中药脊髓Ⅰ号对脊髓厚片Ca2+荧光强度的影响

目的　探讨中药脊髓Ⅰ号对脊髓厚片Ca2 + 荧光强度的影响。方法　将 33只Wistar大鼠随机分为 3组 :下胸段脊髓半横断组 (损伤组 )、对照组和中药脊髓Ⅰ号治疗组。快速处死大鼠 ,取下胸段脊髓 ,切脊髓厚片 ,用Fluo 3荧光染料孵育 ,激光共聚焦显微镜观察。结果　损伤组、对照组和中药治疗组左侧Ca2 + 荧光强度分别为 12 6 3± 3 2 7、13 34± 3 5 1和 12 89±3 31,右侧分别为 2 1 6 8± 3 6 9、14 72± 2 12和 12 97± 3 6 0 ,损伤组脊髓厚片损伤侧Ca2 + 荧光强度显著升高 ,治疗组两侧灰质Ca2 + 荧光强度无显著差异。结论　 (1)损伤侧Ca2 + 荧光强度显著升高 ;(2 )中药脊髓Ⅰ号对Ca2 + 荧光强度的升高有一定抑制作用。     

大鼠脊髓慢性压迫损伤模型的建立

目的 建立一种大鼠脊髓慢性压迫性损伤模型.方法 将慢性膨胀物于显微镜下植入大鼠T8/9水平,随着压迫物的膨胀,逐渐形成不同程度的慢性压迫脊髓损伤实验动物模型.手术后通过BBB评分进行行为学功能评定,检测压迫段脊髓病理标本及通过电脑图像分析系统半定量检测凋亡启动基因P53.结果 术后观察行为学、组织学、病理学上的改变,3者相符合.结论 此模型较以往模型相比,具有制作简单,损伤程度可调整,脊髓损伤能表现出不同的压迫程度,可重复性强等优点.为进一步研究脊髓慢性压迫损伤病理机制奠定基础.     

BK channels in intact clonal rat pituitary cells are activated by physiological elevations of the cytosolic Ca2+ concentration at the normal resting potential

Activation of large conductance Ca²⁺-activated K⁺ channels (BK channels) in intact clonal rat pituitary cells (GH₄ cells) was investigated using the cell-attached patch-clamp configuration. This method prevents loss of intracellular factors which might influence channel activity. BK channels are generally considered to be inactive at the resting membrane potential in excitable cells. However, at the resting potential (0 mV pipette potential), 40% of the cell-attached patches displayed spontaneously active BK channels, which remained active even at 20 mV hyperpolarization. The peptide thyroliberin (TRH) elevates the cytosolic Ca²⁺ concentration ([ Ca²⁺]_i) in GH cells by IP₃-induced release of Ca²⁺ from intracellular stores. This rise in [Ca²⁺]_i occurs concomitantly with membrane hyperpolarization. TRH stimulation caused activation of BK channels in nine out of 30 silent cell-attached patches, and caused enhanced channel activity in seven out of 29 cell-attached patches containing spontaneously active BK channels. The Ca²⁺ ionophore ionomycin activated silent BK channels in three out of 10 cell-attached patches, and increased the activity of spontaneously active BK channels in seven out of 16 cell-attached patches. The pipette potential was clamped to 0 mV in all these experiments. We conclude that the BK channels in GH₄ cells may be active at the resting membrane potential and more negative membrane potentials. The channels may also be activated further by physiological elevations of [Ca²⁺]_i in the same potential range. Our results point towards new possible physiological roles for the BK channels in GH₄ cells. This is in agreement with the emerging picture of BK channels highly sensitive to [Ca²⁺]_i in a wide variety of cell types.     

Miniature Ca2+ channels in excised plasma-membrane patches: activation by IP3

 In the present work, we characterized the receptor properties and the conductive features of the inositol (1,4,5)-trisphosphate (IP₃)-activated Ca²⁺ channels present in excised plasma-membrane patches obtained from mouse macrophages and A431 cells. We found that the receptor properties of the channels tested were similar to those of the IP₃ receptor (IP₃R) expressed in the endoplasmic reticulum (ER) membrane. These properties include activation by IP₃, inhibition by heparin, time-dependent inactivation by high IP₃ concentrations, activation by guanosine 5′o-thiotriphosphate and regulation by arachidonic acid. On the other hand, in terms of conductive properties, the channel closely resembles Ca²⁺-release-activated Ca²⁺ channels (I _crac). These conductive properties include extremely low conductance (≈1 pS), very high selectivity for Ca²⁺ over K⁺ (P _Ca/P _K>1000), inactivation by high intracellular Ca²⁺ concentration and, importantly, strong inward rectification. Notably, the same channel was activated by: (1) agonists in the cell-attached mode of channel recording, and (2) cytosolic IP₃ after patch excision. Although the possibility cannot be completely excluded that a novel type of IP₃R is expressed exclusively in the plasma membrane, in their entirety our findings suggest that the plasma membrane of mouse macrophages and A431 cells contains I _crac-like Ca²⁺ channels coupled to an IP₃-responsive protein which displays properties similar to those of the IP₃R expressed in the ER membrane. Received: 16 June 1998 / Received after revision: / 24 August 1998 / Accepted: 1 September 1998     

