Sustained intraspinal delivery of neurotrophic factor encapsulated in biodegradable nanoparticles following contusive spinal cord injury

Glial cell line derived neurotrophic factor (GDNF) induces neuronal survival and tissue repair after spinal cord injury (SCI). A continuous GDNF supply is believed to gain greater efficacy in the neural restoration of the injured spinal cord. Accordingly, nanovehicle formulation for their efficient delivery and sustained release in injured spinal cord was examined. We first used fluorescence-labeled bovine serum albumin (FBSA) loaded in biodegradable poly(lactic acid-co-glycolic acid) (PLGA) for intraspinal administration after SCI and for in vitro study. Our results showed that the preservation of PLGA-FBSA was observed in the injured spinal cord at 24h, and PLGA-FBSA nanoparticles were well absorbed by neurons and glia, indicating that PLGA as a considerable nanovehicle for the delivery of neuroprotective polypeptide into injured spinal cord. Furthermore, intraspinal injection of GDNF encapsulated in PLGA (PLGA-GDNF) nanoparticles into the injured spinal cord proximal to the lesion center had no effect on gliosis when compared to that observed in SCI rats receiving PLGA injection. However, local administration of PLGA-GDNF effectively preserved neuronal fibers and led to the hindlimb locomotor recovery in rats with SCI, providing a potential strategy for the use of PLGA-GDNF in the treatment of SCI.     

Rolipram attenuates acute oligodendrocyte death in the adult rat ventrolateral funiculus following contusive cervical spinal cord injury

Rolipram, an inhibitor of phosphodiesterase 4 (PDE4) proteins that hydrolyze cAMP, increases axonal regeneration following spinal cord injury (SCI). Recent evidence indicate that rolipram also protects against a multitude of apoptotic signals, many of which are implicated in secondary cell death post-SCI. In the present study, we used immunohistochemistry and morphometry to determine potential spinal cord targets of rolipram and to test its protective potential in rats undergoing cervical spinal cord contusive injury. We found that 3 PDE4 subtypes (PDE4A, B, D) were expressed by spinal cord oligodendrocytes. OX-42 immunopositive microglia only expressed the PDE4B subtype. Oligodendrocyte somata were quantified within the cervical ventrolateral funiculus, a white matter region critical for locomotion, at varying time points after SCI in rats receiving rolipram or vehicle treatments. We show that rolipram significantly attenuated oligodendrocyte death at 24 h post-SCI continuing through 72 h, the longest time point examined. These results demonstrate for the first time that spinal cord glial cells express PDE4 subtypes and that the PDE4 inhibitor rolipram protects oligodendrocytes from secondary cell death following contusive SCI. They also indicate that further investigations into neuroprotection and axonal regeneration with rolipram are warranted for treating SCI.     

Cold and mechanical allodynia in both hindpaws and tail following thoracic spinal cord hemisection in rats: time courses and their correlates

We assessed (1) the time courses of cold and mechanical allodynia in both hindpaws and the tail, and (2) the relationship of the allodynia signs between different sites following spinal cord hemisection. Under enflurane anesthesia, rats were subjected to spinal hemisection at T13. The hemisected rats exhibited a significant increase in mechanical and cold allodynia signs of both hindpaws and the tail for 22-26 weeks postoperatively. In addition, mechanical allodynia signs were significantly correlated not only between the ipsilateral and the contralateral hindpaws, but also between the hindpaws and the tail. These results suggested that cold and mechanical allodynia developed extensively and lasted for a long time following spinal cord hemisection, and mechanical allodynia shown at different sites may be induced at least in part by common generating mechanisms.     

急性脊髓挫伤后内皮素-1 mRNA表达变化

目的：观察脊髓损伤（SCI）后内皮素-1（ET-1）mRNA表达的解剖和空间以及含量变化规律。方法：改良Allen's法（50 g-cm）制备急性大鼠脊髓挫伤模型。原位杂交检测SCI前后脊髓组织中ET-1 mRNA。图像分析半定量测定伤区邻近段ET-1 mRNA含量。结果：SCI后损伤邻近段脊髓组织中ET-1 mRNA阳性表达的神经元、胶质细胞与血管内皮细胞数量多于及信号强于对照组，以神经元表达改变为主。除48 h组，伤后各时点脊髓灰质ET-1 mRNA阳性染色的阳性单位与对照组比较差异显著（P<0.05）。伤区脊髓中ET-1 mRNA阳性染色神经元随时间逐渐减少，而胶质细胞阳性表达增加。结论：SCI后脊髓组织中ET-1 mRNA表达上调，提示ET-1参与SCI后病理生理改变。神经元是SCI后脊髓组织中ET-1升高的主要来源。     

