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.

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

Spinal cord injury chronically alters cardiac structure and function and is associated with increased odds for cardiovascular disease. Here, we investigate the cardiac consequences of spinal cord injury on the acute-to-chronic continuum, and the contribution of altered bulbospinal sympathetic control to the decline in cardiac function following spinal cord injury. By combining experimental rat models of spinal cord injury with prospective clinical studies, we demonstrate that spinal cord injury causes a rapid and sustained reduction in left ventricular contractile function that precedes structural changes. In rodents, we experimentally demonstrate that this decline in left ventricular contractile function following spinal cord injury is underpinned by interrupted bulbospinal sympathetic control. In humans, we find that activation of the sympathetic circuitry below the level of spinal cord injury causes an immediate increase in systolic function. Our findings highlight the importance for early interventions to mitigate the cardiac functional decline following spinal cord injury.

Development of a Spinal Cord Injury Model Permissive to Study the Cardiovascular Effects of Rehabilitation Approaches Designed to Induce Neuroplasticity.

As primary medical care for spinal cord injury (SCI) has improved over the last decades there are more individuals living with neurologically incomplete (vs. complete) cervical injuries. For these individuals, a number of promising therapies are being actively researched in pre-clinical settings that seek to strengthen the remaining spinal pathways with a view to improve motor function. To date, few, if any, of these interventions have been tested for their effectiveness to improve autonomic and cardiovascular (CV) function. As a first step to testing such therapies, we aimed to develop a model that has sufficient sparing of descending sympathetic pathways for these interventions to target yet induces robust CV impairment. Twenty-six Wistar rats were assigned to SCI (n = 13) or naïve (n = 13) groups. Animals were injured at the T3 spinal segment with 300 kdyn of force. Fourteen days post-SCI, left ventricular (LV) and arterial catheterization was performed to assess in vivo cardiac and hemodynamic function. Spinal cord lesion characteristics along with sparing in catecholaminergic and serotonergic projections were determined via immunohistochemistry. SCI produced a decrease in mean arterial pressure of 17 ± 3 mmHg (p < 0.001) and left ventricular contractility (end-systolic elastance) of 0.7 ± 0.1 mmHg/µL (p < 0.001). Our novel SCI model produced significant decreases in cardiac and hemodynamic function while preserving 33 ± 9% of white matter at the injury epicenter, which we believe makes it a useful pre-clinical model of SCI to study rehabilitation approaches designed to induce neuroplasticity.

Experimental high thoracic spinal cord injury impairs the cardiac and cerebrovascular response to orthostatic challenge in rats.

Spinal cord injury (SCI) impairs the cardiovascular responses to postural challenge, leading to the development of orthostatic hypotension (OH). Here, we apply lower body negative pressure (LBNP) to rodents with high-level SCI to demonstrate the usefulness of LBNP as a model for experimental OH studies, and to explore the effect of simulated OH on cardiovascular and cerebrovascular function following SCI. Male Wistar rats (n = 34) were subjected to a sham or T3-SCI surgery and survived into the chronic period postinjury (i.e., 8 wk). Cardiac function was tracked via ultrasound pre- to post-SCI to demonstrate the clinical utility of our model. At study termination, we conducted left-ventricular (LV) catheterization and insonated the middle cerebral artery to investigate the hemodynamic, cardiac, and cerebrovascular response to a mild dose of LBNP that is sufficient to mimic clinically defined OH in rats with T3-SCI but not sham animals. In response to mimicked OH, there was a greater decline in stroke volume, cardiac output, maximal LV pressure, and blood pressure in SCI compared with sham (P < 0.034), whereas heart rate was increased in sham but decreased in SCI (P < 0.029). SCI animals also had an exaggerated reduction in peak, minimum and mean middle cerebral artery flow, for a given change in blood pressure, in response to LBNP (P < 0.033), implying impaired dynamic cerebral autoregulation. Using a preclinical SCI model of OH, we demonstrate that complete high thoracic SCI impairs the cardiac response to OH and disrupts dynamic cerebral autoregulation.NEW & NOTEWORTHY This is the first use of LBNP to interrogate the cardiac and cerebrovascular responses to simulated OH in a preclinical study of SCI. Here, we demonstrate the utility of our simulated OH model and use it to demonstrate that SCI impairs the cardiac response to simulated OH and disrupts dynamic cerebrovascular autoregulation.

