Noninvasive Neuroprosthesis Promotes Cardiovascular Recovery After Spinal Cord Injury

Spinal cord injury (SCI) leads to severe impairment in cardiovascular control, commonly manifested as a rapid, uncontrolled rise in blood pressure triggered by peripheral stimuli-a condition called autonomic dysreflexia. The objective was to demonstrate the translational potential of noninvasive transcutaneous stimulation (TCS) in mitigating autonomic dysreflexia following SCI, using pre-clinical evidence and a clinical case report. In rats with SCI, we show that TCS not only prevents the instigation of autonomic dysreflexia, but also mitigates its severity when delivered during an already-triggered episode. Furthermore, when TCS was delivered as a multisession therapy for 6 weeks post-SCI, the severity of autonomic dysreflexia was significantly reduced when tested in the absence of concurrent TCS. This treatment effect persisted for at least 1 week after the end of therapy. More importantly, we demonstrate the clinical applicability of TCS in treatment of autonomic dysreflexia in an individual with cervical, motor-complete, chronic SCI. We anticipate that TCS will offer significant therapeutic advantages, such as obviating the need for surgery resulting in reduced risk and medical expenses. Furthermore, this study provides a framework for testing the potential of TCS in improving recovery of other autonomic functions such lower urinary tract, bowel, and sexual dysfunction following SCI.

Pulmonary artery injury in left atrial appendage closure device implantation: a systematic review of a potentially fatal complication

Background

Pulmonary artery (PA) injury is a rarely reported complication following percutaneous left atrial appendage closure (LAAC). This study aims to systematically review all reported cases of PA injury associated with LAAC.

Methods

PubMed/Medline, SCOPUS, EMBASE, Google Scholar and the MAUDE databases were searched to find studies reporting PA injury during or after LAAC with the Amplatzer Amulet (AA), Amplatzer Cardiac Plug (ACP) or Watchman device through October 2019. Categorical data were reported in terms of numbers and/or percentages (%).

Results

We found 13 cases (mean age 71.4 yrs) with reported PA injury associated with LAAC. Of these, 9 were case reports, 3 were reported in observational studies, and 1 was in the MAUDE database. Most cases (n=8) were reported in Europe followed by Australia (n=2) and Asia (n=2). The indication for device implantation in all patients was a high bleeding risk with anticoagulation for atrial fibrillation. Five cases were reported with the ACP (1/5 patients died), 5 with AA (2/5 patients died), and 3 with the Watchman (1/2 patients died). Acute and late presentations following implantation were reported for all three devices. 69.2% of cases (9/13) occurred acutely (during or within 24 hours of intervention). Of these, 3/9 occurred during device implantation. 2/4 of the delayed cases occurred >2 weeks following implantation. The mortality rate for acute and delayed cases was 22% (2/9 patients) and 50% (2/4 patients), respectively. A majority of the cases were attributable to barb/strut/hook injury of the PA. PA injury was associated with a mortality rate of approximately 31%. All surviving patients were managed with surgical intervention.

Conclusion

PA injury is an infrequently reported complication following LAAC and is associated with high mortality. Cases can present acutely (intra-procedurally or within 24 hours) or delayed (>24 hours post-implantation). A majority of cases are due to direct injury of the PA by the struts/hooks/barbs of the device. Practitioners should be cognizant of this life-threatening complication, which requires a high index of suspicion for diagnosis and can occur weeks after device implantation.

Funding Acknowledgement

Type of funding source: None

Rates and causes of readmissions following index admissions for Takotsubo syndrome-a meta-analysis of 118,941 index hospitalizations

Background

Rising trends in takotsubo syndrome (TTS)-related complications warrant data to identify the rate, causes and predictors of readmission on a large scale. We conducted the first-ever meta-analysis to evaluate the pooled rate of short-term and long-term readmissions after index TTS admissions.

Methods

PubMed/Medline, EMBASE and SCOPUS databases were systematically reviewed to find studies through October 2019 reporting rates and causes of readmission following index TTS admissions. Random effects models were used to estimate pooled rates and causes of readmissions and I2 statistics were used to report inter-study heterogeneity.

