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.     

Preganglionic neurons in the sacral spinal cord of the rat: an HRP study.

The pelvic nerve in the rat was exposed to HRP in order to localize the cells of origin of preganglionic fibers coursing in this nerve. Labeled cells were located in spinal segments L₆-S₁, primarily in the lateral intermediate gray. Occassionally, an HRP-filled cell was observed in the ventral horn in association with somatic motoneurons.     

Sexual dimorphism of the motoneurons in the human spinal cord

There have been few morphometric studies on the size of the motoneurons of the human spinal cord. The purpose of the present study is to report the differences in the size of the motoneurons between males and females in the human spinal cord. We examined numbers and transverse cell body areas of the motoneurons of the anterior horn using 16 male and 21 female human spinal cords at levels C5 and L3. The sizes of the motoneurons were larger in males than in females, but their numbers were practically the same. These results can be of great importance in setting standard values for the understanding of morphological and functional correlations.     

Anatomical studies on the ovine spinal cord

The root attachment lengths were consistently greater in the cranial cervical (C3), midthoracic (T7), caudal lumbar (L5) and cranial sacral (S1) cord segment levels than the corresponding caudal cervical, caudal thoracic, cranial lumbar and caudal sacral levels respectively. As to the root emergence length the greatest values were obtained bilaterally at C3, T1, L4 and S1 cord segment levels respectively. The interroot intervals were maximum at C3, T13, L1 and S1 cord levels in the respective regions. The longest cord segments were located at C2, T13, L3 and S1 levels; the shortest were at C8, T1, L6, and S4 cord levels. The greatest diameter and cross-sectional area were confined to the last cervical, first 2 thoracic, last lumbar and first sacral cord segment levels. The spinal cord segments C2, T13, L4 and S1 were most voluminous in the respective regions. The topography of cord segments and the level of termination of the spinal cord have been studied and recorded.     

Topographical arrangement of hypoglossal motoneurons: an HRP study in the cat

Myotopical localization of hypoglossal motoneurons and representation of the main branches of the hypoglossal nerve within the hypoglossal nucleus were examined in the cat by the HRP method. The hypoglossal nucleus is divided cytoarchitectonically into the ventromedial and dorsolateral divisions; the medial and lateral branches of the hypoglossal nerve are represented respectively in the ventromedial and dorsolateral divisions. The genioglossus motoneurons are located in the ventrolateral part of the ventromedial division, and the geniohyoid motoneurons are in the most ventral part of the ventromedial division. The hypoglossus and styloglossus motoneurons are located in the lateral and dorsolateral parts of the dorsolateral division.     

胸腰段脊髓动脉的解剖学

目的:系统研究胸腰段脊髓动脉的局部解剖关系,明确胸腰段脊髓动脉分布及吻合情况.方法:选用50例脊髓动脉完整无损的成年尸体标本,解剖并观察胸腰段脊髓动脉及其动脉之间的走行分布及吻合情况.结果:胸腰段脊髓动脉主要为脊髓前后正中动脉和Adamkiewicz动脉.脊髓前、后正中动脉与各肋间后动脉、腰动脉发出脊髓支之间存在吻合,...     

Intracellular recording from spinal cord motoneurons in the chronic cat

This report describes chronic intracellular techniques for identifying spinal cord motoneurons and recording from them for prolonged periods of time. The preparation is the intact, unanesthetized, undrugged, normally respiring cat. Comparisons are made between data obtained in the chronic state with that reported in the “acute” preparation, and standards are suggested for intracellular recording in the chronic preparation. Various traditionally used tests of neuronal functioning are outlined in the context of determining basic electrophysiological properties of motoneurons as a function of state-dependent influences.     

GABA- and glycine-immunoreactive terminals contacting motoneurons in lamprey spinal cord

Double postembedding GABA- and glycine-immunostaining was performed on the lamprey (Lampetra fluviatilis) spinal cord after previous HRP labeling of motoneurons. Immunopositive boutons contacting motoneurons were counted and distinguished as GABA (39%), glycine (30%) and both GABA+glycine-immunopositive (31%). Densely-packed, flattened synaptic vesicles were only observed in glycine-immunopositive boutons while GABA-immunoreactive and GABA+glycine-immunoreactive boutons contained rounded or oval synaptic vesicles. Dense-core vesicles of different diameters were associated with conventional synaptic vesicles in 74% of GABA-only-immunopositive boutons, 50% of double GABA+glycine-immunopositive boutons, but were only observed in 9% of glycine-only-immunopositive boutons. The presence of terminals immunoreactive to either GABA or glycine contacting the motoneurons suggests that there is a morphological substrate for both GABAergic and glycinergic postsynaptic inhibition of motoneurons in the lamprey spinal cord.     

Raphé-produced excitation of spinal cord motoneurons in the cat

In all motoneurons examined, both flexor and extensor, raphé (pallidus) stimulation consistently produced an excitatory postsynaptic potential (EPSP). Upon interaction with a group Ia EPSP there was summation resulting in neuronal discharge. The raphé-induced EPSP also facilitated the initial segment-somadendritic coupling and hence the motoneuron excitability. These data support an excitatory role for raphé-spinal fibers on cat hindlimb motoneurons.     

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).     