Cardio-centric hemodynamic management improves spinal cord oxygenation and mitigates hemorrhage in acute spinal cord injury.

Chronic high-thoracic and cervical spinal cord injury (SCI) results in a complex phenotype of cardiovascular consequences, including impaired left ventricular (LV) contractility. Here, we aim to determine whether such dysfunction manifests immediately post-injury, and if so, whether correcting impaired contractility can improve spinal cord oxygenation (SCO2), blood flow (SCBF) and metabolism. Using a porcine model of T2 SCI, we assess LV end-systolic elastance (contractility) via invasive pressure-volume catheterization, monitor intraparenchymal SCO2 and SCBF with fiberoptic oxygen sensors and laser-Doppler flowmetry, respectively, and quantify spinal cord metabolites with microdialysis. We demonstrate that high-thoracic SCI acutely impairs cardiac contractility and substantially reduces SCO2 and SCBF within the first hours post-injury. Utilizing the same model, we next show that augmenting LV contractility with the ß-agonist dobutamine increases SCO2 and SCBF more effectively than vasopressor therapy, whilst also mitigating increased anaerobic metabolism and hemorrhage in the injured cord. Finally, in pigs with T2 SCI survived for 12 weeks post-injury, we confirm that acute hemodynamic management with dobutamine appears to preserve cardiac function and improve hemodynamic outcomes in the chronic setting. Our data support that cardio-centric hemodynamic management represents an advantageous alternative to the current clinical standard of vasopressor therapy for acute traumatic SCI.

A porcine model for studying the cardiovascular consequences of high-thoracic spinal cord injury.

KEY POINTS: We have developed a novel porcine model of high-thoracic midline contusion spinal cord injury (SCI) at the T2 spinal level. We describe this model and the ensuing cardiovascular and neurohormonal responses, and demonstrate the model is efficacious for studying clinically relevant cardiovascular dysfunction post-SCI. We demonstrate that the high-thoracic SCI model, but not a low-thoracic SCI model, induces persistent hypotension along with a gradual reduction in plasma noradrenaline and increases in plasma aldosterone and angiotensin II. We additionally conducted a proof-of-concept long-term (12 weeks) survival study in animals with T2 contusion SCI demonstrating the potential utility of this model for not only acute experimentation but also long-term drug studies prior to translation to the clinic. ABSTRACT: Cardiovascular disease is a leading cause of morbidity and mortality in the spinal cord injury (SCI) population, especially in those with high-thoracic or cervical SCI. With this in mind, we aimed to develop a large animal (porcine) model of high-thoracic (T2 level) contusion SCI and compare the haemodynamic and neurohormonal responses of this injury against a low-thoracic (T10 level) model. Ten Yorkshire pigs were randomly subjected to 20 cm weight drop contusion SCI at either the T2 or the T10 spinal level. Systolic blood pressure (SBP), mean arterial pressure (MAP) and heart rate (HR) were continuously monitored until 4 h post-SCI. Plasma noradrenaline (NA), aldosterone and angiotensin II (ANGII) were measured pre-SCI and at 30, 60, 120 and 240 min post-SCI. Additionally, two Yucatan pigs were subjected to T2-SCI and survived up to 12 weeks post-injury to demonstrate the efficacy of this model for long-term survival studies. Immediately after T2-SCI, SBP, MAP and HR increased (P < 0.0001). Between decompression (5 min post-SCI) and 30 min post-decompression in T2-SCI, SBP and MAP were lower than pre-SCI (P < 0.038). At 3 and 4 h after T2-SCI, SBP remained lower than pre-SCI (P = 0.048). After T10-SCI, haemodynamic indices remained largely unaffected. Plasma NA was lower in T2- vs. T10-SCI post-SCI, whilst aldosterone and ANGII were higher. Both chronically injured pigs demonstrated a vast reduction in SBP at 12 weeks post-SCI. Our model of T2-SCI causes a rapid and sustained alteration in neurohormonal control and cardiovascular function, which does not occur in the T10 model.

Skilled reaching deterioration contralateral to cervical hemicontusion in rats is reversed by pregabalin treatment conditional upon its early administration.

