Scanning electron microscope observations on the muscle innervation of Oikopleura dioica fol (appendicularia,tunicata) with notes on the arrangement of connective tissue fibres

Critical point dried and fractured appendicularia of the species Oikopleura dioica have been examined in the scanning electron microscope. The dorsal nerve cord with ganglion cells and peripheral nerve fibres could easily be observed. Thick peripheral nerve fibres leave the nerve cord as bilateral pairs at constant intervals along the tail. Most of these fibres branch from the naked nerve cord, but some evidently originate in ganglion perikarya bulging out from the nerve cord itself. These paired peripheral nerves always have elaborate end-arborizations on the medial surface of the lateral muscle cells. They are accordingly interpreted as motor axons. Some thinner peripheral nerve fibres originate at irregular intervals from both the nerve cord and the ganglion cells. Due to the numerous extracellular fibrils that connect the bilateral layers of the epidermal fins and the muscle cells to each other, these thin nerve fibres can seldom be traced to their termination. A few ones can, however, be traced ventrally between the notochord and the muscle cells and seem to end in singular bulb-like expansions. Clusters of synaptic vesicles are present in transmission electron micrographs of such nerves, and they are accordingly believed to carry efferent impulses. The extracellular fibrils are arranged in a highly ordered pattern with thick bundles crossing the gap between the structures to be interconnected and with numerous radiating insertions on the surface of the tissues.     

Physiology of Photoreceptor Neurons in the Abdominal Nerve Cord of the Crayfish

Nerve fibers which respond to illumination of the sixth abdominal ganglion were isolated by fine dissection from connectives at different levels in the abdominal nerve cord of the crayfish. Only a single photosensitive neuron is found in each connective; its morphological position and pattern of peripheral connections are quite constant from preparation to preparation. These cells are "primary" photoreceptor elements by the following criteria: (1) production of a graded depolarization upon illumination and (2) resetting of the sensory rhythm by interpolated antidromic impulses. They are also secondary interneurons integrating mechanical stimuli which originate from appendages of the tail. Volleys in ipsilateral afferent nerves produce short-latency graded excitatory postsynaptic potentials which initiate discharge of one or two impulses; there is also a higher threshold inhibitory pathway of longer latency and duration. Contralateral afferents mediate only inhibition. Both inhibitory pathways are effective against both spontaneous and evoked discharges. In the dark, spontaneous impulses arise at frequencies between 5 and 15 per second with fairly constant intervals if afferent roots are cut. Since this discharge rhythm is reset by antidromic or orthodromic impulses, it is concluded that an endogenous pacemaker potential is involved. It is postulated that the increase in discharge frequency caused by illumination increases the probability that an inhibitory signal of peripheral origin will be detected.     

Remote electrodermic response to an algogenic stimulus. Pathway and spinal integration

The pathway of a non-segmental sudomotor reflex was studied in rabbits (New Zealand white). By means of thermic stimulation (45 degrees during 30") at the lateral border of the foot, a sudoral response was evoked in a circumscribed area of the pinna. By sequential sections of different nerves and the nervous network around the saphenous and femoral vessels, it was possible to establish the following afferent pathways to the spinal cord: lateral plantar nerve, tibial nerve up to the tuber calcanei, saphenous perivascular network, femoral perivascular network and femoral nerve. The fibres responsible for the podo-auricular sudomotor reflex penetrate into the spinal cord above L4, because the spinal transection at this level does not alter the auricular response. Since the hemisection of the spinal cord at T6 suppresses this reflex in the pinna of the same side, it must be concluded that the spinal pathway is ipsilateral. The efferent pathway abandons the spinal cord beneath segment C6: in fact, the spinal transection at C6 does not alter the auricular response to plantar stimulation. Finally, the sudomotor impulses reach the pinna sweat glands with the auricular vessels.     

The central consequences of the application of capsaicin to one peripheral nerve in adult rat