成年家犬胸腰段脊髓营养动脉的解剖学研究

目的 :了解成年家犬胸腰段脊髓营养动脉的数目、管径和配布特点。方法 :7只成年家犬动脉灌注乳胶后取脊髓全长 ,对其胸腰段脊髓营养动脉进行观测。结果 :胸腰段脊髓的前根髓动脉 (12 .6± 2 .1)条 ,管径 (0 .2 182± 0 .0 773 )mm ,基本不成对分布 ,左侧者居多 ;最大前根髓动脉位于中腰髓 ,管径 (0 .3 83 6± 0 .0 3 3 1)mm ,动脉干长 (9.17± 1.68)mm。胸腰段脊髓后根髓动脉数目 (12 .7± 3 .4)条 ,管径 (0 .1663± 0 .0 3 72 )mm ,多不成对分布。前正中动脉在胸髓较细 ,管径为 (0 .14 68± 0 .0 2 5 2 )mm ,在腰髓较粗 ,管径为 (0 .2 677± 0 .0 414 )mm。两条后外侧动脉均较细 ,其间多吻合。结论 :与人类不同 ,成年家犬胸腰段脊髓动脉血供相当丰富 ,以犬为实验动物 ,制作急性脊髓缺血损伤模型时必须考虑到被阻断血流动脉的级别、节段、侧别、数目等因素对局部脊髓血供的影响。     

Electrical properties of frog motoneurons in the in situ spinal cord.

Electrical properties of the spinal motoneurons of Rana temporaria and R. esculenta were investigated in the in situ spinal cord at 20-22 degrees C by means of intracellular recording and current injection. Input resistance values depended on the method of measurement in a given cell but were generally inversely related to axon conduction velocity. The membrane-potential response to a subthreshold current pulse was composed of at least two exponentials with mean time constants of 2.5 and 20 ms. The membrance potential reached by the peak of a spike depended on the mode of spike initiation and membrane potential. Preceding a suprathreshold depolarization by a hyperpolarizing pulse could delay and eliminate spike initiation, similar to effects reported in certain invertebrate neurons. Antidromic invasion frequently failed in motoneurons of normal resting potential. Antidromic spike components (m,IS, SD) were similar to those of cat motoneurons. The delayed depolarization and the long afterhyperpolarization following an antidromic spike had many properties in common with the analogous afterpotentials of cat motoneurons. The reversal potential of the short afterhyperpolarization occurring immediately after the spike varied with resting potential and could not be used to determine potassium equilibrium potential. Sustained rhythmic firing could be evoked by continuous synaptic drive or long pulses of injected current. The plot of firing rate versus current strength had a substantial linear region. Both steady firing and adaptation properties varied markedly with motoneuron input resistance.     

Direct projections from the Ediger-Westphal nucleus to the cerebellum and spinal cord in the cat: An HRP study

A vast majority of neurons in the Edinger-Westphal nucleus (EW), consisting of the anteromedian nucleus (AM) and the posterior part of the EW (EWp: so-called visceral nucleus), were labeled retrogradely with horseradish peroxidase (HRP) injected into the cerebellum in the cat. The pattern of distribution of these HRP-labeled EW neurons was similar to that of EW neurons labeled with HRP injected into the spinal cord. A tendency, however, was noted that EW neurons located in the nuclear areas close to the midline remained unlabeled in the cats injected with the enzyme into the spinal cord. It was assumed that some EW neurons might contribute fibers by way of axon collaterals both to the cerebellum and to the spinal cord. Possible function of the EW as a relay nucleus for retinal inputs to the cerebellum and the spinal cord was discussed.     

Replacement of missing motoneurons by embryonic grafts in the rat spinal cord

The ventral quadrant of embryonic spinal cord with its motoneurons prelabelled by 5-bromo-2'-deoxyuridine was grafted into the spinal cord of adult rats. The ventral horn of the host had been previously partially depleted of its own motoneurons by a neonatal nerve lesion. To enhance the chances of survival of the transplanted embryonic motoneurons a target muscle was provided for their axons. Two to three months after the grafts were inserted into the cord nuclei containing 5'-bromo-2'-deoxyuridine were found in the graft and in the host's spinal cord. Many of the stained nuclei were much larger than those of embryonic motoneurons, and their size distribution was similar to that of nuclei from control motoneurons. Retrograde labelling with horseradish peroxidase, injected into the target muscle provided for the embryonic motoneurons, showed that some motoneurons had reached the muscle and presumably made contact with it. Physiological and histological examination of the target muscle showed that it was innervated and that it contained at least three different types of muscle fibres. Thus embryonic motoneurons can survive and develop in the adult spinal cord. Moreover, they seem to be able to make functional connections with skeletal muscle fibres. The heterogeneity of the muscle indicates that the motoneurons that supply them are able to differentiate into various types of cells.     

Lithium distribution across the membrane of motoneurons in the isolated frog spinal cord

Lithium sensitive microelectrodes were used to investigate the transmembrane distribution of lithium ions (Li⁺) in motoneurons of the isolated frog spinal cord. After addition of 5 mmol·l^–1 LiCl to the bathing solution the extracellular diffusion of Li⁺ was measured. At a depth of 500 m, about 60 min elapsed before the extracellular Li⁺ concentration approached that of the bathing solution. Intracellular measurements revealed that Li⁺ started to enter the cells soon after reaching the motoneuron pool and after up to 120 min superfusion, an intra — to extracellular concentration ratio of about 0.7 was obtained. The resting membrane potential and height of antidromically evoked action potentials were not altered by 5 mmol·l^–1 Li⁺.     

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。