Differences between the tactile sensitivity on the anterior torso of normal individuals and those having suffered complete transection of the spinal cord

Using the method of limits and a magnitude estimation procedure, the sense of touch was examined at multiple sites on the anterior torso of normal subjects. Their performance was compared with the performance of individuals having experienced a functionally complete spinal cord transection more than 6 months prior to the tests. Near the insentient regions of the spinal cord-injured patients there was a zone wherein the threshold for light touch was elevated and variable. Within this same transition zone, estimates of the magnitude of a brushing stimulus increased as a linear function of distance from the border for approximately 12 cm away from insentient skin. Throughout the rest of the thorax, spinal cord-injured patients displayed touch thresholds 67% higher than normals and, at the same test sites, spinal cord-injured patients offered estimates of the intensity of the brushing stimulus that averaged 62% higher than normal subjects. The greater intensity of the sensations experienced by spinal cord-injured patients with even very weak stimuli and the smaller range within which they were able to scale stimulus intensity, produced a situation wherein the patients made frequent errors of judgement even on skin regions far from the body parts affected by the lesion. These observations support the hypothesis that spinal cord lesions interrupt tonic modulatory mechanisms having global influences on the sense of touch. This loss produces an elevation of the touch threshold and a reduction of the normal dynamic range of tactile sensory perception for all skin surfaces on the anterior torso.     

Comparing sensibility for touch,cold, and warmth in different skin areas

The primary objective of this pilot study was to assess if the magnitude estimation of suprathreshold brushing, warmth (40?°C), and cold (25?°C) stimuli of the skin over the dorsum of the hand and the dorsum of the foot are comparable to the perceived intensity for the same stimuli applied to the skin over any of the following areas: forehead, m. trapezius, m. deltoideus, thoracic back, and lumbar back, respectively. Thirty-two subjects aged 18–64 years were included. Participants were examined by two physicians on two different occasions, 1–58 days apart. Participants rated the magnitude of the perceived sensation of each stimulus on an 11-point numerical rating scale (NRS) 0–10, where 0 was anchored to “no sensation at all for touch/cold/warmth” and 10 anchored to “the most intense imaginable non-painful sensation of touch/cold/warmth”. The criterion for sensory equivalence for one modality was arbitrarily considered satisfactory if two regions had the same numerical rating ±1 point in at least 85% of the individuals. Based on the pre-study criteria for sensory equivalence applied in this study only one area was found to be equivalent to the foot skin for the percept of brushing, that is, the skin over the deltoid muscle and one area for the hand, that is, the skin over the forehead. We failed to find any area with equivalent sensitivity to the hand or the foot for the cold or warm stimuli.     

Detection Theory Applied to the Absolute Sensitivity of Sensory Systems

Mainly the skin senses touch and warmth have been investigated. It is shown that the decision model describes the experimental data better than the threshold model. The experiments lead to the assumption that an internal noise exists, which is a neural activity being undistinguishable from the neural activity caused by small stimuli and which adds to the neural activity caused by the stimulus. The probability distribution of this internal noise can be considered to be gaussian. The relation between stimulus and neural activity is alinear for the touch sense. The question of whether noise of a multiplicative nature must be assumed is discussed.     

Pattern of expiratory muscle activation during lower thoracic spinal cord stimulation.

