神经生长因子受体TrkA在新生鼠、幼鼠及成鼠脊髓表达差异的研究

为了探讨神经生长因子 ( NGF)受体 Trk A在新生鼠、幼鼠及成鼠脊髓的分布状况、进而分析 NGF的作用机制 ,用免疫组化技术检测了新生鼠、幼鼠及成鼠脊髓 NGF受体 Trk A的表达。结果显示 ,新生鼠脊髓前角运动神经元只有胞核 Trk A表达明显 ,胞浆及胞膜无表达 ,中间带、背角均无表达。幼鼠前角运动神经元胞浆 Trk A表达明显 ,胞核少量表达 ,胞膜无表达 ;部分中间带、背角神经元胞浆有表达。成鼠前角运动神经元胞浆及部分胞膜都有 Trk A表达 ,胞核无表达 ,中间带、背角神经元胞浆以及胶质细胞也明显表达。推论 ,新生鼠时胞核中 Trk A可与配体结合引起神经元的生物效应 ;成鼠 Trk A则主要作为一种膜受体与配体结合而发挥生物效应     

Origin of phasic synaptic inhibition in myotomal motoneurons during fictive locomotion in the lamprey

The periodic membrane potential fluctuations in motoneurons during fictive locomotion in the lamprey, a primitive vertebrate, involve phasic synaptic excitation and inhibition. This paper investigates the origin of the phasic synaptic input to lamprey myotomal motoneurons in the in vitro spinal cord preparation with regard to the relative contribution of descending propriospinal input from interneurons in the local segment. The synaptic drive to myotomal motoneurons in the most rostral and the most caudal part of the spinal cord preparation are compared before and after selective spinal cord lesions. Current clamp recordings of the same cell before and after lesion showed that neither the excitatory phase nor the inhibitory phase was abolished after interruption of the descending or the ascending ipsilateral input, or after interrupting crossing segmental input by a local longitudinal midline incision. None of these sources thus appears to be alone responsible for the phasic synaptic drive. To quantitatively evaluate these effects, and in particular the contribution from the descending propriospinal fibres to the inhibitory phase, voltage clamp recordings were made in combination with a spinal cord hemisection just rostral to the motoneuron. The input from propriospinal interneurons in approximately 15 rostral segments may be responsible for as much as 70% of the phase of inhibitory current during the locomotor cycle. In accordance with these findings, a similar voltage clamp analysis of rostrally and caudally located motoneurons showed that the average peak-to-peak amplitude of the current fluctuations in rostral cells was approximately 50% of that in caudal cells.     

Myelinated dendrites in the spinal cord of frogs (Rana esculenta)

Summary Myelinated dendrites — probably of motoneurons — were found in the spinal cord of the frog. It is assumed that the myelin sheath, by increasing the membrane resistance, improves the function of the dendrite as a cable.Supported by the Deutsche Forschungsgemeinschaft     

牛脊髓前角匀浆皮下注射损伤豚鼠脊髓运动神经元

目的探讨牛脊髓前角匀浆对豚鼠脊髓、前根及坐骨神经的影响。方法采用新鲜牛脊髓前角匀浆免疫豚鼠。观察脊髓、前根、坐骨神经光镜及超微结构的变化。结果豚鼠体重在第4次免疫后明显下降。脊髓前角运动神经元变性和丢失,有卫星、噬节及墓穴现象形成。电镜下最主要的表现是线粒体异常;其次神经元核周质内异常神经丝聚集,形成包涵体;轴突内异常神经丝聚集形成轴索球。前根及坐骨神经的变化,表现为轴索变性及继发的髓鞘改变。结论牛脊髓前角匀浆可以作为抗原引起豚鼠脊髓、前根及坐骨神经免疫所介导的损伤,为进一步研究运动神经元病的发病机制提供了可靠的方法。     

Monoaminergic and GABAergic terminations in phrenic nucleus of rat identified by immunohistochemical labeling

