摘要:

AbstractWe have characterized, by electron microscopy, the growth of pioneering axons from the retina into the visual pathway during early development ofXenopus laevis.The subsequent development of following fibers from the growing retinal margin as they accumulated in the ganglion cell fiber layer (GCFL) of the retina was also studied.Extracellular channels bordered by neuroepithelial cells appear in the developing retina in a dorsal to ventral gradient before any pioneering axons are seen. Pioneering axons are subsequently observed in these channels, usually surrounded by neuroepithelial cell processes. Ruthenium red treatment of embryonic retinas reveals extracellular matrix (ECM) within these retinal channels, while extracellular spaces in the proximal optic stalk, just beyond the optic disc, lack this material. ECM is also seen in optic tectum wherever ingrowing retinal and nonretinal axons are found. The channels and the ECM contained within them may provide guidance cues for pioneering retinal axons. The early association of pioneering retinal axons with neuroepithelial cell processes (putative glia) appears to be important in further development of the GCFL.The so‐called following fibers of ganglion cells, arising later in development, fasciculate with pioneer axons in extracellular spaces and form fiber bundles of the GCFL on top of the layer of glial cell endfeet. It is not clear whether pioneering axons, glial cell surfaces, or both serve as guidance cues for following fiber migratio

ISSN:0092-7317    

DOI:10.1002/cne.902640202

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractAn antibody prepared against adult canary brain, 40E‐C, stains ventricular zone cells that send long, unbranched processes into the forebrain parenchyma. We identify these cells as radial glia. The same antibody also stains a subset of brain astroglia and reacts with nonbrain material such as mesenchyme, Sertoli cells, and the Z‐line of muscle. A weaker reaction is given by erythrocytes and some endothelial cells. 40E‐C also reacts with the radial glia of the developing rat brain but fails to show any such glia in adult rodent brain. Western blot analysis shows that this antibody recognizes vimentin, a molecule shared by all 40E‐C‐positive cell types. We believe that the presence of radial glia in the adult avian forebrain and their apparent absence in mammals is related to neurogenesis in adulthood, which occurs in birds and much less or not at all in mammals. In addition, the presence of radial glia in adult birds may also relate to other, stillhypothetical, differences in the physiology of adult avian and mammali

ISSN:0092-7317    

DOI:10.1002/cne.902640203

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe development of corticogeniculate synapses was studied in 16 cats ranging in age from newborn to adult. Tritiated proline was injected into areas 17 and 18 of the visual cortex in order to label corticogeniculate terminals in lamina A of the dorsal lateral geniculate nucleus. The labeled terminals were then characterized ultrastructurally using electron microscopic autoradiography.Labeled synaptic profiles were found in newborn kittens, indicating that corticogeniculate connections are present in the cat at birth. Morphologically, however, many corticogeniculate endings in newborn and 1‐week‐old kittens are different from those in older animals in that they do not form well‐defined terminal boutons, and their synaptic vesicles are often loosely packed. In kittens 2 weeks of age and older, corticogeniculate axons end as RSD terminals exclusively; i.e., they are relatively small in size and contain round, densely packed synaptic vesicles, and occasionally an electron‐dense mitochondrion (Guillery:Z. Zellforsch. 99: 1–38, '69). However, not all RSD terminals in the LGN represent input from visual cortex. Injections of3H‐proline into the mesencephalic reticular formation also label RSD terminals selectively in the lateral geniculate nucleus.At all ages corticogeniculate axons make synaptic contacts with dendrites exclusively, and they are always presynaptic. This suggests that the essential pattern of corticogeniculate synapses is formed early and is not altered during subsequent development. Quantitatively, there is no significant change in the size of corticogeniculate terminals or their synaptic vesicles in kittens 2 weeks of age (the youngest measured) and older. In contrast, the synaptic contact lengths of these terminals decrease about 28% between 2 and 12 weeks. During this same period there is approximately a twofold increase in the density of corticogeniculate terminals in the neuropil of lamina A. Since the volume of neuropil in lamina A increases almost fourfold between 2 and 12 weeks, the doubling of corticogeniculate terminal density represents about an eightfold increase in terminal number. After 12 weeks there is little change in the length, density, or number of corticogeniculate synaptic contacts, which suggests that the morphological development of the corticogeniculate pathway is essentially complete

