Spinal Cord Transection In Rats Research Articles

Changes in Motoneuron Properties and Synaptic Inputs Related to Step Training after Spinal Cord Transection in Rats

Although recovery from spinal cord injury is generally meager, evidence suggests that step training can improve stepping performance, particularly after neonatal spinal injury. The location and nature of the changes in neural substrates underlying the behavioral improvements are not well understood. We examined the kinematics of stepping performance and cellular and synaptic electrophysiological parameters in ankle extensor motoneurons in nontrained and treadmill-trained rats, all receiving a complete spinal transection as neonates. For comparison, electrophysiological experiments included animals injured as young adults, which are far less responsive to training. Recovery of treadmill stepping was associated with significant changes in the cellular properties of motoneurons and their synaptic input from spinal white matter [ipsilateral ventrolateral funiculus (VLF)] and muscle spindle afferents. A strong correlation was found between the effectiveness of step training and the amplitude of both the action potential afterhyperpolarization and synaptic inputs to motoneurons (from peripheral nerve and VLF). These changes were absent if step training was unsuccessful, but other spinal projections, apparently inhibitory to step training, became evident. Greater plasticity of axonal projections after neonatal than after adult injury was suggested by anatomical demonstration of denser VLF projections to hindlimb motoneurons after neonatal injury. This finding confirmed electrophysiological measurements and provides a possible mechanism underlying the greater training susceptibility of animals injured as neonates. Thus, we have demonstrated an "age-at-injury"-related difference that may influence training effectiveness, that successful treadmill step training can alter electrophysiological parameters in the transected spinal cord, and that activation of different pathways may prevent functional improvement.

Role of spinal metabotropic glutamate receptors in regulation of lower urinary tract function in the decerebrate unanesthetized rat

The role of spinal metabotropic glutamate receptors (mGluRs) in control of lower urinary tract functions was evaluated in rats using an mGluR antagonist administered via the intrathecal route. Cystometrograms in combination with external urethral sphincter (EUS) EMG recordings were performed on 13 decerebrate unanesthetized Sprague-Dawley female rats (n=6 for spinal cord intact rats; n=7 for spinal cord transected rats). In spinal cord intact rats, a group I/II mGluR antagonist, (+/-)-alpha-methyl-4-carboxyphenylglycine (MCPG), at doses of 3-30 microg, changed neither bladder nor EUS EMG activity, whereas a larger dose (100 microg) produced a significant facilitation of EUS EMG activity (41% increase in the peak activity) with little effect on bladder contractions. In chronically spinal cord transected rats, MCPG (3-100 microg) had no effect on bladder and EUS EMG activity. The results suggest that group I/II mGluRs are likely to be involved in inhibition of the excitatory pathway to the EUS but not involved in the control of the bladder. The lack of effect of MCPG on the EUS EMG activity in chronic spinal cord transected rats indicates that mGluR-mediated inhibitory control of the EUS was eliminated after spinal cord injury.

The combination of peripheral nerve grafts and acidic fibroblast growth factor enhances arginase I and polyamine spermine expression in transected rat spinal cords

Treatment with a combination of peripheral nerve grafts and acidic fibroblast growth factor improves hind limb locomotor function after spinal cord transection. This study examined the effect of treatment on expression of arginase I (Arg I) and polyamines. Arg I expression was low in the spinal cords of normal rats but increased following spinal injury. Only fully repaired spinal cords expressed higher Arg I levels 6--14 days following repair. In 10-day repaired spinal cords, high Arg I immunoreactivity was detected in motoneurons and alternatively activated macrophages in the graft area and graft–stump edges, and high levels of the polyamine spermine were expressed by macrophages within the intercostal nerve graft. Thus, in addition to enhancing the expression of Arg I and spermine in repaired spinal cords, our treatment may recruit activated macrophages and create a more favorable environment for axonal regrowth.

