Autonomic Dysreflexia, Induced by Noxious or Innocuous Stimulation, Does Not Depend on Changes in Dorsal Horn Substance P

Contribution of Brain Processes to Tissue Loss After Spinal Cord Injury: Does a Pain-Induced Rise in Blood Pressure Fuel Hemorrhage?

Pain (nociceptive) input soon after spinal cord injury (SCI) expands the area of tissue loss (secondary injury) and impairs long-term recovery. Evidence suggests that nociceptive stimulation has this effect because it promotes acute hemorrhage. Disrupting communication with the brain blocks this effect. The current study examined whether rostral systems exacerbate tissue loss because pain input drives an increase in systolic blood pressure (BP) and flow that fuels blood infiltration. Rats received a moderate contusion injury to the lower thoracic (T12) spinal cord. Communication with rostral processes was disrupted by cutting the spinal cord 18 h later at T2. Noxious electrical stimulation (shock) applied to the tail (Experiment 1), or application of the irritant capsaicin to one hind paw (Experiment 2), increased hemorrhage at the site of injury. Shock, but not capsaicin, increased systolic BP and tail blood flow in sham-operated rats. Cutting communication with the brain blocked the shock-induced increase in systolic BP and tail blood flow. Experiment 3 examined the effect of artificially driving a rise in BP with norepinephrine (NE) in animals that received shock. Spinal transection attenuated hemorrhage in vehicle-treated rats. Treatment with NE drove a robust increase in BP and tail blood flow but did not increase the extent of hemorrhage. The results suggest pain input after SCI can engage rostral processes that fuel hemorrhage and drive sustained cardiovascular output. An increase in BP was not, however, necessary or sufficient to drive hemorrhage, implicating other brain-dependent processes.

Pharmacological Inhibition of Soluble Tumor Necrosis Factor-Alpha Two Weeks after High Thoracic Spinal Cord Injury Does Not Affect Sympathetic Hyperreflexia

After a severe, high-level spinal cord injury (SCI), plasticity to intraspinal circuits below injury results in heightened spinal sympathetic reflex activity and detrimentally impacts peripheral organ systems. Such sympathetic hyperreflexia is immediately apparent as an episode of autonomic dysreflexia (AD), a life-threatening condition characterized by sudden hypertension and reflexive bradycardia following below-level sensory inputs; for example, pressure sores or impacted fecal matter. Over time, plasticity within the spinal sympathetic reflex (SSR) circuit contributes to the progressive intensification of AD events, as the frequency and severity of AD events increase greatly beginning ∼2 weeks post-injury (wpi). The neuroimmune system has been implicated in driving sympathetic hyperreflexia, as inhibition of the cytokine soluble tumor necrosis factor-alpha (sTNFα) using the biological mimetic XPro1595 beginning within days post-SCI has been shown to attenuate the development of AD. Here, we sought to further understand the effective therapeutic time window of XPro1595 to diminish sympathetic hyperreflexia, as indicated by AD. We delayed the commencement of continuous intrathecal administration of XPro1595 until 2 weeks after a complete, thoracic level 3 injury in adult rats. We examined the severity of colorectal distension-induced AD biweekly. We found that initiation of sTNFα inhibition at 2 wpi does not attenuate the severity or intensification of sympathetic hyperreflexia compared with saline-treated controls. Coupled with previous data from our group, these findings suggest that central sTNFα signaling must be targeted prior to 2 weeks post-SCI in order to decrease sympathetic hyperreflexia.

Intraspinal Plasticity Associated With the Development of Autonomic Dysreflexia After Complete Spinal Cord Injury

Traumatic spinal cord injury (SCI) leads to disruption of sensory, motor and autonomic function, and triggers structural, physiological and biochemical changes that cause reorganization of existing circuits that affect functional recovery. Propriospinal neurons (PN) appear to be very plastic within the inhibitory microenvironment of the injured spinal cord by forming compensatory circuits that aid in relaying information across the lesion site and, thus, are being investigated for their potential to promote locomotor recovery after experimental SCI. Yet the role of PN plasticity in autonomic dysfunction is not well characterized, notably, the disruption of supraspinal modulatory signals to spinal sympathetic neurons after SCI at the sixth thoracic spinal segment or above resulting in autonomic dysreflexia (AD). This condition is characterized by unmodulated sympathetic reflexes triggering sporadic hypertension associated with baroreflex mediated bradycardia in response to noxious yet unperceived stimuli below the injury to reduce blood pressure. AD is frequently triggered by pelvic visceral distension (bowel and bladder), and there are documented structural relationships between injury-induced sprouting of pelvic visceral afferent C-fibers. Their excitation of lumbosacral PN, in turn, sprout and relay noxious visceral sensory stimuli to rostral disinhibited thoracic sympathetic preganglionic neurons (SPN) that manifest hypertension. Herein, we review evidence for maladaptive plasticity of PN in neural circuits mediating heightened sympathetic reflexes after complete high thoracic SCI that manifest cardiovascular dysfunction, as well as contemporary research methodologies being employed to unveil the precise contribution of PN plasticity to the pathophysiology underlying AD development.

