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Noninvasive transcranial magnetic stimulation (TMS) of the motor cortex was used to evoke electromyographic (EMG) responses in persons with spinal cord injury (n = 97) and able-bodied subjects (n = 20, for comparative data). Our goal was to evaluate, for different levels and severity of spinal cord injury, potential differences in the distribution and latency of motor responses in a large sample of muscles affected by the injury. The spinal cord injury (SCI) population was divided into subgroups based upon injury location (cervical, thoracic, and thoracolumbar) and clinical status (motor-complete versus motor-incomplete). Cortical stimuli were delivered while subjects attempted to contract individual muscles, in order to both maximize the probability of a response to TMS and minimize the response latency. Subjects with motor-incomplete injuries to the cervical or thoracic spinal cord were more likely to demonstrate volitional and TMS-evoked contractions in muscles controlling their foot and ankle (i.e., distal lower limb muscles) compared to muscles of the thigh (i.e., proximal lower limb muscles). When TMS did evoke responses in muscles innervated at levels caudal to the spinal cord lesion, response latencies of muscles in the lower limbs were delayed equally for persons with injury to the cervical or thoracic spinal cord, suggesting normal central motor conduction velocity in motor axons caudal to the lesion. In fact, motor response distribution and latencies were essentially indistinguishable for injuries to the cervical or thoracic (at or rostral to T10) levels of the spine. In contrast, motor-incomplete SCI subjects with injuries at the thoracolumbar level showed a higher probability of preserved volitional movements and TMS-evoked contractions in proximal muscles of the lower limb, and absent responses in distal muscles. When responses to TMS were seen in this group, the latencies were not significantly longer than those of able-bodied (AB) subjects, strongly suggestive of "root sparing" as a basis for motor function in subjects with injury at or caudal to the T11 vertebral body. Both the distribution and latency of TMS-evoked responses are consistent with highly focal lesions to the spinal cord in the subjects examined. The pattern of preserved responsiveness predominating in the distal leg muscles is consistent with a greater role of corticospinal tract innervation of these muscles compared to more proximal muscles of the thigh and hip.

A device is described which combines arm crank ergometry and neuromuscular electrical stimulation (NMS) delivered at different phases of the crank cycle. Details of the device including circuit schematics are shown. The device was evaluated by non-paralyzed subjects for its operational safety and by tetraplegic subjects for its effectiveness as a muscle-strengthening tool. All subjects showed improvement in one or more of their manual muscle scores. The most dramatic increased motor score occurred in the triceps muscle group. There was an average increase in the manual muscle score of 1.1 +/- 0.2 for the left triceps and 0.7 +/- 0.1 for the right triceps after eight weeks of NMS assisted exercise. No adverse effects were experienced and it appears to meet safety considerations necessary for this group of individuals. Preliminary observations indicate that an eight-week exercise protocol that utilizes this device can be beneficial for this population.

Objective: To describe performance parameters and effects on anthropometric measures in spinal cord injured subjects training with the Parastep® 1 system. Design: Before-after trial. Setting: Human spinal cord injury applied research laboratory. Participants: Thirteen men and 3 women with thoracic (T4–T11) motor-complete spinal cord injury: mean age, 28.8yrs; mean duration postinjury, 3.8yrs. Intervention: Thirty-two functional neuromuscular stimulation ambulation training sessions using a commercially available system (Parastep-1). The hybrid system consists of a microprocessor-controlled stimulator and a modified walking frame with finger-operated switches that permit the user to control the stimulation parameters and activate the stepping. Outcome Measures: Distance walked, time spent standing and walking, pace, circumferential (shoulders, chest, abdomen, waist, hips, upper arm, thigh, and calf) and skinfold (chest, triceps, axilla, subscapular, supraillium, abdomen, and thigh) measurements, body weight, thigh cross-sectional area, and calculated lean tissue. Results: Statistically significant changes in distance, time standing and walking, and pace were found. Increases in thigh and calf girth, thigh cross-sectional area, and calculated lean tissue, as well as a decrease in thigh skinfold measure, were all statistically significant. Conclusions: The Parastep® 1 system enables persons with thoracic-level spinal cord injuries to stand and ambulate short distances but with a high degree of performance variability across individuals. The factors that influence this variability have not been completely identified.

