摘要:

AbstractThe distribution and density of SRIF receptors (SRIF‐R) were studied during development in the rat somatosensory cortex by in vitro autoradiography with monoiodinated [Tyr0‐DTrp8]S14. In 16‐day‐old fetuses (E16), intense labeling was evident in the intermediate zone of the cortex while low concentrations of SRIF‐R were detected in the marginal and ventricular zones. The highest density of SRIF‐R was measured in the intermediate zone at E18. At this stage, labeling was also intense in the internal part of the developing cortical plate; in contrast, the concentration of binding sites associated with the marginal and ventricular zones remained relatively low. Profound modifications in the distribution of SRIF‐R appeared at birth. In particular, a transient reduction of receptor density occurred in the cortical plate. During the first postnatal week, the density of receptors measured in the intermediate zone decreased gradually; conversely, high levels of SRIF‐R were observed in the developing cortical layers (II to VI). At postpartum day 13 (P13), a stage which just precedes completion of cell migration in the parietal cortex, the most intensely labeled regions were layers V–VI and future layers II–III. From P13 to adulthood, the concentrations of SRIF‐R decreased in all cortical layers (I to VI) and the pattern of distribution of receptors at P21 was similar to that observed in the adults.Detailed analysis of the results revealed (i) a close association between the distribution of SRIF‐R and the areas containing migrating neuroblasts and (ii) a temporal correlation between the presence of SRIF‐R and the transient expression of the neuropeptide SRIF in the developing somatosensory cortex. Taken together, our data suggest the existence of two populations of SRIF‐R: a transient population, which could be implicated in the development of the parietal neocortex from E16 to P13, and a population of SRIF‐R only expressed after the first postnatal week, which is likely to be involved in the

ISSN:0092-7317    

DOI:10.1002/cne.903050202

出版商:Wiley‐Liss, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe intracellular distribution of nerve growth factor receptor immunoreactivity was examined by electron microscopy in the cerebellum of adult and postnatal day 12 rats. The very faint immunostaining in Purkinje cells of naive adult animals was greatly amplified after colchicine treatment. Neonatal cerebellum, in contrast, contained prominent immunoreactivity in both Purkinje cells and germinal cells of the external granular layer. Intracellular distribution of the nerve growth factor receptor reaction product was very similar in Purkinje cells of both neonatal and colchicine‐treated adult animals. It was consistently present along the perikaryal cell membrane, in segments of the rough endoplasmic reticulum and Golgi complex. Numerous membrane‐bound aggregates of immunoreactive vesicles resembling multivesicular bodies (secondary lysosomes) were scattered throughout the cell soma, although less frequently in neonatal rats. Bulbous expansions along the proximal axons of colchicine‐treated Purkinje cells were filled with such immunoreactive multivesicular bodies. These cells also displayed evidence of nerve growth factor receptor internalization in the form of immunoreactive coated vesicles situated near the cell membrane. In addition to the staining in Purkinje cells, neonatal cerebellum contained high amounts of nerve growth factor receptor reaction product along the cell membrane of germinal cells in the external granular layer. Although Purkinje cells of naive adult animals possessed little or no cell membrane‐related nerve growth factor receptor immunoreactivity, reaction product was sometimes seen in cisternae of the rough endoplasmic reticulum and Golgi apparatus. These findings provide electron microscopic immunocytochemical evidence of nerve growth factor receptor synthesis, internalization, and catabolism in noncholinergic neurons of the central nervous

ISSN:0092-7317    

DOI:10.1002/cne.903050203

出版商:Wiley‐Liss, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractSegmentally homologous neurogenesis and neuronal differentiation processes characterize the formation of the peripheral nervous system in the developing mouthparts of the grasshopper embryo. The peripherally located neurons derive from the ectoderm in each of the embryonic mouthparts. The major nerve branches serving the mandibles, maxillae, and labium are established by peripheral pioneer neurons, which project their axons into the central nervous system via a set of guidepost cells. The two secondary nerve branches in each appendage are established by fasciculation of peripheral afferent pioneers and central efferent pioneers or by efferent pioneers alone. Sensory cells differentiate and connect with the peripheral nerve branches after a basic peripheral nerve scaffold has been established. The serial homology of these developmental processes in the mouthparts and in the thoracic legs is striking and can be documented at the level of individual identified cells. Thus despite the enormous differences in gross structure and function among cephalic mouthparts and true thoracic legs, many aspects of neurogenesis and early neuronal differentiation are remarkably conserved in all of these appendages.