Large positive airway pressures (Paws) can be generated by lower thoracic spinal cord stimulation (SCS), which may be a useful method of restoring cough in spinal cord-injured patients. Optimal electrode placement, however, requires an assessment of the pattern of current spread during SCS. Studies were performed in anesthetized dogs to assess the pattern of expiratory muscle recruitment during SCS applied at different spinal cord levels. A multicontact stimulating electrode was positioned over the surface of the lower thoracic and upper lumbar spinal cord. Recording electromyographic electrodes were placed at several locations in the abdominal and internal intercostal muscles. SCS was applied at each lead, in separate trials, with single shocks of 0.2-ms duration. The intensity of stimulation was adjusted to determine the threshold for development of the compound action potential at each electrode lead. The values of current threshold for activation of each muscle formed parabolas with minimum values at specific spinal root levels. The slopes of the parabolas were relatively steep, indicating that the threshold for muscle activation increases rapidly at more cephalad and caudal sites. These results were compared with the effectiveness of SCS (50 Hz; train duration, 1-2 s) at different spinal cord levels to produce changes in Paw. Stimulation at the T9 and T10 spinal cord level resulted in the largest positive Paws with a single lead. At these sites, threshold values for activation of the internal intercostal (7-11th interspaces) upper portions of external oblique, rectus abdominis, and transversus abdominis were near their minimum. Threshold values for activation of the caudal portions of the abdominal muscles were high (>50 mA). Our results indicate that 1) activation of the more cephalad portions of the abdominal muscles is more important than activation of caudal regions in the generation of positive Paws and 2) it is not possible to achieve complete activation of the expiratory muscles with a single electrode lead by using modest current levels. In support of this latter conclusion, a two-electrode lead system results in more uniform expiratory muscle activation and significantly greater changes in Paw.     

Spinal tracts producing slow components of spinal cord potentials evoked by descending volleys in man

Slow negative (N) and slow positive (P) waves are frequently produced in the posterior epidural space at the lumbosacral enlargement by epidural stimulation of the rostral part of human spinal cord. The production of these slow potentials are thought to be responsible for analgesia at the stimulated segment as well as below that level. In order to define the spinal tract which mediates these slow potentials, we stimulated directly or from the epidural space the dorsal, dorsolateral, lateral and ventral columns at the cervical or thoracic level, and epidurally recorded spinal cord potentials (des.SCPs) at the lumbosacral enlargement in 7 patients who underwent spine or spinal cord surgery. The des.SCPs recorded in the lumbosacral enlargement consisted of polyphasic spike potentials followed by slow N and P waves. At a near threshold level of stimulus intensity the slow N and P potentials were consistently elicited only by stimulation of the dorsal column. The slow waves were also produced by intense stimulation of other tracts, but remained significantly (P < 0.05−P <0.01) smaller than those evoked by dorsal column stimulation when compared at the same stimulus intensity. Moreover, the slow P wave could not be elicited even by intense stimulation (10 times the threshold strength for the initial spike potentials) of the ventral column. Thus, the results suggest that the slow N and P waves are mostly mediated by the antidromic impulses descending through the dorsal column.     

Differences in the sensations of warmth on the anterior torso of normal and spinal-cord transected individuals

The threshold to warming was measured at 10 sites on the anterior torso between the umbilicus and the clavicle of normal and spinal-cord transected individuals. In normal individuals, thresholds were higher on the thorax than on the abdomen. Men had higher and more variable thresholds than women. Magnitude estimations of supra-threshold stimuli showed that men offer verbal estimates of warmth that are about half of the size of the estimates given by women to the same stimuli. The psychometric function shows that in women, the sensation of warmth grows more rapidly than in men after starting from a higher initial value. After spinal-cord injury, thresholds for detection of warming were elevated. This effect was most noticeable within 8 cm of the anesthetic zone, but farther away, thresholds were still elevated but uniform as a function of distance, being about 30% higher than in normal individuals. After spinal-cord injury, the psychometric functions show that small stimuli elicit relatively large sensations and that these sensations grow more slowly with increasing skin temperatures than for normal individuals. Thus, for small warm stimuli spinal-cord-injured patients (both men and women) have a response similar to normal women but the slope of the psychometric function is flat, being similar to the slope observed for normal men.     