ISSN:0092-7317    

DOI:10.1002/cne.902640204

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractDefects of the cerebral cortex and corpus callosum of mice subjected prenatally to gamma irradiation were evaluated as a function of dose and of embryonic age at irradiation. Pregnant mice were exposed to a gamma source at 16, 17, and 19 days of gestation (E16, E17, and E19, respectively), with total doses of 2 Gy and 3 Gy, in order to produce brain defects on their progeny. At 60 postnatal days, the brains of the offspring were analyzed qualitatively and quantitatively and compared with those of nonirradiated animals. Mice irradiated at E16 were all acallosal. Those that were exposed to 2 Gy displayed an aberrant longitudinal bundle typical of other acallosals, but this was not the case in those irradiated with 3 Gy. The corpus callosum of animals irradiated at E17 with 3 Gy was pronouncedly hypotrophic, but milder effects were observed in the other groups. Quantitative analysis confirmed a dependence of callosal midsagittal area upon dose and age at irradiation, and, in addition, indicated an interaction between these variables. The neocortex of irradiated animals was hypotrophic: layers II‐III were much more affected than layer V, and this was more affected than layer VI. Quantitative analysis indicated that this effect also depended on dose and age at irradiation and that it was due to a loss of cortical neurons. Furthermore, a positive correlation was found between the number of neurons within layers II‐III, and V and the midsagittal area of the corpus callosum. Ectopic neurons were found in the white matter and in layer I of animals irradiated at E16 and E17, indicating that fetal exposure to ionizing radiation interfered with the migration of cortical neurobla

ISSN:0092-7317    

DOI:10.1002/cne.902640205

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractCells of origin of ascending afferents to the mammillary nuclei and the afferents' fields of termination within these nuclei were studied by using retrograde and anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase in the rat.The pars compacta of the superior central nucleus projects bilaterally to the median region of the medial mammillary nucleus. The ventral tegmental nucleus projects ipsilaterally to the medial mammillary nucleus, except for its median region, in a topographic manner such that the rostrodorsolateral part of the ventral tegmental nucleus projects to the medial quadrant of the medial mammillary nucleus; the rostroventromedial part projects to the dorsal quadrant; the caudodorsolateral part projects to the ventral quadrant; and the caudoventromedial part projects to the lateral quadrant. These projection fields extend throughout the longitudinal axis of the medial mammillary nucleus, except for its most caudal region, to which only the dorsolateral part of the ventral tegmental nucleus projects. This nucleus also projects topographically to the ipsilateral dorsal premammillary nucleus; the rostral part of the ventral tegmental nucleus projects to the dorsal part of the dorsal premammillary nucleus, whereas the caudal part projects to the ventral part. The periaqueductal gray around the dorsal tegmental nucleus projects bilaterally to the supramammillary nucleus. The pars alpha of the pontine periaqueductal gray projects bilaterally to the peripheral part of the lateral mammillary nucleus, whereas the pars ventralis of the dorsal tegmental nucleus projects ipsilaterally to the lateral mammillary nucleus.The results show that the tegmentomammillary projections are organized in a gradient fashion, with the rostral to caudal position of cells of origin within the tegmental nuclei of Gudden being reflected by the medial to lateral position of fields of termination within the mammillary nuclei.

ISSN:0092-7317    

DOI:10.1002/cne.902640206

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractTransganglionic transport of horseradish peroxidase was used to trace the pattern of medullary terminations of the glossopharyngeal and vagal nerve complex in the channel catfish,Ictalurus punctatus.The glossopharyngeal root terminates centrally in the anterior end of the vagal lobe except for two fascicles that terminate in separate regions of the nucleus intermedius of the facial lobe. Vagal nerve branches innervating regions of the oropharynx terminate in an overlapping, segmental fashion throughout the ipsilateral vagal lobe and the nucleus intermedius of the vagal lobe. The descending branch of the vagus, innervating the abdominal viscera, terminates in the general visceral nucleus and in the nucleus intermedius of the vagal lobe. In addition, abdominal visceral fibers decussate through the commissural nucleus of Cajal and terminate in the general visceral nucleus of the contralateral side. Efferents included in the oropharyngeal and abdominal branches of the vagus also originate from two morphologically separable populations of motor neurons.

ISSN:0092-7317    

DOI:10.1002/cne.902640207

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe coelomic root of the vagus nerve in goldfish is connected with sensory and motor nuclei of the medulla that are distinct from those serving the orobranchial roots of the same nerve. The primary sensory nucleus for coelomic sensation is itself divisible into medial and lateral subnuclei on the basis of afferent input and immunocytochemistry. The lateral subnucleus receives sensory input from the specialized chewing organ in the posterior pharynx and is poor in both substance P‐like and tyrosine‐hydroxylase‐like immunoreactivities. The medial subnucleus receives input from the subdiaphragmatic gastrointestinal tract and is rich in substance P‐like and tyrosine‐hydroxylase‐like immunoreactivities. The primary sensory fibers that innervate the gastrointestinal tract also project directly to the area postrema and to the vicinity of subdiaphragmatic visceral motor neurons.The vagal motor neuronal pool is divisible into three columns: paramedian (cardiac), medial, and lateral. The paramedian group innervates the heart and is situated in a loosely aggregated column at the boundary zone between the ventricular ependyma and the underlying brainstem. The medial vagal motor neurons innervate the subdiaphragmatic viscera, while the lateral column motor neurons innervate the posterior pharynx and muscles of the chewing organ. The motor neurons in this motor column are arranged in a topographic rostrocaudal order within the motor column according to the muscle of innervation.Thus both the general visceral sensory and general visceral motor nuclei of the medulla are organized into functional domains. Furthermore, in the goldfish, the special visceral (gustatory) and general visceral sensory nuclei form a continuous series in the medulla with the external and oral systems represented anteriorly and the pharyngeal and digestive systems represented

