大鼠脊髓腰节段神经营养因子及其受体的增龄变化

目的 观察不同月龄(1、3、6、12、18和24月龄)大鼠脊髓腰节段神经营养因子及其受体的变化,探讨其与增龄之间的关系。方法 用免疫组织化学和Western blot 法观察脊髓腰节段神经营养因子及其受体的表达,用尼氏染色法观察脊髓腰节段存活神经元数量。结果 大鼠脊髓腰节段神经生长因子(NGF)及其受体TrkA、脑源性神经营养因子(BDNF)及其受体TrkB和胶质细胞源性神经营养因子(GDNF)表达具有明显的随增龄变化规律,即1月龄（幼年期）时表达量较低,随年龄增高逐渐上升,至6月龄（青年期）达高峰,24月龄（老年期）明显减低,其中以GDNF的变化更为明显。大鼠脊髓腰节段存活神经元数量在1月龄至6月龄均保持在较高水平,之后开始逐渐下降,24月龄时降至最低。结论 神经营养因子及其受体在大鼠脊髓腰节段中的表达存在增龄变化,特别是老年期表达量显著降低,可能是导致脊髓老化的重要机制之一。     

脊髓损伤早期凋亡调控蛋白的表达与电生理变化的关系

目的： 通过观察大鼠急性脊髓损伤后早期细胞凋亡调控基因Bcl-2和Bax的表达与电生理皮层体感诱发电位（CSEP）和运动诱发电位（MEP）的变化,探讨细胞凋亡调控基因的表达与脊髓的电生理变化关系。方法： 56只Wistar 大鼠随机分成7组,6组制成急性脊髓损伤模型,另一组作为对照组,分别于伤后0 h、6 h、12 h、24 h、48 h、72 h描记CSEP和MEP,随后采集脊髓标本,分别进行HE染色和免疫组化检测细胞凋亡调控蛋白Bcl-2和Bax的表达。结果： CSEP和MEP的峰峰值在伤后立即下降或消失,6 h有所上升,12 h又下降,24 h较12 h略上升,48 h上升较明显,72 h继续上升,但较正常峰峰值略低。峰峰值呈下降-升高-再下降-再升高的双谷态势,潜伏期相对应不同程度延长。Bcl-2和Bax都在术后6 h可见阳性表达,Bcl-2表达在24 h达到高峰, Bax的表达在12 h达到高峰。结论：CSEP和MEP的变化与脊髓损伤程度密切相关,可以作为判断脊髓损伤后运动功能及预后的电生理指标。     

Immunocytochemical localization of substance P in the rat spinal cord with special reference to fibers within the ventral column of the rostral lumbar segments

The distribution of substance P (SP) in the rat spinal cord was investigated by peroxidase-anti-peroxidase (PAP) immunocytochemistry. A dense network of SP-immunoreactive fibers and terminals was detected in the ventral column of the rostral lumbar cord with a different density and extent from the other segmental levels. These fibers and terminals were accumulated within and around the centromedial nucleus (CM) of the L1 and L2 segments, with some bundles of immunoreactive fibers between the CM and other areas; i.e. laminae V and X and the contralateral CM. They formed a dense network, such as in arborization of immunoreactive fibers and terminals on the transverse plane and in a comb-shaped structure on the horizontal plane. The origin of the SP in this network was examined. It was determined that neither a total transection of spinal cord at a low thoracic level or mid-lumbar level, nor at an ipsilateral or bilateral section of the 3-5 dorsal roots, containing L1 and L2 roots, induced any visible changes in the SP staining pattern. An intrathecal injection of colchicine revealed the presence of SP-immunoreactive neurons in the dorsal horn and intermediate gray matter at the spinal cord including the rostral lumbar cord. The present findings suggested that the majority of SP immunoreactivities in the above network are derived from local circuit interneurons of the spinal cord.     

Bilateral dorsal root potentials in the lower sacral spinal cord

Summary Bilateral dorsal root potentials (DRPs) evoked in the S3 dorsal roots by stimulation of the S2 and L6 dorsal roots and the cutaneous afferents entering the spinal cord in the lumbar segments have been studied in spinal cats. Stimulation of all these afferents produces DRPs which have the same amplitude on both sides of the spinal cord. During longlasting repetitive stimulation the negativity of the ipsilateral dorsal root is maintained only when this stimulation is applied to the neighbouring dorsal root. Depression of the testing DRPs produced by preceding single volleys or repetitive stimulation is only slightly larger on the contralateral side of the cord. The difference between depression of the DRPs on both sides of the cord is significantly smaller in the S3 than in the L7 segment. Following conditioning tetanization both ipsi- and contralateral DRPs undergo depression. The pattern of bilateral DRPs in the S3 segment significantly differs from that observed in the L7 segment and these differences correspond to the already known distinct arrangement of the substantia gelatinosa in the two parts of the cord.     