The termination patterns of axons in the phrenic nucleus immunoreactive to synthetic enzymes for catecholamines and for serotonin and GABA were studied in rats. Spinal cord tissue in which phrenic motoneurons were retrogradely labeled with horseradish peroxidase was incubated with antisera against dopamine beta-hydroxylase, phenylethanolamine-N-methyltransferase, 5-hydroxytryptamine, and GABA to identify presumptive terminations of monoaminergic and GABAergic neurons onto identified phrenic motoneurons. In the C3 to C5 spinal cord, 5-hydroxytryptamine-, dopamine beta-hydroxylase- and GABA-like positive terminals with varicosities formed a dense network, with presumptive synaptic contacts on dendrites and somas of phrenic motoneurons. A similar pattern of terminations was also observed in adjacent (non-respiratory muscle) motoneuron pools. There were fewer phenylethanolamine-N-methyltransferase-positive terminal arborizations in the cervical spinal cord compared to thoracic spinal cord; phenylethanolamine-N-methyltransferase terminals were not seen in the vicinity of phrenic motoneurons. These results suggest that phrenic motoneuronal activity is influenced by multiple supraspinal inputs utilizing different neurotransmitters. These transmitters also mediate inputs to other (nearby) spinal motoneurons and thus are not unique for signal transmission to phrenic motoneurons.     

Evidence for electrotonic coupling between frog motoneurons in the in situ spinal cord.

A recurrent EPSP was observed on antidromic stimulation of motoneurons in the in situ spinal cord of Rana temporaria and R. esculenta at 20-22C. The EPSP was finely graded and not refractory following full or partial antidromic spike components in a given neuron. The EPSP amplitude varied in parallel with the antidromic field potential under different conditions, suggesting transmission of the EPSP to the recorded motoneuron depended on invasion of the somadendritic membrane or neighboring motoneurons by the antidromic spike. The latency of the EPSP with respect to antidromic invasion of the local motoneuron pool was too short for the EPSP to be mediated by chemical transmission. It was concluded the EPSP was electrically transmitted between the somadendritic membranes of the motoneurons. Under certain conditions, the EPSP magnitude could be made to vary with membrane potential in a direction opposite to that expected from a chemical EPSP. Dendritic spikes were sometimes associated with the EPSP.     

异种脊髓前角匀浆对豚鼠前角运动神经元的影响

目的：观察豚鼠脊髓前角运动神经元在异种脊髓前角匀浆免疫后的变化。方法：猪脊髓前角匀浆免疫豚鼠后,豚鼠脊髓前角以苏木精-伊红、甲苯胺蓝及IgG免疫组化染色,同时电镜下观察前角运动神经元的超微变化。结果：豚鼠脊髓前角运动神经元存在变性和丢失,以神经元固缩、胶质细胞围绕破坏的神经元形成卫星现象及小墓穴为主,脊髓前角运动神经元胞质内IgG沉积呈颗粒状分布。运动神经元胞质内内质网扩张、线粒体肿胀。结论：猪脊髓前角匀浆作为抗原可引起豚鼠下运动神经元损伤,说明猪与豚鼠运动神经元存在共同抗原,自身免疫机制可能参与了运动神经元变性过程。     

Suprasegmentary control of the intraspinal pathways of visceromotor reflexes

Summary Experiments on spinal cats under chloraeose-nembutal anesthesia (45 mg and 15 mg per kg of body weight) were carried out to study the time and spatial sequence of activation of different neuron structures of the 5th lumbar segment of the spinal cord in stimulation of the ipsilateral splanchnic nerve.The descending fast pathways of visceral impulses passing in the medial part of the dorsal columns of the spinal cord are outside of the sphere of control by the supraspinal centers. Analogous pathways passing in the region of the substantia gelatinosa and part of the lateral columns of the spinal cord adjoining the gray matter are under the tonic inhibitory influence of the supraspinal centers.Breaking off connections of the spinal cord with the suprasegmentary structures considerably facilitates the transmission of visceral impulses to the segmentary neurons. This disconnection also eliminates the transmission of introceptive inhibitory influences to extensor motoneurons.(Presented by Active Member of the Academy of Medical Sciences of the USSR V. V. Parin). Translated from Byulleten' Éksperimental'noi Bioloii i Meditsiny, Vol. 62, No. 10, pp. 3–7, October, 1966.     

Measurement and analysis of postsynaptic potentials using a novel voltage-deconvolution method

This study investigated cellular and synaptic mechanisms of cholinergic neuromodulation in the in vitro lamprey spinal cord. Most spinal neurons tested responded to local application of acetylcholine (ACh) with depolarization and decreased input resistance. The depolarization persisted in the presence of either tetrodotoxin or muscarinic antagonist scopolamine and was abolished with nicotinic antagonist mecamylamine, indicating a direct depolarization through nicotinic ACh receptors. Local application of muscarinic ACh agonists modulated synaptic strength in the spinal cord by decreasing the amplitude of unitary excitatory and inhibitory postsynaptic potentials. The postsynaptic response to direct application of glutamate was unchanged by muscarinic agonists, suggesting a presynaptic mechanism. Cholinergic feedback from motoneurons was assessed using stimulation of a ventral root in the quiescent spinal cord while recording intracellularly from spinal motoneurons or interneurons. Mainly depolarizing potentials were observed, a portion of which was insensitive to removal of extracellular Ca2+, indicating electrotonic coupling. Hyperpolarizing potentials were also observed and were attenuated by the glycinergic antagonist strychnine, whereas depolarizing responses were potentiated by strychnine. Mecamylamine also reduced hyperpolarizing responses. The pharmacology of these responses suggests a Renshaw-like feedback pathway in lamprey. Immunohistochemistry for choline acetyltransferase, performed in combination with retrograde filling of motoneurons, demonstrated a population of nonmotoneuron cholinergic cells in the lamprey spinal cord. Thus endogenous cholinergic modulation of the lamprey spinal locomotor network is likely produced by both motoneurons and cholinergic interneurons acting via combined postsynaptic and presynaptic actions.     

Cable properties of spinal cord motoneurons in adult and aged cats

1. The electrophysiological properties of spinal cord alpha-motoneurons were investigated in adult cats (1-3 yr old) and old cats (14-15 yr old) using intracellular recording techniques. Voltage transients following depolarizing pulses of current were analyzed according to the procedure described by Ito and Oshima (15). The input resistance of each cell, together with the passive electrical time constants, were used to estimate the electrotonic length and total cell capacitance of each motoneuron. 2. Adult and old motoneurons both exhibited an undershoot of the membrane potential following the cessation of a subthreshold depolarizing current pulse (15). The average time constant for the decay of this undershoot in membrane potential was statistically indistinguishable in motoneurons of adult and aged animals. 3. The average membrane time constant of motoneurons in aged cats was 19% longer than that of motoneurons in adult cats. 4. The average total cell capacitance of motoneurons in aged cats was 16% smaller than that of motoneurons in adult cats. 5. The average electrotonic length of old motoneurons was statistically indistinguishable from that of motoneurons in adult cats. 6. From these results, we conclude that there is an age-dependent increase in the membrane resistance and an age-dependent decrease in cell surface area of alpha-motoneurons of the lumbar spinal cord in aged cats. Both of these phenomena are believed to contribute to the age-dependent increase in input resistance that has been previously reported to occur in motoneurons in aged cats (18).     

Mechanism of disturbance of inhibitory electrogenesis in spinal α-motoneurons in experimental local botulinus poisoning

The character of changes in postsynaptic inhibition in spinal -motoneurons of cats was studied in the course of experimental local botulinus poisoning. At the beginning of development of the local paralytic syndrome a marked decrease in the amplitude of the reciprocal, and a smaller decrease in amplitude of the polysynaptic IPSPs was observed. On the appearance of total paralysis of the muscles from botulinus poisoning the reciprocal and polysynaptic IPSPs were inhibited even more, but they never disappeared completely and were never converted into depolarization potentials. During the development of the IPSP the synaptic permeability of the motneurons as a rule was reduced.Department of Pathological Physiology, N. A. Semashko Moscow Medical Stomatological Institute. Department of Pathological Physiology, Saratov Medical Institute. (Presented by Academician of the Academy of Medical Sciences of the USSR A. D. Ado.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 83, No. 6, pp. 651–654, June, 1977     

Dual effect of GABA on descending monosynaptic excitatory postsynaptic potential in frog lumbar motoneurons

Monosynaptic excitatory postsynaptic potentials (EPSPs) evoked by stimulating ipsilateral ventrolateral column (VLC) in the thoracic section were recorded in lumbar motoneurons within the isolated spinal cord of the frog Rana ridibunda. Bath application of the selective GABAB receptor agonist (-)-baclofen (0.05 mM) caused a reduction in the peak amplitude of VLC EPSP. Baclofen did not cause any consistent change in the membrane potential or in the EPSP waveform within frog motoneurones. The selective GABA(B) receptor antagonist saclofen (0.1 mM) completely blocked the effect of (-)-baclofen on VLC EPSP. A decrease in VLC EPSP peak amplitude was also observed during GABA (0.5 mM) application. Unlike (-)-baclofen, inhibition of VLC EPSP induced by GABA was accompanied by a shortening of the EPSP time course and a reduction in membrane input resistance within lumbar motoneurons. The decrease in VLC EPSP peak amplitude induced by (-)-baclofen and GABA was accompanied by an increase in the paired-pulse facilitation. These data provide evidence for a dual pre- and postsynaptic GABAergic inhibition of the VLC monosynaptic EPSP in lumbar motoneurons within the frog spinal cord.     

NADPH-Diaphorase Activity in Motoneurons in Different Segments of the Spinal Cord in White Rats in Normal Conditions and after Deafferentation

Age-related changes in NADPH-diaphorase activity were studied using a histochemical method in spinal cord ventral horn motoneurons at different segmental levels in rats aged 3–90 days from birth in normal conditions and after modeling of chemical deafferentation by i.p. administration of capsaicin. Wave-like age-related changes in enzyme activity were seen in motoneurons at the T_II, L_IV, and S_II segments of the spinal cord, with an increase by age 60 days followed by a significant decrease by 90 days. Age-related changes in NADPH-diaphorase activity in spinal cord motoneurons in intact rats characterize constructive processes in neurons, while changes seen after deafferentation provide evidence of motoneuron damage resulting in sharp increases in enzyme activity by age 90 days.     

Microtubules and their interrelations with subsynaptic structures and the nuclear membrane in human neuroblasts

The dynamics of appearance of microtubules and the development of their connections with synapses and the nuclear membrane was studied by electron microscopy in differentiating neuroblasts from the anterior horns of the human spinal cord during the first half of antenatal development. A hypothesis is put forward to explain the function of the connections discovered between the microtubules and subsynaptic zone of the neuroblast and its nucleus.Laboratory of Development of the Human Nervous System, Institute of Human Morphology, Academy of Medical Sciences of the USSR, Moscow. (Presented by Academician of the Academy of Medical Sciences of the USSR A. P. Avtsyn.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 85, No. 3, pp. 368–370, March, 1978.     

Whole-cell patch clamp recordings from rhythmically active motoneurons in the isolated spinal cord of the chick embryo

Whole-cell patch clamp recordings were obtained during motor activity from electrically identified motoneurons within the spinal cord of the chick embryo maintained in vitro. Most recordings were performed on E11-E13 motoneurons although it was also possible to record from younger cells (E7-E9). Voltage clamp recordings were used to characterize the synaptic currents expressed in femoro-tibialis (extensor) motoneurons during motor activity. These motoneurons exhibited rhythmic excitatory currents with reversal potentials near 0 mV. This powerful technique enables high resolution recordings from identified motoneurons in situ and allows investigation of the membrane and synaptic mechanisms involved in the development of embryonic motility.     

The development of the dendritic organization of primary and secondary motoneurons in the spinal cord of Xenopus laevis. An HRP study

Summary During embryonic and larval development of the clawed toad, Xenopus laevis, two different populations of motoneurons appear in the spinal cord. In this study the development of primary motoneurons which innervate the axial musculature (used during embryonic locomotion) and of secondary motoneurons which innervate the extremity musculature (used for locomotion during metamorphosis and thereafter) was analyzed with horseradish peroxidase (HRP) as a neuronal marker. After application of HRP to the axial musculature (rostral five postotic myotomes) the first labeled primary motoneurons were found at stage 24/25. During development gradually more labeled neurons were observed. These primary motoneurons send their dendrites into the marginal zone (white matter). At first only dorsal and lateral dendrites develop (stages 25–33), followed by ventral dendrites (stage 37/38). Up till stage 48 the developing dendrites extend throughout the marginal zone. Hereafter the marginal zone increases particularly at the dorsolateral edge, a development which is not followed by the dendrites of the primary motoneurons. The dendrites of mature primary motoneurons (stages 58–62) occupy the ventral and ventrolateral parts of the marginal zone.At stage 48, shortly after the hindlimb bud arises (stage 46, early metamorphosis), the first neurons related to this developing extremity could be labeled in the ventrolateral part of the lumbar spinal cord. At first these secondary motoneurons bear only a few dorsal dendrites of which only the tips reache out in the adjacent white matter. Already at stage 50 these dorsal dendrites have invaded the whole dorsolateral part of the marginal zone. Also the first ventral dendrites were observed at this stage. Later, at stage 53/54 also some ventral dendrites have reached the white matter together with a few lateral dendrites. At these early metamorphic stages already some primary afferent fibers were found making contact with the dorsomedial dendrites. At stage 58 for the first time recurrent axon collaterals were found, which extend into the ventromedial part of the marginal zone. The development of motoneurons in the spinal cord seems to be characterized by two phases: (1) establishment of contacts between motoneurons and target muscles, and (2) subsequent formation of connections of these motoneurons with other nerve cells within the central nervous system. The dendrites of primary motoneurons follow the development of the marginal zone, while dendrites of secondary motoneurons develop into an already well developed marginal zone. Generally, the dendrites of mature motoneurons of the axial musculature were observed in the ventromedial and ventrolateral parts of the marginal zone. The dendrites of themotoneurons which innervate the musculature of the hindlimbs were observed predominantly in the dorsolateral and ventromedial parts of the marginal zone.     