Influence of age on L-type Ca2+ channels in the pulmonary artery and vein of spontaneously hypertensive rats

The influence of age on the density and localization of L-type Ca²⁺ channels was studied during development of hypertension in the pulmonary artery and vein of spontaneously hypertensive rats (SHR) and age-matched normotensive Wistar–Kyoto (WKY) rats by radioligand binding assay and light microscope autoradiography. SHR were examined at 6 weeks (juvenile, pre-hypertensive stage), 12 weeks (young, developing hypertension) and 24 weeks (mature, established hypertension). The dihydropyridine-type Ca²⁺ antagonist [³H]nicardipine was used as a radioligand. It was bound specifically to sections of rat pulmonary artery and vein. Dissociation constant (K_d) values were similar in WKY rats and SHR, whereas maximum density of binding sites (B_max) values increased in SHR in comparison with WKY rats. This increase was noticeable from the pre-hypertensive phase. The pharmacological profile of [³H]nicardipine binding was similar in different age groups of either normotensive and hypertensive rats. Quantitative analysis of autoradiographs from SHR revealed a progressive increase of silver grains in smooth muscle of tunica media and to a lesser extent in the adventitia of pulmonary artery but not of pulmonary vein from pre-hypertensive stage to developing hypertension. No further changes were observed in established hypertension. The above data indicate that the density of L-type Ca²⁺ channels of pulmonary arteries is increased in SHR. This augmentation after the pre-hypertensive phase suggests the occurrence of dysregulation of Ca²⁺ handling in the pulmonary vasculature of developing SHR.     

Kinetic components of the gating currents of human cardiac L-type Ca2+ channels

 It has been reported previously that the β subunit increases both the ionic current and the gating charge movement of the human cardiac L-type Ca²⁺ channel α₁ subunit, and that steady-state measurements reveal the presence of two distinct components of the charge movement [Josephson IR, Varadi G (1996) Biophys J 70:1285–1293]. The present work identifies and characterizes the kinetic properties of the components of the human cardiac L-type Ca channel gating currents (I _g), and determines the relationship of these components to the activation of the Ca channel ionic current (I _Ca). Cloned human cardiac L-type α₁+α₂+β₃ subunits were transiently expressed in HEK293 cells and calcium channel gating currents were recorded following the addition of 5 mM Co²⁺. The steady-state charge integrals of the gating currents (Q _ON-V _m) were fit by a sum of two Boltzmann components: Q _ON1, which ranged over more negative potentials, and Q _ON2, which ranged over more positive potentials. The kinetic components of the ON and OFF gating currents were identified using bi-exponential curve fitting. Reconstruction of the two kinetic components of charge (Q _ONfast and Q _ONslow) yielded distributions that were similar in their voltage dependence and relative proportion to those measured directly by steady-state integration of Q _ON1 and Q _ON2. Changes in the initial conditions were found to affect Q _ON1 and Q _ON2 differently. The time constants of the ON gating current decays were similar to those of the activation of I _Ca. The results suggest that: (1) the activation of the human cardiac L-type Ca channel involves the movements of at least two, functionally distinct gating structures; (2) a fast charge movement (≈1/4 of the total charge; Q _ON1 or Q _ONfast) precedes a slower charge movement (≈3/4 of the total charge; Q _ON2 or Q _ONslow); and (3) channel opening is associated with the conformational change(s) producing Q _ONslow. Received: 7 June 1996 / Received after revision: 24 September 1996 / Accepted: 1 October 1996     

嗅球成鞘细胞移植对脊髓半横断后脊髓灰质内Ca2+荧光强度的影响

目的：研究嗅球成鞘细胞(OECs)的移植对脊髓半横断后脊髓灰质细胞内游离钙离子浓度([Ca^2 ]i)的影响,探索OECs促进脊髓再生的机制。方法：将体外培养的OECs制成细胞悬浮液移植到上颈段脊髓半横断的动物模型中,用激光扫描共聚焦显微镜观察颈段脊髓厚片[Ca^2 ]i荧光强度的变化。结果：移植组与损伤组比较,损伤组损伤侧与非损伤侧[Ca^2 ]i荧光强度差异非常显著;而移植组损伤侧与非损伤侧[Ca^2 ]i荧光强度无显著差异。结论：(1)OECs对脊髓的再生有良好的促进作用;(2)OECs能够抑制[Ca^2 ]i的升高,改善损伤部位的微环境。     