Previous reports have described significant limitations in the daily use of functional neuromuscular stimulation (FNS) ambulation systems by persons with spinal cord injuries (SCI). The potential application of these devices to provide physiological benefits as an exercise modality has prompted a reconsideration of the technology. However, the acute physiological effects related to the use of FNS systems have not been thoroughly examined. The purpose of this study was to investigate the relationships of oxygen consumption (VO2), heart rate (HR), and ratings of perceived exertion (RPE) during FNS ambulation by persons with SCI paraplegia. Eleven persons with thoracic level paraplegia, aged 21.5 to 38.0 years, participated in an incremental FNS ambulation test. Metabolic measures were collected continuously via open circuit spirometry as the subjects performed a series of ambulation passes of progressively increasing pace. At the end of each ambulation pass, HR and RPE measures were collected. The test was terminated when either the subjects judged the effort to be maximal or when the investigators deemed the effort to be maximal based on HR. A strong linear relationship was documented between the VO2 and HR measures of all subjects throughout subpeak levels of FNS ambulation. RPE did not vary proportionally with VO2 until relatively high levels of exercise intensity were reached. This study indicates that HR, but not RPE, is an appropriate indicator of exercise intensity for persons with SCI paraplegia using a FNS ambulation system.

Force was measured from triceps brachii motor units in individuals with chronic cervical spinal cord injury (SCI) and in able-bodied (A-B) control subjects using spike-triggered averaging (175 and 48 units, respectively). Eleven percent of units from the SCI population generated normal electromyograms (EMGs) but exerted no measurable force, 65% generated force comparable to the control data, while 24% were stronger than usual. Weak units probably reflect disuse. Muscle shortening, densely innervated territories, and polyphasic EMG potentials suggested strong units resulted from intact axons sprouting to reinnervate denervated muscle. Many units from SCI subjects had faster than normal contraction times (CTs). The force and CT distributions from the SCI and A-B populations differed significantly. Motor units of SCI subjects were recruited in order of increasing force output and increasing contraction time. Chronic cervical SCI therefore seems to alter the expected triceps brachii motor unit force-speed relations.

The effectiveness of neuromuscular stimulation (NMS)-assisted arm ergometry for strengthening triceps brachii was evaluated in 34 cervical spinal cord injured persons. Group I (n = 12) received eight weeks of NMS-assisted ergometry. Group II (n = 11) received four weeks of NMS-assisted ergometry followed by four weeks of arm ergometry alone. Group III (N = 11) received only arm ergometry (control group). Seventeen of 24 muscles in Group I subjects had improved manual muscle test scores after eight weeks, compared with 10 of 22 Group II muscles and five of 22 Group III muscles. Including only muscles with initial scores < or = 3, Group I demonstrated significant improvements versus Group III after four weeks (p < .003) and after eight weeks (p < .0005) of exercise. A difference was also found between Groups II and III (p < .03) after eight weeks. These results suggest that NMS-assisted ergometry is effective for strengthening voluntary triceps muscle contractions in tetraplegics.

A test of locomotor behavior using the coordinates of ipsilateral limb positions of rats walking on a moving treadmill is described. Specific points on the forelimb and hindlimb were digitized from video records for 20-sec continuous sequences of locomotion, and step periods and step distances were calculated. The extent to which a given limb position would predict its own position--or the position of another limb--at different points in time was mathematically determined by autocorrelation and cross-correlation, respectively. Autocorrelation of position data was performed using a three-step window and the standard formula for correlating phasic data. A novel method of data preparation, which included normalization of the step data to eliminate variability introduced by differences in step period length, was used prior to cross-correlations of forelimb to hindlimb positions. Rats walking at 0.10, 0.15, and 0.25 m/sec had high limb autocorrelations, comparable forelimb/hindlimb phase relationships, and consistently high average cross-correlation coefficients. This analysis has resulted in the quantification of rat locomotor behavior in terms of the degree of limb movement rhythmicity and the strength of the forelimb/hindlimb coordination, and has provided baseline data for comparisons with spinal cord-injured rats that have retained or recovered alternating hindpaw movements.

We examined Hoffmann (H) and tendon (T) reflexes in 3 populations of adult subjects: acute SCI (2 weeks post injury), controls, and chronic SCI (1 year post injury). We further investigated the effects of continuous tendon vibration and different stimulus rates on the size of evoked H reflexes in these subject populations. All reflex amplitudes were expressed as a function of the maximum direct muscle response (M wave), to allow comparison between subjects. Both H and T reflexes were successfully elicited from all subjects examined, including those in 'spinal shock.' Tendon vibration caused a marked attenuation of H reflexes in acute SCI subjects, intermediate attenuation in controls, and relatively little effect in the chronic SCI group. H reflexes showed greatest attenuation for a given stimulus rate in acute SCI subjects compared to controls (intermediate attenuation) or chronic SCI (limited attenuation) subjects. Both rate sensitivity and vibration influence have been linked to presynaptic inhibitory mechanisms. We suggest that spinal cord injury disrupts the supraspinal influence over segmental interneurons mediating presynaptic inhibition, and that the hyporeflexia associated with 'spinal shock' is due in part to a substantial increase in the efficacy of presynaptic inhibition. Conversely, over time the level of presynaptic inhibition of ankle extensor Ia input in SCI subjects declines to levels less than those of control subjects, contributing to the enhancement of spinal reflexes consistent with the clinical state of 'spasticity' seen in chronic SCI.