Results

A total of 16 cohorts with 118,941 TTS index admissions (mean age 65–75 yrs; female >85%, median follow-up 272.5 days) revealed a 16.6% [95% CI-13.2%-20.3%, I2=99%] pooled rate of readmission. Short-term and long-term pooled readmission rates are displayed in Fig.1. The readmission rate was higher in cohorts with young patients (<70 vs. >70 yrs), smaller sample size (n<100 vs. n>100) and single-centres vs. multicentres. Studies published from the USA (16.4% vs. 14.9%) had a higher readmission rate as compared to Italy. The most frequent causes were cardiac (40.6%), respiratory (15.7%) and renal (7.0%). Among readmissions with cardiac diagnoses, heart failure was most common (40.1%).

Conclusions

This global meta-analysis revealed that the pooled rate of readmission following index TTS admissions was ∼17% and causes were mainly cardiac or respiratory.

Funding Acknowledgement

Type of funding source: None

Vascular-Cognitive Impairment following High-Thoracic Spinal Cord Injury Is Associated with Structural and Functional Maladaptations in Cerebrovasculature

Individuals living with chronic spinal cord injury (SCI) often exhibit impairments in cognitive function, which impede their rehabilitation and transition into the community. Although a number of clinical studies have demonstrated the impact of impaired cardiovascular control on cognitive impairment, the mechanistic understanding of this deleterious relationship is still lacking. The present study investigates whether chronic disruption of cardiovascular control following experimental SCI results in cerebrovascular decline and vascular cognitive impairment. Fourteen weeks following a high thoracic SCI (at the third thoracic segment), rats were subjected to a battery of in vivo and in vitro physiological assessments, cognitive-behavioral tests, and immunohistochemical approaches to investigate changes in cerebrovascular structure and function in the middle cerebral artery (MCA). We show that in the MCA of rats with SCI, there is a 55% (SCI vs. control: 13.4 ± 1.9% vs. 29.63 ± 2.8%, respectively) reduction in the maximal vasodilator response to carbachol, which is associated with reduced expression of endothelial marker cluster of differentiation 31 (CD31) and transient receptor potential cation channel 4 (TRPV 4) channels. Compared with controls, MCAs in rats with SCI were found to have 50% (SCI vs. control: 1.5 ± 0.2 vs. 1 ± 0.1 a.u., respectively) more collagen 1 in the media of vascular wall and 37% (SCI vs. control: 30.5 ± 2.9% vs. 42.0 ± 4.0%, respectively) less distensibility at physiological intraluminal pressure. Further, the cerebral blood flow (CBF) in the hippocampus was reduced by 32% in the SCI group (SCI vs. control: 44.3 ± 4.5 mL/100 g/min vs. 65.0 ± 7.2 mL/100 g/min, respectively) in association with impairment of short-term memory based on a novel object recognition test. There were no changes in the sympathetic innervation of the vasculature and passive structure in the SCI group. Chronic experimental SCI is associated with structural alterations and endothelial dysfunction in cerebral arteries that likely contribute to significantly reduced CBF and vascular cognitive impairment.

Acute Cardiovascular Responses to Vagus Nerve Stimulation after Experimental Spinal Cord Injury

Pairing vagus nerve stimulation (VNS) with rehabilitation has emerged as a potential strategy to enhance plasticity and improve recovery in a range of neurological disorders. A recent study highlights the therapeutic promise of VNS in promoting motor recovery after spinal cord injury (SCI). We investigated the safety of acute VNS in a rat model of chronic SCI. We measured the cardiovascular response to various VNS paradigms following chronic high-thoracic SCI that is known to deleteriously impact cardiovascular control. Dose-response experiments with continuous VNS revealed an SCI-dependent increase in sensitivity for heart rate (HR) and blood pressure (BP) compared with controls. A clinically relevant intermittent VNS resulted in transient reduction in HR in rats with SCI; however, BP remained unaltered. In all experiments, the effect lasted only while the VNS stimulus train was present, as HR and BP restored to baseline values as soon as VNS ended. No prolonged episodes of persisting hypotension were seen in either group. Further, VNS did not trigger autonomic dysreflexia or exacerbate the severity of autonomic dysreflexia when induced during or after stimulation sessions. Overall, these findings provide initial evidence that intermittent VNS at parameters used for targeted plasticity therapy (30 Hz, 0.8 mA) appears safe and supports further investigation of this potential therapy for use following SCI.