Influence of cross-linked hyaluronic acid hydrogels on neurite outgrowth and recovery from spinal cord injury

Therapies that use bioactive materials as replacement extracellular matrices may hold the potential to mitigate the inhibition of regeneration observed after central nervous system trauma. Hyaluronic acid (HA), a nonsulfated glycosaminoglycan ubiquitous in all tissues, was investigated as a potential neural tissue engineering matrix. Chick dorsal root ganglia were cultured in 3D hydrogel matrices composed of cross-linked thiol-modified HA or fibrin. Samples were cultured and images were acquired at 48-, 60-, and 192-hour time points. Images of all samples were analyzed at 48 hours of incubation to quantify the extent of neurite growth. Cultures in crosslinked thiolated HA exhibited more than a 50% increase in neurite length compared with fibrin samples. Furthermore, cross-linked thiolated HA supported neurites for the entire duration of the culture period, whereas fibrin cultures exhibited collapsed and degenerating extensions beyond 60 hours. Two concentrations of the thiolated HA (0.5 and 1%) were then placed at the site of a complete thoracic spinal cord transection in rats. The ability of the polymer to promote regeneration was tested using motor evoked potentials, retrograde axonal labeling, and behavioral assessments. There were no differences in any of the parameters between rats treated with the polymer and controls. The use of a cross-linked HA scaffold promoted robust neurite outgrowth. Although there was no benefit from the polymer in a rodent spinal cord injury model, the findings in this study represent an early step in the development of semisynthetic extracellular matrice scaffolds for the treatment of neuronal injury.

Observation of locomotor functional recovery in adult complete spinal rats with BWSTT using semiquantitative and qualitative methods

Experimental rat model of spinal cord transection . China rehabilitation research center. To investigate locomotor functional recovery in spinal rats with BWSTT using semiquantitative and qualitative methods. Five-day postoperative (dpo), adult female complete spinal rats (at T(8) level) received 40 days of body weight-supported treadmill training (BWSTT). Signs of functional recovery were examined with average combined scores (ACOS) and Basso Beattie and Bresnahan (BBB) scales at different time points. At 1-dpo, none of the spinal rats exhibited hindlimb movements. The spinal rats displayed functional progress with time, but the rare could recover to full weight-bearing hindlimb at 45-dpo. BBB and ACOS scores in the BWSTT group obtained better scores than those in the spinal cord injury (SCI) group at 30- and 45-dpo. Furthermore, all BBB and ACOS scores of spinal rats reached statistical significance between 7- and 30-dpo, and between 15- and 30-dpo. However, only ACOS but not BBB scores in the SCI and BWSTT groups showed statistics differences between 15- and 45-dpo, and between 30- and 45-dpo. The Spearman correlation coefficients of BBB and ACOS scores were 0.913 and 0.972 for the SCI and BWSTT groups, respectively. The results confirmed the existence of partial spontaneous hindlimb functional recovery in adult chronically spinal cord-transected rats, and that BWSTT can improve motor performance. In addition, our study suggests that qualitative and semiquantiative methods are strongly correlated with locomotor recovery in spinal rats, and the latter may be more sensitive in reflecting minor variance at different time points.

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.

2′, 3′‐cyclic nucleotide 3′‐phosphodiesterase cells derived from transplanted marrow stromal cells and host tissue contribute to perineurial compartment formation in injured rat spinal cord