This study tested the efficacy of biofeedback when administered in conjunction with physical rehabilitation therapy to chronic C5–7 quadriplegics. Triceps brachii, biceps brachii, wrist extensors, and wrist flexors were tested. The studied muscles were compromised by the injury to varying degrees, but were often still useful to these subjects. An exercise regimen was given to all subjects. In addition, subjects were separated into two groups: those who received biofeedback training and those who did not. Two measures of performance were tested: manual muscle scores and functional activities scores. Both groups scored significantly higher on both measures after 12 weeks of rehabilitation therapy. We found no evidence that biofeedback generally increased the amount of improvement seen. These results do not support the routine use of biofeedback in the treatment of chronic spinal cord injury, but rather further stress the importance of exercise therapy for such injuries.

In a large, single-center study of subjects with acute traumatic spinal cord injury (SCI), we describe the sample population with respect to gender, age, cause of injury, and severity of injury, to see whether these properties are similar to those of other large-scale studies of acute SCI conducted in the past.As part of a study to examine the natural pattern of recovery after acute SCI (presented elsewhere), descriptive information was gathered in relation to subject population and injury properties.A total of 229 subjects were recruited. The study population had a higher percentage of women and a higher mean age of men and women than those of most other published studies of acute SCI. A greater percentage of incomplete subjects was also encountered. The incidence of gunshot injury as a cause of SCI was considerably lower in this study than had been the case 10 years previously in Dade County, Florida.The demography of acute SCI within a major urban center of South Florida suggests a trend toward less severe injury than in years past. These findings support the development of animal models for testing SCI treatment that include cohorts having mild to moderate injury severity, in order to achieve greater clinical relevance.

Objective Previous reports from our laboratory have described short-latency contractions in muscles of the distal upper limb following stimulation of lower limb nerves or skin in persons with injury to the cervical spinal cord. It takes 6 or more months for interlimb reflexes (ILR) to appear following acute spinal cord injury (SCI), suggesting they might be due to new synaptic interconnections between lower limb sensory afferents and motoneurons in the cervical enlargement. In this study, we asked if once formed, the strength of these synaptic connections increased over time, a finding that would be consistent with the above hypothesis. Methods We studied persons with sub-acute and/or chronic cervical SCI. ILR were elicited by brief trains of electrical pulses applied to the skin overlying the tibial nerve at the back of the knee. Responses were quantified based on their presence or absence in different upper limb muscles. We also generated peri-stimulus time histograms for single motor unit response latency, probability, and peak duration. Comparisons of these parameters were made in subjects at sub-acute versus chronic stages post-injury. Results In persons with sub-acute SCI, the probability of seeing ILR in a given muscle of the forearm or hand was low at first, but increased substantially over the next 1–2 years. Motor unit responses at this sub-acute stage had a prolonged and variable latency, with a lower absolute response probability, compared to findings from subjects with chronic (i.e. stable) SCI. Conclusions Our findings demonstrate that interlimb reflex activity, once established after SCI, shows signs of strengthening synaptic contacts between afferent and efferent components, consistent with ongoing synaptic plasticity. Significance Neurons within the adult human spinal cord caudal to a lesion site are not static, but appear to be capable of developing novel—yet highly efficacious—synaptic contacts following trauma-induced partial denervation. In this case, such contacts between ascending afferents and cervical motoneurons do not appear to provide any functional benefit to the subject. In fact their presence may limit the regenerative effort of supraspinal pathways which originally innervated these motoneurons, should effort in animal models to promote regeneration across the lesion epicenter be successfully translated to humans with chronic SCI.

Objective: Use the tendon reflex to examine spinal cord excitability after acute spinal cord injury (SCI), relating excitability findings to prognosis. Methods: We conducted repeated measures of reflex responses to mechanical taps at the patellar and Achilles tendons of the lower limbs, and the wrist flexor tendons of the upper limbs in persons with acute SCI, beginning as early as the day of injury. The single largest EMG response (peak-to-peak) for each site was recorded. Subjects were compared based on level of injury and final neurologic status of lower limb motor function (i.e. absence of any voluntary recruitment in a lower limb muscle: motor-complete; voluntary recruitment in 1 or more lowerlimb muscles: motor-incomplete). Results: We studied 229 subjects with acute SCI. Persons with injury to the cervical or thoracic spinal cord and who were (or became) motor-incomplete showed large tendon responses, even at the time of initial evaluation. In combination with larger tendon response amplitudes, the presence of the ‘crossed-adductor’ response to patellar tendon taps at the acute stage was highly predictive of functional motor recovery following SCI. In marked contrast, tendon responses were small (e.g. , 0.1 mV) or absent in persons with acute, motorcomplete injury (and which remained motor-complete), and the crossed-adductor response was never seen. Reflex amplitudes and the incidence of the crossed-adductor response increased somewhat over time in persons with motor-complete SCI, but did not approach the values seen in motor-incomplete subjects. Conclusions: Taken together, tendon response amplitude and reflex spread were sensitive and specific indicators of preserved supraspinal control over lower limb musculature in subjects with acute SCI. A simple algorithm using these outcome measures predicted a ‘motorcomplete’ status with 100% accuracy, and a motor-incomplete status with accuracy exceeding 91%. q 2004 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.