This paper reviews the central consequences of local application of capsaicin to one nerve in adult animals. 1) Marked chemical changes occur in the central terminals of C fibres. These include depletion of the enzyme FRAP and the peptides SP, CCK, somatostatin, CGRP and an increase of VIP. Maximal depletions occur if the nerve is soaked with capsaicin solutions with a concentration higher than 3 mM. The depletion begins by 7 days and is complete by 11. Recovery begins at about 110 days and is largely complete by 200. Our studies have concentrated on the effects of 40 mM capsaicin examined 14 days after the application. 2) Capsaicin treatment of a peripheral nerve decreased the ability of C fibres in that nerve to excite or to inhibit spinal cord cells. It produces a marked expansion of receptive fields of some cells in the dorsal horn which respond to A fibre stimulation. It is proposed that this change is not due to anatomical changes but to disinhibition. A further example of receptive field expansion is seen after treatment of the mouse infraorbital nerve which defocuses the normally precise projection of individual whiskers onto single cells in the barrel field of the somatosensory cortex. 3) Behavioural consequences follow the treatment of one adult nerve with capsaicin. In the area subserved by the treated nerve, there is a raised threshold to response to chemical and thermal stimuli, no change in the response to mechanical stimuli and an increase of autotomy following nerve section. 4) The aim of the experiments was to determine the role of C fibres in producing the changes seen in spinal cord following peripheral nerve section. Capsaicin treatment of nerve imitates the central effect of complete nerve section in certain important ways. Both result in a marked expansion of the receptive field of some cells. The effect is produced by a change of chemical transport. The results show that C fibres influence the connection of A fibres onto spinal cord cells.     

Electrical potentials from the eye and optic nerve of Strombus: effects of electrical stimulation of the optic nerve.

1. Photic stimulation of the mature eye of Strombus can evoke in the optic nerve 'on' activity in numerous small afferent fibres and repetitive 'off' bursts of afferent impulses in a smaller number of larger fibres. 2. Synchronous invasion of the eye by electrically evoked impulses in small optic nerve fibres (apparently the 'on' afferents, antidromically activated) can evoke a burst of impulses in the larger 'off' fibres which propagate away from the eye. Invasion of the eye via one branch of optic nerve can evoke an answering burst in another branch. 3. Such electrically evoked bursts are similar to light-evoked 'off' bursts with respect to their impulse composition, their ability to be inhibited by illumination of the eye, and their susceptibility to MgCl2 anaesthesia. 4. Invasion of the eye by a train of repetitive electrically evoked impulses in the absence of photic stimulation can give rise to repetitive 'off' bursts as well as concomitant oscillatory potentials in the eye which are similar to those normally evoked by cessation of a photic stimulus. 5. The electrically evoked 'off' bursts appear to be caused by an excitatory rebound following the cessation of inhibitory synaptic input from photoreceptors which can be antidromically activated by electrical stimulation of the optic nerve. 6. The experimental results suggest that the rhythmic discharge of the 'off' fibres evoked by the cessation of a photic stimulus is mediated by the abrupt decrease of inhibitory synaptic input from the receptors.     

Neuromechanisms of reciprocal interrelation between jaw-opening and jaw-closing muscles in the cat (author's transl)]

Neural controlling mechanisms between the digastric (jaw-opening) and masseter (jaw-closing) muscles were studied in the cat. High threshold afferent impulses from the anterior belly of the digastric muscle to masseteric montoneurons in the trigeminal motor nucleus induced an EPSP-IPSP sequence of potentials with long latency, and high threshold afferent impulses from the masseter muscle also exerted a similar effect on digastric motoneurons in the same nucleus innervating the anterior belly of the digastric muscle. These results suggest that reciprocal inhibition via Ia interneurons as observed between the flexor and extensor muscles in the spinal cord does not exist between the digastric and masseter muscles in the cat. However, the respective motoneurons innervating the masseter and digastric muscles receive inputs of early excitation-late inhibition via high threshold afferent nerve fibers from each antagonistic muscle. As such, since EPSPs preceding IPSPs are recognized, these high threshold afferent impulses may exert not only a reciprocal inhibitory effect, but also a synchronous excitatory or inhibitory effect on the antagonistic motoneurons.     

The giant neurone system in ophiuroids

Summary The nervous system of Ophiura texturata contains nerve fibres and cell bodies that are an order of magnitude larger than anything previously described in the Asteroidea and Echinoidea. These large nerve cells are designated giant fibres. Giant nerve cells are present in both the ectoneural and hyponeural nervous system. The layout of these nerve cells is described and it is shown that the organization is repeated in each segmental ganglion that makes up the radial nerve cord. The circumoral nerve ring is composed, in the main, of tracts of nerve fibres joining the radial nerves, and it contains only limited areas of neuropil associated with the alimentary canal and muscles of the disc and jaws. Degeneration studies have shown that each segmental ganglion of the radial nerve cords contains a discrete population of neurones separate from adjacent ganglion and that there are not anatomically continuous giant fibres along the whole length of the nerve cord.     