Transdifferentiation of transplanted marrow stromal cells (MSCs) and reactive changes of glial cells in a completely transected rat spinal cord were examined. Marrow stromal cells exhibited 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP) at the plasma membrane and this has allowed their identification after transplantation by immunoelectron microscopy. In the control rats, the lesion site showed activated microglia/neural macrophages and some elongated cells, whose cytoplasm was immunoreactive for CNP. Cells designated as CNP1 and apparently host-derived expressed CXCR4. In experimental rats receiving MSCs transplantation, CNP1 cells were increased noticeably. This was coupled with the occurrence of a different subset of CNP cells whose plasma membrane was CNP-immunoreactive and expressed CXCR4. These cells, designated as CNP2, enclosed both myelinated and unmyelinated neurites thus assuming a spatial configuration resembling that of Schwann cells. A remarkable feature was the extensive ramifications of CNP1 cells with long filopodia processes delineating the CNP2 cells and their associated neurites, forming many perineurial-like compartments. Present results have shown that CNP2 cells considered to be MSCs-derived can transform into cells resembling Schwann cells based on their spatial relation with the regenerating nerve fibers, whereas the CNP1 glial cells participate in formation of perineurial compartments, probably serving as conduits to guide the nerve fiber growth. The chemotactic migration of CNP cells either derived from host tissue or MSCs bearing CXCR4 may be attracted by stromal derived factor-1alpha (SDF-1alpha) produced locally. The coordinated cellular interaction between transplanted MSCs and local glial cells may promote the growth of nerve fibers through the lesion site.

Serotonergic drugs and spinal cord transections indicate that different spinal circuits are involved in external urethral sphincter activity in rats

Lower urinary tract function is regulated by spinal and supraspinal reflexes that coordinate the activity of the urinary bladder and external urethral sphincter (EUS). Two types of EUS activity (tonic and bursting) have been identified in rats. This study in urethane-anesthetized female rats used cystometry, EUS electromyography, spinal cord transection (SCT) at different segmental levels, and analysis of the effects of 5-HT(1A) receptor agonist (8-OH-DPAT) and antagonist (WAY100635) drugs to examine the origin of tonic and bursting EUS activity. EUS activity was elicited by bladder distension or electrical stimulation of afferent axons in the pelvic nerve (pelvic-EUS reflex). Tonic activity evoked by bladder distension was detected in spinal cord-intact rats and after acute and chronic T8-9 or L3-4 SCT but was abolished after L6-S1 SCT. Bursting activity was abolished by all types of SCT except chronic T8-9 transection. 8-OH-DPAT enhanced tonic activity, and WAY100635 reversed the effect of 8-OH-DPAT. The pelvic-EUS reflex consisted of an early response (ER) and late response (LR) when the bladder was distended in spinal cord-intact rats. ER remained after acute or chronic T8-9 and L3-4 SCT, but was absent after L6-S1 SCT. LR occurred only in chronic T8-9 SCT rats where it was enhanced or unmasked by 8-OH-DPAT. The results indicate that spinal serotonergic mechanisms facilitate tonic and bursting EUS activity. The circuitry for generating different patterns of EUS activity appears to be located in different segments of the spinal cord: tonic activity at L6-S1 and bursting activity between T8-9 and L3-4.

Effect of Robotic-Assisted Treadmill Training and Chronic Quipazine Treatment on Hindlimb Stepping in Spinally Transected Rats

The purpose of this study was to determine if robotic-assisted treadmill training improved hindlimb stepping in complete spinal cord transected (ST) rats. In addition, we examined whether chronic quipazine treatment would enhance the effectiveness of robotic-assisted training. Hindlimb stepping was examined in four groups of ST rats: trained + quipazine; trained + vehicle; untrained + quipazine; and untrained + vehicle. To train the rats to step, a robotic device was used that moved the hindlimbs in a semi-fixed trajectory during treadmill stepping. The robotic device was also used to assess treadmill stepping. Quipazine or vehicle was administered to the lumbar spinal cord using an intrathecal cannula. The groups that received robotic-assisted training performed more stepping movements on the treadmill than the untrained groups 10 weeks after ST. However, no differences were found between the robotic-assisted and untrained groups 16 weeks after ST. Kinematic analyses revealed that abnormally small step cycles were performed by all of the groups of ST rats. There was no significant effect of combining robotic-assisted training and quipazine treatment on stepping recovery. These data suggest that robotic-assisted training may generate hindlimb sensory stimuli that are effective in enhancing the ability of the lumbar spinal cord to generate hindlimb stepping. However, the effectiveness of robotic-assisted training may be limited to the early stages of recovery following spinal cord transection.

