Spinal cord injury impairs cardiac function due to impaired bulbospinal sympathetic control

'Time is of the essence': upper-body aerobic exercise to improve cardiovascular health during inpatient rehabilitation within the first year following spinal cord injury - protocol for a randomised clinical trial

INTRODUCTION

Individuals with spinal cord injury (SCI) face heightened cardiovascular disease (CVD) risks. While general exercise guidelines are promoted for SCI individuals, when and how to incorporate exercise during the subacute phase post-SCI remains unclear. Consequently, early aerobic exercise to reduce CVD risks is not standard practice in subacute SCI care, potentially missing an opportunity for optimal cardiovascular rehabilitation, especially given observed reductions in cardiac structure and function within the first year post-SCI. Addressing this gap could improve long-term cardiovascular health and health-related quality of life (HRQOL) for individuals with SCI. Early intervention might prevent worsening cardiovascular function and establish beneficial exercise habits. However, few studies have evaluated the effectiveness of early exercise interventions in this population. This study aims to provide insight into the impact of moderate-intensity arm-crank exercise training (ACET) on cardiometabolic, HRQOL, functional and fitness parameters in individuals with subacute (<12 months postinjury) SCI.

METHODS AND ANALYSIS

We will conduct a single-centre, two-group, single-blind randomised controlled trial with 42 participants who have sustained a cervical or thoracic SCI within the past year. The non-intervention group will receive hospital standard of care (control group) while the intervention group will receive hospital standard of care plus moderate-intensity ACET for 10 weeks in line with the SCI-specific exercise guidelines to improve cardiometabolic health. The primary outcome measure will be central arterial stiffness (carotid-to-femoral pulse wave velocity). Secondary outcomes include assessments of (1) blood biomarkers linked to CVD, (2) cardiac structure and function, (3) extracranial vasculature, (4) HRQOL, (5) cognitive function, (6) physical activity level, (7) cardiorespiratory fitness, (8) motor function and (9) feasibility outcomes. Assessments will occur at baseline (rehabilitation centre admission, -2 weeks), preintervention (0 weeks), postintervention (10 weeks) and follow-up (6 months after postintervention), for HRQOL outcomes only.

ETHICS AND DISSEMINATION

Ethical approval was obtained from the Wales Research Ethics Committee (HREC 22/WA/0329). Outcome data will be presented at international conferences, patient advocacy groups, health professional networks and community health events. Findings will be published in peer-reviewed journals and widely disseminated through strategic channels to reach researchers, healthcare providers, patients and the public.

TRIAL REGISTRATION NUMBER

ISRCTN99941302.

Making the Invisible Visible: Understanding Autonomic Dysfunctions Following Spinal Cord Injury

Autonomic dysfunctions are a major challenge to individuals following spinal cord injury. Despite this, these consequences receive far less attention compared with motor recovery. This review will highlight the major autonomic dysfunctions following SCI predominantly based on our present understanding of the anatomy and physiology of autonomic control and available clinical data.

Therapeutic Efficacy of Hemodynamic Management Using Norepinephrine on Cardiorespiratory Function Following Cervical Spinal Cord Contusion in Rats

Cervical spinal cord injury usually leads to cardiorespiratory dysfunction due to interruptions of the supraspinal pathways innervating the phrenic motoneurons and thoracic sympathetic preganglionic neurons. Although clinical guidelines recommend maintaining the mean arterial pressure within 85-90 mmHg during the first week of injury, there is no pre-clinical evidence from animal models to prove the therapeutic efficacy of hemodynamic management. Accordingly, the present study was designed to investigate the therapeutic efficacy of hemodynamic management in rats with cervical spinal cord contusion. Adult male rats underwent cervical spinal cord contusion and the implantation of osmotic pumps filled with saline or norepinephrine (NE) (125 μg/(kg·h) for 1 week). The cardiorespiratory function of unanesthetized rats was examined using a non-invasive blood pressure analyzer and double-chamber plethysmography. Cervical spinal cord contusion caused a long-term reduction in the mean arterial pressure and tidal volume. This hypotensive response was significantly reversed in contused rats receiving NE (1 day: 88 ± 19 mmHg; 2 weeks: 96 ± 13 mmHg) compared with contused rats receiving saline (1 day: 72 ± 15 mmHg; 2 weeks: 82 ± 10 mmHg). NE also significantly improved the tidal volume 1 day post-injury (contused + NE: 0.7 ± 0.2 mL; contused + saline: 0.5 ± 0.1 mL). Immunofluorescence staining results revealed that injury-induced reductions of noradrenergic and glutamatergic fibers within the thoracic spinal cord were significantly improved by NE. These results provided the evidence demonstrating that hemodynamic management using NE significantly improves cardiorespiratory function by alleviating neural pathway damage after cervical spinal cord contusion.