Differences in the sensations of warmth on the anterior torso of normal and spinal-cord transected individuals

The threshold to warming was measured at 10 sites on the anterior torso between the umbilicus and the clavicle of normal and spinal-cord transected individuals. In normal individuals, thresholds were higher on the thorax than on the abdomen. Men had higher and more variable thresholds than women. Magnitude estimations of supra-threshold stimuli showed that men offer verbal estimates of warmth that are about half of the size of the estimates given by women to the same stimuli. The psychometric function shows that in women, the sensation of warmth grows more rapidly than in men after starting from a higher initial value. After spinal-cord injury, thresholds for detection of warming were elevated. This effect was most noticeable within 8 cm of the anesthetic zone, but farther away, thresholds were still elevated but uniform as a function of distance, being about 30% higher than in normal individuals. After spinal-cord injury, the psychometric functions show that small stimuli elicit relatively large sensations and that these sensations grow more slowly with increasing skin temperatures than for normal individuals. Thus, for small warm stimuli spinal-cord-injured patients (both men and women) have a response similar to normal women but the slope of the psychometric function is flat, being similar to the slope observed for normal men.     

Blessé médullaire: prise en charge en andrologie

Sexual reactions are under neurological control. Spinal cord trauma alters neurological structure and induces sexual dysfunction. Pharmacological drugs used currently allow erectile function to be recovered in spinal cord-injured men, an essential step towards the resumption of a sex life. Triggering of ejaculation is often difficult. Perineal stimulation techniques, used either in isolation or in association with pharmacological treatment, promote ejaculation and allow sperm collection and freezing. The possibility of achieving ejaculation during sexual intercourse in spinal cord-injured men remains rare and there is as yet no real therapy available. Despite poor semen quality, spinal cord-injured men maintain reproductive possibilities in 40 to 60% of couples. The use of assisted reproductive technologies is often required. Management of sexual dysfunction in spinal cord-injured men must be integrated into a rehabilitation and re-insertion programme.     

Optimal stimulation of paralyzed muscle after human spinal cord injury.

Muscle properties change profoundly as a result of disuse after spinal cord injury. To study the extent to which these changes can be reversed by electrical stimulation, tibialis anterior muscles in complete spinal cord-injured subjects were stimulated for progressively longer times (15 min, 45 min, 2 h, and 8 h/day) in 6-wk intervals. An index of muscle endurance to repetitive stimulation doubled (from 0.4 to 0.8), contraction and half-relaxation times increased markedly (from 70 to approximately 100 ms), but little or no change was measured in twitch or tetanic tension with increasing amounts of stimulation. The changes observed with 2 h/day of stimulation brought the physiological values close to those for normal (control) subjects. A decrease in the stimulation period produced a reversal of the changes. No effects were observed in the contralateral (unstimulated) muscle at any time, nor was there evidence of decreased numbers of motor units in these subjects secondary to spinal cord injury. Motor unit properties changed in parallel with those of the whole muscle. The occasional spasms occurring in these subjects are not sufficient to maintain normal muscle properties, but these properties can largely be restored by 1-2 h/day of electrical stimulation.     

脐带间充质干细胞移植治疗脊髓损伤的临床研究

目的:探讨脐带间充质干细胞移植治疗脊髓损伤的疗效及安全性。方法:40例脊髓损伤患者给予脐带间充质干细胞移植治疗,移植方法采用静脉输注联合腰穿鞘内注射的方法。术后随访1年余定期观察患者临床症状及各项指标的变化并进行综合分析。移植过程中为促进干细胞的生长和分化,根据患者病情及身体状况给予相应的康复功能锻炼。结果:与入院时比较,脐带间充质干细胞移植治疗3、6、12个月后,不完全性脊髓损伤患者针刺觉评分、轻触觉评分、运动评分均有明显改善(P<0.05或0.01),完全性脊髓损伤患者针刺觉评分、轻触觉评分、运动评分均无明显变化(P>0.05),两组残损分级均无明显改善(P>0.05)。移植后各项生化指标正常,未出现严重的并发症和明显的不良反应。结论:脐带间充质干细胞移植治疗脊髓损伤近期疗效明显,可以改善患者的临床症状,提高患者的生存质量,是一种值得借鉴的治疗方法。     