Which Spinal Cutaneous Nociceptive Neurons Are Inhibited by Intravenous Lidocaine in the Rat?

Intravenous lidocaine (IVL) produces analgesia in multiple painful disorders. The neurophysiological effects of IVL are not well defined, but studies in visceral nociceptive systems have shown that IVL has differential effects on subgroups of spinal neurons. The present study determined whether a similar differential effect of IVL occurs in spinal neurons excited by noxious cutaneous stimuli. In decerebrate, cervical spinal cord-transected rats, the lumbosacral spinal cord was exposed by a laminectomy. Single-unit recordings were made of dorsal horn neurons excited by noxious cutaneous stimuli. Each neuron's response to noxious (pinch) and nonnoxious (brush) cutaneous stimuli were determined and the effect of a counterirritation stimulus (noxious skin pinch presented in the upper body) on spontaneous activity quantified. In a subset of neurons, sequential doses of IVL were administered, and responses of each neuron to repeated 50 degrees C heating of the hindpaw/tail were determined. IVL dose-dependently inhibited neurons excited by heating of the hindpaw/tail. IVL produced significantly greater inhibition of both spontaneous and heat-evoked activity in neurons that did not show counterirritation effects when compared with those neurons that did show counterirritation effects. Standard classification of neurons as wide-dynamic range or nociceptive-specific was less predictive of the IVL effect. IVL had differential inhibitory effects on 2 spinal cutaneous nociceptive neuron populations. Other drugs could also have differential effects on sensory pathways, suggesting a mechanism whereby certain drugs differentially affect different types of pain.

A re-assessment of the consequences of delayed transplantation of olfactory lamina propria following complete spinal cord transection in rats

This study is part of the NIH “Facilities of Research-Spinal Cord Injury” contract to support independent replication of published studies. We repeated a study reporting that delayed transplantation of olfactory lamina propria (OLP) into the site of a complete spinal cord transection led to significant improvement in hindlimb motor function and induced axon regeneration. Adult female rats received complete spinal cord transections at T10. Thirty days post-injury, pieces of OLP, which contains olfactory ensheathing cells (OECs), or respiratory lamina propria (RLP), which should not contain OECs, were placed into the transection site. Hindlimb motor function was tested using the BBB scale from day 1 post-injury through 10 weeks following transplantation. To assess axonal regeneration across the transection site, Fluorogold was injected into the distal segment, and the distribution of 5HT-containing axons was assessed using immunostaining. BBB analyses revealed no significant recovery after OLP transplantation and no significant differences between OLP vs. RLP transplant groups. Fluorogold injections into caudal segments did not lead to retrograde labeling in any animals. Immunostaining for 5HT revealed that a few 5HT-labeled axons extended into both RLP and OLP transplants and a few 5HT-labeled axons were present in sections caudal to the injury in 2 animals that received OLP transplants and 1 animal that received RLP transplants. Our results indicate that, although OLP transplants may stimulate regeneration under some circumstances, the effect is not so robust as to reliably overcome the hostile setting created by a complete transection paradigm.

Re‐growth of catecholaminergic fibers and protection of cholinergic spinal cord neurons in spinal repaired rats

The extent of re-growth of catecholaminergic fibers, the survival of cholinergic neurons and the degree of autonomic dysreflexia were assessed in complete spinal cord-transected adult rats that received a repair treatment of peripheral nerve grafts and acidic fibroblast growth factor (aFGF). The rats were randomly divided into three groups: (1) sham control group (laminectomy only); (2) spinal cord transection at T8 (transected group); and (3) spinal cord transection at T8, followed by aFGF treatment and peripheral nerve graft (repaired group). The spinal cords and brains of all rats were collected at 6 months post-surgery. Immunohistochemistry for tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (DBH), and fluoro-gold (FG) retrograde tracing were used to evaluate axon growth across the damage site, and immunocytochemistry for choline acetyl transferase (ChAT) was used to evaluate cholinergic neuronal cell survival following the injury and treatment. When comparing with the transected group, the repaired group showed: (1) lower elevation of mean arterial pressure during colorectal distension; (2) retrogradely labeled neurons in the hypothalamus, zona incerta, subcoeruleus nuclei and rostral ventrolateral medulla following application of FG below the repair site; (3) the presence of TH- and DBH-labeled axons below the lesion site; (4) higher numbers of ChAT-positive neurons in ventral horn and intermediolateral column near the lesion site. We conclude that peripheral nerve graft and aFGF treatments facilitate the re-growth of catecholaminergic fibers, also protect sympathetic preganglionic neurons and spinal motor neurons, and reduce autonomic dysfunction in a T-8 spinal cord-transected rat model.

Intrinsic locomotor outcome in dorsal transection of rat spinal cord: predictive value of minimal incision depth

Experimental, prospective, blinded, animal study. Subtotal transection models in rodents are widely used in spinal cord injury (SCI) research. In this model, we investigate the effect of the dorso-ventral incision depth (ID) of the spinal cord on functional locomotor outcome using the Basso, Beattie, Bresnahan (BBB) scale. We introduce the minimal incision depth (ID(min)) and the average lesion depth (ID(mean)) as reliable, fast and easily available predictive parameters for intrinsic locomotor function. Tuebingen, Germany. Dorsal over-hemisection at the level of T8 was performed in male Lewis rats. Functional outcome 4 weeks after SCI and histological analysis of the lesion were studied and correlated in 36 animals. Animals reaching weight support (BBB> or =9) were considered as having reached functional recovery. Data analysis was performed in linear (ordinary least squares; OLS) and nonlinear (logistic) regression models for correlation of histological parameters and functional outcome. BBB scores revealed a strong correlation with ID(mean) and ID(min), showing a higher value in predicting functional outcome for the latter parameter. Based on logistic regression analysis, animals with an ID(min) of 69% would have a 95% probability of reaching weight support. These results demonstrate that histological analysis is crucial when functional outcome parameters are used in the dorsal over-hemisection SCI model. A simple and feasible histological evaluation can reliably predict spontaneous functional locomotor recovery in dorsal transection models and could provide a simple tool to identify treatment effects of new experimental therapeutic approaches.

Integration of genetically modified adult astrocytes into the lesioned rat spinal cord

Combination of ex vivo gene transfer and cell transplantation is now considered as a potentially useful strategy for the treatment of spinal cord injury. In a perspective of clinical application, autologous transplantation could be an option of choice. We analyzed the fate of adult rat cortical astrocytes genetically engineered with a lentiviral vector transplanted into a lesioned rat spinal cord. Cultures of adult rat cortical astrocytes were infected with an HIV-1-derived vector (TRIP-CMV-GFP) and labeled with the fluorescent dye Hoechst. Transfected and labeled astrocyte suspension was injected at T11 in rats in which spinal cord transection at T7-T8 levels had been carried out 1 week earlier. Six weeks after grafting, the animals were sacrificed and transplants were retrieved either by Hoechst fluorescence or by immunohistochemistry for detection of glial fibrillary acidic protein (GFAP) and vimentin. Grafted astrocytes expressing green fluorescent protein (GFP) were found both at the injection and transection sites. Genetically modified astrocytes thus survived, integrated, and migrated within the host parenchyma when grafted into the completely transected rat spinal cord. In addition, they retained some ability to express the GFP transgene for at least 6 weeks after transplantation. Adult astrocytes infected with lentiviral vectors can therefore be a valuable tool for the delivery of therapeutic factors into the lesioned spinal cord.