Acute intermittent hypoxia elicits sympathetic neuroplasticity independent of peripheral chemoreflex activation and spinal cord tissue hypoxia in a rodent model of high-thoracic spinal cord injury

The loss of medullary control of spinal circuits controlling the heart and blood vessels is a unifying mechanism linking both hemodynamic instability and the risk for cardiovascular diseases (CVD) following spinal cord injury (SCI). As such, new avenues to regulate sympathetic activity are essential to mitigate CVD in this population. Acute intermittent hypoxia (AIH) induces a type of neuroplasticity known as long-term facilitation (LTF), a persistent increase in nerve activity post-AIH in spinal motor circuits. Whether LTF occurs within the sympathetic circuit following SCI is largely unknown. We aimed to test whether AIH elicits sympathetic LTF (i.e., sLTF) and attenuates hypoactivity in sub-lesional splanchnic sympathetic circuits in a male rat model of SCI. In 3 experimental series, we tested whether 1) high-thoracic contusion SCI induces hypoactivity in splanchnic sympathetic nerve activity, 2) AIH elicits sLTF following SCI, and 3) sLTF requires carotid chemoreflex activation or spinal cord tissue hypoxia. Our results indicate that a single-session of AIH therapy (10 × 1 min of FiO2 = 0.1, interspersed with 2 min of FiO2 = 1.0) delivered at 2 weeks following SCI attenuates SCI-induced sympathetic hypoactivity by eliciting sLTF 90 min post-treatment that is independent of peripheral chemoreflex activation and/or spinal cord hypoxia. These findings advance our mechanistic understanding of AIH in the field and yield new insights into factors underpinning AIH-induced sLTF following SCI in a rat model. Our findings also set the stage for the chronic application of AIH to alleviate secondary complications resulting from sympathetic hypoactivity following SCI.

Synthetic embryology of the human heart

The evolution of stem cell-based heart models from cells and tissues to organoids and assembloids and recently synthetic embryology gastruloids, is poised to revolutionize our understanding of cardiac development, congenital to adult diseases, and patient customized therapies. Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) have already been integrated into transplantable patches and are in preclinical efforts to reverse fibrotic scarring from myocardial infarctions. To inform on the complexity of heart diseases, multi-tissue morphogenic heart models are needed that replicate fundamental components of heart function to heart organogenesis in vitro and which require a deep understanding of heart development. Organoid and assembloid models capture selected multicellular cardiac processes, such as chamber formation and priming events for vascularization. Gastruloid heart models offer deeper insights as synthetic embryology to mimic multi-staged developmental events of in vivo heart organogenesis including established heart fields, crescent formation and heart tube development along with vascular systemic foundation and even further steps. The human Elongating Multi-Lineage Organized Cardiac (EMLOC) gastruloid model captures these stages and additional events including chamber genesis, patterned vascularization, and extrinsic central and intrinsic cardiac nervous system (CNS-ICNS) integration guided by spatiotemporal and morphogenic processes with neural crest cells. Gastruloid synthetic embryology heart models offer new insights into previously hidden processes of development and provide powerful platforms for addressing heart disease that extends beyond cardiomyocytes, such as arrhythmogenic diseases, congenital defects, and systemic injury interactions, as in spinal cord injuries. The holistic view that is emerging will reveal heart development and disease in unprecedented detail to drive transformative state-of-the-art innovative applications for heart health.

Short- and long-term effects of transcutaneous spinal cord stimulation on autonomic cardiovascular control and arm-crank exercise capacity in individuals with a spinal cord injury (STIMEX-SCI): study protocol

INTRODUCTION

Individuals with higher neurological levels of spinal cord injury (SCI) at or above the sixth thoracic segment (≥T6), exhibit impaired resting cardiovascular control and responses during upper-body exercise. Over time, impaired cardiovascular control predisposes individuals to lower cardiorespiratory fitness and thus a greater risk for cardiovascular disease and mortality. Non-invasive transcutaneous spinal cord stimulation (TSCS) has been shown to modulate cardiovascular responses at rest in individuals with SCI, yet its effectiveness to enhance exercise performance acutely, or promote superior physiological adaptations to exercise following an intervention, in an adequately powered cohort is unknown. Therefore, this study aims to explore the efficacy of acute TSCS for restoring autonomic function at rest and during arm-crank exercise to exhaustion (AIM 1) and investigate its longer-term impact on cardiorespiratory fitness and its concomitant benefits on cardiometabolic health and health-related quality of life (HRQoL) outcomes following an 8-week exercise intervention (AIM 2).