Modulation of Ca channels by activation of adenosine A1 receptors in rat striatal glutamatergic nerve terminals

We determined that activation of adenosine A₁ receptors in striatal synaptosomes with 100 nM N⁶-cyclopentyladenosine (CPA) inhibited both the release of endogenous glutamate and the increase of intracellular free Ca²⁺ concentration ([Ca²⁺]_i), due to 4-aminopyridine (4-AP) stimulation, by 28 and 19%, respectively. Furthermore, CPA enhanced the inhibition of endogenous glutamate release due to ω-conotoxin GVIA (ω-Cgtx GVIA), ω-Cgtx MVIIC or ω-Cgtx GVIA plus ω-Cgtx MVIIC. Similar effects were observed in the [Ca²⁺]_i signal. The inhibitory effects of CPA and ω-Cgtx GVIA were additive, but the effects of CPA and ω-Cgtx MVIIC were only partially additive. These results suggest that P/Q-type Ca²⁺ channels and other type(s) of Ca²⁺ channel(s), coupled to glutamate release, are inhibited subsequently to activation of adenosine A₁ receptors.     

T-type Ca2+ channels mediate propagation of odor-induced Ca2+ transients in rat olfactory receptor neurons

Propagation of odor-induced Ca(2+) transients from the cilia/knob to the soma in mammalian olfactory receptor neurons (ORNs) is thought to be mediated exclusively by high-voltage-activated Ca(2+) channels. However, using confocal Ca(2+) imaging and immunocytochemistry we identified functional T-type Ca(2+) channels in rat ORNs. Here we show that T-type Ca(2+) channels in ORNs also mediate propagation of odor-induced Ca(2+) transients from the knob to the soma. In the presence of the selective inhibitor of T-type Ca(2+) channels mibefradil (10-15 microM) or Ni(2+) (100 microM), odor- and forskolin/3-isobutyl-1-methyl-xanthine (IBMX)-induced Ca(2+) transients in the soma and dendrite were either strongly inhibited or abolished. The percentage of inhibition of the Ca(2+) transients in the knob, however, was 40-50% less than that in the soma. Ca(2+) transients induced by 30 mM K(+) were partially inhibited by mibefradil, but without a significant difference in the extent of inhibition between the knob and soma. Furthermore, an increase of as little as 2.5 mM in the extracellular K(+) concentration (7.5 mM K(+)) was found to induce Ca(2+) transients in ORNs, and such responses were completely inhibited by mibefradil or Ni(2+). Total replacement of extracellular Na(+) with N-methyl-d-glutamate inhibited none of the odor-, forskolin/IBMX- or 7.5 mM K(+)-induced Ca(2+) transients. Positive immunoreactivity to the Ca(v)3.1, Ca(v)3.2 and Ca(v)3.3 subunits of the T-type Ca(2+) channel was observed throughout the soma, dendrite and knob. These data suggest that involvement of T-type Ca(2+) channels in the propagation of odor-induced Ca(2+) transients in ORNs may contribute to signal transduction and odor sensitivity.     

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.     

Effect of acidosis on Ca2+-activated K+ channels in cultured porcine coronary artery smooth muscle cells