The spinal cord, anesthesia and immobility: A re-examination

There has been much recent emphasis on the spinal cord as an important site of anesthetic action with respect to immobility. For example, decerebration or spinal cord transection in rats appears to have little effect on minimum alveolar anesthetic concentration (MAC) needed to produce immobility. Likewise, selective delivery of isoflurane, halothane or thiopental to the brain circulation necessitates increased anesthetic concentrations to provide immobility. However, we have observed that chronic spinal cord transection or acute spinal cooling results in lower MAC and reduced force of limb movement. Others have shown that discrete drug microinjections at various brain sites (gabazine in tuberomammillary nucleus or pentobarbital in the pontine tegmentum) alter anesthetic requirements or produce anesthesia. Collectively, these data suggest that, while the spinal cord is a major site of action for the immobilizing properties for anesthetics, supraspinal sites still play an important role in determining MAC.

Acute and delayed transplantation of olfactory ensheathing cells promote partial recovery after complete transection of the spinal cord

The present study was undertaken to determine whether olfactory ensheathing cells (OECs) from the olfactory bulb were capable to promote axonal regeneration and functional recovery when transplanted either acutely or 1 week delayed into the T8 transected rat spinal cord. OEC transplants increased recovery of functional outcomes, as shown electrophysiologically by return of motor evoked potentials and by reduction of hindlimb hyperreflexia, and behaviorally by recovery of movements of hindlimb joints. Axonal regeneration was proven histologically by demonstrating long axonal outgrowth of raphespinal, coerulospinal, and corticospinal tracts within the caudal cord stump. Expression of GFAP and NG2 was down-regulated in perilesional cord segments in transplanted animals, indicating a more suitable environment for axonal regeneration. Overall, earlier recovery and better functional and histological results were observed in rats receiving acute than delayed OEC transplants. The beneficial effects obtained with transplantation after transection are encouraging for the application of OECs in the human injured spinal cord.

Cholinergic modulation of the urethro genital reflex in spinal cord-transected rats

The aim of this study was to determine which of the muscarinic receptor subtypes are involved in the modulation of the urethrogenital reflex (UGR) in male, spinal cord-transected rats. The electromyographic (EMG) responses of the bulbospongiosus muscle (BS) to the topical spinal application of muscarine and the combination of muscarine and the selective muscarine receptor antagonists methoctramine (M2), AFDX (M2), 4DAMP (M3) and tropicamide (M4) were determined before and after the elicitation of UGR by way of the mechanical stimulation of the urethra. When 50- and 100-μg doses of muscarine were applied without urethral stimulation, a rhythmic activity of the BS was observed, similar to the one found when UGR was evoked. The M3 and M4 – but not the M2 – antagonists prevented BS response to muscarine when urethral stimulation was not performed. When UGR was elicited following urethral stimulation muscarine produced an increase in burst duration and a decrease in burst frequency. The M2 antagonist reverted the effects of muscarine on the UGR, while the M3 and M4 antagonists produced a significant increase in the frequency and in the bursts number, when compared to the control muscarine response. The differences observed in BS responses to muscarine and muscarine antagonists before and after UGR elicitation were probably linked to the intrinsic effects of the endogenous acethylcholine (Ach) released after urethral stimulation. The present results suggest a cholinergic modulation of UGR in spinal cord-transected rats mediated by the M2, M3 and M4 muscarinic receptor subtypes.

Transplantation of Bone Marrow Stromal Cell-Derived Schwann Cells Promotes Axonal Regeneration and Functional Recovery after Complete Transection of Adult Rat Spinal Cord

The aim of this study was to evaluate whether transplantation of Schwann cells derived from bone marrow stromal cells (BMSC-SCs) promotes axonal regeneration and functional recovery in completely transected spinal cord in adult rats. Bone marrow stromal cells (BMSCs) were induced to differentiate into Schwann cells in vitro. A 4-mm segment of rat spinal cord was removed completely at the T7 level. An ultra-filtration membrane tube, filled with a mixture of Matrigel (MG) and BMSC-SCs (BMSC-SC group) or Matrigel alone (MG group), was grafted into the gap. In the BMSC-SC group, the number of neurofilament- and tyrosine hydroxylase-immunoreactive nerve fibers was significantly higher compared to the MG group, although 5-hydroxytryptamine- or calcitonin gene-related peptide-immunoreactive fibers were rarely detectable in both groups. In the BMSC-SC group, significant recovery of the hindlimb function was recognized, which was abolished by retransection of the graft 6 weeks after transplantation. These results demonstrate that transplantation of BMSC-SCs promotes axonal regeneration of lesioned spinal cord, resulting in recovery of hindlimb function in rats. Transplantation of BMSC-SCs is a potentially useful treatment for spinal cord injury.