Sensory pathways in amphioxus larvae I. Constituent fibres of the rostral and anterodorsal nerves, their targets and evolutionary significance

Serial and interval electron micrograph series were used to examine the rostral and anterodorsal nerves of 12.5‐day‐old amphioxus larvae and trace selected fibres to their targets in the nerve cord. The nerves contain a variety of fibre types, including axons from at least two types of epithelial sensory cells and neurites derived from dorsal (Retzius) bipolar cells located within the cord. The rostral epithelial cells form basal synapses with a population of peripheral neurites that probably derive from the dorsal bipolar cells, though other sources are possible. Varicosities containing dense‐core vesicles occur at the tip of the rostrum, indicating the presence of efferent innervation at this site. Within the cord, some peripherally derived rostral afferents terminate at the level of the anterior cerebral vesicle, others synapse directly with both motoneurones and the notochord, but those in the largest bundle target the dendrites of the large paired neurones (LPNs) located in the primary motor centre. LPN dendrites also receive synapses from sensory fibres arriving via the anterodorsal nerves, from the anterior‐most of the dorsal bipolar cells, referred to here as tectal cells, and from a single fibre derived from the frontal eye. This convergence of multiple inputs accords with other evidence that the LPNs are key intermediaries in the sensorimotor pathway that activates the larval escape response. The rostral nerves are much larger at metamorphosis, but the ventral tracts that derive from them are still comparatively small. This is because the majority of rostral fibres are diverted into a late‐developing dorsal tract that travels within the cord to the front end of the dorsolateral neuropile, where most of its fibres disperse and form synapses. The positioning of the dorsal and ventral tracts strongly suggests homology with vertebrate olfactory and terminal nerves, respectively. This, and the question of whether the amphioxus central nervous system has anything comparable to the olfactory bulb, a telencephalic structure, is discussed.     

Interpretation of the Repetitive Firing of Nerve Cells

Eccentric cells of Limulus respond with repetitive firing to sustained depolarizing currents. Following stimulation with a step of current, latency is shorter than first interval and later intervals increase progressively. A shock of intensity twice threshold can evoke firing 25 msec. after an impulse. But in the same cell, a current step twice rheobase evokes a second impulse more than 50 msec. after the first, and current intensity must be raised to over five times rheobase to obtain a first interval of about 25 msec. Repetitive firing was evoked by means of trains of shocks. With stimuli of moderate intensity, firing was evoked by only some of the shocks and intervals between successive impulses increased with time. This is ascribed to accumulation of refractoriness with successive impulses. Higher frequencies of firing are obtained with shocks of intensity n x threshold than with constant currents of intensity n x rheobase. It is concluded that prolonged currents depress the processes leading to excitation and that (in the cells studied) repetitive firing is controlled both by the after-effects of firing (refractoriness) and by the depressant effects of sustained stimuli (accommodation). Development of subthreshold "graded activity" is an important process leading to excitation of eccentric cells, but is not the principal factor determining frequency of firing in response to constant currents.     

Growth behaviour of human mononuclear cells derived from bone marrow and cord blood on a collagen carrier for osteogenic regeneration]

We investigated the biocompatibility and osteogenetic potency of a porcine collagen I/III carrier in a human bone marrow and cord blood cell culture system. METHODS: Human mesenchymal mononuclear cells were isolated from cord blood and iliac crest bone marrow and cultivated in various cell densities on a semipermeable porcine collagen I/III carrier. After 14 days of in vitro cultivation both cultures were subjected to osteogenic stimulation by dexamethasone, ascorbic acid and beta-glycerol phosphate (DAG) until day 40. Semiquantitative immunochemical evaluation based on osteoblastic and progenitor cell markers was then done. RESULTS: With regard to the minimal local cell density required for growth and osteogenic differentiation, cord blood derived progenitor cells showed lower tolerance in comparison with bone marrow derived cells. For both cell culture systems three-dimensional growth and calcification within the collagen fibres were seen after osteogenic stimulation. CONCLUSION: Human cord blood and bone marrow derived mesenchymal stem cell are capable of differentiating into osteoblasts after incubation with a collagen I/III biomaterial.     