INTRODUCTION: Gabapentinoids are first-line treatments for painful traumatic and nontraumatic central nervous system disorders. Evidence from a large human study suggests that early use of gabapentinoids after spinal cord injury improves motor scores. The underlying mechanism is unknown. OBJECTIVES: We sought to examine the effects of early pregabalin (PGB, a gabapentinoid) treatment on performance in a fine motor task (skilled reaching) after cervical hemicontusion. We also asked whether early PGB administration affected PGB responsiveness later on. METHODS: Rats received C4/5 cervical hemicontusions. Injury severities ranged from 80 to 150 kdyn. We monitored evidence of skin irritation (peri-incisional and elsewhere) and quantified food pellet retrieval using the Montoya staircase test. Behaviours were assessed in rats receiving early (for 3 weeks from injury induction) and/or late (resuming or beginning at week 8) PGB treatment in animals with 150-kdyn injuries. RESULTS: Contralateral skilled reaching waned in control animals with 150-kdyn injuries. This was prevented in animals, which received early PGB as long as treatment continued. Deterioration of skilled reaching was reversed by later (week 8) PGB only in animals that had received early treatment. Ipsilateral reaching impairment was not improved by PGB. Relief of skin irritation verified early PGB efficacy. CONCLUSION: Hemicontusive spinal cord injury produces a contralateral motor phenotype evocative of on-going neuropathic pain. Early PGB preserves sensitivity to subsequent PGB treatment, indicating that motor function is impaired by neuropathic pain and can be improved indirectly by early PGB administration. Direct effects of PGB on motor circuitry cannot be excluded but are not supported by our data.

Neuropathic pain following traumatic spinal cord injury: Models, measurement, and mechanisms.

Neuropathic pain following spinal cord injury (SCI) is notoriously difficult to treat and is a high priority for many in the SCI population. Resolving this issue requires animal models fidelic to the clinical situation in terms of injury mechanism and pain phenotype. This Review discusses the means by which neuropathic pain has been induced and measured in experimental SCI and compares these with human outcomes, showing that there is a substantial disconnection between experimental investigations and clinical findings in a number of features. Clinical injury level is predominantly cervical, whereas injury in the laboratory is modeled mainly at the thoracic cord. Neuropathic pain is primarily spontaneous or tonic in people with SCI (with a relatively smaller incidence of allodynia), but measures of evoked responses (to thermal and mechanical stimuli) are almost exclusively used in animals. There is even the question of whether pain per se has been under investigation in most experimental SCI studies rather than simply enhanced reflex activity with no affective component. This Review also summarizes some of the problems related to clinical assessment of neuropathic pain and how advanced imaging techniques may circumvent a lack of patient/clinician objectivity and discusses possible etiologies of neuropathic pain following SCI based on evidence from both clinical studies and animal models, with examples of cellular and molecular changes drawn from the entire neuraxis from primary afferent terminals to cortical sensory and affective centers. © 2016 Wiley Periodicals, Inc.

Tamoxifen induces cellular stress in the nervous system by inhibiting cholesterol synthesis.

BACKGROUND: Tamoxifen (TAM) is an important cancer therapeutic and an experimental tool for effecting genetic recombination using the inducible Cre-Lox technique. Despite its widespread use in the clinic and laboratory, we know little about its effects on the nervous system. This is of significant concern because TAM, via unknown mechanisms, induces cognitive impairment in humans. A hallmark of cellular stress is induction of Activating Transcription Factor 3 (Atf3), and so to determine whether TAM induces cellular stress in the adult nervous system, we generated a knock-in mouse in which Atf3 promoter activity drives transcription of TAM-dependent Cre recombinase (Cre-ERT2); when crossed with tdtomato reporter mice, Atf3 induction results in robust and permanent genetic labeling of cells in which it is up-regulated even transiently. RESULTS: We found that granular neurons of the olfactory bulb and dentate gyrus, vascular cells and ependymal cells throughout the brain, and peripheral sensory neurons expressed tdtomato in response to TAM treatment. We also show that TAM induced Atf3 up-regulation through inhibition of cholesterol epoxide hydrolase (ChEH): reporter expression was mitigated by delivery in vitamin E-rich wheat germ oil (vitamin E depletes ChEH substrates), and was partially mimicked by a ChEH-specific inhibitor. CONCLUSIONS: This work demonstrates that TAM stresses cells of the adult central and peripheral nervous systems and highlights concerns about clinical and experimental use of TAM. We propose TAM administration in vitamin E-rich vehicles such as wheat germ oil as a simple remedy.