Changes of intracellular free calcium following mechanical injury in a spinal cord slice preparation

Intracellular calcium ions are, in addition to free radicals, an important mediator of tissue destruction following traumatic injury to the spinal cord. In vivo measurements of calcium in the interstitial space and in the tissue suggest the occurrence of a posttraumatic shift of calcium from the extracellular to the intracellular compartment at the injury site. No information is, however, available on the posttraumatic changes of calcium in the intracellular compartment, where the ion exerts its crucial messenger function. We developed an in vitro model of local traumatic spinal injury, using a spinal cord slice preparation, allowing us to investigate injury-related changes of intracellular free calcium. The injury consisted of the impact of a small needle, and intracellular free calcium was measured with fura-2. Application of the injury at different places within the gray matter caused a transient and reproducible increase in the fura-2 fluorescence ratio. This injury-induced ratio increase was largely, but not completely, suppressed under zero extracellular calcium conditions. It was also largely depressed in the presence of high extracellular potassium and in the absence of extracellular sodium. It was modestly depressed by the calcium channel blocker nifedipin, by the calcium release channel blocker dantrolene, and by the gap junction blockers halothane and octanol. The calcium channel blocker flunarizine, the N-methyl d-aspartate (NMDA)-receptor-channel blocker MK-801 and the endoplasmic reticulum calcium-ATPase blocker thapsigargin had no effect. The experiments suggest that injury is associated with an increase in intracellular free calcium that is mediated by calcium influx, in part via L-type calcium channels. They furthermore give evidence that sodium influx and gap junctions are involved in these injury-associated changes of intracellular free calcium.     

脊髓损伤大鼠内皮祖细胞与脊髓血管新生

背景：诸多脑损伤实验表明,改善损伤组织缺血缺氧有助于促进损伤组织的修复,并有保护神经功能的目的。 目的：探讨挫伤型脊髓损伤后大鼠外周血中内皮祖细胞的变化及其与创伤灶周围早期血管新生情况的关系。 方法：成年雄性SD大鼠60只,随机数字表法均分为实验组与对照组。实验组采用Allen’s原理制作脊髓损伤模型,对照组只行椎板切除暴露脊髓,不予打击致伤。分别于术前及术后3,6,24,48,72,168 h取大鼠外周血,流式细胞仪检测外周血中内皮祖细胞数量。并于术前及术后1,4,7,14 d处死大鼠取脊髓,采用血管内皮标志物CD31免疫组化染色方法观察创伤区血管的新生情况。 结果与结论：两组大鼠外周血内皮祖细胞水平于伤后3 h均有所下降,6 h开始上升,24 h达高峰,随后逐渐达稳定水平。实验组高峰值明显高于对照组。同时微血管数量呈逐渐增多的趋势。说明大鼠脊髓损伤后,外周血内皮祖细胞数量明显增加,内皮祖细胞参与血管新生和损伤组织的修复,最终促进神经功能恢复。     

Up-regulation of tumor necrosis factor-alpha in spinal cord contributes to vincristine-induced mechanical allodynia in mice

Chronic treatment with vincristine (VCR) causes mechanical allodynia as an adverse effect. We previously reported that peripheral macrophage-derived interleukin-6 played a critical role in VCR-induced allodynia. However, the involvement of glial cell activation and central sensitization in VCR-induced allodynia is still unclear. In this study, we focused on tumor necrosis factor-alpha (TNF-alpha) in spinal cord, and investigated the role of TNF-alpha in VCR-induced allodynia in mice. VCR (0.1mg/kg, i.p.) was administered to mice once per day for 7 days. The expression of TNF-alpha mRNA and the protein in spinal cord was evaluated by quantitative real-time PCR and immunohistochemistry, respectively. In VCR-treated mice, TNF-alpha mRNA gradually increased and was significantly up-regulated on day 7. As measured by immunohistochemistry, microglia and astrocytes were activated in the spinal dorsal horn on day 7 of VCR administration. The immunoreactivity of TNF-alpha was co-localized in some of the activated microglia and astrocytes. In behavioral analysis, a neutralizing antibody of TNF-alpha, which was injected intrathecally on days 0, 3, and 6, significantly attenuated VCR-induced mechanical allodynia on days 4 and 7. These results suggest that VCR treatments elicited the activation of glial cells in spinal cord, and up-regulated TNF-alpha in these cells may play an important role in VCR-induced mechanical allodynia.     