第二触觉系统:编码触觉情绪成分的C纤维

过去曾认为,人类触觉信息特异地由大直径有髓(Aβ)神经纤维传导。然而最近的研究表明,哺乳动物皮肤的机械感受器不仅有Aβ纤维分布,还有大量低阈值、低传导速度的小直径无髓(C)神经纤维分布,后者对轻微的非伤害性皮肤变形反应敏感,而对快速的皮肤运动反应微弱。初级传入C纤维投射至脊髓浅层,并与脊髓板层II内的次级感觉神经元形成突触联系,再通过脊髓丘脑束投射至岛叶。功能磁共振(fMRI)研究发现,缓慢移动的触觉刺激可以明显地激活岛叶并引起愉悦感,同时还可以激活眶额叶内与愉悦味觉和嗅觉激活区域邻近的部位。这些反应的性质和所激活的部位说明,C纤维触觉主要与边缘系统的功能有关,编码触觉的情绪成分。     

Role of endogenous opiates and extracellular K+ accumulation in the inhibition of frog spinal reflexes by electrical skin stimulation

Electrical skin stimulation of the hind limb (10-100 Hz, 30 s-5 min) at the intensity which leads only to the excitation of low threshold afferents depressed (for 1-30 min) the flexor reflex evoked in spinal frogs by nociceptive stimuli. The inhibition, which lasted for longer than 5 min was blocked by naloxone. Short-term poststimulation effects were associated with an increase of extracellular K+ concentration (delta [K]e) and were not blocked by naloxone. Enkephalins or morphine applied to the spinal cord surface increased the threshold for flexor reflexes while naloxone decrease their threshold. The stimulation was followed by short-term hyperpolarization of primary afferents (PAH; 1-5 min) and by depression of dorsal root potentials (DPRs) which had a similar time course to the delta [K]e, and were not blocked by naloxone. This period was frequently followed by longlasting PAH and enhancement of DRPs (5-30 min), which were abolished by naloxone. Superfusion of the isolated spinal cord with opioids produced PAH and enhanced DRPs evoked by nociceptive stimuli, while naloxone or increase of [K] in Ringer solution depolarized primary afferents and depressed DRPs. It is suggested that the antinociceptive effects of electrical stimulation of low threshold cutaneous afferents in spinal frogs involves at least two mechanisms. The short-term effect may result from delta [K]e, especially at high stimulus strength and is equally effective against noxious and non-noxious stimuli. The longlasting effects selectively affecting nociceptive transmission appear to be produced by endogenous opioids.     

Early locomotor behaviour and the structure of the nervous system in embryos and larvae of the Australian lungfish, Neoceratodusforsteri‡

This paper describes the development of early locomotor responses to mechanical stimulation in the Australian lungfish Neoceralodus and compares them with structural changes in the spinal cord. Initial movements occur spontaneously prior to innervation of myotomal muscles, and are therefore myogenic. After muscle innervation, embryos only move when stimulated; the first type of response to sharp touch is a unilateral flexion away from the stimulus, then at a later stage the contralateral response is followed by a homolateral flexure which, later still, passes into bursts of swimming. The initial contralateral response occurs when decussating interneurons are detectable but before spinal sensory innervation of the trunk; however, the trigeminal sensory pathway has been established by this time and probably mediates the first mechanoreceptive signals from trunk epidermis. Later, Rohon-Beard cells innervate the trunk skin, and then dorsal root neurons take over the major sensory role. The secondary homolateral response and bursts of swimming are paralleled by the development of several types of spinal interneurons and the ingrowth of Mauthner cell axons.     

C-fos gene expression in the rat spinal cord and brain cells during stress and the use of different types of halothane anesthesia

C-fos gene expression was studied as a marker of nervous cells activation in the rat spinal cord and brain cells under different conditions (different kinds of narcosis). Using of 1.5% light halothane narcosis allowed the detection of c-Fos-like proteins expression in the spinal cord cells only. Under initial 1.5% halothane narcosis, c-Fos-like proteins expression in the rat spinal cord (lumbar segments) and the brain cells was observed after placing the rats into the hammock, noxious mechanical stimulation (NMS) or high frequency electromagnetic irradiation of the skin (EHF). The pattern of the brain structures reacting on the NMS by c-Fos proteins expression, was determined. It was shown that NMS increases the c-Fos positive cell quantity in the lateral hypothalamic area (LHA), ventro-medial (VMH), dorso-medial (DMH) hypothalamic nuclei and anterior hypothalamic area (AHN) by 116, 199, 101 and 157% resp., in comparison with the c-Fos immunoreactive cell quantity in intact animals. EHF irradiation of the skin decreased the intensity of c-Fos-like proteins synthesis induced by NMS in the most of the investigated structures (LHA, VMH, DMH and AHA by 32.8, 29, 15 and 33%, resp.). It was shown that only initial halothane narcosis allowed to determine the hypothalamic structures which realized the responses to the NMS, and modification effects of EHF skin irradiation on the intensity of these responses.     