Morphological maladaptations in sympathetic preganglionic neurons following an experimental high-thoracic spinal cord injury

Spinal cord injury (SCI) disrupts the supraspinal vasomotor pathways to sympathetic preganglionic neurons (SPNs) leading to impaired blood pressure (BP) control that often results in episodes of autonomic dysreflexia and orthostatic hypotension. The physiological cardiovascular consequences of SCI are largely attributed to the plastic changes in spinal SPNs induced by their partial deafferentation. While multiple studies have investigated the morphological changes in SPNs following SCI with contrasting reports. Here we investigated the morphological changes in SPNs rostral and caudal to a high thoracic (T3) SCI at 1-, 4- and 8-weeks post injury. SPNs were identified using Nicotinamide adenine dinucleotide hydrogen phosphate-diaphorase (NADPH- diaphorase) staining and were quantified for soma size and various dendritic measurements. We show that rostral to the lesion, soma size was increased at 1 week along with increased dendritic arbor. The total dendritic length was also increased at chronic stage (8 weeks post SCI). Caudal to the lesion, the soma size or dendritic lengths did not change with SCI. However, dendritic branching was enhanced within a week post SCI and remained elevated throughout the chronic stages. These findings demonstrate that SPNs undergo significant structural changes form sub-acute to chronic stages post-SCI that likely determines their functional consequences. These changes are discussed in context of physiological cardiovascular outcomes post-SCI.

Diverse cognitive impairment after spinal cord injury is associated with orthostatic hypotension symptom burden

This study: 1) compared cognitive functioning between individuals with chronic (>1 year) spinal cord injury (SCI) and non-injured controls and, 2) assessed associations between symptoms of autonomic dysreflexia and orthostatic hypotension with cognitive functioning in SCI participants with a history of unstable blood pressure (BP). Thirty-two individuals with SCI (C4-L2, American Spinal Injury Association Impairment Scale A-D) and thirty age, sex-matched non-injured controls participated in this study. Participants completed a motor-free neuropsychological test battery assessing 1) memory, 2) attention/concentration/psychomotor speed and, 3) executive function. Nineteen participants with SCI who had injuries ≥T6 and a history of unstable BP also completed the Autonomic Dysfunction Following Spinal Cord Injury (ADFSCI) questionnaire. Cognitive function was significantly lower in people with SCI across measures of memory and executive function compared to non-injured controls. Significant, moderate-to-large associations were observed between cumulative (frequency x severity) orthostatic hypotension and total BP instability symptoms scores, with measures of attention/concentration/psychomotor speed and executive function. These data demonstrate a 10 - 65% reduced performance across specific realms of cognitive functioning in individuals with SCI relative to non-injured controls. Furthermore, cumulative subjective scores for symptoms of unstable BP were associated with diverse cognitive deficits. These findings, in individuals without co-occurring traumatic brain injury, imply cardiovascular dysregulation plays a role in cognitive deficits observed in this population.

Reliability of Cognitive Measures in Individuals With a Chronic Spinal Cord Injury

BACKGROUND

Following spinal cord injury (SCI), up to 64% of individuals experience cognitive deficit. However, the reliability of commonly used neuropsychological tests is currently unknown in this population.

OBJECTIVES

To evaluate the test-retest reliability of cognitive measures in individuals with SCI.

DESIGN

Cross-sectional study.

SETTING

Vancouver General Hospital.

PARTICIPANTS

Individuals with a chronic (>2 years) SCI (n = 22).

METHODS

Across three visits (separated by ~16 days), 22 participants with chronic SCI completed a neuropsychological battery evaluating memory (Rey Auditory-Verbal Learning Test [RAVLT]), attention/concentration/psychomotor speed (Digit Span Task, Stroop Test), and executive function (Trail Making Test A&B, Symbol Digit Modalities Test, Controlled Oral Word Association Test). Coefficients of variation (CV_intra ) and intraclass correlation coefficients (ICCs) were calculated to determine the reliability of each test between visits. Linear regressions were performed to assess the associations between variability (CV_intra ) and participant characteristics, such as age or highest education level attained. Repeated-measures, one-way analysis of variance (ANOVA) was conducted to determine any significant practice effects, and smallest real differences (SRDs) were calculated.

MAIN OUTCOME MEASUREMENTS

Repeated scores on aforementioned neuropsychological tests.

RESULTS

ICCs ranged from 0.77 to 0.93, with the exception of RAVLT recognition score (ICC = 0.27). Age showed a moderate association with CV_intra in RAVLT interference recall scores (r = 0.43, P = .047), but was not a confounding factor for other measures. Education was not associated with CV_intra . Significant practice effects were noted for most of the cognitive tests assessed.

CONCLUSIONS

Other than the RAVLT recognition score, these cognitive measures demonstrated good-to-excellent reliability. Although this is encouraging, test-retest variability should be considered when interpreting the efficacy of various cognitive training strategies to mitigate cognitive decline in this population. Thus, the SRD values presented herein will allow researchers and clinicians to identify "true" changes in cognitive function with repeated testing.

