Decentralized cardiovascular autonomic control and cognitive deficits in persons with spinal cord injury

Cardiovascular Physiology and Responses to Sexual Activity in Individuals Living with Spinal Cord Injury

Background: Spinal cord injury (SCI) may profoundly impact autonomic function producing a variable degree of dysfunction in cardiovascular, bronchopulmonary, sweating, bladder, bowel, and sexual function. The cardiovascular system is crucially important for sexual function, as it is responsible for blood flow shifts to cavernous and musculoskeletal tissue during sexual activity. This system is prone to 3 main abnormalities after SCI including low resting blood pressure (LRBP), orthostatic hypotension (OH), and autonomic dysreflexia (AD), all of which have important effects on sexual function. Methods: We review the current etiological mechanisms and manifestations of cardiovascular dysfunction after SCI and discuss how this is documented to impact sexual function in individuals living with SCI. Conclusions: All individuals with SCI at or above the T6 neurologic level have an increased risk of AD during sexual stimulation, with increasing risk associated with higher levels of injury and greater completeness of injury. AD can be silent, and individuals living with SCI should be aware of blood pressure values at baseline and during sexual activity. Clinicians performing vibrostimulation fertility procedures need to be aware of the risk of AD and consider pretreatment if needed. Researchers studying the cardiovascular response to sexual stimulation should consider continuous monitoring of blood pressure, as intermittent monitoring may underestimate true blood pressure values.

Endoplasmic Reticulum Stress and Disrupted Neurogenesis in the Brain Are Associated with Cognitive Impairment and Depressive-Like Behavior after Spinal Cord Injury

Clinical and experimental studies show that spinal cord injury (SCI) can cause cognitive impairment and depression that can significantly impact outcomes. Thus, identifying mechanisms responsible for these less well-examined, important SCI consequences may provide targets for more effective therapeutic intervention. To determine whether cognitive and depressive-like changes correlate with injury severity, we exposed mice to sham, mild, moderate, or severe SCI using the Infinite Horizon Spinal Cord Impactor and evaluated performance on a variety of neurobehavioral tests that are less dependent on locomotion. Cognitive impairment in Y-maze, novel objective recognition, and step-down fear conditioning tasks were increased in moderate- and severe-injury mice that also displayed depressive-like behavior as quantified in the sucrose preference, tail suspension, and forced swim tests. Bromo-deoxyuridine incorporation with immunohistochemistry revealed that SCI led to a long-term reduction in the number of newly-generated immature neurons in the hippocampal dentate gyrus, accompanied by evidence of greater neuronal endoplasmic reticulum (ER) stress. Stereological analysis demonstrated that moderate/severe SCI reduced neuronal survival and increased the number of activated microglia chronically in the cerebral cortex and hippocampus. The potent microglial activator cysteine-cysteine chemokine ligand 21 (CCL21) was elevated in the brain sites after SCI in association with increased microglial activation. These findings indicate that SCI causes chronic neuroinflammation that contributes to neuronal loss, impaired hippocampal neurogenesis and increased neuronal ER stress in important brain regions associated with cognitive decline and physiological depression. Accumulation of CCL21 in brain may subserve a pathophysiological role in cognitive changes and depression after SCI.

Rigid and remodelled: cerebrovascular structure and function after experimental high-thoracic spinal cord transection

High-thoracic or cervical spinal cord injury (SCI) is associated with several critical clinical conditions related to impaired cerebrovascular health, including: 300-400% increased risk of stroke, cognitive decline and diminished cerebral blood flow regulation. The purpose of this study was to examine the influence of high-thoracic (T3 spinal segment) SCI on cerebrovascular structure and function, as well as molecular markers of profibrosis. Seven weeks after complete T3 spinal cord transection (T3-SCI, n = 15) or sham injury (Sham, n = 10), rats were sacrificed for either middle cerebral artery (MCA) structure and function assessments via ex vivo pressure myography, or immunohistochemical analyses. Myogenic tone was unchanged, but over a range of transmural pressures, inward remodelling occurred after T3-SCI with a 40% reduction in distensibility (both P < 0.05), and a 33% reduction in vasoconstrictive reactivity to 5-HT trending toward significance (P = 0.09). After T3-SCI, the MCA had more collagen I (42%), collagen III (24%), transforming growth factor β (47%) and angiotensin II receptor type 2 (132%), 27% less elastin as well as concurrent increased wall thickness and reduced lumen diameter (all P < 0.05). Sympathetic innervation (tyrosine hydroxylase-positive axon density) and endothelium-dependent dilatation (carbachol) of the MCA were not different between groups. This study demonstrates profibrosis and hypertrophic inward remodelling within the largest cerebral artery after high-thoracic SCI, leading to increased stiffness and possibly impaired reactivity. These deleterious adaptations would substantially undermine the capacity for regulation of cerebral blood flow and probably underlie several cerebrovascular clinical conditions in the SCI population.