Chronically isolated lumbar half spinal cord generates locomotor activities in the ipsilateral hindlimb of the cat

The lumbar spinal cord of the cat was both hemisected (at L2 or L3) and longitudinally myelotomized in order to make half lumbar cord isolated from descending as well as contralateral impulses. The chronic cats recovered the ability to stand with their two forelimbs and a hindlimb, contralateral to the hemisection, 17.2 +/- 10.8 days after the operations. Two days later the hindlimb innervated by the isolated half lumbar cord regained walking capability. Phase relationships between the fore- and hindlimb muscles during locomotion were studied by recording EMGs from bilateral triceps brachii, vastus lateris and tibialis anterior muscles. Phase relationships between bilateral triceps brachii were 0.97 +/- 0.13 pi to 1.09 +/- 0.12 pi, indicating that the two forelimbs were stepping alternately and rhythmically. Phase relationships between bilateral vastus lateralis muscles were highly variable step by step, suggesting that the stepping of the hindlimb innervated by the isolated half lumbar cord was independently carried out, possibly evoked by peripheral receptors such as joint, muscle and cutaneous receptors.     

活性氧在脊髓损伤中的作用及损伤机制

目的研究脊髓损伤(SCI)后脊髓组织中丙二醛(MDA)的动态水平变化和神经细胞凋亡及其凋亡相关因子表达的变化,探讨活性氧(ROS)在SCI后的作用及其分子机制。方法成年雄性大鼠132只,用改良的Allen法复制大鼠急性SCI模型,致大鼠脊髓(T10)中度挫伤,采用化学比色法测定不同时间段受损脊髓组织的MDA含量;免疫组织化学法分析受损脊髓组织区域凋亡相关因子Caspase-3、Bcl-2和Bax的表达变化;荧光原位缺口末端标记法(TUNEL)检测细胞凋亡。结果SCI后6h,脊髓组织中MDA含量明显增高并维持到损伤后5d,期间在6h和3d出现两次高峰,7d基本恢复正常;SCI后6h脊髓组织中凋亡细胞开始增多,3d达高峰,以后逐渐减少,各时间点与假手术组比较有显著性的差异;Bcl-2和Bax蛋白损伤后6h开始有较多的表达,以后快速增多,5d达高峰,然后逐渐回落。Caspase-3蛋白在损伤后6h开始增多,3d达高峰,以后逐渐减少。3种凋亡相关因子在各时间点与假手术组比较有显著性差异;甲基强的松龙(MPSS)治疗组与SCI组比较:MDA含量、凋亡细胞数、凋亡因子Caspase-3和Bax表达减少,Bcl-2表达增加,并且在部分时间点有显著性差异。结论在SCI后ROS可能通过促进Caspase-3表达和降低Bcl-2/Bax之间的比值诱导神经细胞凋亡,从而加重了SCI继发性损伤。     

Effects of electrical stimulation of the thoracic spinal cord on bladder and external urethral sphincter activity in the decerebrate cat

Summary Electrical stimulation of the spinal cord above the sacral segments was used to produce coordinated micturition in the paralysed decerebrate cat. Stimulation of the superficial aspect of the dorsolateral funiculus (DLF) within the lower thoracic (T9-T13) segments produced a bladder contraction coordinated with decreased activity in the external urethral sphincter (EUS) branch of the pudendal nerve during which time fluid was expelled. In addition, a similar response was observed with DLF stimulation at the boundary of the L5/L6 segments. At the second cervical spinal segment, however, stimulation of a more lateral and ventral portion of the superficial spinal white matter was the only effective site for producing micturition. The spinal cord-evoked response was comparable to the micturition evoked by electrical stimulation of the pontine micturition centre (PMC) within the brainstem. A bilateral lesion of the dorsal columns (DC) and the dorsolateral funiculi (DLF) at the lower thoracic levels abolished reflex micturition evoked by bladder distension. However stimulation rostral to the lesion, within the PMC or thoracic DLF, continued to produce coordinated bladder and sphincter response during voiding. Stimulation caudal to the lesion produced a decrease in pudendal nerve activity but did not produce a void or bladder pressure change. This reduction in pudendal nerve activity could be abolished with a second lesion of the superficial DLF caudal to the stimulation site. It was concluded that stimulation of the thoracic dorsolateral funiculus activates both ascending and descending fibres which can influence the bladder and/or sphincter muscles. The spinal cordevoked voiding was hypothesized to be due to activation of some portion of the ascending limb of the spinobulbospinal micturition reflex loop. The decreased activity produced by stimulation of the thoracic DLF caudal to a bilateral DC/DLF subtotal cord lesion may be mediated by fibres descending in the dorsolateral funiculus. The possibility that the spinal cord stimulation antidromically activated axons of neurons having segmental collaterals capable of influencing pudendal neural activity cannot be exclused at this time.     