LEVEL OF EVIDENCE

III.

The Blood Pressure Pendulum following Spinal Cord Injury: Implications for Vascular Cognitive Impairment

Cognitive impairment following spinal cord injury (SCI) has received considerable attention in recent years. Among the various systemic effects of SCI that contribute towards cognitive decline in this population, cardiovascular dysfunction is arguably one of the most significant. The majority of individuals with a cervical or upper-thoracic SCI commonly experience conditions called orthostatic hypotension and autonomic dysreflexia, which are characterized by dangerous fluctuations in systemic blood pressure (BP). Herein, we review the potential impact of extreme BP lability on vascular cognitive impairment (VCI) in individuals with SCI. Albeit preliminary in the SCI population, there is convincing evidence that chronic hypotension and hypertension in able-bodied individuals results in devastating impairments in cerebrovascular health, leading to VCI. We discuss the pertinent literature, and while drawing mechanistic comparisons between able-bodied cohorts and individuals with SCI, we emphasize the need for additional research to elucidate the mechanisms of cognitive impairment specific to the SCI population. Lastly, we highlight the current and potential future therapies to manage and treat BP instability, thereby possibly mitigating VCI in the SCI population.

Cognitive function after spinal cord injury: A systematic review

OBJECTIVE

To systematically examine the incidence of cognitive impairment in individuals with spinal cord injury (SCI), as well as identify potential contributing and confounding factors.

METHODS

Studies quantitatively reporting cognitive ability after spinal cord injury were searched electronically via Medline, CINAHL, Embase, and PsycINFO. Manual screening for references within articles was also performed. A total of 2,481 studies were screened and a total of 70 were included in this review, 21 reporting cognitive function after SCI compared to an able-bodied control group and 49 with no able-bodied controls. Studies were analyzed for the incidence of impairment and the interactions with concomitant traumatic brain injury, psychological or somatic complaints, decentralized cardiovascular control, sleep apnea, neurologic level of injury, and age.

RESULTS

There is a high volume of evidence reporting substantial cognitive impairment in individuals with SCI. Potential co-contributors include concomitant brain injury, psychological or somatic comorbidities, decentralized cardiovascular control, and sleep apnea. Cognitive functioning was negatively correlated with age. No clear agreement was found for the incidence of cognitive impairment or its association with level of injury.

CONCLUSION

Current evidence suggests that individuals with SCI should be examined and addressed for cognitive impairment. Future studies aimed at identifying potential secondary causative factors should employ stringent controls for co-occurring brain trauma since it appears to be a major contributor and confounder to impaired cognition.

Transient Hypertension after Spinal Cord Injury Leads to Cerebrovascular Endothelial Dysfunction and Fibrosis

We aimed to create a clinically relevant pre-clinical model of transient hypertension, and then evaluate the pathophysiological cerebrovascular processes resulting from this novel stimulus, which has recently been epidemiologically linked to cerebrovascular disease. We first developed a clinically relevant model of transient hypertension, secondary to induced autonomic dysreflexia after spinal cord injury and demonstrated that in both patients and rats, this stimulus leads to drastic acute cerebral hyperperfusion. For this, iatrogenic urodynamic filling/penile vibrostimulation was completed while measuring beat-by-beat blood pressure and cerebral blood flow (CBF) in patients. We then developed a rodent model mimicking the clinical reality by performing colorectal distention (to induce autonomic dysreflexia) using pre-clinical beat-by-beat blood pressure and CBF assessments. We then performed colorectal distension in rats for four weeks (6x/day) to evaluate the long-term cerebrovascular consequences of transient hypertension. Outcome measures included middle cerebral artery endothelial function, remodeling, profibrosis and perivascular innervation; measured via pressure myography, immunohistochemistry, molecular biology, and magnetic resonance imaging. Our model demonstrates that chronic repetitive cerebral hyperperfusion secondary to transient hypertension because of autonomic dysreflexia: (1) impairs cerebrovascular endothelial function; (2) leads to profibrotic cerebrovascular stiffening characterized by reduced distensibility and increased collagen deposition; and (3) reduces perivascular sympathetic cerebrovascular innervation. These changes did not occur concurrent to hallmark cerebrovascular changes from chronic steady-state hypertension, such as hypertrophic inward remodeling, or reduced CBF. Chronic exposure to repetitive transient hypertension after spinal cord injury leads to diverse cerebrovascular impairment that appears to be unique pathophysiology compared with steady-state hypertension in non-spinal cord injured models.