Experimental study of neural repair of the transected spinal cord using peripheral nerve graft

It has been reported that transected spinal cord shows signs of axonal regeneration after peripheral nerve (PN) graft. We studied the membrane excitability and ion distribution in axons from transected rat spinal cord 3 weeks after PN graft using the spinal cord evoked potential, electron probe X-ray microanalysis, and the patch-clamp technique. Axonal structures were also observed using conventional electron microscopy. At the Th11 level, laminectomy was performed (=control) and the left thoracic segments of the spinal cord 2 mm in length were excised (=nongrafted group). PN sections from 8-week-old male Wistar rats were grafted into the spinal cord gap (=PN-grafted group). The spinal cord evoked potential in the PN-grafted group partly recovered in contrast to that in the nongrafted group, which showed no recovery. Higher Na, Cl, and Ca peaks and lower K peaks in the PN-grafted group were demonstrated compared with those in the nongrafted group. In the PN-grafted group, a higher current signal appeared in the axonal membrane of the spinal cord, suggesting a greater membrane activity compared with that in the nongrafted group. Unlike the nongrafted group, in which no myelinated axons were found, demyelinated axons that were myelinated by Schwann cells from the grafted peripheral nerve were observed in the PN-grafted group. These findings suggested that Schwann cells from the transplanted PN contributed to the repair of the transected spinal cord.

Spastic long-lasting reflexes in the awake rat after sacral spinal cord injury.

Following chronic sacral spinal cord transection in rats the affected tail muscles exhibit marked spasticity, with characteristic long-lasting tail spasms evoked by mild stimulation. The purpose of the present paper was to characterize the long-lasting reflex seen in tail muscles in response to electrical stimulation of the tail nerves in the awake spastic rat, including its development with time and relation to spasticity. Before and after sacral spinal transection, surface electrodes were placed on the tail for electrical stimulation of the caudal nerve trunk (mixed nerve) and for recording EMG from segmental tail muscles. In normal and acute spinal rats caudal nerve trunk stimulation evoked little or no EMG reflex. By 2 wk after injury, the same stimulation evoked long-lasting reflexes that were 1) very low threshold, 2) evoked from rest without prior EMG activity, 3) of polysynaptic latency with >6 ms central delay, 4) about 2 s long, and 5) enhanced by repeated stimulation (windup). These reflexes produced powerful whole tail contractions (spasms) and developed gradually over the weeks after the injury (< or =52 wk tested), in close parallel to the development of spasticity. Pure low-threshold cutaneous stimulation, from electrical stimulation of the tip of the tail, also evoked long-lasting spastic reflexes, not seen in acute spinal or normal rats. In acute spinal rats a strong C-fiber stimulation of the tip of the tail (20 x T) could evoke a weak EMG response lasting about 1 s. Interestingly, when this C-fiber stimulation was used as a conditioning stimulation to depolarize the motoneuron pool in acute spinal rats, a subsequent low-threshold stimulation of the caudal nerve trunk evoked a 300-500 ms long reflex, similar to the onset of the long-lasting reflex in chronic spinal rats. A similar conditioned reflex was not seen in normal rats. Thus there is an unusually long low-threshold polysynaptic input to the motoneurons (pEPSP) that is normally inhibited by descending control. This pEPSP is released from inhibition immediately after injury but does not produce a long-lasting reflex because of a lack of motoneuron excitability. With chronic injury the motoneuron excitability is increased markedly, and the pEPSP then triggers sustained motoneuron discharges associated with long-lasting reflexes and muscle spasms.