神经降压素对大鼠脊髓背角胶状质内突触前神经递质释放的影响

目的:研究内源性神经肽神经降压素(neurotensin,NT)在脊髓背角胶状质(substantia gelatinosa,SG)内对突触前神经递质释放的影响。方法:采用全细胞电压膜片钳记录方法,在脊髓薄片上观察NT对SG内微小兴奋性突触后电流(mEPSCs)和微小抑制性突触后电流(mIPSCs)的频率和幅值的影响。结果:(1)灌流NT(2μmol/L)对SG内神经元mEPSCs的频率和幅值均无明显影响,说明NT不影响SG内兴奋性神经递质的释放;(2)灌流NT(2μmol/L)能增加SG内神经元mIPSCs的频率,但对幅值无明显影响,即NT可引起突触前抑制性神经递质的释放增加,但对突触后神经元无明显影响。结论:NT可通过增加SG内抑制性神经递质释放的途径抑制伤害性信息的传递,从而实现镇痛效应。     

Locomotor and reflex adaptation after partial denervation of ankle extensors in chronic spinal cats

This work investigates the capacity of the spinal cord to generate locomotion after a complete spinal section and its ability to adapt its locomotor pattern after a peripheral nerve lesion. To study this intrinsic adaptive capacity, the left lateral gastrocnemius-soleus (LGS) nerve was sectioned in three cats that expressed a stable locomotion following a complete spinal transection. The electromyograph (EMG) of multiple hindlimb muscles and reflexes, evoked by stimulating the left tibial (Tib) nerve at the ankle, were recorded before and after denervation during treadmill locomotion. Following denervation, the mean amplitude of EMG bursts of multiple hindlimb muscles increased during locomotion, similar to what is found after an identical denervation in otherwise intact cats. Reflex changes were noted in ipsilateral flexors, such as semitendinosus and tibialis anterior, but not in the ipsilateral knee extensor vastus lateralis following denervation. The present results demonstrate that the spinal cord possesses the circuitry necessary to mediate increased EMG activity in multiple hindlimb muscles and also to produce changes in reflex pathways after a muscle denervation. The similarity of changes following LGS denervation in cats with an intact and transected spinal cord suggests that spinal mechanisms play a major role in the locomotor adaptation.     

Dose dependence of the 5-HT agonist quipazine in facilitating spinal stepping in the rat with epidural stimulation

Epidural electrical stimulation (ES) at spinal cord segment L2 can produce coordinated step-like movements in completely spinalized adult rats [R.M. Ichiyama, Y.P. Gerasimenko, H. Zhong, R.R. Roy, V.R. Edgerton, Hindlimb stepping movements in complete spinal rats induced by epidural spinal cord stimulation, Neurosci. Lett. 383 (2005) 339-344]. Plantar placement of the paws, however, was rarely observed. Here, we sought to determine the dose dependence of a 5-HT agonist (quipazine) on stepping kinematics when administered in combination with ES. Six adult female Sprague-Dawley rats received a complete mid-thoracic spinal cord transection and were implanted with epidural electrodes at the L2 spinal cord level. Quipazine (i.p.) was tested at doses of 0.1, 0.2, 0.3, 0.4, and 0.5 mg/kg. Rats were placed in a body weight support system, allowing them to walk bipedally on a moving treadmill belt (7 cm/s). 3D step kinematics analysis revealed that coordinated alternating bilateral stepping was induced by L2 stimulation (50 Hz) alone and by quipazine alone. Furthermore, the combination treatment produced significantly greater numbers of plantar steps and improved quality of stepping compared to either intervention alone. Both number and quality of stepping peaked at the intermediate dose of 0.3-0.4 mg/kg. The results indicate that quipazine and ES can have complementary effects on spinal circuits and that quipazine dosage is an important factor in differentially modulating these circuitries to improve the quality of the bipedal stepping on a treadmill belt.     