Exercise and Peripheral Nerve Grafts as a Strategy To Promote Regeneration after Acute or Chronic Spinal Cord Injury

Therapeutic interventions after spinal cord injury (SCI) routinely are designed to address multiple aspects of the primary and/or secondary damage that occurs. Exercise has a demonstrated efficacy for post-SCI complications such as cardiovascular dysfunction, neuropathic pain, and chronic inflammation, yet there is little understanding of the mechanisms by which improvements might result from this non-invasive approach. Here we review several of our observations of molecular and cellular changes within the injured spinal cord following acute or delayed exercise regimens that illustrate the potential for positive effects on neuroprotection and rehabilitation. Further, we provide new information about the role of exercise in promoting the regeneration of spinal axons into peripheral nerve grafts (PNGs) placed immediately or 6 weeks after injury. Acute and chronically injured propriospinal neurons within the lumbar spinal cord displayed the greatest propensity for enhanced regeneration after exercise, which correlates with the direct sensory input to this region from exercised hindlimb muscles. Future studies will extend these observations by testing whether exercise will boost the regenerative effort of axons to extend beyond the graft, interact with intraspinal targets, and establish functional connections across a lesion.

Innate and humoral recognition of the products of cell death: differential antigenicity and immunogenicity in lupus

While apoptotic debris is believed to constitute the original antigenic insult in lupus (which is characterized by a time-dependent diversification of autoreactivity), whether such debris and autoantibodies specifically recognizing its constituents mediate differential effects on innate and humoral responses in lupus-prone mice is currently unknown. Apoptotic blebs (as opposed to cellular lysate) enhanced preferentially the maturation of dendritic cells (DCs) from bone marrow precursors drawn from lupus-prone mice. Murine, somatically mutated, apoptotic cell-reactive immunoglobulin (Ig)G monoclonal antibodies demonstrated enhanced recognition of DCs and also displayed a prominent lupus strain-specific bias in mediating DC maturation. Further, immunization of such antibodies specifically in lupus-prone mice resulted in widespread humoral autoreactivity; hypergammaglobulinaemia (a hallmark of systemic autoimmunity) was observed, accompanied by enhanced antibody titres to cellular moieties. Induced antibodies recognized antigens distinct from those recognized by the antibodies employed for immunization; in particular, nephritis-associated anti-double stranded (ds) DNA antibodies and neonatal lupus-associated anti-Ro60 antibodies were elicited by a non-dsDNA, non-Ro60 reactive antibody, and Sm was a favoured target. Further, only in lupus-prone mice did such immunization enhance the kinetics of humoral anti-self responses, resulting in the advanced onset of glomerulosclerosis. These studies reveal that preferential innate and humoral recognition of the products of cell death in a lupus milieu influence the indices associated with autoimmune pathology.

Evaluation of supraspinatus strengthening exercises based on fiber bundle architectural changes

Supraspinatus strengthening is an integral part of rehabilitation programs. However, there is disparity regarding the best exercise. Thus, we investigated the effects of supraspinatus strengthening exercises on muscle fiber bundle architecture using real-time ultrasound. Participants were randomized into full-can (FC; n = 12), empty-can (EC; n = 11,) and prone horizontal abduction (PHA; n = 11) groups and performed three sessions/week for 8 weeks. Each session involved four sets of exercise for weeks 1-4 and six sets for weeks 5-8 with eight repetitions/set. Images of supraspinatus were captured in 0° (relaxed) and 60° (contracted) glenohumeral abduction. Fiber bundle length (FBL), pennation angle, and muscle thickness were measured at beginning, mid, and end of training. Maximum isometric abduction strength was measured in full-can, empty-can, and prone horizontal abduction positions using a hand-held dynamometer. FBL decreased after 4 weeks in FC [relaxed: Δ = -0.54 cm, P = 0.001, d = 0.92; contracted: Δ = -0.27 cm, P = 0.008, d = 0.27] and EC [relaxed: Δ = -0.59 cm, P = 0.008, d = 0.86; contracted: Δ = -0.36 cm, P = 0.013, d = 0.59], but not in PHA [relaxed: Δ = -0.11, P = 0.121, d = 0.31; contracted: Δ = -0.06 cm, P = 0.486, d = 0.13]. Strength increased significantly from week 4-8 only in PHA (Δ = +0.96 kg, P = 0.004, d = 0.47) when tested in prone horizontal abduction position. Maintenance of FBL with increased strength indicates prone horizontal abduction may be a better exercise to strengthen supraspinatus.