METHODS AND ANALYSIS

Sixteen individuals aged ≥16 years with a chronic, motor-complete SCI between the fifth cervical and sixth thoracic segments will undergo a baseline TSCS mapping session followed by an autonomic nervous system (ANS) stress test battery, with and without cardiovascular-optimised TSCS (CV-TSCS). Participants will then perform acute, single-session arm-crank exercise (ACE) trials to exhaustion with CV-TSCS or sham TSCS (SHAM-TSCS) in a randomised order. Twelve healthy, age- and sex-matched non-injured control participants will be recruited and will undergo the same ANS tests and exercise trials but without TSCS. Thereafter, the SCI cohort will be randomly assigned to an experimental (CV-TSCS+ACE) or control (SHAM-TSCS+ACE) group. All participants will perform 48 min of ACE twice per week (at workloads corresponding to 73-79% peak oxygen uptake), over a period of 8 weeks, either with (CV-TSCS) or without (SHAM-TSCS) cardiovascular-optimised stimulation. The primary outcomes are time to exhaustion (AIM 1) and cardiorespiratory fitness (AIM 2). Secondary outcomes for AIM 1 include arterial blood pressure, respiratory function, cerebral blood velocity, skeletal muscle tissue oxygenation, along with concentrations of catecholamines, brain-derived neurotrophic factor and immune cell dynamics via venous blood sampling pre, post and 90 min post-exercise. Secondary outcomes for AIM 2 include cardiometabolic health biomarkers, cardiac function, arterial stiffness, 24-hour blood pressure lability, energy expenditure, respiratory function, neural drive to respiratory muscles, seated balance and HRQoL (eg, bowel, bladder and sexual function). Outcome measures will be assessed at baseline, pre-intervention, post-intervention and after a 6-week follow-up period (HRQoL questionnaires only).

ETHICS AND DISSEMINATION

Ethical approval has been obtained from the Wales Research Ethics Committee 7 (23/WA/0284; 03/11/2024). The recruitment process began in February 2024, with the first enrolment in July 2024. Recruitment is expected to be completed by January 2026. The results will be presented at international SCI and sport-medicine conferences and will be submitted for publication in peer-reviewed journals.

TRIAL REGISTRATION NUMBER

ISRCTN17856698.

The Effect of Non-Invasive, Non-Pharmacological Interventions on Autonomic Regulation of Cardiovascular Function in Adults with Spinal Cord Injury: A Systematic Review with Meta-Analysis

Autonomic regulation of cardiovascular function is often disrupted following a spinal cord injury (SCI). A systematic review was undertaken to evaluate the effect of non-invasive, non-pharmacological (NINP) interventions on cardiovascular autonomic biomarkers in adults with SCI. AMED, CENTRAL, CINAHL EMBASE, and MEDLINE were searched from inception to May 17, 2024. Randomized controlled trials (RCTs) of NINP interventions for cardiovascular autonomic biomarkers (heart rate variability [HRV], systolic blood pressure variability [SBPV], or baroreflex gain) in adults (≥18 years of age) with SCI (>3 months) were included. Primary outcomes included HRV (low-frequency power [HRV-LF], high-frequency power [HRV-HF], root mean square of successive differences [RMSSD]), SBPV (low-frequency power [SBPV-LF]), and baroreflex sensitivity. The quality and certainty of the evidence were assessed using version 2 of the Cochrane risk of bias tool and the Preferred Reporting Items for Systematic Reviews and Meta-Analysis tool, respectively. Of 2651 records identified, six RCTs were included (participants, n = 123). HRV-LF (four studies; participants, n = 69) and HRV-HF (five studies; participants, n = 93) showed no to small changes in favor of NINP interventions ([g = 0.25; 95% confidence interval [CI] = -0.23, 0.73; p = 0.31; I2 = 0%], [g = 0.00; 95% CI = -0.41, 0.42; p = 0.98; I2 = 0%], respectively). Limited evidence was available for RMSSD, SBPV-LF, and baroreflex gain. This review found that the evidence is inconclusive regarding the effect of NINP interventions on the included HRV, BPV, and BRS parameters in adults with SCI. Further research with strong methodological rigor is needed to provide greater insights in this area.