Hindlimb stepping movements in complete spinal rats induced by epidural spinal cord stimulation

The locomotor ability of the spinal cord of adult rats deprived of brain control was tested by epidural spinal cord stimulation. The studies were performed on six rats that had a complete spinal cord transection (T7-T9) and epidural electrode implantations 2-3 weeks before testing was initiated. The stimulating epidural electrodes were implanted at the T12-L6 spinal segments. Epidural electrical stimulation of the dorsal surface of the spinal cord at frequencies between 1 and 50 Hz and intensities between 1 and 10 V without any pharmacological facilitation was used. Stimulation at each of the lumbar spinal cord segments elicited some rhythmic activity in the hindlimbs. However, stimulation at most segmental levels usually evoked activity in only one leg and was maintained for short periods of time (< 10s). Bilateral hindlimb locomotor activity was evoked most often with epidural stimulation at 40-50 Hz applied at the L2 segment. A necessary condition for initiation of locomotor activity was providing a specific amount (at least 5%) of body weight support. Therefore, the rat spinal cord isolated from brain control is capable of producing bilateral stepping patterns induced most readily by epidural stimulation applied at the L2 spinal segment. Furthermore, the induced stepping patterns were dependent on sensory feedback associated with weight bearing.     

Comparison of spontaneous motor pattern generation in non-hemisected and hemisected mouse spinal cord.

Spontaneous electromyogram (EMG) patterns in the gastrocnemius (G) and tibialis anterior (TA) muscles of spinal cord-hindlimb explants from neonatal mice were investigated. Compared to non-hemisected explants, neither longitudinal hemisection of the spinal cord nor hemisection plus transection at L1 significantly altered the incidence of spontaneous motor rhythm. Therefore, not only does each half of the neonatal spinal cord contain sufficient circuitry to generate motor rhythm, but the more reduced preparations were just as likely to produce such activity. Hemisected preparations, however, exhibited slower rhythm, perhaps due to the loss of excitatory commissural connections. No correlation was found between the number of cycles in a rhythmic sequence and cycle period. In hemisected as well as non-hemisected explants, sequences of spontaneous EMG rhythm occurred in either the G or TA muscle, but not in both muscles simultaneously. Consequently, cycle-to-cycle alternation between rhythmic bursting in the G and TA muscles was not observed. The excitability in such preparations was apparently insufficient for maintained activations of both muscles (either for cycle-to-cycle alternation or for co-contraction).     

Instrumental learning within the rat spinal cord: localization of the essential neural circuit

Following spinal transection of the upper thoracic spinal cord, male Sprague-Dawley rats given legshock whenever a hindlimb is extended learn to maintain the leg in a flexed position. The region of the cord that mediates this instrumental learning was isolated using neuroanatomical tracing, localized infusion of lidocaine, and surgical transections. DiI and Fluoro-Gold microinjection at the site of shock application labeled motor neuron bodies of lamina IX in the lower lumbar region. Local application of the Na-super++ channel blocker lidocaine disrupted learning when it was applied over a region extending from the lower lumbar (L3) to upper sacral (S2) cord. The drug had no effect rostral or caudal to this region. Surgical transections as low as L4 had no effect on learning. Learning also survived a dual transection at L4 and S3, but not L4 and S2. The results suggest that the essential neural circuit lies between L4 and S3.     

Finite element analysis of the spondylolysis in lumbar spine

Spondylolysis is a fracture of the bone lamina in the pars interarticularis and has a high risk of developing spondylolisthesis, as well as traction on the spinal cord and nerve root, leading to spinal disorders or low back pain when the lumbar spine is subjected to high external forces. Previous studies mostly investigated the mechanical changes of the endplate in spondylolysis. However, little attention has been focused on the entire structural changes that occur in spondylolysis. Therefore, the purpose of this study was to evaluate the biomechanical changes in posterior ligaments, disc, endplate, and pars interarticularis between the intact lumbar spine and spondylolysis. A total of three finite element models, namely the intact L2-L4 lumbar spine, lumbar spine with unilateral pars defect and with bilateral pars defect were established using a software ANSYS 6.0. A loading of 10 N.m in flexion, extension, left torsion, right torsion, left lateral bending, and right lateral bending respectively were imposed on the superior surface of the L2 body. The bottom of the L4 vertebral body was completely constrained. The finite element models estimated that the lumbar spine with a unilateral pars defect was able to maintain spinal stability as the intact lumbar spine, but the contralateral pars experienced greater stress. For the lumbar spine with a bilateral pars defect, the rotation angle, the vertebral body displacement, the disc stress, and the endplate stress, was increased more when compared to the intact lumbar spine under extension or torsion.     

运动诱发电位和BBB评分在大鼠脊髓损伤功能评价中的相关性研究

目的 探讨大鼠脊髓损伤功能评价指标运动诱发电位(MEP)和Basso-Beattie-Bresnahan (BBB)评分的相关性。方法 成年雌性SD大鼠16只,采用数字表法随机分为对照组和实验组,每组8只。对照组只施行手术,不给予外力打击。实验组应用PSI-IH装置复制脊髓损伤模型。记录并分析损伤前以及损伤后3 h、1 d、3 d、1周、2周、3周、4周、5周、6周大鼠脊髓运动诱发电位(scMEP)和肌肉运动诱发电位(mMEP),同时采用BBB评分对大鼠后肢运动功能进行评定。6周后观察大鼠脊髓组织学结构变化。结果 实验组大鼠脊髓损伤后3 h scMEP波幅减小,为正常波幅的32.69%±0.83%,2周后为正常波幅的52.93%±2.23%并处于稳定状态,但均低于对照组(P值均＜0.01);损伤后3 h mMEP波形消失,1 d后恢复至正常波幅的1.16%±0.17%,3 d后波幅明显恢复,4周后达正常波幅的48.20%± 3.70%并处于稳定状态,但均低于对照组(P值均＜0.01)。实验组大鼠脊髓损伤后3 h和1 d,所有大鼠BBB评分均为0分,3 d后评分(1.38±0.52)分,4周后评分(11.50±0.93)分,达到稳定状态,但均低于对照组(P值均＜0.01)。实验组大鼠脊髓损伤后3 h~6周,scMEP与BBB评分均为显著相关(r值为0.732~0.908,P值均＜0.05)。实验组大鼠脊髓损伤后1~6周mMEP与BBB评分呈中度至高度相关(r值为0.718～0.951,P值均＜0.05)。对照组大鼠以上各指标均无显著变化。结论 大鼠脊髓损伤发生后,scMEP、mMEP和BBB评分三个脊髓功能指标会先后顺序恢复,而且scMEP、mMEP与BBB评分均存在着一定的相关性。大鼠脊髓损伤后,scMEP、mMEP是较BBB评分更为灵敏的脊髓功能评价指标。     

Afterhyperpolarization modulation in lumbar motoneurons during locomotor-like rhythmic activity in the neonatal rat spinal cord in vitro

Motoneuron afterhyperpolarization (AHP) amplitude and somatic input conductance were monitored during pharmacologically induced, locomotorlike ventral root activity using an isolated neonatal rat spinal cord preparation (transected at the C1 level). Nonspontaneously firing motoneurons were selected for study. Single spikes were evoked at regular intervals by brief depolarizing current pulse injections, while somatic input conductance was monitored by hyperpolarizing current pulses. The induction of rhythmic ventral root activity was associated with tonic depolarization of motoneurons as well as superimposed rhythmically alternating membrane depolarization and hyperpolarization (locomotor drive potentials, LDPs). In 9 of 13 trials (six of eight cells) the peak amplitude of AHPs following current-evoked action potentials was reduced during both the hyperpolarized and the depolarized phases of the LDP, compared with the pre-locomotor condition. The peak AHP amplitude increased during the depolarized phase of the LDP in 4 of 13 trials (three of eight cells); however, in 3 of these 4 trials measurement of the AHP later in the course of its trajectory, using a half decay time (HDt) reference point, demonstrated AHP amplitude reduction during rhythmic activity compared with the prelocomotor condition. In seven of eight motoneurons the induction of rhythmic activity was associated with a decrease in input conductance. The pattern of AHP amplitude and conductance modulation during the two phases of the LDP was consistent for individual trials; however, there was considerable intertrial variation. The results suggest that AHP modulation during locomotor-like activity in this preparation can be mediated independently of supraspinal influences by intrinsic spinal cord mechanisms, and the observed AHP suppression does not appear to be the passive result of an increase in background conductance. The discrepancy between peak and HDt-based AHP amplitude measurements during the depolarized phase of the LDP in some trials may be due to competing effects of passively enhanced potassium currents and a mechanism that actively reduces the calcium-dependent potassium conductance. The possibility that both the AHP amplitude and the input conductance changes observed during locomotor-like activity reflect a regulation of potassium channels is discussed.     