The neuron of the fast conducting system in hirudo medicinalis: identification and synaptic connections with primary afferent neurons.

A single neuron, located in the center of each segmental ganglion of H. medicinalis is antidromically activated by electrical stimulation of the ventral cord anteriorly and posteriorly to the ganglion, at the same threshold as the fast conducting system (FCS) and with a latency equal to the FCS conduction time. This neuron is activated trans-synaptically by tactile and photic stimulation of the skin and by stimulation of high-threshold fibres running along the cord. A spike evoked by intracellular stimulation of this neuron propagates along the FCS. Intracellular staining shows that this neuron sends two axonal branches in the anterior and posterior median connectives. Direct electrical stimulation of touch cells (T cells), as well as mechanical stimulation of the skin, lowers the threshold of and may eventually fire, the FCS neurons, not only at the level of the ganglion to which they belong, but also at the level of the neighbouring ganglia. This effect is mediated by bilateral pathwasy located in the lateral connectives. It is concluded that the FCS consists of a chain of single neurons, located in each ganglion and electrotonically coupled to each other. Touch cells project with excitatory synapses on the FCS neurons.     

Characteristics of the tonic stretch reflex in spastic spinal cord and head-injured patients

Spasticity is a known sequelae of spinal cord injury and head injury. We sought to examine whether there were any significant differences in the characteristics or underlying mechanisms of spasticity in these two groups in the chronic period which may be related to the level of injury of the neuraxis. The response to vibration applied to the muscle, or the tonic vibratory reflex, has been shown to be related to the degree of spasticity, and was therefore studied along with phasic reflexes and passive movements. These studies were carried out on cooperative, stabilized patients who were otherwise healthy, 5 with head injuries, and 5 with spinal cord injuries. The patients were examined in a supine position while surface EMG recordings were made of quadriceps and triceps surae muscles bilaterally. Tendon jerk responses, passive and volitional movements, and responses to a powerful vibratory stimulator were measured. In both head injury and spinal cord injury patient groups, a large EMG response was elicited by passive maneuvers, and tendon jerks were exaggerated. The tonic vibratory response, previously shown to be dependent upon brain influence, was present in both groups. These observations suggest that similar suprasegmental mechanisms may be responsible for hypertonia in both head-injured and spinal cord-injured patients.     

Regional distribution of blood flow during mild dynamic leg exercise in the baboon

Five chair-restrained baboons were trained with operant techniques and a food reward to perform dynamic leg exercise. Cardiac output and blood flows to most tissues were determined by radioactive microsphere distribution. After 2 min of exercise mean arterial blood pressure had increased by 11 +/- 3% (SE), heart rate by 34 +/- 7%, cardiac output by 50 +/- 12%, and O2 consumption by 157 +/- 17%. The blood flow to exercising leg muscle increased by 585 +/- 338% and to the myocardium by 35 +/- 19%. Blood flow to torso and limb skin fell by 38 +/- 4 and 38 +/- 6%, respectively, and similar reductions occurred in adipose tissue blood flow. Nonworking skeletal muscle blood flow decreased by 30 +/- 10%. Renal blood flow was lowered by 16 +/-2%. The lower visceral organs had more variable responses, but when grouped together total splanchnic blood flow fell by 21 +/- 9%. Blood flow to the brain was unchanged with exercise, whereas spinal cord perfusion increased 23 +/- 3%. Thus during short dynamic exercise baboons redistributed blood flow away from skin, fat, nonworking muscles, and visceral organs to supply the needs of exercising muscles. Our data suggest the baboon is a useful animal model for investigating vascular responses of tissues, such as torso skin, adipose, individual visceral organs, and the spinal cord, that cannot be examined in humans.     