 Although acidosis induces vasodilation, the vascular responses mediated by large-conductance Ca²⁺-activated K⁺ (K_Ca) channels have not been investigated in coronary artery smooth muscle cells. We therefore investigated the response of porcine coronary arteries and smooth muscle cells to acidosis, as well as the role of K_Ca channels in the regulation of muscular tone. Acidosis (pH 7.3–6.8), produced by adding HCl to the extravascular solution, elicited concentration-dependent relaxation of precontracted, endothelium-denuded arterial rings. Glibenclamide (20 μM) significantly inhibited the vasodilatory response to acidosis (pH 7.3-6.8). Charybdotoxin (100 nM) was effective only at pH 6.9–6.8. When we exposed porcine coronary artery smooth muscle cells to a low-pH solution, K_Ca channel activity in cell-attached patches increased. However, pretreatment of these cells with 10 or 30 μM O, O′-bis(2-aminophenyl)ethyleneglycol-N,N,N′,N′-tetraacetic acid tetrakis(acetoxymethyl)ester (BAPTA-AM), a Ca²⁺ chelator for which the cell membrane is permeable, abolished the H⁺-mediated activation of K_Ca channels in cell-attached patches. Under these circumstances H⁺ actually inhibited K_Ca channel activity. When inside-out patches were exposed to a [Ca²⁺] of 10^–6 M [adjusted with ethyleneglycolbis(β-aminoethylester)-N,N,N′,N′-tetraacetic acid (EGTA) at pH 7.3], K_Ca channels were activated by H⁺ concentration dependently. However, when these patches were exposed to a [Ca²⁺] of 10^–6 M adjusted with BAPTA at pH 7.3, H⁺ inhibited K_Ca channel activity. Extracellular acidosis had no significant direct effect on K_Ca channels, suggesting that extracellular H⁺ exerts its effects after transport into the cell, and that K_Ca channels are regulated by intracellular H⁺ and by cytosolic free Ca²⁺ modulated by acute acidosis. These results indicate that the modulation of K_Ca channel kinetics by acidosis plays an important role in the determination of membrane potential and, hence, coronary arterial tone. Received: 20 January 1998 / Received after revision: 9 April 1998 / Accepted: 22 April 1998     

龟板对脊髓损伤后大鼠功能和骨形态发生蛋白4表达的影响

目的　观察龟板对大鼠损伤脊髓骨形态发生蛋白 4 (BMP4 )表达和后肢功能恢复的影响。方法　应用改良Allen脊髓损伤模型 ,于术后 1、7、14、2 1、2 8d分别对大鼠进行Tarlov评分和斜板试验检查后肢功能。应用免疫组织化学技术检测BMP4的表达 ,观察龟板对脊髓损伤后BMP4的影响。结果　脊髓损伤后第 1d ,在两组受损伤脊髓灰质中都可见到BMP4的表达。第 14d时达到高峰 ,龟板组为 37 2 4± 5 73,损伤组 2 1 4 8± 6 83(P <0 0 5 )。龟板组可使损伤的脊髓BMP4持续高表达至术后第 2 8d ,而损伤组仅持续表达至术后 2 1d。增加的BMP4阳性细胞数与神经功能的改善平行。结论　龟板可减轻神经损伤症状和促进脊髓损伤后BMP4表达     

脊髓横断伤后Fos在脑内与内脏和心血管相关核团中的表达

目的为阐明急性脊髓损伤对内脏及心血管活动的影响机制提供形态学资料。方法脊髓T4节段横断术后3h,用免疫组织化学方法观察脑与脊髓内脏和心血管相关核团内Fos表达。结果T4水平损伤3h后,中央杏仁核、下丘脑室旁核、中缝背核、导水管周围灰质、臂旁核、蓝斑、孤束核、延髓腹外侧网状核与脊髓中间带外侧核等核团中Fos阳性神经元数目较假手术组显著增加(P<0.01)。结论急性脊髓损伤可引起中枢神经系统的内脏和心血管相关核团内神经元产生特异性反应,但反应的机制不同。     

腓肠神经移植修复大鼠陈旧性脊髓损伤的作用

目的:探讨利用自体周围神经组织移植修复大鼠陈旧性脊髓损伤病理机制,为临床应用提供实验依据。方法:利用改良Allens撞击方法建立脊髓打击损伤模型,12周后,将大鼠分为2组,实验组切取后肢腓肠神经,利用显微外科技术去除神经外膜,将其修剪成小段,游离移植于脊髓损伤处,对照组不作处理。分别于术后2、4、12周,在光镜及电镜下观察脊髓损伤段及移植周围神经再生情况。术后4、8及12周分别对两组动物进行脊髓诱发电位检查。结果:对照组脊髓变性,可见瘢痕和空洞,实验组术后12周,损伤区脊髓与周围神经融合良好。脊髓诱发电位检查神经移植组优于对照组。结论:周围神经组织游离移植修复大鼠陈旧性脊髓损伤后,存活良好,为再生轴突跨越损伤段脊髓提供通道。     

