摘要:

AbstractThis essay discusses the directional movements of metazoan tissue cells generally, with special emphasis on neurons, in an attempt to show that the directional movements of all share fundamental similarities.

ISSN:0360-4012    

DOI:10.1002/jnr.490130102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

摘要:

AbstractWe have examined the primary growth of neurites by Rohon‐Beard sensory neurones in embryos ofXenopus, Rana, andAmbystoma. Using transmission electron microscopy we have confirmed that some central longitudinal neurites first grow directly under the basal lamina which surrounds the spinal cord inXenopusembryos. Using scanning electron microscopy of dissected embryos we have followed the growth of neurites from the spinal cord to their target tissue, the skin. Comparisons between the three genera are made and detailed observations on growth cones during fasciculation, on the somites and on the basal lamina of the skin are presented. The observations are discussed in relation to possible influences on the course of growth of the developing neurite

ISSN:0360-4012    

DOI:10.1002/jnr.490130103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

摘要:

AbstractThe internal structure of the membranes of axonal and Schwann cell growth processes was examined by freeze‐fracture in the growing olfactory nerve, a simple in vivo system consisting of a homogeneous neuronal population. Excision of the mature nerve of adult bullfrogs provides well‐synchronized primary neuritic outgrowth that is highly enriched in growth cones at its distalmost segment. The extreme uniformity of olfactory axons in terms of their diameter and their intramembrane particle (IMP) composition permits clear identification of the cellular origin of the growth cone structures observed in replicas. In vivo, growth cones of the olfactory nerve appear as irregularly shaped enlargements of the distal tip; filopodia are only infrequently exposed by the fracture plane. Axonal and Schwann cell growth cones are distinguished by (1) the larger size of the Schwann cell growth cone and the smaller diameter of its attached processes, and (2) the distinct differences in IMP composition of Schwann cell and axonal growth cones and cell processes. Schwann cell growth cones display a uniformly high IMP density on their P‐face leaflet, with the exception of circumscribed moundlike protrusions that are relatively free of IMPs. In contrast, axonal growth cones display sharp regional variation in IMP density on their P‐face: broad regions almost devoid of IMPs are interspersed with zones of high IMP density. Cytotic profiles occur within high IMP density zones located, most often, at the base of the axonal growth cone. A comparison of IMP size histograms of both high and low‐density regions of axonal growth cones and that of the neighboring distal shaft of the axon indicates a strict partitioning of membrane components between these two regions. The IMP profile of the axonal growth cone, notable for its relative enrichment in large‐diameter particles, suggests that IMP components of the growth cone are delivered to the distal tip by a mechanism that is distinct from the lateral diffusion process described for particles of the growing axon's shaft [cf. Small and Pfenninger, 1984]. The IMP profile of the concave P‐face leaflet of the internal vesicles found clustered at the base of the growth cone is more similar in composition to the profile of the neuronal shaft than that of th

ISSN:0360-4012    

DOI:10.1002/jnr.490130104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

摘要:

AbstractFew studies have focused on the transformation of growth cones to mature synaptic arbors. To study these events in developing axons in vivo, we have labeled growing cerebellar axons with horseradish peroxidase (HRP) in postnatal stages [Mason and Gregory, 1984]. This report will provide the first data on embryonic cerebellar axons, and will ask whether growth cones differ in tracts and in target tissue and what features characterize axons that enter the cerebellum in fetal periods.During the earliest embryonic (E) periods examined (E16–19), axons in tracts have enlarged growth cones with lamellopodia and short filopodia that contain small and large vesicles. In contrast, axons within the cerebellar anlage from E16‐postnatal day (P) 5 have fine calibers with a minimum of branching, and have small tapered growing tips. If synaptic contacts are made by such growing tips, there is little concomitant change in their shape. As target cells form layers and as their dendrites extend (P5–P7), growing tips and synaptic boutons differentiate according to the type of synaptic arrangement in which they engage. Enlarged, irregular expansions of growing tips correspond to synaptic contacts with multiple dendritic partners and are filled with large and small clear vesicles. Filopodia arising from such swellings, like the small undifferentiated growing tips of the type seen on embryonic axons, contain a mixture of vesicle types but make simple synapses with single profiles. Many axons make both kinds of synaptic structures, especially during the period when maturing axons give rise to long filopodia.Thus, growing tips have immature forms long after synaptogenesis begins, and use filopodial structures to elaborate synaptic arrangements. This analysis should elucidate the changes in growth cone form and cytology that reflect cell‐cell interactions during synapto