Efficiency of electrical transmission in reticulomotoneuronal synapses of lamprey spinal cord

Summary Synaptic responses in motoneurons in the isolated spinal cord of the lamprey during stimulation of the reticulospinal axons were examined. Chemical transmission in the synapses was partially or completely blocked by temperature reduction of the perfusing solution, pentobarbitone application or substitution of Mn²⁺ ions for Ca²⁺ in the perfusate. Excitatory postsynaptic potentials (EPSPs) which were indifferent to the influences mentioned above, had an amplitude of 6–12 mV and were capable of evoking action potentials (APs) in motoneurons due to their high amplitude, the absence of a shunting effect at the postsynaptic membrane and the fast rise-time of the wave front. The suggestion is made that the electrical transmission is involved in functioning of the lamprey nervous system. Its stability and efficiency are likely to ensure functional connection between the brain and spinal cord under such unfavourable conditions when the chemical transmission does not operate and when the ability for locomotion would be prerequisite for the individual to survive.     

Electrophysiological evidence for vasopressin V(1) receptors on neonatal motoneurons, premotor and other ventral horn neurons

Prominent arginine-vasopressin (AVP) binding and AVP V(1) type receptors are expressed early in the developing rat spinal cord. We sought to characterize their influence on neural excitability by using patch-clamp techniques to record AVP-induced responses from a population of motoneurons and interneurons in neonatal (5-18 days) rat spinal cord slices. Data were obtained from 58 thoracolumbar (T(7)-L(5)) motoneurons and 166 local interneurons. A majority (>90%) of neurons responded to bath applied AVP (10 nM to 3 microM) and (Phe(2), Orn(8))-vasotocin, a V(1) receptor agonist, but not V(2) or oxytocin receptor agonists. In voltage-clamp, postsynaptic responses in motoneurons were characterized by slowly rising, prolonged (7-10 min) and tetrodotoxin-resistant inward currents associated with a 25% reduction in a membrane potassium conductance that reversed near -100 mV. In interneurons, net AVP-induced inward currents displayed three patterns: decreasing membrane conductance with reversal near -100 mV, i.e., similar to that in motoneurons (24 cells); increasing conductance with reversal near -40 mV (21 cells); small reduction in conductance with no reversal within the current range tested (41 cells). A presynaptic component recorded in most neurons was evident as an increase in the frequency but not amplitude (in motoneurons) of inhibitory and excitatory postsynaptic currents (IPSCs and EPSCs), in large part due to AVP-induced firing in inhibitory (mainly glycinergic) and excitatory (glutamatergic) neurons synapsing on the recorded cells. An increase in frequency but not amplitude of miniature IPSCs and EPSCs also indicated an AVP enhancement of neurotransmitter release from axon terminals of inhibitory and excitatory interneurons. These observations provide support for a broad presynaptic and postsynaptic distribution of AVP V(1) type receptors and indicate that their activation can enhance the excitability of a majority of neurons in neonatal ventral spinal cord.     

Vascular endothelial growth factor protects motoneurons from serum deprivation–induced cell death through phosphatidylinositol 3-kinase-mediated p38 mitogen-activated protein kinase inhibition

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by the selective degeneration and death of motoneurons in the spinal cord, brainstem and motor cortex which causes progressive muscle weakness and paralysis. Although the molecular mechanisms causing the disease remain unknown, excitotoxicity and loss of trophic support have been proposed as causes of degeneration.     

Postnatal transient expression of long-lasting descending inhibitory effect on spinal reflexes in the rat

In the spinal cord isolated from neonatal rats, stimulation of the ipsilateral lateral column at the thoracic level strongly inhibited monosynaptic segmental reflex in the lumbar cord for about 60 s. The descending inhibition was not associated with any changes in the membrane potential or conductance in lumbar motoneurons when the excitatory postsynaptic potentials in response to stimulation of the dorsal root were depressed. The descending inhibition was diminished with age and could not be detected at 5 months of age. It is suggested that certain inhibitory pathways in the descending spinal tract are rearranged during postnatal development of rats.