Objective: Multi-channel electromyogram (EMG) was used to examine the pattern and time-course of voluntary contraction recovery in subjects with acute traumatic spinal cord injury (SCI), concentrating on the latest time after injury at which a given muscle would begin to show voluntary recruitment. Methods: We conducted repeated measures of voluntary contractions of 12 lower limb muscles (for all subjects) and 12 upper-limb muscles (for subjects with cervical injury), beginning within days of the injury and extending for 1 or more years post-injury. The EMG interference pattern was scored in a blinded fashion from tape records. Results: We recruited 229 subjects, including 152 from whom repeated measures were made. Several different patterns of recovery were identified. For persons with motor-incomplete injury to the cervical or thoracic spine, EMG recruitment had not yet occurred by 5 weeks post-injury in roughly 1/2 of all lower limb muscles, and prolonged delays between injury and recruitment onset were sometimes seen. Injury to the thoracolumbar spine was frequently associated with very long delays (i.e. . 1 year) between injury and resumption of volitional contraction of distal lower limb muscles. Discussion: The incidence of neurologically incomplete SCI is rising. In such subjects, delays of 1 or more months between injury and the onset of voluntary contraction are common for muscles of the distal upper limbs (for cervical injury) and lower limbs. Given the abbreviated period of in-patient rehabilitation now routine in the United States, these subjects in particular will benefit from frequent follow-up evaluations to assess spontaneous recovery and design appropriate rehabilitation strategies to maximize functional independence. Moreover, the potential for delayed recovery must be considered when designing and implementing novel clinical interventions for treating SCI, to better differentiate between spontaneous and treatment-related improvements in neurologic function. q 2004 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.

Object. The authors attempted to determine if there is a significant relationship between the incidence of medical complications and the prophylactic use of methylprednisolone (MP) during spine surgery in patients with acute spinal cord injury (SCI) who had already received MP on hospital admission (typically in the setting of an Emergency Room/Trauma Center). Methods. The authors studied 73 patients with acute SCI who were admitted to the hospital for at least 7 days postinjury. All patients 1) received a 24-hour regimen of MP in the acute period of hospitalization; and 2) underwent surgery to stabilize the spine and/or decompress the spinal cord. Patients were separated into two groups on the basis of whether they received additional MP therapy during spine surgery. A chart review was conducted retrospectively to determine the incidence of complications up to 6 weeks postinjury. Muscle strength and American Spinal Injury Association grades were determined prospectively throughout the follow-up period. In patients who received two courses of MP following acute SCI (one at initial hospitalization and one during surgery), a significantly increased probability of complications was demonstrated compared with those who received no MP therapy during surgery. This was particularly evident when the incidences of serious complications were compared. Conclusions. Prophylactic use of MP as a neuroprotective agent during spine surgery in patients with acute SCI should be avoided in those in whom MP was administered on admission to the hospital.

Persons with long-standing injury to the cervical spinal cord resulting in complete or partial paralysis typically develop a wide spectrum of involuntary movements in muscles receiving innervation caudal to the level of injury. We have previously shown that these movements include brief and discrete contraction of muscles in the hand and forearm in response to innocuous sensory stimulation to the feet and legs, but we have been unable to replicate these interlimb reflexes in able- bodied subjects. Properties of these muscle responses indicate that the synaptic contacts between ascending sensory fibres and motor neurones of the cervical enlargement are more efficacious than normal. If these connections are present at all times, and require the more rostrally-placed spinal cord injury to allow their emergence, one might expect their appearance relatively soon following injury, as has been shown for studies of 'latent' synapses. Conversely, delayed appearance of these interlimb reflexes would suggest either the development of new synaptic connections or a profound strengthening of existing circuits in the cervical spinal cord due to a combination of afferent target loss and motor neurone denervation from motor tracts originating rostral to the injury site. In this study, we used repeated examinations of persons with acute injury to the cervical spinal cord to examine the time post-injury at which interlimb reflexes are first seen. Using tibial nerve stimulation at the knee as a screening test, a total of 24 subjects were found to develop interlimb reflexes following spinal cord injury. Latencies between stimulation and EMG were as brief as 32 ms for muscles of the forearm and 44 ms for muscles in the hand. These minimal delays all but rule out a supraspinal route for these interlimb reflexes. Interlimb reflexes first became evident no sooner than approximately 6 months following injury, and in some individuals were not seen until well over 1 year post-injury. Enhanced lower limb segmental excitability had emerged in nearly all of these subjects weeks or months prior to the first appearance of interlimb reflexes, arguing against a manifestation of traditional post-traumatic spasticity as a basis for this activity. This prolonged delay between time of injury and emergence of interlimb reflex activity lends support to the hypothesis that this activity represents an example of plasticity-and perhaps 'regenerative sprouting'-in the human spinal cord following traumatic injury.