Contemporary Cardiovascular Concerns after Spinal Cord Injury: Mechanisms, Maladaptations, and Management

Cardiovascular (CV) issues after spinal cord injury (SCI) are of paramount importance considering they are the leading cause of death in this population. Disruption of autonomic pathways leads to a highly unstable CV system, with impaired blood pressure (BP) and heart rate regulation. In addition to low resting BP, on a daily basis the majority of those with SCI suffer from transient episodes of aberrantly low and high BP (termed orthostatic hypotension and autonomic dysreflexia, respectively). In fact, autonomic issues, including resolution of autonomic dysreflexia, are frequently ranked by individuals with high-level SCI to be of greater priority than walking again. Owing to a combination of these autonomic disturbances and a myriad of lifestyle factors, the pernicious process of CV disease is accelerated post-SCI. Unfortunately, these secondary consequences of SCI are only beginning to receive appropriate clinical attention. Immediately after high-level SCI, major CV abnormalities present in the form of neurogenic shock. After subsiding, new issues related to BP instability arise, including orthostatic hypotension and autonomic dysreflexia. This review describes autonomic control over the CV system before injury and the mechanisms underlying CV abnormalities post-SCI, while also detailing the end-organ consequences, including those of the heart, as well as the systemic and cerebral vasculature. The tertiary impact of CV dysfunction will also be discussed, such as the potential impediment of rehabilitation, and impaired cognitive function. In the recent past, our understanding of autonomic dysfunctions post-SCI has been greatly enhanced; however, it is vital to further develop our understanding of the long-term consequences of these conditions, which will equip us to better manage CV disease morbidity and mortality in this population.

Isolated spinal cord contusion in rats induces chronic brain neuroinflammation, neurodegeneration, and cognitive impairment. Involvement of cell cycle activation

Cognitive dysfunction has been reported in patients with spinal cord injury (SCI), but it has been questioned whether such changes may reflect concurrent head injury, and the issue has not been addressed mechanistically or in a well-controlled experimental model. Our recent rodent studies examining SCI-induced hyperesthesia revealed neuroinflammatory changes not only in supratentorial pain-regulatory sites, but also in other brain regions, suggesting that additional brain functions may be impacted following SCI. Here we examined effects of isolated thoracic SCI in rats on cognition, brain inflammation, and neurodegeneration. We show for the first time that SCI causes widespread microglial activation in the brain, with increased expression of markers for activated microglia/macrophages, including translocator protein and chemokine ligand 21 (C-C motif). Stereological analysis demonstrated significant neuronal loss in the cortex, thalamus, and hippocampus. SCI caused chronic impairment in spatial, retention, contextual, and fear-related emotional memory-evidenced by poor performance in the Morris water maze, novel objective recognition, and passive avoidance tests. Based on our prior work implicating cell cycle activation (CCA) in chronic neuroinflammation after SCI or traumatic brain injury, we evaluated whether CCA contributed to the observed changes. Increased expression of cell cycle-related genes and proteins was found in hippocampus and cortex after SCI. Posttraumatic brain inflammation, neuronal loss, and cognitive changes were attenuated by systemic post-injury administration of a selective cyclin-dependent kinase inhibitor. These studies demonstrate that chronic brain neurodegeneration occurs after isolated SCI, likely related to sustained microglial activation mediated by cell cycle activation.

Reliability and Validity of the Sensory Component of the International Standards for Neurological Classification of Spinal Cord Injury (ISNCSCI): A Systematic Review

BACKGROUND

Since 1982, the International Standards for Neurological Classification of Spinal Cord Injury (ISNCSCI) has been used to classify sensation of spinal cord injury (SCI) through pinprick and light touch scores. The absence of proprioception, pain, and temperature within this scale creates questions about its validity and accuracy.

OBJECTIVE

To assess whether the sensory component of the ISNCSCI represents a reliable and valid measure of classification of SCI.