Adult stem cells and multiple sclerosis

Multiple sclerosis (MS) is a common neurological disease and a major cause of disability, particularly affecting young adults. It is characterized by patches of damage occurring throughout the brain and spinal cord, with loss of myelin sheaths - the insulating material around nerve fibres that allows normal conduction of nerve impulses - accompanied by loss of cells that make myelin (oligodendrocytes). In addition, we now know that there is damage to nerve cells (neurones) and their fibres (axons) too, and that this occurs both within these discrete patches and in tissue between them. The cause of MS remains unknown, but an autoimmune reaction against oligodendrocytes and myelin is generally assumed to play a major role, and early acute MS lesions almost invariably show prominent inflammation. Efforts to develop cell therapy in MS have long been directed towards directly implanting cells capable of replacing lost oligodendrocytes and regenerating myelin sheaths. Accordingly, the advent of techniques to generate large numbers of oligodendrocytes from embryonic stem cells appeared a significant step towards new stem cell treatments for MS; while the emerging consensus that adult stem cells from, for example, the bone marrow had far less potential to turn into oligodendrocytes was thought to cast doubt on their potential value in this disease. A number of scientific and medical concerns, not least the risk of tumour formation associated with embryonic stem cells, have however, prevented any possible clinical testing of these cells in patients. More recently, increasing understanding of the complexity of tissue damage in MS has emphasized that successful cell therapy may need to achieve far more than simply offering a source of replacement myelin-forming cells. The many and varied reparative properties of bone marrow-derived (mesenchymal) stem cells may well offer new and attractive possibilities for developing cell-based treatments for this difficult and disabling condition.     

Human dorsal root ganglion neurons from embryonic donors extend axons into the host rat spinal cord along laminin-rich peripheral surroundings of the dorsal root transitional zone

Following dorsal root crush, the lesioned axons regenerate in the peripheral compartment of the dorsal root, but stop at the boundary between the peripheral and the central nervous system, the dorsal root transitional zone. We have previously shown that fibres from human fetal dorsal root ganglia grafted to adult rat hosts are able to grow into the spinal cord, but were not able to specify the route taken by the ingrowing fibres. In this study we have challenged the dorsal root transitional zone astrocyte boundary with human dorsal root ganglion transplants from 5–8-week-old embryos. By tracing immunolabelled human fibres in serial sections, we found that fibres consistently grow around the dorsal root transitional zone astrocytes in laminin-rich peripheral surroundings, and extend into the host rat spinal cord along blood vessels, either into deep or superficial laminae of the dorsal horn, or into the dorsal funiculus. Human fibres that did not have access to blood vessels grew on the spinal cord surface. These findings indicate, that in spite of a substantial growth capacity by axons from human embryonic dorsal root ganglion cells as well as their tolerance to non-permissive factors in the mature mammalian CNS, these axons are still sensitive to the repellent effects of astrocytes of the mature dorsal root transitional zone. Furthermore, this axonal ingrowth is consistently associated with laminin-expressing structures until the axons reach the host spinal cord.     

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.     

The vestibular nuclei in the domestic hen (Gallus domesticus). VII.--Afferents from the spinal cord

Lesions of different parts of the spinal cord at different levels in the hen have been made and the resulting degeneration in the vestibular complex has been studied in silver impregnated sections. Spinovestibular fibres originate from cervical as well as lumbosacral levels of the cord and run in the dorsal part of the lateral funiculus. The spinovestibular fibres from all levels of the spinal cord terminate ipsilaterally in the nucleus Deiters ventralis, the nucleus Deiters dorsalis, the medial nucleus and rostrally in the descending nucleus. The spinovestibular fibres terminating in the above nuclei are few in number while spinovestibular fibres terminating bilaterally in the caudal part of the descending nucleus are much more abundant. In a few cases HRP injections in the vestibular complex resulted in labelled cells in upper cervical segments of the spinal cord localized in lamina VII. The findings are discussed in the light of data concerning the spinovestibular pathway in mammals.     

猫腰髓白质年龄相关的形态学变化

以青年成年猫(1-3龄,2-2．5 kg)和老年猫(12龄,3-3．5kg)L6段脊髓白质为研究对象,用 神经丝蛋白(NF)免疫染色显示神经纤维,用改良的Holzer结晶紫染色显示所有胶质细胞并用成年动物Golgi 法显示其形态,用胶质纤维酸性蛋白(GFAP)免疫染色显示星形胶质细胞。光镜下对青年猫与老年猫腰髓白质 中神经纤维和胶质细胞进行形态学观察和定量研究。与青年猫相比,老年猫腰髓白质中的神经纤维密度显著下 降(P相似文献   

GABA and Prolonged Spinal Inhibition

TWO explanations have been provided for the relatively long latency and prolonged (often exceeding 100 ms) inhibition of firing of spinal motoneurones which is caused by repetitive impulses produced by electrical or natural stimulation^1–4 in muscle and cutaneous afferent fibres. This prolonged inhibitory process is exemplified by the reduction in the amplitude of monosynaptic excitatory synaptic potentials (EPSPs) and reflexes of extensor motoneurones by tetanic stimulation of group I afferents of flexor motoneurones². In contrast with “direct” inhibition, the prolonged inhibition is not reduced by strychnine but is diminished by Picrotoxin^4,6.     