The purpose of this study was to compare the electromyography (EMG) score during contraction of a given muscle to the independently measured manual muscle test (MMT) score for that same muscle (or muscle group), to determine whether EMG measures could serve as a reasonable approximation of muscle contraction force in persons with acute spinal cord injury (SCI).We examined the strength of relationship between surface-recorded EMG and estimated muscle strength using the MMT in a population of 45 subjects with acute (1 week) traumatic SCI. Eight different muscle groups were compared in each individual; measures were repeated on these subjects approximately 2 months later. A 6-point numeric index was used for assignment of EMG scores, all of which were done in a blinded fashion by 1 investigator from tape-recorded evaluations.Nearly all of the individual muscle comparisons led to positive and significant (P.01) correlations between EMG and MMT scores, at both the acute and subacute time points following injury.These findings support the use of EMG scoring as an indicator of recovery of volitional strength following SCI in a given subject. However, caution must be used when attempting to extrapolate EMG scores to absolute forces or when comparing EMG scores among different subjects.

Objectives : To examine the basis for delay in the excitatory effects of transcranial magnetic stimulation (TMS) of motor cortex on motoneuron pools of muscles left partially-paralyzed by traumatic spinal cord injury (SCI). Methods : The effect of subthreshold transcranial magnetic stimulation (TMS) on just-suprathreshold H-reflex amplitude was examined in subjects ( n =10) with incomplete cervical SCI, and in able-bodied (AB) subjects ( n =20) for comparison. EMG activity was recorded from the soleus and the abductor hallucis muscles, and H-reflex was elicited by stimulation of the tibial nerve behind the knee. Comparison of the peak-to-peak amplitude of the TMS-conditioned H-reflex to that of the H-reflex alone (i.e. unconditioned H-reflex) was made for different conditioning-test intervals with multivariate analysis of variance and (when called for) t testing. Results : The absolute latencies of motor responses to suprathreshold TMS delivered during a weak voluntary contraction of the soleus and abductor hallucis were significantly prolonged in the SCI group relative to AB subjects. For the TMS-conditioned H-reflex, the time-course effect of TMS on the H-reflex amplitude in different AB subjects included an early effect (typically facilitation, but occasionally inhibition) seen between −5 and 0 ms, followed by a later period (i.e. >5 ms) of H-reflex facilitation. In contrast, the earliest indication of a TMS effect on H-reflex excitability in SCI subjects was between 5 and 10 ms after TMS. This difference between SCI and AB subjects of approximately 10 ms was similar to the prolongation of TMS-evoked response latencies in the soleus and the abductor hallucis muscles of the SCI subjects. Conclusions : The results suggest that motor conduction slowing after traumatic SCI most likely occurs across the population of the descending tract axons mediating the TMS-evoked motor responses.

Numerous methods have been pursued to evaluate function in central motor pathways during surgery in the anesthetized patient. At this time, no standard has emerged, possibly because each of the methods described to date requires some degree of compromise and/or lacks sensitivity.Object. The goal of this study was to develop and evaluate a protocol for intraoperative monitoring of spinal motor conduction that: 1) is safe; 2) is sensitive and specific to motor pathways; 3) provides immediate feedback; 4) is compatible with anesthesia requirements; 5) allows monitoring of spontaneous and/or nerve root stimulus—evoked electromyography; 6) requires little or no involvement of the surgical team; and 7) requires limited equipment beyond that routinely used for somatosensory evoked potential (SSEP) monitoring. Using a multipulse electrical stimulator designed for transcranial applications, the authors have developed a protocol that they term “threshold-level” multipulse transcranial electrical stimulation (TES).Methods. Patients considered at high risk for postoperative deficit were studied. After anesthesia had been induced and the patient positioned, but prior to incision, “baseline” measures of SSEPs were obtained as well as the minimum (that is, threshold-level) TES voltage needed to evoke a motor response from each of the muscles being monitored. A brief, high-frequency pulse train (three pulses; 2-msec interpulse interval) was used for TES in all cases. Data (latency and amplitude for SSEP; threshold voltage for TES) were collected at different times throughout the surgical procedure. Postoperative neurological status, as judged by evaluation of sensory and motor status, was compared with intraoperative SSEP and TES findings for determination of the sensitivity and specificity of each electrophysiological monitoring technique.Of the 34 patients enrolled, 32 demonstrated TES-evoked responses in muscles innervated at levels caudal to the lesion when examined after anesthesia induction and positioning but prior to incision (that is, baseline). In contrast, baseline SSEPs could be resolved in only 25 of the 34 patients. During surgery, significant changes in SSEP waveforms were noted in 12 of these 25 patients, and 10 patients demonstrated changes in TES thresholds. Fifteen patients experienced varying degrees and durations of postoperative neurological deficit. Intraoperative changes in TES thresholds accurately predicted each instance of postoperative motor weakness without error, but failed to predict four instances of postoperative sensory deficit. Intraoperative SSEP monitoring was not 100% accurate in predicting postoperative sensory status and failed to predict five instances of postoperative motor deficit. As a result of intraoperative TES findings, the surgical plan was altered or otherwise influenced in six patients (roughly 15% of the sample population), possibly limiting the extent of postoperative motor deficit experienced by these patients.Conclusions. This novel method for intraoperative monitoring of spinal motor conduction appears to meet all of the goals outlined above. Although the risk of postoperative motor deficit is relatively low for the majority of spine surgeries (for example, a simple disc), high-risk procedures, such as tumor resection, correction of vascular abnormalities, and correction of major deformities, should benefit from the virtually immediate and accurate knowledge of spinal motor conduction provided by this new monitoring approach.