ISSN:0360-4012    

DOI:10.1002/jnr.490130105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

摘要:

AbstractWe have previously reported that there is a dramatic increase in polyribosomes associated with dendritic spines during periods of synapse growth induced by denervating lesions. We suggested that polyribosomes at the postsynaptic site may somehow be involved in the growth of synapses. To evaluate this hypothesis further, the present study determines whether synapses which are growing in the developmental period also have accumulations of polyribosomes. We examined the dentate gyrus of the developing rat electron microscopically at 7, 10, 15, 20, and 28 days of age, which spans the major period of synaptogenesis in this structure. Qualitative observations revealed dramatic accumulations of polyribosomes under spine synapses in the youngest animals (7 and 10 days of age). With synapse development, the accumulations of polyribosomes became less dramatic, so that by 28 days of age, the neuropil of the dentate gyrus appeared qualitatively mature. To determine the relationship between polyribosomes under spine synapses and synapse development, quantitative electron microscopic methods were use to evaluate synapse density (number of synapses/100 μm2), and the incidence of polyribosome‐containing spines (proportion of spine synapses with underlying polyribosomes) in the neuropil of the dorsal blade of the dentate gyrus at each age. An inverse relationship was found between synapse density and the proportion of spines with polyribosomes. Synapse density increased in an almost linear fashion between 7 and 28 days of age to levels which were actually somewhat higher than in mature rats, whereas the incidence of polyribosome‐containing spines was highest at the youngest ages and decreased with development. Thus, polyribosomes were most prominent under spine synapses during the period of maximal synapse growth. These results, together with our previous observations of increased numbers of polyribosomes under spines during lesion‐induced growth, suggest that the polyribosomes represent a structural specialization of dendrites at sites of synapse construction. We propose that they produce protein(s) that are involved in synapse

ISSN:0360-4012    

DOI:10.1002/jnr.490130106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

摘要:

AbstractThe growth cones of retinal ganglion cell axons were studied in the optic tract and tectum with hoseradish peroxidase (HRP) histochemistry and electron microscopy. The ganglion cell growth cones has many morphological features similar to those described in vitro and in other in vivo systems. However, we found that some processes formed highly differentiated terminal arborizations, while retaining growth cones on many of their branches. In addition, ultrastructural examination of the tectal neuropil revealed that many ganglion cell axonal processes had characteristics of both growth cones and presynaptic endings. These findings are discussed in the context of the hypothesis of shifting connections and the evidence that retinotectal map formation involves several mechanisms, including a process that depends on the action potential activity in the optic fibers.

ISSN:0360-4012    

DOI:10.1002/jnr.490130107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

摘要:

AbstractThe outgrowth of axons from the early retina in vivo is compared with that from retinal explants in two types of culture systems. The normal time course of axonal growth along the primordial optic pathway to the optic tectum is characterized, using tritiated proline and horseradish peroxidase (HRP) as anterograde tracers. The rate of axonal elongation in vivo is estimated to be about 32 μm/hr at 22°C. The HRP technique allows visualization of retinal growth cones in vivo. Observations can thus be made on their microanatomy and on the environment through which they navigate. The growth cones of retinal ganglion cells in the embryo have lamellipodia and fairly short filopodia ( ∼ 10 μm) which are directed forward. The growth cones are found near the pial surface of the brain but do not seem to maintain contact with it.Two culture systems were developed to investigate axonal pathways in vitro. In the first, different substrates and culture media were explored. Results indicate that growth cones prefer a polyornithine substrate over a collagen one. The media that promotes the best neurite outgrowth consists of L15 (60%), fetal calf serum (10%) andXenopusembryo extract (1 mg/ml). Time‐lapse video monitoring of substrate cultures reveals an average rate of outgrowth of about 18 μm/hr with great variability. The growth cones in these cultures are large, flattened, and complex compared to those in vivo, and their filopodia extend in many different directions.The second culture system is a collagen gel infiltrated with growth medium. In these conditions neurite outgrowth more closely mimics that in vivo. The rate is faster than on substrates, and the growth cones appear morphologically similar to those in the embryo. Preliminary experiments using the gel culture system to test for chemotaxis of retinal axons toward their targets failed to demonstrate such an