大鼠外周神经损伤后脊髓背角HMGB1表达上调参与机械性痛觉超敏

目的:研究HMGB1(high mobility group box-1)在神经病理性痛大鼠脊髓水平的表达变化,探索HMGB1在神经病理性痛发生发展中的作用,为治疗神经病理性痛提供新的理论依据和治疗靶点。方法:(1)雄性SD大鼠(180～220)g 12只,随机均分为三组:NS组:鞘内注射生理盐水;A组:鞘内注射HMGB1 1μg;B组:鞘内注射HMGB1 10μg。盲法用von Frey测定给药前及给药后1 h、1、3、7、14、21、28 d大鼠50%机械缩足阈值(me-chanical withdrawal threshold,MWT);(2)雄性SD大鼠(180～220)g 5只,免疫荧光双标观察HMGB1在脊髓背角的表达定位;(3)雄性SD大鼠(180～220)g 42只,随机均分为对照组(6只),SNL模型组(每时间点6只),West-ern Blot方法观察大鼠脊髓背角HMGB1对照及术后1、3、7、14、21、28 d的表达变化。结果:(1)大鼠脊髓鞘内注射HMGB1后诱发长时程机械性痛敏,A组在鞘内给药后7 d MWT明显下降(P<0.01),B组给药后1 h MWT即显著下降,且持续存在至少28 d;(2)免疫荧光双标显示:HMGB1主要表达于NeuN标记的神经元,而GFAP阳性的星形胶质细胞以及OX42阳性的小胶质细胞几乎不表达HMGB1;(3)Western Blot结果显示,脊髓背角HMGB1在SNL模型术后缓慢增高,7 d时增高最为显著,且持续至少28 d。结论:以上结果表明,外周神经损伤后脊髓水平HMGB1的表达上调可能在神经病理性痛的产生和维持中起着重要作用。     

Locomotor recovery and mechanical hyperalgesia following spinal cord injury depend on age at time of injury in rat

We tested the effect of age at the time of spinal cord injury (SCI) on locomotor recovery, in open field tests, and mechanical hyperalgesia, using paw withdrawal frequency (PWF) in response to noxious mechanical stimuli, in male Sprague-Dawley rats after spinal hemisection at T13 in young (40 days), adult (60 days) and middle-age (1 year) groups. Behavioral outcomes were measured weekly for 4 weeks in both SCI and sham groups. Following SCI, the young and adult groups recovered significantly more locomotor function, at a more rapid rate, than did the middle-age group. The PWF of the young group was significantly increased, the adult group was significantly decreased, and the middle-age group showed no significant change in fore- and hindlimbs when compared to other age groups, pre-injury and sham controls. These results support age-dependent behavioral outcomes after SCI.     

BMP7蛋白对大鼠急性脊髓损伤后神经元修复作用的研究

目的探索骨形态发生蛋白7(bone morphogenetic protein 7,BMP7)是否具有促进大鼠急性脊髓损伤后神经元修复的作用。方法实验大鼠分为阴性对照组(negative control,NC)和BMP7实验组,以Allen's打击法建立大鼠脊髓损伤模型,BMP7组大鼠每天在脊髓损伤处注射50ng BMP7蛋白,连续7天,NC组对应注射等体积的0.9%氯化钠注射液。两组大鼠分别于术后6小时、3天、1周、2周、4周、8周进行HE染色以观察脊髓损伤处病理学改变;两组大鼠分别于术后6小时、3天、1周、2周、4周、8周进行免疫组化实验以检测损伤节段脊髓神经丝蛋白200(neurofilament protein 200,NF200)、胶质纤微酸性蛋白(glial fibrillary acidic protein,GFAP)及突触素(Synaptophysin,SYP)蛋白表达水平。结果 HE染色结果表明两组大鼠造模后脊髓损伤处神经元数量减少,神经突触数量减少,尼式体淡染且数量减少,组织中可见空洞形成,1周后,BMP7实验组大鼠脊髓损伤处尼式体染色逐渐加深,神经突触数量增多,变化较NC组明显。免疫组化结果表明BMP7实验组大鼠NF200阳性表达细胞数造模3天后逐渐增多,至第4周时达到高峰,且在1周、2周、4周及8周时均大于NC组;BMP7实验组及NC组术后GFAP阳性表达细胞数变化均不明显,且两组阳性细胞数差异不显著;BMP7实验组大鼠SYP阳性表达细胞数造模3天后逐渐增多,且在1周、2周、4周及8周时均大于NC组。结论 BMP7蛋白可以促进大鼠脊髓损伤后神经元的修复。     

Plasticity in sublesionally located neurons following spinal cord injury

Neuronal plasticity has been traditionally associated with learning and memory processes in the hippocampal regions of the brain. It is now generally accepted that plasticity phenomena are also associated with other kinds of cellular changes and modifications occurring in all areas of the CNS after injury or intense neuronal activity. For instance, spinal cord injuries have been associated with a series of cellular modifications and adaptations taking place distally in sublesional areas. Some of these modifications include changes in the expression of immediate early genes (e.g., c-fos and nor-1), TNF-alpha, preprodynorphin, neurotrophic factors (e.g., BDNF and NT-3), and several subtypes of transmembranal receptors (e.g., 5-HT(1A) and 5-HT(2A)). This review constitutes an update of the current knowledge regarding this broadly defined plasticity phenomenon that occurs spontaneously or can be modulated by training in sublesional segments of the spinal cord. Spinal cord plasticity is an increasingly popular field of research, believed by many as being a complex phenomenon that may contribute to the development of innovative therapeutics and rehabilitative approaches for spinal cord injured patients.     

自制脊髓打击器致大鼠脊髓损伤的组织形态学演变特征

目的:通过大鼠脊髓组织H-E染色和电镜观察,以评价自制撞击型脊髓打击器的应用价值。方法:采用自制脊髓打击器分别从2、3 cm和4 cm高度将10 g撞击头自由下落对脊髓进行撞击,以制备大鼠脊髓损伤模型,于制模术后3、7、14 d及28 d随机选取各组大鼠样品,对其脊髓组织进行H-E染色及电镜观察。结果:假手术组各观察时间点脊髓组织结构均完整;2 cm高度打击组脊髓损伤后至第7天组织坏死明显,14 d后受损组织部分修复;3 cm和4 cm高度打击组随时间延长受损脊髓组织坏死加重。电镜观察3个打击组随时间延长,髓鞘板层均表现为逐渐松解,轴突逐渐消失,尤以3 cm和4 cm高度打击组的损害更为严重。结论:本研究采用的自制脊髓打击器具有随打击高度的不同而出现不同程度组织损伤的演变特征,是一种较为理想的脊髓损伤制模装置。     

小鼠脊髓损伤模型的行为学评估方法

目前已存在多种针对小鼠脊髓损伤(spinal cord injury,SCI)模型的行为学评分方法,常用的包括Basso Mouse Scale(BMS)法、单帧运动分析、爬梯实验和斜面实验等。其中,BMS和单帧运动分析属运动学分析,前者的评分与损伤程度有较高一致性,但是较为复杂,后者观察指标简单,但是只能做粗略的评估;爬梯实验和斜面实验是观察小鼠完成某一任务的能力而评分,指标客观,但前者应用前提是小鼠已恢复到可负重行走,并需要事先对小鼠进行训练,后者的敏感性可能有品系差异。     

Interlimb reflexes following cervical spinal cord injury in man

Summary The reflex interconnection of lower and upper extremity muscles was investigated in subjects with chronic (> 1 year post-injury) lesions to the cervical spinal cord. Lower extremity mixed nerves were stimulated with single shocks or with brief trains of high-frequency stimuli of varying intensities. EMG from a number of lower and upper extremity muscles was recorded on magnetic tape for later analysis. In one population of spinal cord injury (SCI) subjects, single stimuli to lower extremity nerves resulted in muscle responses in both ipsi- and contralateral upper extremity muscles. The minimal response latency to a single shock was typically much less in muscles on the ipsilateral side than for contralateral upper extremity muscles. Application of brief trains of stimuli (for example, 2 stimulus pulses at 500 Hz) typically resulted in a large reduction in latency to the contralateral motor response, such that it was now approximately equal to the ipsilateral motor response latency. This decline in response latency was not gradual with increasing afferent input. Instead, the response occurred either early or late, but not at intermediate latencies. Stimuli which were subthreshold for evoking M-waves or H-reflexes were sometimes still adequate to evoke upper extremity motor responses. Once the threshold had been exceeded, the magnitude of the evoked response appeared to be independent of the stimulus magnitude. These reflex interconnections of lower and upper extremities were obtained only from subjects with chronic and motor-complete cervical spinal cord injury. No such interlimb responses were seen in control subjects, or in subjects who had recovered some motor function below the level of their injury, and were now considered to be motor-incomplete quadriplegics.     