Elucidation of the potential disease-promoting influence of IgM apoptotic cell-reactive antibodies in lupus

The undigested remnants of apoptosis are believed to stimulate the generation of autoantibodies in lupus. The biological properties of initiator, disease-specific IgM antibodies that specifically recognize apoptotic cells, readily detected in the sera of lupus patients, remain unclear. Apoptotic cell-reactive IgM monoclonal antibodies (generated from lupus-prone mice), as opposed to control IgM, preferentially stimulated maturation of bone marrow-derived dendritic cells (BMDCs) derived from such mice, relative to BMDCs derived from healthy mice. An influence of both antibody specificity and cell genotype was also apparent in the secretion of signature inflammatory cytokines. Immunization of such antibodies in lupus-prone animals induced increases in total serum IgG levels, with the elicited antibodies also preferentially recognizing moieties on dying cells. An expanded specificity was apparent both upon Western blot on cellular lysate and from the enhanced recognition of dsDNA, Ro60, RNP68 and Sm; the antibody most efficient in mediating autoreactive diversity, while being germline encoded, also induced the highest degree of phenotypic changes on BMDCs. Apoptotic cell-reactive IgM antibodies may therefore be potentially capable of influencing the course of systemic autoimmune disease by affecting both innate and adaptive immunity.

Intra-axonal protein synthesis - a new target for neural repair?

Although initially argued to be a feature of immature neurons with incomplete polarization, there is clear evidence that neurons in the peripheral nervous system retain the capacity for intra-axonal protein synthesis well into adulthood. This localized protein synthesis has been shown to contribute to injury signaling and axon regeneration in peripheral nerves. Recent works point to potential for protein synthesis in axons of the vertebrate central nervous system. mRNAs and protein synthesis machinery have now been documented in lamprey, mouse, and rat spinal cord axons. Intra-axonal protein synthesis appears to be activated in adult vertebrate spinal cord axons when they are regeneration-competent. Rat spinal cord axons regenerating into a peripheral nerve graft contain mRNAs and markers of activated translational machinery. Indeed, levels of some growth-associated mRNAs in these spinal cord axons are comparable to the regenerating sciatic nerve. Markers of active translation tend to decrease when these axons stop growing, but can be reactivated by a second axotomy. These emerging observations raise the possibility that mRNA transport into and translation within axons could be targeted to facilitate regeneration in both the peripheral and central nervous systems.

Exercise dependent increase in axon regeneration into peripheral nerve grafts by propriospinal but not sensory neurons after spinal cord injury is associated with modulation of regeneration-associated genes

Insufficient regeneration of central nervous system (CNS) axons contributes to persisting neurological dysfunction after spinal cord injury (SCI). Peripheral nerve grafts (PNGs) support regeneration by thousands of injured intraspinal axons and help them bypass some of the extracellular barriers that form after SCI. However this number represents but a small portion of the total number of axons that are injured. Here we tested if rhythmic sensory stimulation during cycling exercise would boost the intrinsic regenerative state of neurons to enhance axon regeneration into PNGs after a lower thoracic (T12) spinal transection of adult rats. Using True Blue retrograde tracing, we show that 4 weeks of cycling improves regeneration into a PNG from lumbar interneurons but not by primary sensory neurons. The majority of neurons that regenerate their axon are within 5 mm of the lesion and their number increased 70% with exercise. Importantly propriospinal neurons in more distant regions (5-20 mm from the lesion) that routinely exhibit very limited regeneration responded to exercise by increasing the number of regenerating neurons by 900%. There was no exercise-associated increase in regeneration from sensory neurons. Analyses using fluorescent in situ hybridization showed that this increase in regenerative response is associated with changes in levels of mRNAs encoding the regeneration associated genes (RAGs) GAP43, β-actin and Neuritin. While propriospinal neurons showed increased mRNA levels in response to SCI alone and then to grafting and exercise, sensory neurons did not respond to SCI, but there was a response to the presence of a PNG. Thus, exercise is a non-invasive approach to modulate gene expression in injured neurons leading to an increase in regeneration. This sets the stage for future studies to test whether exercise will promote axon outgrowth beyond the PNG and reconnection with spinal cord neurons, thereby demonstrating a potential clinical application of this combined therapeutic intervention.