ISSN:0092-7317    

DOI:10.1002/cne.902640208

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractDuring normal development, tadpoles ofXenopus laevisdemonstrate large variations in body size that are carried through metamorphosis. This variation in size exists at the stages when lumbar lateral motor column (L‐LMC) motoneurons are produced and when neuronal cell death in this neuron population occurs. Body size, hindlimb size, motoneuron number, and motoneuron size (i.e., neuron nuclear cross‐sectional area) were measured in animals from three developmental stages: one prior to significant amounts of cell death, one at the peak rate of cell death, and one after cell death. The hypothesis that neuron population size is matched to peripheral size was tested by using the natural size variation found at each of these stages.The ranges of values for the measurements at the three stages were large. Significant correlations between body size and motoneuron number, as well as between motoneuron number and muscle fiber number, were present after cell death. Since these correlations emerged as cell death reduced neuron numbers, size matching may have occurred and cell death may have adjusted the L‐LMC motoneuron population's size to variation in body size. In addition to the correlations between body size and motoneuron number at the end of cell death, neuron numbers before and after cell death were significantly correlated among groups of siblings. The possibility that the number of neurons after cell death was also influenced by differences in the number of L‐LMC progenitors is di

ISSN:0092-7317    

DOI:10.1002/cne.902640209

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractSynaptic terminals from the axons of type 3 neurons in the A‐laminae of the cat LGN impregnated with the Golgi gold‐toning procedure were examined at light and electron microscopic levels. The axons were identified by their somatic origin, thin diameter, and, in one of these cells, by dense undercoating beneath the axolemma, which is a known characteristic of the axon initial segment. The axon of one of the analyzed cells was profusely branched and extended throughout most of lamina A within the dendritic domains of the cell, and both types of processes were oriented along projection lines in LGN. This suggests that the dendrites and axons of type 3 cells receive inputs and exert effects, of probably inhibitory nature, within restricted retinotopic regions of LGN. The vast majority of the axon terminals of these cells were distributed in series along axonal branches. In one of the type 3 cells, however, a dense cluster of terminals arising from a secondary axonal branch was observed. Ultrastructurally, the analyzed synaptic terminals of the type 3 cells contained flattened or pleomorphic synaptic vesicles, dark mitochondria, and established synapses that appeared to be of symmetrical type when the membranes were perpendicularly cut. On the basis of these characteristics these terminals are classified as F boutons, following Guillery's (Z. Zellforsch. 96: 1–38, '69), nomenclature. The postsynaptic elements to the axon terminals were dendrites of small to medium size, which received “en passant” synaptic contacts in extraglomerular regions of the geniculate neuropil by the terminals distributed in series. The axon terminals located in clusters, however, made synapses with dendrites in glomerular regions of the neuropil, where they were not seen postsynaptic to retinal or other types of terminals. This is in contrast to the postsynaptic nature of F2 boutons in the same glomeruli, which have been identified as dendritic appendages of the GABA positive type 3 neurons in the cat LGN (Montero:J. Comp. Neurol 254: 223–245, '86). On the other hand, the axonal F terminals differ from F1 boutons in terms of synaptic relations and ultrastructure, since the latter have been shown to be presynaptic to F2s and sonata and to contain crowded populations of flat synaptic vesicles which give them a characteristic dark appearance. Terminals equivalent to F1 boutons have been shown to originate from perigeniculate cells in the rat LGN. From these observations it is suggested that the geniculate GABAergic interneurons support two morphologically and functionally different types of inhibitory terminals synapsing the dendrites of relay cells: the dendritic F2 terminals that in microcircuits are under the influence of retinal, cortical, perigeniculate, and cholinergic terminals from the midbrain, and the axonal F boutons, which would convey to the postsynaptic relay cell the unaltered output of these i

ISSN:0092-7317    

DOI:10.1002/cne.902640210

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractWhen silicone regeneration chambers are implanted empty, axonal regeneration fails if the interstump gap length is greater than 10 mm. Previous experiments using the 10‐mm gap model demonstrated that regeneration success correlated with the dimension and/or consistency of the naturally formed acellular fibrin matrix. Both spatial and temporal parameters of regeneration could be stimulated through modifications of the fibrin matrix by prefilling the chambers at the time of implantation either with phosphate‐buffered saline or plasma dialyzed against phosphate‐buffered saline. In the present experiments, similar modification of matrix formation was found to promote successful regeneration across 15‐mm and 20‐mm interstump gap lengths. In addition, prefilling 15‐mm‐gap chambers with dialyzed plasma resulted in a 3.5‐fold increase in the incidence of functional restitution detected at 8 weeks after implantation over the outcome with chambers prefilled with phosphate

ISSN:0092-7317    

DOI:10.1002/cne.902640211

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY