dextran fluorescent dye via two-photon laser scanning microscopy (TPLSM) and dye extravasation at 3 and 7 days post-AL quantified to assess microvascular permeability. The TA microvascular endothelial ultrastructure was analyzed by transmission electron microscopy (TEM). Compared with control (0.40 ± 0.15 µm3 × 106), using TPLSM, the volumetrically determined interstitial leakage of fluorescent dye measured at 3 (3.0 ± 0.40 µm3 × 106) and 7 (2.5 ± 0.8 µm3 × 106) days was increased (both P < 0.05). Capillary wall thickness was also elevated at 3 (0.21 ± 0.06 µm) and 7 (0.21 ± 0.08 µm) days versus control (0.11 ± 0.03 µm, both P < 0.05). Capillary endothelial cell swelling was temporally and quantitatively associated with elevated vascular permeability in the AL model of PAD but these changes occurred in the absence of elevations in protein levels of vascular endothelial growth factor (VEGF) its receptor (VEGFR2 which decreased by AL-7 day) or matrix metalloproteinase. The temporal coherence of endothelial cell swelling and increased vascular permeability supports a common upstream mediator. TPLSM, in combination with TEM, provides a sensitive and spatially discrete technique to assess the mechanistic bases for, and efficacy of, therapeutic countermeasures to the pernicious sequelae of compromised peripheral arterial function.

Spaceflight and hind limb unloading induces an arthritic phenotype in knee articular cartilage and menisci of rodents.

Reduced knee weight-bearing from prescription or sedentary lifestyles are associated with cartilage degradation; effects on the meniscus are unclear. Rodents exposed to spaceflight or hind limb unloading (HLU) represent unique opportunities to evaluate this question. This study evaluated arthritic changes in the medial knee compartment that bears the highest loads across the knee after actual and simulated spaceflight, and recovery with subsequent full weight-bearing. Cartilage and meniscal degradation in mice were measured via microCT, histology, and proteomics and/or biochemically after: (1) ~ 35 days on the International Space Station (ISS); (2) 13-days aboard the Space Shuttle Atlantis; or (3) 30 days of HLU, followed by a 49-day weight-bearing readaptation with/without exercise. Cartilage degradation post-ISS and HLU occurred at similar spatial locations, the tibial-femoral cartilage-cartilage contact point, with meniscal volume decline. Cartilage and meniscal glycosaminoglycan content were decreased in unloaded mice, with elevated catabolic enzymes (e.g., matrix metalloproteinases), and elevated oxidative stress and catabolic molecular pathway responses in menisci. After the 13-day Shuttle flight, meniscal degradation was observed. During readaptation, recovery of cartilage volume and thickness occurred with exercise. Reduced weight-bearing from either spaceflight or HLU induced an arthritic phenotype in cartilage and menisci, and exercise promoted recovery.

An Exercise Mimetic Approach to Reduce Poststroke Deconditioning and Enhance Stroke Recovery.

Evidence supports early rehabilitation after stroke to limit disability. However, stroke survivors are typically sedentary and experience significant cardiovascular and muscular deconditioning. Despite growing consensus that preclinical and clinical stroke recovery research should be aligned, there have been few attempts to incorporate cardiovascular and skeletal muscle deconditioning into animal models of stroke. Here, we demonstrate in rats that a hindlimb sensorimotor cortex stroke results in both cardiovascular and skeletal muscle deconditioning and impairments in gait akin to those observed in humans. To reduce poststroke behavioral, cardiovascular, and skeletal muscle perturbations, we then used a combinatorial intervention consisting of aerobic and resistance exercise in conjunction with administration of resveratrol (RESV), a drug with exercise mimetic properties. A combination of aerobic and resistance exercise mitigated decreases in cardiovascular fitness and attenuated skeletal muscle abnormalities. RESV, beginning 24 hours poststroke, reduced acute hindlimb impairments, improved recovery in hindlimb function, increased vascular density in the perilesional cortex, and attenuated skeletal muscle fiber changes. Early RESV treatment and aerobic and resistance exercise independently provided poststroke benefits, at a time when individuals are rapidly becoming deconditioned as a result of inactivity. Although no additive effects were observed in these experiments, this approach represents a promising strategy to reduce poststroke behavioral impairments and minimize deconditioning. As such, this treatment regime has potential for enabling patients to engage in more intensive rehabilitation at an earlier time following stroke when mechanisms of neuroplasticity are most prevalent.

Chronic Ouabain Prevents Na,K-ATPase Dysfunction and Targets AMPK and IL-6 in Disused Rat Soleus Muscle.

Sustained sarcolemma depolarization due to loss of the Na,K-ATPase function is characteristic for skeletal muscle motor dysfunction. Ouabain, a specific ligand of the Na,K-ATPase, has a circulating endogenous analogue. We hypothesized that the Na,K-ATPase targeted by the elevated level of circulating ouabain modulates skeletal muscle electrogenesis and prevents its disuse-induced disturbances. Isolated soleus muscles from rats intraperitoneally injected with ouabain alone or subsequently exposed to muscle disuse by 6-h hindlimb suspension (HS) were studied. Conventional electrophysiology, Western blotting, and confocal microscopy with cytochemistry were used. Acutely applied 10 nM ouabain hyperpolarized the membrane. However, a single injection of ouabain (1 µg/kg) prior HS was unable to prevent the HS-induced membrane depolarization. Chronic administration of ouabain for four days did not change the α1 and α2 Na,K-ATPase protein content, however it partially prevented the HS-induced loss of the Na,K-ATPase electrogenic activity and sarcolemma depolarization. These changes were associated with increased phosphorylation levels of AMP-activated protein kinase (AMPK), its substrate acetyl-CoA carboxylase and p70 protein, accompanied with increased mRNA expression of interleikin-6 (IL-6) and IL-6 receptor. Considering the role of AMPK in regulation of the Na,K-ATPase, we suggest an IL-6/AMPK contribution to prevent the effects of chronic ouabain under skeletal muscle disuse.

Succinate Injection Rescues Vasculature and Improves Functional Recovery Following Acute Peripheral Ischemia in Rodents: A Multimodal Imaging Study.

Succinate influences angiogenesis and neovascularization via a hormonelike effect on G-protein-coupled receptor 91 (GPR91). This effect has been demonstrated in the pathophysiology of diabetic retinopathy and rheumatoid arthritis. To evaluate whether succinate can play a role in acute peripheral ischemia, a preclinical study was conducted with ischemic mice treated with succinate or PBS and evaluated by imaging. Acute ischemia was followed by an increased in GPR91 expression in the ischemic muscle. As assessed with LASER-Doppler, succinate treatment resulted in an earlier and more intense reperfusion of the ischemic hindlimb compared to the control group (* p = 0.0189). A microPET study using a radiolabeled integrin ligand ([68Ga]Ga-RGD2) showed an earlier angiogenic activation in the succinate arm compared to control mice (* p = 0.020) with a prolonged effect. Additionally, clinical recovery following ischemia was better in the succinate group. In conclusion, succinate injection promotes earlier angiogenesis after ischemia, resulting in a more effective revascularization and subsequently a better functional recovery.