Immunocytochemical study of the relations of acetylcholinesterase, enkephalin-, substance P-, choline acetyltransferase- and calcitonin gene-related peptide-immunoreactive structures in the ventral horn of rat spinal cord.

Calcitonin gene-related peptide (CGRP)-like immunoreactivity was localized immunocytochemically in the large motoneurons in the ventral horn of rat spinal cord. Using fluorescence double-labelling substance P (SP)-immunoreactive nerve fibres were found to surround both the CGRP-positive and negative motoneurons, whereas enkephalin (ENK)-immunoreactive fibres surrounded mainly CGRP-negative cells. All CGRP-like immunoreactive motoneurons were also choline acetyltransferase (ChAT)- and acetylcholinesterase (AChE)-positive. On the other hand a large population of ChAT- and AChE-positive motoneurons were devoid of CGRP-immunoreactivity. It is probable that CGRP/ChAT/AChE-positive cells surrounded by SP-positive fibres have different functions in motoric nervous system than the CGRP-negative ChAT/AChE-positive cells, which are surrounded by ENK-immunoreactive fibres.     

Relations of single semicircular canals to the pontine reticular formation.

The effects of afferent vestibular impulses on single pontine reticular formation units and on a small filament of the IIIrd cranial nerve were recorded with tungsten microelectrodes in 40 curarized guinea pigs. Single-shock and repetitive electrical stimulations were applied by means of stimulating electrodes inserted bilaterally into the perilymphatic space of single ampullae of the anterior and lateral semicircular canals. The reticular unitary response consisted mainly in excitation of the resting discharge rate: most units showed vestibular convergence being affected by separate stimulation of the single four ampullae. the reticular evoked field and unitary potentials accounted for latency values ranging from 0.3 to 2.5 msec. As for the early latencies they can be interpreted as responses mediated by direct vestibulo-reticular fibres. A delimited vestibular projection field in the parameidan pontine reticular formation was not identified.     

正常猫膈神经单纤维电活动特征

在麻醉猫和麻痹的切断迷走神经的清醒猫,观察了膈神经单纤维电活动特征。1.电活动类型:按膈神经单纤维放电与其总干放电的相位关系分为三种类型。(1)完全同步型,即单纤维放电与总干放电同时开始并同时停止,占76.9％。(2)部分同步型占15.4％,其中早期同步,即单纤维放电与总干放电同时开始,但提前终止,占1.9％,中期同步,即单纤维放电较总干放电开始晚,又提前终止,占5.8％,晚期同步,即单纤维放电较总干放电开始晚,但两者同时终止,占7.7％。(8)非同步型,即吸气相和呼气相都有放电,但呼气相时冲动频率较低,占7.7％。前两型为单纯的吸气性放电,共占92.3％。2.单纤维放电平均参数值:麻醉猫每次吸气发放11个冲动,其频率为21次/秒,清醒猫每次吸气发放18个冲动,其频率为34次/秒。结果表明:猫膈神经单纤维放电类型和文献上报导的直接记录膈神经运动神经元放电一致,即以单纯的吸气性放电为最多。     

Immunocytochemical study of the relations of acetylcholinesterase,enkephalin-, substance P-, choline acetyltransferase- and calcitonin gene-related peptide-immunoreactive structures in the ventral horn of rat spinal cord

Summary Calcitonin gene-related peptide (CGRP)-like immunoreactivity was localized immunocytochemically in the large motoneurons in the ventral horn of rat spinal cord. Using fluorescence double-labelling substance P (SP)-immunoreactive nerve fibres were found to surround both the CGRP-positive and negative motoneurons, whereas enkephalin (ENK)-immunoreactive fibres surrounded mainly CGRP-negative cells. All CGRP-like immunoreactive motoneurons were also choline acetyltransferase (ChAT)- and acetylcholinesterase (AChE)-positive. On the other hand a large population of ChAT- and AChE-positive motoneurons were devoid of CGRP-immunoreactivity. It is probable that CGRP/ChAT/AChE-positive cells surrounded by SP-positive fibres have different functions in motoric nervous system than the CGRP-negative ChAT/AChE-positive cells, which are surrounded by ENK-immunoreactive fibres.