ISSN:0092-7317    

DOI:10.1002/cne.903050204

出版商:Wiley‐Liss, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractIdentified entorhino‐hippocampal projection neurons were investigated for their ultrastructure. Spinous projection neurons (pyramidal and spiny stellate cells) display common features such as symmetric axosomatic terminals on their somata, asymmetric synapses on the spines, and both types of synapses on the dendritic shafts. Their axons descend towards the white matter, branching occasionally via collaterals which establish contact with local spines and rarely on dendritic shafts and somata. The sparsely spinous projection neurons (multipolar and horizontal‐bipolar) typically show deep nuclear infolds and symmetric and asymmetric synapses on their somata and dendritic shafts. Axons also collateralize in the soma vicinity and form local synapses. It is concluded that the entorhino‐hippocampal projection neurons (both spiny and sparsely spinous) act locally and distally thus performing simultaneously as local‐circuit and as projection neurons. In accordance with other morphological and electrophysiological reports it appears likely that the generation, modulation, and suppression of entorhinal excitation waves is mediated by these neurons through direct excitation, feed‐forward and feed‐back inhibition, and di

ISSN:0092-7317    

DOI:10.1002/cne.903050205

出版商:Wiley‐Liss, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe synaptic connections within the lamina, the first of the optic neuropiles underlying the insect's compound eye, have been little studied inDrosophila melanogasteruntil now, despite the genetic advantages of this animal. Here we report the reconstruction through its entire depth of one of the lamina modules, or cartridges, of a female wild‐typeDrosophila, for which a series of EM cross sections was analysed at levels extending from the retinal basement membrane to the first optic chiasma. A complete, comprehensive catalogue of the synaptic connections of all columnar elements has been compiled from this single series, confirmed from comparisons with less completely photographed cartridges. Combinations of the 12 types of cartridge neurons form divergent multiple‐contact synapses (dyads, triads, and tetrads) throughout the lamina's depth. These 12 neuron types include 11 narrow‐field elements (one class of receptor terminal, R1–R6, providing input to the cartridge; two types of long visual fiber from the ommatidium, R7 and R8; five types of monopolar cell, L1–5; and three types of medulla cell–two centrifugal neurons C2 and C3, and a third, T1) as well as a wide‐field intrinsic or amacrine cell. Connections within the lamina formed by L4 from two adjacent cartridges (posterodorsal and posteroventral) contribute to the matrix of connections. In addition, connections of at least one other wide‐field element have also be

ISSN:0092-7317    

DOI:10.1002/cne.903050206

出版商:Wiley‐Liss, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe distribution of galanin (GAL) binding sites in the visual cortex of cat and monkey was determined by autoradiographic visualization of [125I]‐GAL binding to tissue sections. Binding conditions were optimized and, as a result, the binding was saturable and specific. In cat visual cortex, GAL binding sites were concentrated in layers I, IVc, V, and VI. Areas 17, 18, and 19 exhibited a similar distribution pattern. In monkey primary visual cortex, the highest density of GAL binding sites was observed in layers II/III, lower IVc, and upper V. Layers IVA and VI contained moderate numbers of GAL binding sites, while layer I and the remaining parts of layer IV displayed the lowest density. In monkey secondary visual cortex, GAL binding sites were mainly concentrated in layers V–VI. Layer IV exhibited a moderate density, while the supragranular layers contained the lowest proportion of GAL binding sites. In both cat and monkey, we found little difference between regions subserving central and those subserving peripheral vision. Similarities in the distribution of GAL and acetylcholine binding sites are discus

ISSN:0092-7317    

DOI:10.1002/cne.903050207

出版商:Wiley‐Liss, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe present study was carried out to analyze the topography of spinal projections to the anterior and posterior lobes of the cerebellum and to investigate whether projections to the two lobes come from different spinocerebellar neurons or from branching axons of the same cells. We used orthograde transport of horseradish peroxidase conjugated with wheat germ agglutinin (WGA‐HRP) to identify the cerebellar areas where spinocerebellar axons terminate and retrograde double‐labeling techniques to estimate the incidence of spinocerebellar neurons projecting to both anterior and posterior lobes via axon collaterals. Orthograde labeling confirmed that the rat, like other mammalian species, has spinocerebellar projections to two different regions of cerebellar cortex, i.e., lobules I–V of the anterior lobe and lobule VIII of the posterior lobe, with the highest incidence in lobules II, III, and VIII. We did not observe a clear difference in the distribution of afferents coming from different spinal segments to either of the two lobes. The double‐labeled cells were located primarily in the lower thoracic and upper lumbar segments, almost exclusively in Clarke's column and in the dorso‐lateral part of lamina 7 (in the region of the spinal border cells). It is likely that most or all of the spinocerebellar neurons in these structures project to both anterior and posterior lobes. Therefore, the two lobes of the cerebellum are likely to receive common information from these cells, but different information from the separate populations of spinocerebellar neurons that project only to one lobe or