Functioning of catfish electroreceptors: relation between skin potential and receptor activity

Properties of catfish electroceptors were investigated by simultaneous recording of the skin potential and the activity of an afferent nerve. 1. The normal threshold stimulus intensity induces a potential amplitude of about 10 to 30 muV across the skin (Table I). 2. The average spike frequency in the nerve increases approximately with the logarithm of the stimulus intensity (Fig. 1). 3. The direct current restoring the receptor activity in calcium deficient media makes the skin potential more negative. 4. Presumably, not the skin potential itself but a difference between the skin potential and the e.m.f. generated by the receptor epithelium influences receptor functioning. 5. Amplitude and phase characteristics can be described by a filter circuit (Fig. 4 and 5).     

Glutamate drives the touch response through a rostral loop in the spinal cord of zebrafish embryos

Characterizing connectivity in the spinal cord of zebrafish embryos is not only prerequisite to understanding the development of locomotion, but is also necessary for maximizing the potential of genetic studies of circuit formation in this model system. During their first day of development, zebrafish embryos show two simple motor behaviors. First, they coil their trunks spontaneously, and a few hours later they start responding to touch with contralateral coils. These behaviors are contemporaneous until spontaneous coils become infrequent by 30 h. Glutamatergic neurons are distributed throughout the embryonic spinal cord, but their contribution to these early motor behaviors in immature zebrafish is still unclear. We demonstrate that the kinetics of spontaneous coiling and touch‐evoked responses show distinct developmental time courses and that the touch response is dependent on AMPA‐type glutamate receptor activation. Transection experiments suggest that the circuits required for touch‐evoked responses are confined to the spinal cord and that only the most rostral part of the spinal cord is sufficient for triggering the full response. This rostral sensory connection is presumably established via CoPA interneurons, as they project to the rostral spinal cord. Electrophysiological analysis demonstrates that these neurons receive short latency AMPA‐type glutamatergic inputs in response to ipsilateral tactile stimuli. We conclude that touch responses in early embryonic zebrafish arise only after glutamatergic synapses connect sensory neurons and interneurons to the contralateral motor network via a rostral loop. This helps define an elementary circuit that is modified by the addition of sensory inputs, resulting in behavioral transformation. © 2009 Wiley Periodicals, Inc. Develop Neurobiol 2009     

Morphology of regenerated spinal cord in Sternarchus albifrons

Summary The tail of the gymnotid Sternarchus albifrons, including the spinal cord, regenerates following amputation. Regenerated spinal cord shows a rostro-caudal gradient of differentiation. Cross sections of the most distal regenerated cord show radially enlarged ependymal cells, relatively undifferentiated cells, and numerous blood vessels. More anterior sections contain well differentiated electromotor neurons, glial cells, and myelinated axons. The number of electromotor-neuron cell bodies in cross sections of regenerated spinal cord is three to six times the number in nonregenerated cord. Distinct tracts of axons, easily identifiable in normal cord, are not distinguishable in cross sections of regenerated cord. Some reorganization of the spinal cord also appears to take place anterior to the site of transection.Individual electromotor neurons in the regenerated spinal cord have morphologies largely similar to those of normal electrocytes, i.e., cell bodies are rounded, lack dendrites, have synapses characterized by gap junctions with presynaptic axons, and lack an unmyelinated initial segment. The presence of electromotor neurons with normal morphology in regenerated spinal cord correlates with the re-establishment of relatively normal electrocyte axonSchwann cell relationships in the regenerating electric organ of this sternarchid.Supported in part by the Medical Research Service, Veterans Administration and by a grant from the National Institutes of Health. We also thank the Paralyzed Veterans of America for their support. We thank Mary E. Smith and Susan Cameron for excellent technical support