Muscle weakness and failure of central motor drive were assessed in triceps brachii muscles of individuals with chronic cervical spinal cord injury (SCI) and able-bodied controls. Electrical stimuli were applied to the radial nerve during rest and during triceps submaximal and maximal voluntary contractions (MVCs). The mean forces and integrated EMGs generated by SCI subjects during MVCs were significantly less than those produced by controls (P < 0.01), with 74 and 71% of muscles generating

Muscle recruitment after central cord syndrome (CCS), a cervical spinal cord injury leading to a weaker motor function in the upper limbs versus the lower limbs, was examined in 14 individuals by means of voluntary muscle contractions and transcranial magnetic stimulation (TMS). Previously obtained data from able-bodied (AB) and non-CCS spinal cord injured subjects were used for comparison. Surface EMG was recorded from as many as six pairs of affected muscles. Individual muscle EMG activity was scored from 0 to 5. Cortical stimulation was applied while subjects maintained a weak contraction in each muscle. When CCS subjects attempted to produce a maximal voluntary contraction of an isolated muscle, this frequently resulted in cocontraction of nonsynergists in the same limb or/and in other limbs. Although the EMG scores in both upper and lower extremity muscles improved within postinjury time, in general, the lower extremity muscles, particularly the distal ones, demonstrated better recovery than the upper extremity muscles. CCS and AB subjects showed a similar high probability of "well-defined" responses to TMS (amplitude >150 microV) in all studied muscles. In contrast, latencies to TMS-evoked motor responses were prolonged by significant amounts after CCS. The delays in muscle responses were not significantly different from those observed in subjects with more severe cervical injury. Despite improvement in EMG scores, repeated measurements of TMS-evoked muscle response latencies in the same CCS subjects did not reveal significant shortening in central conduction latency. This argues against remyelination as an important contributor to the recovery process.

Objective: To determine if the bone mineral density loss seen after spinal cord injury (SCI) is reversed by a walking program using the Parastep® 1 system. Design: Before-after trial. Setting: Human SCI applied research laboratory. Participants: Thirteen men and 3 women with thoracic motor- and sensory-complete SCI, mean age 28.8yrs, mean duration postinjury 3.8yrs. Intervention: Thirty-two functional neuromuscular stimulation (FNS) ambulation training sessions using a commercially available system (Parastep® 1). This system consists of a microprocessor-controlled stimulator and a modified walking frame with finger-operated switches that permit the user to control the stimulation parameters and activate the stepping. Outcome Measure: Bone mineral density at the femoral head, neck, and Ward's triangle measured using a Lunar®DP3 dual-photon densitometer. Results: No significant change in bone mineral density was found using repeated measures analyses of variance. Conclusions: Axial loading combined with muscle stimulation and resistive exercise does not result in significant changes in bone mineral density in persons with complete paraplegia.

In persons who have sustained severe injuries to the cervical spinal cord, electrical stimulation of mixed peripheral nerves in a lower limb can evoke short-latency, bilateral motor responses in muscles of the distal upper limbs; such motor responses have been termed interlimb reflexes. In the present study, we investigated the role that cutaneous stimulation plays in evoking interlimb reflexes. Fifteen subjects with chronic injury (> 1 year) to the cervical spinal cord were investigated. Single motor unit activity was recorded from a number of distal upper limb muscles. The lower limb cutaneous area within which stimulation recruited a given motor unit of the upper limb was defined as that motor unit's 'receptive field'. Activity from a total of 48 single motor units was analyzed. The majority of motor units responded to light touch, individual hair movement, and thermal (hot and cold) stimulation. Excitatory responses were observed bilaterally, although contralateral responses predominated. Stimulation occasionally resulted in inhibition of a spontaneously active motor unit. Receptive fields varied a great deal in size, with proximal locations being larger than those encountered in more distal lower limb locations (i.e. the toes). The spinocervical tract is a possible candidate for mediating some portion of these interlimb reflexes, the origin of which may be due to new growth (regenerative sprouting) in the spinal cord caudal to a severe injury.