ISSN:0092-7317    

DOI:10.1002/cne.903050208

出版商:Wiley‐Liss, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractPreferred stimulus orientations of striate cortical cells in the cat were analyzed for possible isotropic or anisotropic distributions. We separated the data twice, into central (0–5°) vs. peripheral subgroups and into upper vs. lower layer cells. In the central group, absolute orientations were counted; in the periphery, a radial test was adopted by normalizing the preferred stimulus orientation of a cell to the line connecting the receptive field center to the retinal center. We found that in the center, vertical and horizontal orientations are overrepresented. In the periphery, the histograms show complementary anisotropies for upper and lower layers, favoring a map for radial orientation detection in upper layers and a more concentric map for orientation detection in lower layers.These results are possibly related to the probabilities different optic flow fields on the retina under natural conditions of stimulation. They are discussed as possible neuronal structures supporting figure‐ground discrimination, the distinction of self motion from object motion, and the location of objects in three‐dimensional

ISSN:0092-7317    

DOI:10.1002/cne.903050209

出版商:Wiley‐Liss, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractWe have examined microtubules and microtubule‐like elements within the toad rod photoreceptor outer segment in order to define regional specializations of the photoreceptor cytoskeleton. “Ciliary” microtubules were localized within the rod outer segment (ROS) by using thin section electron microscopy, immunofluorescence, and rapid‐freeze deep‐etch microscopy. All three methods showed that ciliary microtubules stop short of the extreme ROS distal tip, although abundant microtubule‐like structures distinct from the ciliary microtubules were found within the distal 10–15 μm of the ROS tip. These heretofore undescribed “distal ROS tubules” are clustered at the clefts or incisures of the disk membrane stack and resemble microtubules in overall size and shape, although they are not closely related antigenically to tubulin. The distal ROS tubules are more abundant in green rods than red rods and vary in number during the daily light/dark cycle. Quantitation of these tubules at two time points during the light/dark cycle suggests that there are three‐ to fourfold more tubules in the ROS tip one hour after light onset than one hour before light onset. Retinas prevented from normal disk membrane shedding by separation of the retina from the adjacent pigment epithelium, failed to develop increased numbers of tubules after light onset. This suggests that the newly described distal ROS tubules may modulate or be modulated by light‐induced interactions between the photoreceptors and pigment epithelium, such as those that occur during the disk shedding phas

ISSN:0092-7317    

DOI:10.1002/cne.903050210

出版商:Wiley‐Liss, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractIn a number of mammalian species, fibre outgrowth in the developing retinofugal pathway is coincident with the presence of melanin in the retinal part of the optic stalk. The presence of melanin is transient in this developing system and has been proposed to play a role in the guidance of retinofugal fibres. Further, it has been suggested that this stalk melanin accounts for the differences between the size of the uncrossed retinal component in pigmented and nonpigmented strains. However, a recent study showed that there is no melanin in the optic stalk of Manchester rats during fibre outgrowth. Since such rats supposedly have a normal pigment distribution and a normal pattern of decussation at the optic chiasm, this finding appears to undermine the suggested role played by stalk melanin in establishing the laterality of retinal fibre projections in other mammalian species.The aim of this study was to re‐evaluate the relationship between melanin in the stalk and the development of the retinofugal pathway in three strains of rat: the Wild type, Long Evans Hooded, and the Albino. The Albino rat, which lacks melanin‐bearing cells entirely, was shown to have the smallest uncrossed projection, approximately 1,340 ipsilaterally projecting cells (ipc), whereas the Long Evans (2,760 ipc) and the Wild‐type strain (2425 ipc) were found to have a larger uncrossed retinal component. In both pigmented strains, melanin was restricted to the eye cup and absent from the optic stalk throughout all stages of development. These results extend the finding that in the rat no correlation can be found between the size of the adult uncrossed retinofugal pathway and the existence of stalk melanin during development. Further, it was found that during initial outgrowth the distribution of fibres in the distal stalk was similar for all three strains, providing evidence that fibre topography does not account for the differences in the number of ipsilaterally projecting ganglion cell fibres.Finally, the position of earliest uncrossed fibres in the stalk was determined in the mouse, an animal with melanin‐bearing cells in this region. It was found that these fibres intermingled with crossed fibres throughout the length of the stalk and that their position within the stalk was similar in both pigmented and albino strains. These observations suggest that stalk pigment plays no specific role in the development of the chiasmatic pathway of retinofugal fibres in either the rat or th

ISSN:0092-7317    

DOI:10.1002/cne.903050211

出版商:Wiley‐Liss, Inc.    

年代:1991

数据来源: WILEY