Neuroprotective agents ineffective in mitigating autonomic dysreflexia following experimental spinal cord injury

BACKGROUND AND OBJECTIVES

Loss of supraspinal cardiovascular control and secondary damage following spinal cord injury (SCI) lead to cardiovascular dysfunction, where autonomic dysreflexia (AD), triggered by stimuli below the injury, can cause uncontrolled blood pressure (BP) surges, posing severe health risks such as stroke and seizures. While anti-inflammatory neuroprotective agents have been studied for motor recovery, their impact on cardiovascular function remains under investigated. The objective was to assess the efficacy of four clinically approved neuroprotective agents in promoting cardiovascular recovery following SCI.

METHODS

Male Wistar rats received contusion at the third thoracic spinal segment (T3). Fluoxetine, Glyburide, Valproic acid, and Indomethacin were first administered at 1 h or 6 h post-SCI, and every 12 h for two weeks thereafter. Four weeks following SCI, hemodynamics were measured at rest and during colorectal distension. Locomotor function was assessed prior to SCI and weekly for four weeks after SCI, using the Basso-Beattie-Bresnahan (BBB) locomotor scale. Quantitative comparisons of lesion area were performed.

RESULTS

Contrary to the published literature, Indomethacin and Valproic acid resulted in high morbidity and mortality rates 60 % and 40 % respectively) within 2-3 days of administration. Fluoxetine, and Glyburide were well-tolerated. There were no differences in change in systolic BP with colorectal distension compared to control i.e., all experimental groups experienced severe episodes of AD [F(6, 67) = 0.94, p = 0.47]. There was no significant difference in BBB scores in any experimental group compared to control [F(18, 252) = 0.3, p = 0.99]. No between-group differences were observed in tissue sparing at the lesion epicentre [F(6, 422) = 6.98, p = 0.29].

DISCUSSION

Despite promising beneficial effect reported in previous studies, none of the drugs demonstrated improvement in cardiovascular or motor function. Indomethacin and Valproic acid exhibited unexpected high mortality at doses deemed safe in the literature. This emphasizes the necessity for reproducibility studies in pre-clinical research and underscores the importance of publishing null findings to guide future investigations.

Diurnal variation of heart rate variability in individuals with spinal cord injury

BACKGROUND

Heart rate variability (HRV) may provide objective information about cardiogenic autonomic balance in individuals with spinal cord injury (SCI). The aim of this study was to characterize the diurnal variation of HRV in individuals with SCI at lesion level T6 and above and lesion level below T6.

METHODS

This was a retrospective analysis of a prior cross-sectional study. Individuals with chronic SCI underwent 24 h recording of the time between consecutive R waves (RR interval) to derive parameters of HRV as follows: standard deviation of all normal-to-normal R-R intervals (SDNN) and square root of the mean of the squared differences between successive R-R intervals (RMSSD) (time domain); and high frequency power (HF), low-frequency power (LF), very low frequency power (VLF), ultra-low frequency power (ULF) and total power (TP) (frequency domain). Changes in the magnitude of HRV outcomes over the 24 h period were investigated using a novel multi-component cosinor model constrained to the form of a three-harmonic Fourier series.

RESULTS

Participants were grouped as lesion level T6 and above (n = 22) or below T6 (n = 36). Most of them were male (n = 40, 69%) and the median age (interquartile range) was 50.5 (28) years. Both groups exhibited similar diurnal patterns in most HRV metrics. The lowest values occurred in the late afternoon (4-6 pm) and gradually increased, peaking around midnight to early morning (1-6 am). Exceptions included RMSSD, which peaked before midnight, and ULF, which showed a double peak pattern that peaked from 11 am to 1 pm and 4-6 am in participants with lesion level at T6 and above. The HRV values in participants with lesion level T6 and above were generally lower than participants with lesion level below T6, except for peak values of RMSSD, HF and LF.

CONCLUSION

This study demonstrated substantial diurnal variation of HRV in participants with SCI in both groups of participants. In clinical and research settings, diurnal variations in HRV must be taken into consideration.

Spinal decompression surgery may alleviate vasopressor-induced spinal hemorrhage and extravasation during acute cervical spinal cord injury in rats

BACKGROUND

Cervical spinal injury often disrupts the supraspinal vasomotor pathways projecting to the thoracic sympathetic preganglionic neurons, leading to cardiovascular dysfunction. The current guideline is to maintain the mean arterial blood pressure at 85 to 90 mmHg using a vasopressor during the first week of the injury. Some studies have demonstrated that this treatment might be beneficial to alleviate secondary injury and improve neurological outcomes; however, elevation of blood pressure may exacerbate spinal hemorrhage, extravasation, and edema, exacerbating the initial injury.

PURPOSE

The present study was designed to (1) examine whether vasopressor administration exacerbates spinal hemorrhage and extravasation; (2) evaluate whether spinal decompression surgery relieves vasopressor-induced spinal hemorrhage and extravasation.

STUDY DESIGN

In vivo animal study.

METHODS

Animals received a saline solution or a vasopressor (phenylephrine hydrochloride, 500 or 1000 μg/kg, 7 mL/kg/h) after mid-cervical contusion with or without spinal decompression (ie, incision of the dura and arachnoid mater). Spinal cord hemorrhage and extravasation were examined by expression of Evans blue within the spinal cord section.

RESULTS

The results demonstrated that cervical spinal contusion significantly reduced the mean arterial blood pressure and induced spinal hemorrhage and extravasation. Phenylephrine infusion significantly elevated the mean arterial blood pressure to the preinjury level within 15 to 60 minutes postcontusion; however, spinal hemorrhage and extravasation were more extensive in animals that received phenylephrine than in those that received saline. Notably, spinal decompression mitigated spinal hemorrhage and extravasation in contused rats who received phenylephrine.

CONCLUSIONS

These data indicate that, although phenylephrine can prevent hypotension after cervical spinal injury, it also causes excess spinal hemorrhage and extravasation.

CLINICAL SIGNIFICANCE

Spinal decompressive surgery seemed to minimize the side effect of phenylephrine as vasopressor treatment during acute spinal cord injury.

Increased Risk of Myocardial Infarction, Heart Failure, and Atrial Fibrillation After Spinal Cord Injury

BACKGROUND

Heart diseases are a growing concern for the spinal cord injury (SCI) population.

OBJECTIVES

This study aims to compare the incidence of heart diseases between SCI survivors and the general non-SCI population.

METHODS

We identified 5,083 SCI survivors and 1:3 age- and sex-matched non-SCI controls. Study outcomes were myocardial infarction (MI), heart failure (HF), and atrial fibrillation (AF). The cohort was followed up from the index date (diagnosis date for SCI or corresponding date for matched controls) until 2019.

RESULTS

SCI survivors showed a higher risk for MI (adjusted HR [aHR]: 2.41; 95% CI: 1.93-3.00), HF (aHR: 2.24; 95% CI: 1.95-2.56), and AF (aHR: 1.84; 95% CI: 1.49-2.28) compared to controls. The risks were further increased for those who were registered in the National Disability Registry within 1 year from the index date (SCI survivors with disability): SCI survivors with severe disability had the highest risks of MI (aHR: 3.74; 95% CI: 2.43-5.76), HF (aHR: 3.96; 95% CI: 3.05-5.14), and AF (aHR: 3.32; 95% CI: 2.18-5.05). Cervical and lumbar SCI survivors had an increased risk of heart disease regardless of disability compared to matched controls; these risks were slightly higher in those with disability. Thoracic SCI survivors with disability had significantly increased risk of heart disease compared to matched controls.

CONCLUSIONS

SCI survivors at all levels were at significantly greater risk for heart disease than non-SCI controls, particularly those with severe disability. Clinicians must be aware of the importance of heart disease in SCI survivors.

Reliability of five-minute vs. one-hour heart rate variability metrics in individuals with spinal cord injury

Background

A previous study showed low reliability of 1-h HRV outcomes in participants with spinal cord injury (SCI), but it was not certain whether the low reliability was due to the unrestricted activity of participants. We aimed to investigate test-retest reliability of HRV metrics in individuals with SCI using a 1-h measurement in a supine position.

Methods

Individuals with SCI underwent two sessions of 1-h recording of the time between consecutive R waves (RR-intervals) in a supine position. HRV outcomes were obtained from a single 5-min data segment and for the full 1-h recording. HRV parameters of interest were: standard deviation of all normal-to-normal R-R intervals (SDNN) and square root of the mean of the squared differences between successive R-R intervals (RMSSD) (time domain); and high frequency power (HF), low frequency power (LF), very low frequency power (VLF), ultra-low frequency power (ULF) and total power (TP) (frequency domain). Relative reliability was assessed by intraclass correlation coefficient (ICC). Absolute reliability was assessed by coefficient of variation (CV) and Bland-Altman limits of agreement (LoA).

Results

Data from 37 individuals (14 with tetraplegia and 23 with paraplegia) were included. Relative reliability was higher for the 1-h (ICCs ranged from 0.13-0.71) than for the 5-min duration (ICCs ranged from 0.06-0.50) in the overall SCI group for all HRV metrics. Participants with tetraplegia had lower relative reliability compared to participants with paraplegia in all HRV metrics for the 5-min duration (ICCs ranged from -0.01-0.34 vs. 0.21-0.57). For the 1-h duration, participants with paraplegia showed higher relative reliability than participants with tetraplegia in all HRV metrics (ICCs ranged from 0.18-0.79 vs. 0.07-0.54) except TP (ICC 0.69 vs. 0.82). In terms of absolute reliability, the CVs and LoAs for the 1-h duration were better than for the 5-min duration. In general, time domain metrics showed better reliability than frequency domain metrics for both durations in participants with tetraplegia and paraplegia. The lowest CV and narrowest 95% LoA were found for SDNN in 5-min and 1-h durations overall and in both lesion levels.

Conclusions

The supine position did not provide better reliability compared to unrestricted activity in participants with SCI. HRV analysis using a 5-min duration is of limited value in SCI due to poor reliability. For the 1-h analysis duration, interpretation of the reliability of HRV varies according to lesion level: it is recommended to take lesion level into account when interpreting reliability measures.

Heart Rate Variability Biofeedback in Adults with a Spinal Cord Injury: A Laboratory Framework and Case Series

Heart rate variability biofeedback (HRV-F) is a neurocardiac self-regulation therapy that aims to regulate cardiac autonomic nervous system activity and improve cardiac balance. Despite benefits in various clinical populations, no study has reported the effects of HRV-F in adults with a spinal cord injury (SCI). This article provides an overview of a neuropsychophysiological laboratory framework and reports the impact of an HRV-F training program on two adults with chronic SCI (T1 AIS A and T3 AIS C) with different degrees of remaining cardiac autonomic function. The HRV-F intervention involved 10 weeks of face-to-face and telehealth sessions with daily HRV-F home practice. Physiological (HRV, blood pressure variability (BPV), baroreflex sensitivity (BRS)), and self-reported assessments (Fatigue Severity Scale, Generalised Anxiety Disorder Scale, Patient Health Questionnaire, Appraisal of Disability and Participation Scale, EuroQol Visual Analogue Scale) were conducted at baseline and 10 weeks. Participants also completed weekly diaries capturing mood, anxiety, pain, sleep quality, fatigue, and adverse events. Results showed some improvement in HRV, BPV, and BRS. Additionally, participants self-reported some improvements in mood, fatigue, pain, quality of life, and self-perception. A 10-week HRV-F intervention was feasible in two participants with chronic SCI, warranting further investigation into its autonomic and psychosocial effects.

Comorbidity of cardiorespiratory and locomotor dysfunction following cervical spinal cord injury in the rat

Cervical spinal cord injury interrupts supraspinal pathways innervating thoracic sympathetic preganglionic neurons and results in cardiovascular dysfunction. Both respiratory and locomotor functions were also impaired due to damages of motoneuron pools controlling respiratory and forelimb muscles, respectively. However, no study has investigated autonomic and somatic motor functions in the same animal model. The present study aimed to establish a cervical spinal cord injury model to evaluate cardiorespiratory response and locomotor activity in unanesthetized rats. Cardiovascular response and respiratory behavior following laminectomy or cervical spinal contusion were measured using noninvasive blood pressure analyzer and plethysmography systems, respectively. Locomotor activity was evaluated by an open-field test and a locomotor rating scale. The results demonstrated that mean arterial blood pressure and heart rate were significantly reduced in contused rats compared with uninjured rats at the acute injured stage. Tidal volume was also significantly reduced during the acute and subchronic stages. Moreover, locomotor function was severely impaired, evidenced by decreasing moving ability and locomotor rating scores from the acute to chronic injured stages. Retrograde neurotracer results revealed that cervical spinal cord injury caused a reduction in number of phrenic and triceps motoneurons. Immunofluorescence staining revealed a significant attenuation of serotonergic, noradrenergic, glutamatergic, and GABAergic fibers innervating the thoracic sympathetic preganglionic neurons in chronically contused rats. These results revealed the pathological mechanism underlying the comorbidity of cardiorespiratory and locomotor dysfunction following cervical spinal cord injury. We proposed that this animal model can be used to evaluate the therapeutic efficacy of potential strategies to improve different physiological functions.NEW & NOTEWORTHY The present study establishes a preclinical rodent model to comprehensively investigate physiological functions under unanesthetized condition following cervical spinal cord contusion. The results demonstrated that cervical spinal cord contusion is associated with impairments in cardiovascular, respiratory, and locomotor function. Respiratory and forelimb motoneurons and neurochemical innervations of sympathetic preganglionic neurons were damaged following injury. This animal model can be used to evaluate the therapeutic efficacy of potential strategies to improve different physiological functions.

Chronic intermittent hypobaric hypoxia ameliorates osteoporosis after spinal cord injury through balancing osteoblast and osteoclast activities in rats

INTRODUCTION

As a common complication of spinal cord injury (SCI), most SCI patients suffer from osteoporosis. In our previous study, chronic intermittent hypobaric hypoxia (CIHH) could promote bone fracture healing. We speculated that it may act a role in the progression of osteoporosis. The current study purposed to explore the role of CIHH in the osteoporosis triggered by SCI in rats.

METHODS

A SCI-induced SCI model was established by completed transection at T9-T10 spinal cord of Wistar rats. One week after SCI, the rats were conducted to CIHH treatment (PB = 404 mmHg, Po2 = 84 mmHg) 6 hours a day for continuously 7 weeks.

RESULTS

The results of X-radiography and Micro-CT assessment demonstrated that compared with sham rats, the areal bone mineral density (BMD), bone volume to tissue volume, volumetric BMD, trabecular thickness, trabecular number, and trabecular connectivity were decreased. Trabecular bone pattern factor, trabecular separation, as well as structure model index were increased at the distal femur and proximal tibia of SCI rats, which were effectively reversed by CIHH treatment. Histomorphometry showed that CIHH treatment increased bone formation of SCI rats, as evidenced by the increased osteoid formation, the decreased number and surface of TRAP-positive osteoclasts. Furthermore, ELISA and real time PCR results showed that the osteoblastogenesis-related biomarkers, such as procollagen type 1 N-terminal propeptide, osteocalcin in serum, as well as ALP and OPG mRNAs in bone tissue were decreased, while the osteoclastogenesis-related biomarkers, including scleorostin in serum and RANKL and TRAP mRNAs in bone tissue were increased in SCI rats. Importantly, the deviations of aforementioned biomarkers were improved by CIHH treatment. Mechanically, the protective effects of CIHH might be at least partly mediated by hypoxia-inducible factor-1 alpha (HIF-1α) signaling pathway.

CONCLUSION

The present study testified that CIHH treatment ameliorates osteoporosis after SCI by balancing osteoblast and osteoclast activities in rats.

A cross-species validation of single-beat metrics of cardiac contractility

The assessment of left ventricular (LV) contractility in animal models is useful in various experimental paradigms, yet obtaining such measures is inherently challenging and surgically invasive. In a cross-species study using small and large animals, we comprehensively tested the agreement and validity of multiple single-beat surrogate metrics of LV contractility against the field-standard metrics derived from inferior vena cava occlusion (IVCO). Fifty-six rats, 27 minipigs and 11 conscious dogs underwent LV and arterial catheterization and were assessed for a range of single-beat metrics of LV contractility. All single-beat metrics were tested for the various underlying assumptions required to be considered a valid metric of cardiac contractility, including load-independency, sensitivity to inotropic stimulation, and ability to diagnose contractile dysfunction in cardiac disease. Of all examined single-beat metrics, only LV maximal pressure normalized to end-diastolic volume (EDV), end-systolic pressure normalized to EDV, and the maximal rate of rise of the LV pressure normalized to EDV showed a moderate-to-excellent agreement with their IVCO-derived reference measure and met all the underlying assumptions required to be considered as a valid cardiac contractile metric in both rodents and large-animal models. Our findings demonstrate that single-beat metrics can be used as a valid, reliable method to quantify cardiac contractile function in basic/preclinical experiments utilizing small- and large-animal models KEY POINTS: Validating and comparing indices of cardiac contractility that avoid caval occlusion would offer considerable advantages for the field of cardiovascular physiology. We comprehensively test the underlying assumptions of multiple single-beat indices of cardiac contractility in rodents and translate these findings to pigs and conscious dogs. We show that when performing caval occlusion is unfeasible, single-beat metrics can be utilized to accurately quantify cardiac inotropic function in basic and preclinical research employing various small and large animal species. We report that maximal left-ventricular (LV)-pressure normalized to end-diastolic volume (EDV), LV end-systolic pressure normalized to EDV and the maximal rate of rise of the LV pressure waveform normalized to EDV are the best three single-beat metrics to measure cardiac inotropic function in both small- and large-animal models.

Forsythoside B attenuates neuro-inflammation and neuronal apoptosis by inhibition of NF-κB and p38-MAPK signaling pathways through activating Nrf2 post spinal cord injury

BACKGROUND

Spinal cord injury (SCI) is a ruinous neurological pathology that results in locomotor and sensory impairment. Neuro-inflammation and secondary neuronal apoptosis contribute to SCI, with anti-inflammatory therapies the focus of many SCI studies. Forsythoside B (FTS•B), a phenylethanoid glycoside extracted from the leaves of Lamiophlomis rotata Kudo, has been shown previously to have anti-inflammatory properties. Nevertheless, the therapeutic effect of FTS•B on neuro-inflammation after SCI is unknown.

METHODS

Neuro-inflammation was assessed by western blotting (WB), immunofluorescence (IF) staining, and enzyme-linked immunosorbent assay (ELISA) both in vitro and in vivo. Secondary neuronal apoptosis was simulated in a microglia-neuron co-culture model with the degree of apoptosis measured by WB, IF, and TUNEL staining. In vivo, FTS•B (10 mg/kg, 40 mg/kg) were intraperitoneally injected into SCI mice. Morphological changes following SCI were evaluated by Nissl, Hematoxylin-eosin, and Luxol Fast Blue staining. Basso Mouse Scale scores were used to evaluate locomotor function recovery.

RESULTS

FTS•B markedly decreased the levels of iNOS, COX-2 and signature mediators of inflammation. Phosphorylated p38 and nuclear factor-kappa B (NF-κB) were markedly decreased by FTS•B. Additionally, FTS•B-induced inhibition of NF-κB and p38-MAPK signaling pathways was reversed by Nrf2 downregulation. Administration of FTS•B also significantly reduced apoptosis-related protein levels indicating that FTS•B ameliorated secondary neuronal apoptosis. FTS•B administration inhibited glial scar formation, decreased neuronal death, tissue deficiency, alleviated demyelination, and promoted locomotor recovery.

CONCLUSION

FTS•B effectively attenuates neuro-inflammation and secondary neuronal apoptosis by inhibition of NF-κB and p38-MAPK signaling pathways through activating Nrf2 after SCI. This study demonstrates FTS•B to be a potential therapeutic for SCI.

Temporal Changes of Cardiac Structure, Function, and Mechanics During Sub-acute Cervical and Thoracolumbar Spinal Cord Injury in Humans: A Case-Series

Individuals with cervical spinal cord injury (SCI) experience deleterious changes in cardiac structure and function. However, knowledge on when cardiac alterations occur and whether this is dependent upon neurological level of injury remains to be determined. Transthoracic echocardiography was used to assess left ventricular structure, function, and mechanics in 10 male individuals (median age 34 years, lower and upper quartiles 32–50) with cervical (n = 5, c-SCI) or thoracolumbar (n = 5, tl-SCI) motor-complete SCI at 3- and 6-months post-injury. Compared to the 3-month assessment, individuals with c-SCI displayed structural, functional, and mechanical changes during the 6-month assessment, including significant reductions in end diastolic volume [121 mL (104–139) vs. 101 mL (99–133), P = 0.043], stroke volume [75 mL (61–85) vs. 60 mL (58–80), P = 0.042], myocardial contractile velocity (S') [0.11 m/s (0.10–0.13) vs. 0.09 m/s (0.08–0.10), P = 0.043], and peak diastolic longitudinal strain rate [1.29°/s (1.23–1.34) vs. 1.07°/s (0.95–1.15), P = 0.043], and increased early diastolic filling over early myocardial relaxation velocity (E/E') ratio [5.64 (4.71–7.72) vs. 7.48 (6.42–8.42), P = 0.043]. These indices did not significantly change in individuals with tl-SCI between time points. Ejection fraction was different between individuals with c-SCI and tl-SCI at 3 [61% (57–63) vs. 54% (52–55), P &lt; 0.01] and 6 months [58% (57–62) vs. 55% (52–56), P &lt; 0.01], though values were considered normal. These results demonstrate that individuals with c-SCI exhibit significant reductions in cardiac function from 3 to 6 months post-injury, whereas individuals with tl-SCI do not, suggesting the need for early rehabilitation to minimize cardiac consequences in this specific population.