N- and P/Q-type Ca2+ channels in adrenal chromaffin cells

Ca2+ is the most ubiquitous second messenger found in all cells. Alterations in [Ca2+]i contribute to a wide variety of cellular responses including neurotransmitter release, muscle contraction, synaptogenesis and gene expression. Voltage-dependent Ca2+ channels, found in all excitable cells (Hille 1992), mediate the entry of Ca2+ into cells following depolarization. Ca2+ channels are composed of a large pore-forming subunit, called the alpha1 subunit, and several accessory subunits. Ten different alpha1 subunit genes have been identified and classified into three families, Ca(v1-3) (Dunlap et al. 1995, Catterall 2000). Each alpha1 gene produces a unique Ca2+ channel. Although chromaffin cells express several different types of Ca2+ channels, this review will focus on the Cav(2.1) and Cav(2.2) channels, also known as P/Q- and N-type respectively (Nowycky et al. 1985, Llinas et al. 1989b, Wheeler et al. 1994). These channels exhibit physiological and pharmacological properties similar to their neuronal counterparts. N-, P/Q and to a lesser extent R-type Ca2+ channels are known to regulate neurotransmitter release (Hirning et al. 1988, Horne & Kemp 1991, Uchitel et al. 1992, Luebke et al. 1993, Takahashi & Momiyama 1993, Turner et al. 1993, Regehr & Mintz 1994, Wheeler et al. 1994, Wu & Saggau 1994, Waterman 1996, Wright & Angus 1996, Reid et al. 1997). N- and P/Q-type Ca2+ channels are abundant in nerve terminals where they colocalize with synaptic vesicles. Similarly, these channels play a role in neurotransmitter release in chromaffin cells (Garcia et al. 2006). N- and P/Q-type channels are subject to many forms of regulation (Ikeda & Dunlap 1999). This review pays particular attention to the regulation of N- and P/Q-type channels by heterotrimeric G-proteins, interaction with SNARE proteins, and channel inactivation in the context of stimulus-secretion coupling in adrenal chromaffin cells.     

脊髓挫伤速度对颈脊髓原发性损伤影响的实验研究

目的　确定脊髓挫伤速度是脊髓损伤的因素,探讨不同速度的脊髓挫伤对大鼠颈脊髓原发性损伤的影响。  方法    20只成年雄性Sprague-Dawley大鼠随机分为快速组（500 mm/s,n=8）、慢速组（5 mm/s,n=8）和对照组（n=4）。用直径为4 mm的平头圆锥打击头在C5水平产生1.5 mm的挫伤位移。损伤后即行心脏固定,切取以挫伤部位为中心长约1.5 cm的脊髓组织。行连续矢状位冰冻切片。HE染色观察脊髓大体形态,计算出血量。β-APP免疫组化后观察轴索损伤程度。  结果　挫伤后观察到脊髓表面有一带状出血,且快速组出血带颜色更深。快速组挫伤位移为(1.50±0.05) mm,最大力为(5.3±1.2) N;慢速组挫伤位移为(1.51±0.04) mm,最大力为(2.8±0.6) N,两组间最大力的差异有显著性（P=0.001）。HE染色显示脊髓出血大部分都集中在灰质,白质相对较少。快速组脊髓总出血量、灰质出血量和白质出血量分别为0.94、0.71和0.23 mm3,慢速组分别为0.55、0.43和0.12 mm3,其中两组间总出血量和灰质出血量的差异有显著性（P＜0.05）。β-APP免疫组化观察到快速组轴索断裂比慢速组更为严重。  结论　脊髓挫伤速度是影响脊髓原发性损伤的因素,快速的脊髓挫伤导致的原发性脊髓损伤更为严重,导致更多的脊髓出血和轴索断裂。     

Nesfatin-1 immunoreactivity in rat brain and spinal cord autonomic nuclei

Nesfatin-1 is one of the peptide products of posttranslational processing of the nucleobindin-2 (NUCB2) gene, suggested to have physiological relevance to suppress food intake and body weight gain in rats. Nesfatin-1-immunoreactive cells have been found in distinct nuclei in the rat brain related to circuitries regulating food intake. Here, we report novel yet undescribed localization of NUCB2/nesfatin-1 at the mRNA and protein level in the rat central nervous system. Immunohistochemical staining revealed the localization of NUCB2/nesfatin-1 in the piriform and insular cortex, endopiriform nucleus, nucleus accumbens, lateral septum, bed nucleus of stria terminalis, central amygdaloid nucleus, medial preoptic area, dorsal raphe nucleus, ambiguus nucleus, ventrolateral medulla and gigantocellular reticular nucleus, as well as Purkinje-cells of the cerebellum. In the spinal cord, nesfatin-1 immunoreactivity (IR) was found in both sympathetic and parasympathetic preganglionic neuronal groups and in the dorsal area X from lower thoracic to sacral segments. The immunohistochemical results were confirmed by RT-PCR in the central amygdaloid nucleus, nucleus accumbens, cerebellum and lumbar spinal cord microdissected by punch technique. The features and distributions of nesfatin-1 IR and mRNA expression in the brain and spinal cord suggest that NUCB2/nesfatin-1 could play a wider role in autonomic regulation of visceral-endocrine functions besides food intake.     

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.