Intraspinal injections of lysolecithin were used to produce unilateral demyelination in the dorsal columns of the rat spinal cord. The purpose of this study was to evaluate the effects of demyelination on the conductive properties of axons belonging to a spinal pathway of known origin and site of termination. At 5 and 50 day intervals following injections, animals were prepared for acute experiments during which recordings of tibial nerve evoked potentials were made from the surface of the lumbar spinal cord (L5-L6) and nucleus gracilis (0.5-1.0 mm caudal to obex). Latency, duration, and strength of potentials were evaluated in control (uninjected) and lysolecithin-injected animals. The analysis of these potentials showed increases in latency and decreases in duration and strength of responses recorded 5 days after lysolecithin injections. Animals examined 50 days postinjection showed a decreased latency and increased duration and strength of responses compared to those recorded 5 days postinjection. Ultrastructural examination of lysolecithin injection sites showed these improvements to parallel the remyelination of axons by oligodendrocytes and Schwann cells. The improvement in physiologic characteristics of evoked potentials coupled with the remyelination of dorsal column axons supports the conclusion that remyelination of chemically demyelinated axons is an important factor in reestablishing the functional connectivity of demyelinated axons.

Response and receptive field properties were evaluated for 62 spinomesencephalic tract cells in the upper cervical spinal cord (C1-C3) of cats anesthetized with sodium pentobarbital and alpha-chloralose. Recordings were made from cells in laminae I-VIII and X contralateral to antidromic stimulating electrodes positioned in the rostral, caudal and intercollicular region of the midbrain. The mean antidromic threshold for all cells was 185 +/- 132 microA, and conduction velocities ranged from 2.3 to 38.6 m/sec. Twelve cells were backfired from both midbrain and diencephalic stimulation sites. Receptive fields ranged from simple, i.e., ipsilateral forelimb or face, to complex, i.e., excitatory and/or inhibitory responses from large portions of the body. Peripheral receptive fields included muscles, joints, cornea, dura, forelimbs, hind limbs, tail, and/or testicles. Five functional classes of cells were observed: (a) wide dynamic range (14 cells); (b) high threshold (2 cells): (c) low threshold (4 cells); (d) deep/tap (11 cells); and (e) non-responsive (31 cells). Eight cells were evaluated for responses to different doses (5-150 micrograms) of intravenous (i.v.) serotonin. Two of the 8 cells exhibited excitatory effects, whereas 2 cells classified as deep/tap and 4 cells classified as non-responsive were not affected. The results of this study have shown the upper cervical component of the spinomesencephalic tract is made up of a heterogenous population of cells involved in the integration of varied inputs from large portions of the body. It is proposed that the large population of SMT cells in the upper cervical spinal cord may be involved in pain mechanisms, especially those related to the affective consequences of acute and chronic pain.

Pieces of fetal rat lumbar spinal cord were transplanted into the anterior eye chamber of adult rat hosts. At least seven months later, extracellular single-unit recordings of spontaneously active graft neurons were made prior to and during the superfusion of either glutamate orγ-aminobutyric acid (GABA). Superfusion of glutamate produced an increase (five cells), decrease (three cells), or had no effect (two cells) on the firing rate of neurons tested. Superfusion of GABA decreased the firing rate of all twelve neurons tested, while superfusion of the GABA receptor antagonist bicuculline increased the firing rates of all eight neurons tested. The latency and magnitude of the responses to glutamate and GABA were not related to depth of the recording electrode below the graft surface. Together, these data suggest that the intraocular spinal cord graft is suitable for thein vivostudy of GABA and glutamate neuropharmacology.

Somatosensory information (concerning, e.g., touch, pressure, pain) from the head, face, and oral cavity are received by the endings of primary afferent neurons with processes in the fifth cranial (trigeminal) nerve, and with cell bodies in the trigeminal (or Gasserian) ganglion. The central axon terminals of these ganglion neurons synapse within the trigeminal nuclear complex (TN) in the brainstem (see Figure 1). This complex is a long, sausage-shaped set of subnuclei extending from the caudal pons to the caudal medulla. Its two major histologically defined subdivisions include the most rostral nucleus principalis or main sensory trigeminal nucleus (MTN) and the immediately caudal spinal nucleus of the fifth cranial nerve (SPV). SPV itself has been subdivided into three subnuclei, which from rostral to caudal levels, respectively, include subnucleus oralis (SO), subnucleus interpolaris (SI), and subnucleus caudalis (SC). The primary afferent fibers entering the brainstem from the trigeminal ganglion descend laterally along side of the entire long nuclear complex in the primary descending trigeminal tract (TT), projecting terminating fibers into the nuclear complex from MTN to the most caudal SC region of SPV. Axons of secondary afferent neurons in TN relay the information and sweep medially through the brainstem mostly to the contralateral side as they ascend to the ventrobasal complex of thalamus for final relay to somatosensory cortex.

A modified Golgi staining technique was used to study the neuronal morphology and organization of the fetal rat spinal cord which had developed in the anterior eye chamber of adult rat hosts. Individual neurons in spinal cord grafts displayed profiles which were strikingly similar to previously descibed spinal cord neurons stained in situ . Further, for the population of 464 graft neurons studied, the distributions of average cell body diameters and numbers of primary dendrites were comparable to those of previously published in situ studies. An internal organization of graft neurons was also observed. Similar-shaped neurons were grouped together, which made it possible to identify different regions within a graft, such that a comparison could be made with normal spinal cord morphology. These observations provide further evidence that the intraocular spinal cord graft is a suitable model for studying spinal cord growth, development, and plasticity and indicate that the Golgi stain may be useful for the quantitative study of concomitant changes in neuronal morphology.

Wire knife-cuts lesioning the descending trigeminal tract and trigeminal sensory nuclear complex at the level of subnucleus interpolaris significantly elevated response latencies to noxious thermal stimuli applied to one perioral locus of facial skin. Group analyses of four other ipsilateral sites did not reveal significant effects. Medial cuts, extensively damaging the sensory nuclear complex as well as the tract, were more likely to produce significant elevations than were lateral cuts. These results suggest that tractotomy does not result in complete facial analgesia in the rat, and that the effectiveness of tractotomy may in part be due to interruption of intranuclear trigeminal projections.

The hypoalgesic effects of lesions in the rat spinal trigeminal complex at the levels of subnucleus interpolaris and caudal subnucleus oralis were investigated. Lesions of the trigeminal tract, nucleus, or adjacent reticular formation resulted in significant elevations in escape latencies to noxious thermal stimulation of the ipsilateral perioral area. The nuclear lesions were significantly more effective in producing latency elevations than were the reticular formation lesions. Behavioral and anatomical evidence is presented suggesting that the mid-spinal trigeminal complex, including the ascending trigeminal intranuclear pathways, participate in perioral thermal nociception.

Morphine sulfate (0.75 μg) was microinjected into (rat) rostral and caudal trigeminal areas singly and simultaneously, using cannula-electrode combinations. Also, 0.5 μg or 1.0 μg of morphine was injected into nucleus reticularis paragi-gantocellularis (PGC). Both single trigeminal nuclear microinjections significantly elevated the latency to a defensive face-rub reaction to noxious facial heat, bilaterally. There was no summation effect with the conjoint injection of 1.5 μg total to rostral and caudal nuclear areas. The 0.5 μg injection in PGC had a significantly larger effect than did the 0.75 μg trigeminal injections. The caudal but not the rostral trigeminal injections did elevate the threshold for aversive reaction to caudal trigeminal nuclear stimulation of the injected tissue. This finding contrasts with the previously reported fact that as much as 1.0 μg of morphine in PGC has no effect on this aversive reaction threshold to brain stimulation.

A new technique is described for quantifying orofacial pain in unrestrained, freely moving animals. The key dependent variable is latency to a face-rubbing response executed with any paw. The response is elicited by heating a tiny resistor in contact with facial skin. The latency variability is significantly less than that of hot-plate/paw-lick and other measures. The measure precisely indexes effects of morphine, trigeminal complex lesions, and heat rate manipulations. For these reasons, the technique is potentially useful to all pain and analgesia researchers. Utilization of the face as site of nociceptive stimulation has special relevance for trigeminal studies.

Sagittal knife cuts were made interrupting efferent projections of either the rostral or the caudal trigeminal nuclear complex in the rat. Only rostral cuts resulted in significant, specific deficits in ipsilateral facial nociception. These results are not consistent with a well-known view which emphasizes only caudal nuclear projections as critical for orofacial pain.

Sagittal knife cuts were made medial to rostral trigeminal brainstem nuclei in 11 rats. These cuts resulted in significant group deficits in facial thermal nociception at only two of the 5 ipsilateral sites tested. The affected sites were close to the vibrissa and oral cavity, suggesting that rostral trigeminal projections signal anterior rather than more caudal facial nociception. Three rats were also tested for EEG arousal responsiveness to innocuous air puffs before and after the cuts at the same facial sites. Only one of the rats demonstrated a significant deficit at one of the 5 sites tested, suggesting that the rostral projections interrupted in this study are not necessary for innocuous facial sensation.