Development of a rat model of graded contusive spinal cord injury using a pneumatic impact device

An animal model of spinal cord trauma is essential for understanding the injury mechanisms, cord regeneration, and to aid the development of new therapeutic modalities. This study focused on the development of a graded experimental contusion model for spinal cord injury (SCI) using a pneumatic impact device made in Korea. A contusive injury was made to the dorsal aspect of the cord. Three trauma groups were defined according to the impact velocity (IV). A control group (n=6), received laminectomy only. Group 1 (n=10), 2 (n=10), and 3 (n=10) had IVs of 1.5 m/sec, 2.0 m/sec, and 3.5 m/sec respectively. Functional assessments were made up to the 14th day after injury. The cord was removed at the 14th postinjury day and prepared for histopathologic examination. Significant behavioral and histopathological abnormalities were found in control and each trauma group. All trauma groups showed severe functional impairment immediately after injury but following different rates of functional recovery (Fig. 5). As the impact velocity and impulse increased, the depth of contusive lesion revealed to be profound the results show that the rat model reproduces spinal cord lesions consistently, has a distinctive value in assessing the effects of impact energy.     

Modulation of neuronal activity in dorsal column nuclei by upper cervical spinal cord stimulation in rats

Clinical human and animal studies show that upper cervical spinal cord stimulation (cSCS) has beneficial effects in treatment of some cerebral disorders, including those due to deficient cerebral circulation. However, the underlying mechanisms and neural pathways activated by cSCS using clinical parameters remain unclear. We have shown that a cSCS-induced increase in cerebral blood flow is mediated via rostral spinal dorsal column fibers implying that the dorsal column nuclei (DCN) are involved. The aim of this study was to examine how cSCS modulated neuronal activity of DCN. A spring-loaded unipolar ball electrode was placed on the left dorsal column at cervical (C2) spinal cord in pentobarbital anesthetized, ventilated and paralyzed male rats. Stimulation with frequencies of 1, 10, 20, 50 Hz (0.2 ms, 10 s) and an intensity of 90% of motor threshold was applied. Extracellular potentials of single neurons in DCN were recorded and examined for effects of cSCS. In total, 109 neurons in DCN were isolated and tested for effects of cSCS. Out of these, 56 neurons were recorded from the cuneate nucleus and 53 from the gracile nucleus. Mechanical somatic stimuli altered activity of 87/109 (83.2%) examined neurons. Of the neurons receiving somatic input, 62 were classified as low-threshold and 25 as wide dynamic range. The cSCS at 1 Hz changed the activity of 96/109 (88.1%) of the neurons. Neuronal responses to cSCS exhibited multiple patterns of excitation and/or inhibition: excitation (E, n=21), inhibition (I, n=19), E–I (n=37), I–E (n=8) and E–I–E (n=11). Furthermore, cSCS with high-frequency (50 Hz) altered the activity of 92.7% (51/55) of tested neurons, including 30 E, 24 I, and 2 I–E responses to cSCS. These data suggested that cSCS significantly modulates neuronal activity in DCN. These nuclei might serve as a neural relay for cSCS-induced effects on cerebral dysfunction and diseases.     

Effects of rolipram on adult rat oligodendrocytes and functional recovery after contusive cervical spinal cord injury

Traumatic human spinal cord injury (SCI) causes devastating and long-term hardships. These are due to the irreparable primary mechanical injury and secondary injury cascade. In particular, oligodendrocyte cell death, white matter axon damage, spared axon demyelination, and the ensuing dysfunction in action potential conduction lead to the initial deficits and impair functional recovery. For these reasons, and that oligodendrocyte and axon survival may be related, various neuroprotective strategies after spinal cord injury are being investigated. We previously demonstrated that oligodendrocytes in the adult rat epicenter ventrolateral funiculus (VLF) express 3′-5′-cyclic adenosine monophosphate-dependent phosphodiesterase 4 (PDE4) subtypes and that their death was attenuated up to 3 days after contusive cervical SCI when rolipram, a specific inhibitor of PDE4, was administered. Here, we report that (1) there are more oligodendrocyte somata in the adult rat epicenter VLF, (2) descending and ascending axonal conductivity in the VLF improves, and that (3) there are fewer hindlimb footfall errors during grid-walking at 5 weeks after contusive cervical SCI when rolipram is delivered for 2 weeks. This is the first demonstration of improved descending and ascending long-tract axonal conductivity across a SCI with this pharmacological approach. Since descending long-tract axonal conductivity did not return to normal, further evaluations of the pharmacokinetics and therapeutic window of rolipram as well as optimal combinations are necessary before consideration for neuroprotection in humans with SCI.