Sexual dimorphism of the human spinal cord in the aging process

There have been few morphometric studies on age-related changes in the human spinal cord. The purpose of the present study was to determine the existence of sexual dimorphism of the spinal cord between males and females during the aging process. Spinal cords were removed from cadaver specimens, 26 males and 22 females for anatomic practice, the age at death ranged from 41 to 97 years for males (average, 71.5 years) and from 59 to 92 years for females (average, 76.6 years). Spinal cord segments were embedded in celloidin after secondary fixation and dehydration. Sections were stained with the Luxol fast blue-periodic acid-Schiff-hematoxylin and Klüver-Barrera methods. Morphometric analysis was performed with an electronic optical planimeter and a computer. Each section was enlarged 13.5 times to take a picture. The areas of the transverse section white matter and gray matter of the spinal cord at segments C5 and L3 were measured. Although there was no correlation between the total transverse area of the spinal cord and age either in males or females, we noticed that the area of the gray matter decreased faster in males than in females; while the area of the white matter decreased faster in females than in males. The area ratio of the white matter to the whole segment area of the spinal cord (W/T) at level C5 is larger in males than that in females. Our results suggest that there could be a difference between males and females in changes in the white and gray matters of the spinal cord due to aging.     

肱二头肌不同模式运动任务刺激下的颈髓功能磁共振成像研究

目的 探究肱_二头肌不同模式运动任务刺激下的颈髓激活区分布及是否存在运动刺激-颈髓激活强度的同侧优势性.方法 9例健康右利手受试者行双上肢的肱二头肌负荷任务和屈肘运动仟务试验.采用GE 1.5T磁共振系统运用GRE-EPI扫描序列行颈髓功能磁共振成像(Fmri),行BOLD图像分析,对激活区的信号强度变化进行统计学分析.结果 (1)肱二头肌不同模式运动任务刺激下的颈髓激活区主要分布于C5～C6节段,邻近C7～C8节段亦出现少量激活;(2)单侧上肢运动条件下,脊髓双侧激活现象多见;(3)运动肢体同侧的脊髓激活区信号强度变化显著大于对侧(P<0.05).结论 肱二头肌不同模式运动任务诱发颈髓激活的节段分布与主要收缩肌——肱二头肌的脊髓支配节段(C5、C6)相符合,存在运动刺激-颈髓激活强度的同侧优势性.     

Metachronal coupling between spinal neuronal networks during locomotor activity in newborn rat

In the present study, we investigate spinal cord neuronal network interactions in the neonatal rat during locomotion. The behavioural and physiological relevance of metachronally propagated locomotor activity were inferred from kinematic, anatomical and in vitro electrophysiological data. Kinematic analysis of freely behaving animals indicated that there is a rhythmic sequential change in trunk curvature during the step cycle. The motoneurons innervating back and tail muscles were identified along the spinal cord using retrograde labelling. Systematic multiple recordings from ventral roots were made to determine the precise intrinsic pattern of coordination in the isolated spinal cord. During locomotor-like activity, rhythmic ventral root motor bursts propagate caudo-rostrally in the sacral and the thoracic spinal cord regions. Plotting the latency as a function of the cycle period revealed that the system adapts the intersegmental latency to the ongoing motor period in order to maintain a constant phase relationship along the spinal axis. The thoracic, lumbar and sacral regions were capable of generating right and left alternating motor bursts when isolated. Longitudinal sections of the spinal cord revealed that both the bilateral antiphase pattern observed for the sacral region with respect to the lumbar segment 2 as well as the intersegmental phase lag were due to cross-cord connections. Together, these results provide physiological evidence that the dynamic changes observed in trunk bending during locomotion are determined by the intrinsic organization of spinal cord networks and their longitudinal and transverse interactions. Similarities between this organization, and that of locomotor pattern generation in more primitive vertebrates, suggest that the circuits responsible for metachronal propagation of motor patterns during locomotion are highly conserved.