METHODS

A systematic review of studies examining the reliability and validity of the sensory component of the ISNCSCI published between 1982 and February 2013 was conducted. The electronic databases MEDLINE via Ovid, CINAHL, PEDro, and Scopus were searched for relevant articles. A secondary search of reference lists was also completed. Chosen articles were assessed according to the Oxford Centre for Evidence-Based Medicine hierarchy of evidence and critically appraised using the McMasters Critical Review Form. A statistical analysis was conducted to investigate the variability of the results given by reliability studies.

RESULTS

Twelve studies were identified: 9 reviewed reliability and 3 reviewed validity. All studies demonstrated low levels of evidence and moderate critical appraisal scores. The majority of the articles (~67%; 6/9) assessing the reliability suggested that training was positively associated with better posttest results. The results of the 3 studies that assessed the validity of the ISNCSCI scale were confounding.

CONCLUSIONS

Due to the low to moderate quality of the current literature, the sensory component of the ISNCSCI requires further revision and investigation if it is to be a useful tool in clinical trials.

Reliability and Validity of the Sensory Component of the International Standards for Neurological Classification of Spinal Cord Injury (ISNCSCI): A Systematic Review

BACKGROUND

Since 1982, the International Standards for Neurological Classification of Spinal Cord Injury (ISNCSCI) has been used to classify sensation of spinal cord injury (SCI) through pinprick and light touch scores. The absence of proprioception, pain, and temperature within this scale creates questions about its validity and accuracy.

OBJECTIVE

To assess whether the sensory component of the ISNCSCI represents a reliable and valid measure of classification of SCI.

METHODS

A systematic review of studies examining the reliability and validity of the sensory component of the ISNCSCI published between 1982 and February 2013 was conducted. The electronic databases MEDLINE via Ovid, CINAHL, PEDro, and Scopus were searched for relevant articles. A secondary search of reference lists was also completed. Chosen articles were assessed according to the Oxford Centre for Evidence-Based Medicine hierarchy of evidence and critically appraised using the McMasters Critical Review Form. A statistical analysis was conducted to investigate the variability of the results given by reliability studies.

RESULTS

Twelve studies were identified: 9 reviewed reliability and 3 reviewed validity. All studies demonstrated low levels of evidence and moderate critical appraisal scores. The majority of the articles (~67%; 6/9) assessing the reliability suggested that training was positively associated with better posttest results. The results of the 3 studies that assessed the validity of the ISNCSCI scale were confounding.

CONCLUSIONS

Due to the low to moderate quality of the current literature, the sensory component of the ISNCSCI requires further revision and investigation if it is to be a useful tool in clinical trials.

Orthostatic responses to anticholinesterase inhibition in spinal cord injury

INTRODUCTION

Acetylcholine (Ach) is the pre-synaptic neurotransmitter of the sympathetic nervous system. Increased pre-synaptic Ach may augment post-synaptic release of norepinephrine, thereby increasing systemic blood pressure (BP).

OBJECTIVES

The primary objective of this investigation was to determine the hemodynamic effect of pyridostigmine bromide (PYRIDO: 60 mg), an Ach inhibitor (AchI), compared to no-drug (NO-D) during head-up tilt (HUT) in individuals with spinal cord injury (SCI). Secondarily, we aimed to determine the effects of PYRIDO compared to NO-D on symptoms of orthostatic intolerance (OI) and adverse event reporting (AE).

METHODS

Ten individuals with SCI (C4-C7) were studied on two occasions: visit (1) NO-D and visit (2) PYRIDO. On each visit subjects underwent a progressive HUT maneuver to 15°, 25°, 35° for 5 min at each angle and 45 min at 45°. Supine and orthostatic heart rate (HR), systolic and diastolic BP (SBP and DBP), as well as monitored and symptoms of OI and AE were monitored and recorded.

RESULTS

Supine hemodynamics did not differ between the trials. The significant fall in SBP during the NO-D trial was diminished with PYRIDO, and five subjects had an increased DBP during HUT with PYRIDO compared to the NO-D trial. Individuals that responded to PYRIDO with an increase in orthostatic BP had significantly lower resting HR than non-responders (p < 0.01), which suggests increased levels of pre-synaptic Ach. Subjective symptoms of OI and AE reporting did not differ between the two trials.

CONCLUSIONS

These preliminary data suggest that PYRIDO is safe and may be effective at ameliorating the orthostatic fall in BP in select individuals with SCI.