Central expression of synaptophysin and synaptoporin in nociceptive afferent subtypes in the dorsal horn

Central sprouting of nociceptive afferents in response to neural injury enhances excitability of nociceptive pathways in the central nervous system, often causing pain. A reliable quantification of central projections of afferent subtypes and their synaptic terminations is essential for understanding neural plasticity in any pathological condition. We previously characterized central projections of cutaneous nociceptive A and C fibers, selectively labeled with cholera toxin subunit B (CTB) and Isolectin B4 (IB4) respectively, and found that they expressed a general synaptic molecule, synaptophysin, largely depending on afferent subtypes (A vs. C fibers) across thoracic dorsal horns. The current studies extended the central termination profiles of nociceptive afferents with synaptoporin, an isoform of synaptophysin, known to be preferentially expressed in C fibers in lumbar dorsal root ganglions. Our findings demonstrated that synaptophysin was predominantly expressed in both peptidergic and IB4-binding C fiber populations in superficial laminae of the thoracic dorsal horn. Cutaneous IB4-labeled C fibers showed comparable expression levels of both isoforms, while cutaneous CTB-labeled A fibers exclusively expressed synaptophysin. These data suggest that central expression of synaptophysin consistently represents synaptic terminations of projecting afferents, at least in part, including nociceptive A-delta and C fibers in the dorsal horn.

Rapamycin Exacerbates Cardiovascular Dysfunction after Complete High-Thoracic Spinal Cord Injury

Autonomic dysreflexia (AD) is a potentially life-threatening syndrome in individuals with spinal cord injury (SCI) above the T6 spinal level that is characterized by episodic hypertension in response to noxious stimuli below the lesion. Maladaptive intraspinal plasticity is thought to contribute to the temporal development of AD, and experimental approaches that reduce such plasticity mitigate the severity of AD. The mammalian target of rapamycin (mTOR) has gained interest as a mediator of plasticity, regeneration, and nociceptor hypersensitivity in the injured spinal cord. Based on our preliminary data that prolonged rapamycin (RAP) treatment markedly reduces mTOR activity in the cord weeks after high-thoracic (T4) spinal transection, we sought to determine whether RAP could modulate AD development by impeding intraspinal plasticity. Naïve and injured rats were administered RAP or vehicle every other day, beginning immediately after injury for four weeks, and hemodynamic monitoring was conducted to analyze the frequency of spontaneously occurring AD, as well as the severity of colorectal distention (CRD) induced AD. Results showed that after SCI, RAP significantly exacerbated sustained body weight loss and caused a marked elevation in resting blood pressure, with average daily blood pressure rising above even normal naïve levels within one week after injury. Moreover, RAP significantly increased the frequency of daily spontaneous AD and increased the absolute blood pressure induced by CRD at three weeks post-injury. These dynamic cardiovascular effects were not, however, correlated with changes in the density of nociceptive c-fibers or c-Fos+ neurons throughout the spinal cord, indicating that intraspinal plasticity associated with AD was not altered by treatment. These findings caution against the use of RAP as a therapeutic intervention for SCI because it evokes toxic weight loss and exacerbates cardiovascular dysfunction perhaps mediated by increased peripheral nociceptor sensitivity and/or vascular resistance.

How is chronic pain related to sympathetic dysfunction and autonomic dysreflexia following spinal cord injury?

Autonomic dysreflexia (AD) and neuropathic pain occur after severe injury to higher levels of the spinal cord. Mechanisms underlying these problems have rarely been integrated in proposed models of spinal cord injury (SCI). Several parallels suggest significant overlap of these mechanisms, although the relationships between sympathetic function (dysregulated in AD) and nociceptive function (dysregulated in neuropathic pain) are complex. One general mechanism likely to be shared is central sensitization - enhanced responsiveness and synaptic reorganization of spinal circuits that mediate sympathetic reflexes or that process and relay pain-related information to the brain. Another is enhanced sensory input to spinal circuits caused by extensive alterations in primary sensory neurons. Both AD and SCI-induced neuropathic pain are associated with spinal sprouting of peptidergic nociceptors that might increase synaptic input to the circuits involved in AD and SCI pain. In addition, numerous nociceptors become hyperexcitable, hypersensitive to chemicals associated with injury and inflammation, and spontaneously active, greatly amplifying sensory input to sensitized spinal circuits. As discussed with the aid of a preliminary functional model, these effects are likely to have mutually reinforcing relationships with each other, and with consequences of SCI-induced interruption of descending excitatory and inhibitory influences on spinal circuits, with SCI-induced inflammation in the spinal cord and in DRGs, and with activity in sympathetic fibers within DRGs that promotes local inflammation and spontaneous activity in sensory neurons. This model suggests that interventions selectively targeting hyperactivity in C-nociceptors might be useful for treating chronic pain and AD after high SCI.

Olfactory ensheathing cells but not fibroblasts reduce the duration of autonomic dysreflexia in spinal cord injured rats

Autonomic dysreflexia is a common complication after high level spinal cord injury and can be life-threatening. We have previously shown that the acute transplantation of olfactory ensheathing cells into the lesion site of rats transected at the fourth thoracic spinal cord level reduced autonomic dysreflexia up to 8weeks after spinal cord injury. This beneficial effect was correlated with changes in the morphology of sympathetic preganglionic neurons despite the olfactory cells surviving no longer than 3weeks. Thus the transitory presence of olfactory ensheathing cells at the injury site initiated long-term functional as well as morphological changes in the sympathetic preganglionic neurons. The primary aim of the present study was to evaluate whether olfactory ensheathing cells survive after transplantation within the parenchyma close to sympathetic preganglionic neurons and whether, in this position, they still reduce the duration of autonomic dysreflexia and modulate sympathetic preganglionic neuron morphology. The second aim was to quantify the density of synapses on the somata of sympathetic preganglionic neurons with the hypothesis that the reduction of autonomic dysreflexia requires synaptic changes. As a third aim, we evaluated the cell type-specificity of olfactory ensheathing cells by comparing their effects with a control group transplanted with fibroblasts. Animals transplanted with OECs had a faster recovery from hypertension induced by colorectal distension at 6 and 7weeks but not at 8weeks after T4 spinal cord transection. Olfactory ensheathing cells survived for at least 8weeks and were observed adjacent to sympathetic preganglionic neurons whose overall number of primary dendrites was reduced and the synaptic density on the somata increased, both caudal to the lesion site. Our results showed a long term cell type-specific effects of olfactory ensheathing cells on sympathetic preganglionic neurons morphology and on the synaptic density on their somata, and a transient cell type-specific reduction of autonomic dysreflexia.

"Boosting" in Paralympic athletes with spinal cord injury: doping without drugs

The intentional activation of autonomic dysreflexia (AD, also called "boosting"), a practice sometimes used by athletes affected by spinal cord injury (SCI), is banned by the International Paralympic Committee (IPC). Although various studies have addressed doping and AD as separate issues, studies evaluating AD as a doping method are lacking. The aim of this brief review is to contribute to better understanding of the relationship between doping and AD. We conducted a literature search of the PubMed database (from 1994 onwards). The key search terms "autonomic dysreflexia" and "boosting" were crossreferenced with "sport performance". The official Paralympic website was also viewed. AD is a potent sympathetic reflex, due to a massive release of noradrenaline, that results in marked vasoconstriction distal to the level of the lesion. Athletes with SCI often self-inflict physical suffering in order to induce this phenomenon, which carries high health risks (i.e., hypertension, cerebral hemorrhage, stroke and sudden death). Boosting is a practice that can be compared to doping methods and the IPC expressly prohibits it. Any deliberate attempt to induce AD, if detected, will lead to disqualification from the sporting event and subsequent investigation by the IPC Legal and Ethics Committee.

Autonomic consequences of spinal cord injury

Spinal cord injury (SCI) results not only in motor and sensory deficits but also in autonomic dysfunctions. The disruption of connections between higher brain centers and the spinal cord, or the impaired autonomic nervous system itself, manifests a broad range of autonomic abnormalities. This includes compromised cardiovascular, respiratory, urinary, gastrointestinal, thermoregulatory, and sexual activities. These disabilities evoke potentially life-threatening symptoms that severely interfere with the daily living of those with SCI. In particular, high thoracic or cervical SCI often causes disordered hemodynamics due to deregulated sympathetic outflow. Episodic hypertension associated with autonomic dysreflexia develops as a result of massive sympathetic discharge often triggered by unpleasant visceral or sensory stimuli below the injury level. In the pelvic floor, bladder and urethral dysfunctions are classified according to upper motor neuron versus lower motor neuron injuries; this is dependent on the level of lesion. Most impairments of the lower urinary tract manifest in two interrelated complications: bladder storage and emptying. Inadequate or excessive detrusor and sphincter functions as well as detrusor-sphincter dyssynergia are examples of micturition abnormalities stemming from SCI. Gastrointestinal motility disorders in spinal cord injured-individuals are comprised of gastric dilation, delayed gastric emptying, and diminished propulsive transit along the entire gastrointestinal tract. As a critical consequence of SCI, neurogenic bowel dysfunction exhibits constipation and/or incontinence. Thus, it is essential to recognize neural mechanisms and pathophysiology underlying various complications of autonomic dysfunctions after SCI. This overview provides both vital information for better understanding these disorders and guides to pursue novel therapeutic approaches to alleviate secondary complications.

Disordered cardiovascular control after spinal cord injury

Damage to the spinal cord disrupts autonomic pathways, perturbing cardiovascular homeostasis. Cardiovascular dysfunction increases with higher levels of injury and greater severity. Disordered blood pressure control after spinal cord injury (SCI) has significant ramifications as cord-injured people have an increased risk of developing heart disease and stroke; cardiovascular dysfunction is currently a leading cause of death among those with SCI. Despite the clinical significance of abnormal cardiovascular control following SCI, this problem has been generally neglected by both the clinical and research community. Both autonomic dysreflexia and orthostatic hypotension are known to prevent and delay rehabilitation, and significantly impair the overall quality of life after SCI. Starting with neurogenic shock immediately after a higher SCI, ensuing cardiovascular dysfunctions include orthostatic hypotension, autonomic dysreflexia and cardiac arrhythmias. Disordered temperature regulation accompanies these autonomic dysfunctions. This chapter reviews the human and animal studies that have furthered our understanding of the pathophysiology and mechanisms of orthostatic hypotension, autonomic dysreflexia and cardiac arrhythmias. The cardiovascular dysfunction that occurs during sexual function and exercise is elaborated. New awareness of cardiovascular dysfunction after SCI has led to progress toward inclusion of this important autonomic problem in the overall assessment of the neurological condition of cord-injured people.

Somatosympathetic Vasoconstrictor Reflexes in Human Spinal Cord Injury: Responses to Innocuous and Noxious Sensory Stimulation below Lesion

It is known that the sudden increases in blood pressure associated with autonomic dysreflexia in people with spinal cord injury (SCI) are due to a spinally mediated reflex activation of sympathetic vasoconstrictor neurons supplying skeletal muscle and the gut. Apart from visceral inputs, such as those originating from a distended bladder, there is a prevailing opinion that autonomic dysreflexia can be triggered by noxious stimulation below the lesion. However, do noxious inputs really cause an increase in blood pressure in SCI? Using microelectrodes inserted into a peripheral nerve to record sympathetic nerve activity we had previously shown that selective stimulation of small-diameter afferents in muscle or skin, induced by bolus injection of hypertonic saline into the tibialis anterior muscle or the overlying skin, evokes a sustained increase in muscle sympathetic nerve activity and blood pressure and a transient increase in skin sympathetic nerve activity and decrease in skin blood flow in able-bodied subjects. We postulated that these sympathetic responses would be exaggerated in SCI, with a purely noxious stimulus causing long-lasting increases in blood pressure and long-lasting decreases in skin blood flow. Surprisingly, though, we found that intramuscular or subcutaneous injection of hypertonic saline into the leg caused negligible changes in these parameters. Conversely, weak electrical stimulation over the abdominal wall, which in able-bodied subjects is not painful and activates large-diameter cutaneous afferents, caused a marked increase in blood pressure in SCI but not in able-bodied subjects. This suggests that it is activation of large-diameter somatic afferents, not small-diameter afferents, that triggers increases in sympathetic outflow in SCI. Whether the responses to activation of large-diameter afferents reflect plastic changes in the spinal cord in SCI is unknown.

The dark side of neuroplasticity

Whether dramatic or modest, recovery of neurological function after spinal cord injury (SCI) is greatly due to neuroplasticity--the process by which the nervous system responds to injury by establishing new synaptic connections or by altering the strength of existing synapses. However, the same neuroplasticity that allows locomotor function to recover also produces negative consequences such as pain and dysfunction of organs controlled by the autonomic nervous system. In this review we focus specifically on structural neuroplasticity (the growth of new synaptic connections) after SCI and on the consequent development of pain and autonomic dysreflexia, a condition of episodic hypertension. Neuroplasticity after SCI is stimulated by the deafferentation of spinal neurons below the lesion and by the expression of growth-promoting neurotrophins such as nerve growth factor (NGF). A broad range of therapeutic strategies that affect neuroplasticity is being developed for the treatment of SCI. At one end of the spectrum are therapeutic strategies that directly or indirectly increase NGF in the injured spinal cord, and have the most robust effects on neuroplasticity. At the other end of the spectrum are neuroprotective strategies focused on supporting and rescuing uninjured, or partially injured, axons; these might limit the deafferentation stimulus for neuroplasticity. In the middle of this spectrum are strategies that block axon growth inhibitors without necessarily providing a growth stimulus. The literature supports the view that the negative consequences of neuroplasticity develop more commonly with therapies that directly stimulate nerve growth than they develop in the untreated injured cord. Compared to these conditions, neuroplasticity with negative outcomes is less prevalent after treatments that that neutralize axon growth inhibitors, and least apparent after strategies that promote neuroprotection.

Inhibition of CXCR1 and CXCR2 chemokine receptors attenuates acute inflammation, preserves gray matter and diminishes autonomic dysreflexia after spinal cord injury

STUDY DESIGN

Female Wistar rats (225 g) underwent spinal cord injury (SCI) at the T4 segment and were assigned to one of the three groups treated with: (1) saline; (2) 7.5 mg kg(-1) Reparixin; or (3) 15 mg kg(-1) Reparixin. Reparixin is a small molecule, allosteric noncompetitive inhibitor of CXCR1 and CXCR2 chemokine receptors involved in inflammation.

METHODS

Spinal cord homogenates at 12 and 72 h post-SCI were assayed for tumor necrosis factor α (TNF-α) and cytokine-induced neutrophil chemoattractant (CINC)-1 using enzyme-linked immunosorbant assay (ELISA). Myeloperoxidase activity and western blots for CD68, Fas and p75 content were used to assess inflammation and death receptor ligands, respectively. Histopathology and neurological outcomes were assessed by immunohistochemistry, locomotion scoring and cardiovascular measurement of autonomic dysreflexia 4 weeks post-SCI.

RESULTS

Both 7.5 and 15 mg kg(-1) doses of Reparixin reduced levels of TNF-α and CINC-1 72 h post-SCI and decreased macrophage (CD68) content in the spinal cord lesion. Only 15 mg kg(-1) Reparixin reduced both Fas and p75 levels in the spinal cord compared with untreated SCI. We observed a reduced lesion area and increased neuron number in the gray matter of Reparixin-treated rats. Hindlimb motor scores at 7 and 28 days post-SCI were improved by 15 mg kg(-1) Reparixin treatment. Both 7.5 and 15 mg kg(-1) Reparixin reduced development of autonomic dysreflexia 4 weeks post-SCI. The change in mean arterial pressure, induced by cutaneous or visceral stimulation, was reduced by 40-50%.

CONCLUSION

Acute treatment with 15 mg kg(-1) Reparixin reduces acute inflammation and is associated with minor improvements in motor function and a significant reduction in the severity of autonomic dysreflexia.

Olfactory ensheathing cells reduce duration of autonomic dysreflexia in rats with high spinal cord injury

Autonomic dysreflexia is a common complication in high spinal cord injury and can result in serious consequences and death. Here we have examined the effect of acute transplantation of olfactory ensheathing cells on cardiovascular functions in rats. After T4 transection, radio-telemetric recording in conscious animals was used to study blood pressure and heart rate at rest and during autonomic dysreflexia for up to 8 weeks post-injury. Olfactory ensheathing cells from syngeneic rats were transplanted at the injury site; control animals received culture medium only. At the study end point, we examined morphometric features of sympathetic preganglionic neurons above and below the injury. T4 transection resulted in a fall in resting mean arterial pressure and an increase in resting heart rate. Colorectal distension, used to trigger autonomic dysreflexia, caused episodic hypertension and bradycardia. Although the cell transplantation had no effect on resting cardiovascular parameters, it led to a significantly faster recovery from hypertension, with the recovery time shortened by approximately 25%. The transection resulted in an increase in soma size of sympathetic preganglionic neurons above and below the injury. OEC transplantation normalised this change below the injury and increased dendritic length of preganglionic neurons above the injury, compared to controls. It has been proposed that changes in sympathetic preganglionic neurons following spinal cord transection may be related to the development of autonomic dysreflexia. Our results suggest that olfactory ensheathing cells may alter the morphology of these neurons, and hence modify their activity in the neuronal networks responsible for the dysreflexic reaction.

Gastric electrical stimulation for obesity: the need for a new device using wider pulses

Gastric electrical stimulation (GES) has been proposed as a therapeutic option for obesity. However, its clinical efficacy is not proven, and its mechanisms remain largely unknown. To compare the peripheral and central neural and behavioral effects in rats of GES with a pulse width currently used in clinical trials (GES-A: 6 mA, 0.3 ms, 40 Hz, 2 s on, 3 s off) and GES with a wider pulse (GES-B: same as GES-A, except that the pulse width is 3 ms). Experiment 1: assessing gastric volume changes as a result of GES. Experiment 2: recording the extracellular potentials of a single neuron in the paraventricular nucleus (PVN) with GES. Experiment 3: determining the effects of GES on oxytocin-immunoreactive (OT-IR) neuron expression in the hypothalamus. Experiment 4: determining the effects of GES on food intake and body weight. GES-B, but not GES-A, significantly increased gastric volume. GES-B activated a higher percentage of gastric distention-responsive neurons in the PVN (93% vs. 81%, P = 0.021) and elicited more intensive neuronal responses than GES-A. The number of OT-IR neurons was significantly increased in the PVN and supraoptic nucleus with both methods of GES compared with control groups. The increase in OT-IR neurons in the PVN was higher with GES-B than with GES-A. A 1-week GES treatment significantly reduced daily food intake and body weight. GES-B was more potent than GES-A in producing weight loss (P < 0.001). The effects of GES depend on the stimulation pulse width. GES with a wider pulse is more effective both peripherally and centrally and more potent in reducing body weight in rats.

Pressor response to passive walking-like exercise in spinal cord-injured humans

OBJECTIVE

To examine blood pressure responses during passive walking-like exercise in the standing posture (PWE) in spinal cord-injured (SCI) humans.

METHODS

Twelve motor-complete SCI individuals (cervical level 6 to thoracic level 12, ASIA grade: A or B) and twelve able-bodied controls (CON) participated in this study. SCI individuals were divided into a group with injury level at or above thoracic (T) 6 (HSCI, n = 7) and a group with injury level at or below T10 (LSCI, n = 5). Subjects carried out 6-minute quiet standing and then 12-minute PWE at 1 Hz using a gait training apparatus that enables subjects to stand and move their legs passively.

RESULTS

Mean arterial blood pressures (MAPs) at standing in HSCI, LSCI and CON were 69 +/- 5, 83 +/- 4 and 93 +/- 2 mmHg, respectively. MAP changed significantly during PWE only in HSCI and CON, increasing to 88 +/- 4 (P < 0.001) and 98 +/- 1 mmHg (P < 0.01), respectively. The former group showed a larger increase in MAP (P < 0.001).

INTERPRETATION

Spinal sympathetic reflexes can be induced in a region isolated from the brainstem in response to a stimulus originating below the level of the spinal cord injury, and the magnitude of increase in blood pressure is greater in SCI individuals with lesion level at or above T6 due to loss of supraspinal control of the major sympathetic outflow. This central mechanism may be one of the reasons why greater pressor response to PWE was observed in HSCI.

Selective activation of muscle and skin nociceptors does not trigger exaggerated sympathetic responses in spinal-injured subjects

STUDY DESIGN

Measurement of sympathetic effector organ responses to selective activation of muscle and skin nociceptors below lesion in spinal cord-injured (SCI) subjects.

OBJECTIVES

To test whether selective noxious stimulation below lesion causes exaggerated sympathetic responses in human SCI.

SETTING

Prince of Wales Medical Research Institute, Australia.

METHODS

Twelve subjects (C5-T10, ASIA A-C), none of whom had sensation below the lesion, were included in the study. Selective stimulation of muscle or cutaneous nociceptors was produced by bolus injection of hypertonic (5%) saline into the tibialis anterior muscle or overlying skin and compared with non-noxious electrical stimulation of the abdominal wall. Cutaneous vasoconstrictor (photoelectric plethysmography) and sudomotor (skin conductance) responses, in addition to respiration, heart rate and continuous arterial pressure were monitored.

RESULTS

Electrical stimulation of the abdominal wall caused a significant increase in arterial pressure (31.8+/-6.1%). Conversely, intramuscular or subcutaneous injection of hypertonic saline caused no significant changes in blood pressure (-3.0+/-2.4%; -1.4+/-3.4%) heart rate, skin blood flow or sweat release.

CONCLUSIONS

While hypertonic saline injected into muscle or skin induces strong pain, cutaneous vasoconstriction and sweat release in able-bodied subjects, we saw no evidence of exaggerated sympathoexcitation when these same noxious stimuli were delivered below lesion in subjects with SCI. This suggests that certain types of somatic noxious input may not trigger autonomic dysreflexia, and questions the concept that any painful stimuli originating below lesion can reliably trigger dysreflexia.

Recognition and effective management of autonomic dysreflexia in spinal cord injuries

Autonomic dysreflexia is a potentially life-threatening hypertensive medical emergency that occurs most often in spinal cord-injured individuals with spinal lesions at or above the mid-thoracic spinal cord level. It is a condition that remains poorly recognised outside of spinal cord injury centres, which may result in adverse outcomes including mortality from potentially delayed diagnosis and treatment. Acute autonomic dysreflexia is characterised by severe paroxysmal hypertension associated with throbbing headaches, profuse sweating, nasal stuffiness, flushing of the skin above the level of the lesion, bradycardia, apprehension and anxiety, which is sometimes accompanied by cognitive impairment. The key to effective management is prevention of the condition, by recognition and avoidance of factors that initiate the condition. When it occurs, immediate recognition and reversal of trigger factors along with prompt administration of pharmacological treatment is of paramount importance in order to prevent complications, which include intracranial and retinal haemorrhage, convulsions, cardiac irregularities and death. Promising data from recent animal studies may hold the key to future treatment options.

Effects of polyethylene glycol and magnesium sulfate administration on clinically relevant neurological outcomes after spinal cord injury in the rat

The purpose of this study was to determine the long-term effects of polyethylene glycol (PEG) and magnesium sulfate (MgSO(4)) on clinically relevant motor, sensory, and autonomic outcomes after spinal cord injury (SCI). Rats were injured by clip compression (50 g; T4) and treated 15 min and 6 hr postinjury intravenously (tail vein) with PEG (1 g/kg, 30% w/w in saline; n = 11), MgSO(4) (300 mg/kg; n = 5), PEG + MgSO(4) (n = 6), or saline (n = 10). Behavioral testing lasted for 6 weeks, followed by histological analysis of the spinal cord. Both PEG and MgSO(4) resulted in enhanced locomotor recovery and lower susceptibility to neuropathic pain (mechanical allodynia) compared with saline. At 6 weeks, BBB scores were 7.3 +/- 0.2, 7.7 +/- 0.4, and 6.4 +/- 0.6 in PEG-treated, MgSO(4)-treated, and saline-treated control groups, respectively. Likewise, at 6 weeks PEG-, MgSO(4)-, and saline-treated control animals showed 3.5 +/- 0.4, 2.8 +/- 0.9, and 5.0 +/- 0.5 avoidance responses to at-level touch, respectively. PEG + MgSO(4) improved locomotor recovery and reduced pain but did not provide additional benefit compared with either treatment alone. Neither treatment, nor their combination, attenuated mean arterial pressure (MAP) increases during autonomic dysreflexia. However, saline-treated controls had significantly lower resting MAP than PEG-treated rats and tended to have lower resting MAP than MgSO(4)-treated rats 6 weeks postinjury. MgSO(4) treatment and PEG + MgSO(4) treatment resulted in significant increases in dorsal myelin sparing, and the latter resulted in significant reductions in lesion volume, compared with saline-treated controls. Furthermore, mean lesion volumes correlated negatively with the corresponding mean BBB scores and positively with the corresponding mean pain scores. In conclusion, both PEG and MgSO(4) enhanced long-term clinical outcomes after SCI.

A therapeutic time window for anti-CD 11d monoclonal antibody treatment yielding reduced secondary tissue damage and enhanced behavioral recovery following severe spinal cord injury

OBJECT

The purpose of this study was to investigate the therapeutic time window for antiinflammatory treatment within the first 24 hours of spinal cord injury (SCI). The authors have shown that an anti-CD11d antibody treatment attenuates leukocyte infiltration and improves neurological function when administered beginning 2 hours after SCI. A more clinically relevant time for the initiation of treatment after SCI, however, is 6 or more hours postinjury.

METHODS

In Study 1, the T-4 vertebrae in four groups of rats were injured by a 50-g clip-induced compression method, and the anti-CD11d antibody (1 mg/kg) was intravenously administered starting 2, 6, 12, or 24 hours postinjury. All groups received subsequent doses at 24 and 48 hours, and animals were killed at 72 hours. The anti-CD11d antibody treatment starting at 6 hours postinjury caused significant attenuation of leukocyte infiltration, reactive oxygen species-associated enzymes, and secondary tissue damage. Based on these findings, Study 2 included two groups of rats receiving the aforementioned injury and treatment beginning at 6 hours postinjury (with subsequent treatments at 24 and 48 hours) with the anti-CD11d or a control antibody (1B7); these rats were then observed for 5 weeks. Basso-Beattie-Bresnahan (BBB) scores were significantly higher in anti-CD11d-treated rats (mean BBB score 8.9 +/- 0.1) than controls (mean BBB score 7.7 +/- 0.1) 5 weeks postinjury. Increases in mean arterial pressure during colon distension were smaller in anti-CD11d-treated rats (19.5 +/- 3.7 mm Hg) than in controls (37.4 +/- 4.7 mm Hg).

CONCLUSIONS

These findings suggest that antiinflammatory treatments that reduce secondary tissue damage after SCI may be delayed until 6 hours postinjury and still be effective.

The impact of spinal cord injury on sexual function: concerns of the general population

STUDY DESIGN

Secure, web-based survey.

OBJECTIVES

Obtain information from the spinal cord injured (SCI) population regarding sexual dysfunctions, with the aim of developing new basic science and clinical research and eventual therapies targeting these issues.

SETTING

Worldwide web.

METHODS

Individuals 18 years or older living with SCI. Participants obtained a pass-code to enter a secure website and answered survey questions. A total of 286 subjects completed the survey.

RESULTS

The majority of participants stated that their SCI altered their sexual sense of self and that improving their sexual function would improve their quality of life (QoL). The primary reason for pursuing sexual activity was for intimacy need, not fertility. Bladder and bowel concerns during sexual activity were not strong enough to deter the majority of the population from engaging in sexual activity. However, in the subset of individuals concerned about bladder and/or bowel incontinence during sexual activity, this was a highly significant issue. In addition, the occurrence of autonomic dysreflexia (AD) during typical bladder or bowel care was a significant variable predicting the occurrence and distress of AD during sexual activity.

CONCLUSION

Sexual function and its resultant impact on QoL is a major issue to an overwhelming majority of people living with SCI. This certainly constitutes the need for expanding research in multiple aspects to develop future therapeutic interventions for sexual health and SCI.

Cardiovascular and temperature changes in spinal cord injured rats at rest and during autonomic dysreflexia

In patients with high spinal cord injuries autonomic dysfunction can be dangerous, leading to medical complications such as postural hypotension, autonomic dysreflexia and temperature disturbance. While animal models have been developed to study autonomic dysreflexia, associated temperature changes have not been documented. Our aim here was to use radiotelemetry and infrared thermography in rodents to record the development of cardiovascular and skin temperature changes following complete T4 transection. In adult male Wistar rats (n=5), responses were assessed prior to spinal cord injury (intact) and for 6 weeks following injury. Statistical analysis by a repeated-measure ANOVA revealed that following spinal cord injury (SCI), rats exhibited decreased mean arterial pressure (MAP, average decrease of 26 mmHg; P<0.035) and elevated heart rate (HR, average increase of 65 bpm, P<0.035) at rest. The basal core body temperature following SCI was also significantly lower than intact levels (-0.9 degrees C; P<0.0035). Associated with this decreased basal core temperature following SCI was an increased skin temperature of the mid-tail and hindpaw (+5.6 and +4.0 degrees C, respectively; P<0.0003) consistent with decreased cutaneous vasoconstrictor tone. Autonomic dysreflexia, in response to a 1 min colorectal distension (25 mmHg), was fully developed by 4 weeks after spinal cord transection, producing increases in MAP greater than 25 mmHg (P<0.0003). In contrast to the tachycardia seen in intact animals in response to colorectal distension, SCI animals exhibited bradycardia (P<0.0023). During episodes of autonomic dysreflexia mid-tail surface temperature decreased (approximately -1.7 degrees C, P<0.012), consistent with cutaneous vasoconstriction. This is the first study to compare cardiovascular dysfunction with temperature changes following spinal cord transection in rats.

Genetic manipulation of intraspinal plasticity after spinal cord injury alters the severity of autonomic dysreflexia

Severe spinal cord injuries above mid-thoracic levels can lead to a potentially life-threatening hypertensive condition termed autonomic dysreflexia, which is often triggered by painful distension of pelvic viscera (bladder or bowel) and consequent sensory fiber activation, including nociceptive C-fibers. Interruption of tonically active medullo-spinal pathways after injury causes disinhibition of thoracolumbar sympathetic preganglionic neurons, and intraspinal sprouting of nerve growth factor (NGF)-responsive primary afferent fibers is thought to contribute to their hyperactivity. We investigated spinal levels that are critical for eliciting autonomic dysreflexia using a model of noxious colorectal distension (CRD) after complete spinal transection at the fourth thoracic segment in rats. Post-traumatic sprouting of calcitonin gene-related peptide (CGRP)-immunoreactive primary afferent fibers was selectively altered at specific spinal levels caudal to the injury with bilateral microinjections of adenovirus encoding the growth-promoting NGF or growth-inhibitory semaphorin 3A (Sema3a) compared with control green fluorescent protein (GFP). Two weeks later, cardio-physiological responses to CRD were assessed among treatment groups before histological analysis of afferent fiber density at the injection sites. Dysreflexic hypertension was significantly higher with NGF overexpression in lumbosacral segments compared with GFP, whereas similar overexpression of Sema3a significantly reduced noxious CRD-evoked hypertension. Quantitative analysis of CGRP immunostaining in the spinal dorsal horns showed a significant correlation between the extent of fiber sprouting into the spinal segments injected and the severity of autonomic dysreflexia. These results demonstrate that site-directed genetic manipulation of axon guidance molecules after complete spinal cord injury can alter endogenous circuitry to modulate plasticity-induced autonomic pathophysiology.

Effects of spinal cord injury on synaptic inputs to sympathetic preganglionic neurons

Spinal cord injuries often lead to disorders in the control of autonomic function, including problems with blood pressure regulation, voiding, defecation and reproduction. The root cause of all these problems is the destruction of brain pathways that control spinal autonomic neurons lying caudal to the lesion. Changes induced by spinal cord injuries have been most extensively studied in sympathetic preganglionic neurons, cholinergic autonomic neurons with cell bodies in the lateral horn of thoracic and upper lumbar spinal cord that are the sources of sympathetic outflow. After an injury, sympathetic preganglionic neurons in mid-thoracic cord show plastic changes in their morphology. There is also extensive loss of synaptic input from the brain, leaving these neurons profoundly denervated in the acute phase of injury. Our recent studies on sympathetic preganglionic neurons in lower thoracic and upper lumbar cord that regulate the pelvic viscera suggest that these neurons are not so severely affected by spinal cord injury. Spinal interneurons appear to contribute most of the synaptic input to these neurons so that injury does not result in extensive denervation. Since intraspinal circuitry remains intact after injury, drug treatments targeting these neurons should help to normalize sympathetically mediated pelvic visceral reflexes. Furthermore, sympathetic pelvic visceral control may be more easily restored after an injury because it is less dependent on the re-establishment of direct synaptic input from regrowing brain axons.

Segmental organization of spinal reflexes mediating autonomic dysreflexia after spinal cord injury

Spinal cord injuries above mid-thoracic levels can lead to a potentially life-threatening hypertensive condition termed autonomic dysreflexia that is often triggered by distension of pelvic viscera (bladder or bowel). This syndrome is characterized by episodic hypertension due to sudden, massive discharge of sympathetic preganglionic neurons in the thoracolumbar spinal cord. This hypertension is usually accompanied by bradycardia, particularly if the injury is caudal to the 2nd to 4th thoracic spinal segments. The development of autonomic dysreflexia is correlated with aberrant sprouting of peptidergic afferent fibers into the spinal cord below the injury. In particular, sprouting of nerve growth factor-responsive afferent fibers has been shown to have a major influence on dysreflexia, perhaps by amplifying the activation of disinhibited sympathetic neurons. Using a model of noxious bowel distension after complete thoracic spinal transection at the 4th thoracic segment in rats, we selectively altered C-fiber sprouting, at specified spinal levels caudal to the injury, with microinjections of adenovirus encoding the growth-promoting nerve growth factor or the growth-inhibitory semaphorin 3A. This was followed by assessment of physiological responses to colorectal distension and subsequent histology. Additionally, anterograde tract tracers were injected into the lumbosacral region to compare the extent of labeled propriospinal rostral projections in uninjured cords to those in cords after complete 4th thoracic transection. In summary, overexpression of chemorepulsive semaphorin 3A impeded C-fiber sprouting in lumbosacral segments and mitigated hypertensive autonomic dysreflexia, whereas the opposite results were obtained with nerve growth factor overexpression. Furthermore, compared to naïve rats, there were significantly more labeled lumbosacral propriospinal projections rostrally after thoracic injury. Collectively, our findings suggest that distension of pelvic viscera increases the excitation of expanded afferent terminals in the disinhibited lumbosacral spinal cord. This, in turn, triggers excitation and sprouting of local propriospinal neurons to relay visceral sensory stimuli and amplify the activation of sympathetic preganglionic neurons in the thoracolumbar cord, to enhance transmission in the spinal viscero-sympathetic reflex pathway. These responses are manifested as autonomic dysreflexia.

Autonomic dysreflexia after spinal cord injury: central mechanisms and strategies for prevention

Spinal reflexes dominate cardiovascular control after spinal cord injury (SCI). These reflexes are no longer restrained by descending control and they can be impacted by degenerative and plastic changes within the injured cord. Autonomic dysreflexia is a condition of episodic hypertension that stems from spinal reflexes initiated by sensory input entering the spinal cord caudal to the site of injury. This hypertension greatly detracts from the quality of life for people with cord injury and can be life-threatening. Changes in the spinal cord contribute substantially to the development of this condition. Rodent models are ideal for investigating these changes. Within the spinal cord, injury-induced plasticity leads to nerve growth factor (NGF)-dependent enlargement of the central arbor of a sub-population of sensory neurons. This enlarged arbor can provide increased afferent input to the spinal reflex, intensifying autonomic dysreflexia. Treatments such as antibodies against NGF can limit this afferent sprouting, and diminish the magnitude of dysreflexia. To assess treatments, a compression model of SCI that leads to progressive secondary damage, and also to some white matter sparing, is very useful. The types of spinal reflexes that likely mediate autonomic dysreflexia are highly susceptible to inhibitory influences of bulbospinal pathways traversing the white matter. Compression models of cord injury reveal that treatments that spare white matter axons also markedly reduce autonomic dysreflexia. One such treatment is an antibody to the integrin CD11d expressed by inflammatory leukocytes that enter the cord acutely after injury and cause significant secondary damage. This antibody blocks integrin-mediated leukocyte entry, resulting in greatly reduced white-matter damage and decreased autonomic dysreflexia after cord injury. Understanding the mechanisms for autonomic dysreflexia will provide us with strategies for treatments that, if given early after cord injury, can prevent this serious disorder from developing.

Transient blockade of the CD11d/CD18 integrin reduces secondary damage after spinal cord injury, improving sensory, autonomic, and motor function

The early inflammatory response to spinal cord injury (SCI) causes significant secondary damage. Strategies that nonselectively suppress inflammation have not improved outcomes after SCI, perhaps because inflammation has both adverse and beneficial effects after SCI. We have shown that the selective, time-limited action of a monoclonal antibody (mAb) to the CD11d subunit of the CD11d/CD18 integrin, delivered intravenously during the first 48 hr after SCI in rats, markedly decreases the infiltration of neutrophils and delays the entry of hematogenous monocyte-macrophages into the injured cord. We hypothesized that this targeted strategy would lead to neuroprotection and improved neurological outcomes. In this study the development of chronic pain was detected in rats by assessing mechanical allodynia on the trunk and hindpaws 2 weeks to 3 months after a clinically relevant clip-compression SCI at the twelfth thoracic segment. The anti-CD11d mAb treatment reduced this pain by half. Motor performance also improved as rats were able to plantar-place their hindpaws and use them for weight support instead of sweeping movements only. Improved cardiovascular outcome was shown after SCI at the fourth thoracic segment by significant decreases in autonomic dysreflexia. Locomotor performance was also improved. These functional changes correlated with significantly greater amounts and increased organization of myelin and neurofilament near the lesion. The improved neurological recovery after the specific reduction of early inflammation after SCI demonstrates that this selective strategy increases tissue at the injury site and improves its functional capacity. This early neuroprotective treatment would be an ideal foundation for building later cell-based therapies.