ISSN:0360-4012    

DOI:10.1002/jnr.490130108

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

摘要:

AbstractThe neural cell adhesion molecule (NCAM) has been shown to be a ligand in the formation of cell‐cell bonds. This molecule is present on essentially the entire surface of differentiated nerve cells, including the cell body, neurite shaft, and growth cone. In mediating membrane‐membrane adhesion, NCAM appears to ligate with itself, and one of its most obvious functions is in the self‐association of nerve fibers to form fascicles. In most cases fasciculation occurs by the successive elongation of axons along other axons and, therefore, is likely to represent a growth cone‐neurite shaft interaction as well as a shaft‐to‐shaft adhesion. Competition between neurite shafts and the surrounding substrate for growth cone adhesion probably represents a major factor in the branching of nerve bundles. In addition to neurons, NCAM appears on some glial and muscle cells. Recent experiments suggest that this molecule is involved in growth cone guidance along adhesive pathways on glial precursors in the vertebrate central nervous system, and in the initial interaction of axons with muscle prior to syn

ISSN:0360-4012    

DOI:10.1002/jnr.490130109

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

摘要:

AbstractBy using cell‐cultured identified neurons of the snailHelisoma, we demonstrate that the growth cones of different neurons are intrinsically different from one another in terms of their structure, behavior, and response to environmental signals. Structurally neuron 5 has a greater number of filopodia per growth cone, has shorter filopodia, and has a smaller interfilopodial distance than neuron 19. Behaviorally, the growth cones of neuron 5 advance over the substratum at a faster rate than those of neuron 19; and the growth cones of neuron 19, but not of neuron 5, respond to the presence of serotonin in their environment by retracting their filopodia.In addition to such intrinsic differences between the growth cones of different neurons, we also demonstrate that the separate growth cones of a single neuron, while having identical properties, can act independently of one another. Focal application of serotonin to a growth cone causes only a localized retraction of that growth cones' filopodia. Other growth cones that are attached to the same neuron but that are not exposed to serotonin retain their normal structural feature

ISSN:0360-4012    

DOI:10.1002/jnr.490130110

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

摘要:

AbstractThe extension of filopodia from growth cones of regenerating neurites from rat superior cervical ganglion neurons in tissue culture was studied. Cultures were grown on a thin layer of fibrous collagen and maintained in a medium containing serum and nerve growth factor. Time‐lapse cinematography and computer‐assisted morphometry were used to observe and measure the kinetics of extension of individual filopodia. Filopodia extended from the growth cone margin, trailing neurite, or from each other. Frequently, extension was preceded by the appearance at the cone margin of a nodule of cytoplasm which appeared dense in phasecontrast optics. Branch points between adjacent extending filopodia remained fixed with respect to the growth cone while the filopodia lengthened. The rate of extension was maximum just after initiation (0.12 ± 0.4 μm/sec; mean ± SD; n = 36) and declined thereafter until the filopodium collapsed. This initial rate of extension was directly correlated with the eventual length of the filopodium (r = 0.67). Filopodia of growth cones arising from embryonic neurons exhibited higher initial extension rates (range: 0.07 to 0.20 μm/sec; mean = 0.13 μm/sec) than those of postnatal neurons (range: 0.01 to 0.13 μm/sec; mean = 0.09 μm/sec). These data are discussed in relation to a model proposed by Tilney and Inoue [1982] for the extension, by distal addition of G‐actin to growing filaments, of another type of elongating process filled with microfilaments, the acrosomal process o

ISSN:0360-4012    

DOI:10.1002/jnr.490130111

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY