摘要:

AbstractIn sections of area 17 of monkey visual cortex treated with an antibody to MAP2 the disposition of the cell bodies and dendrites of the neurons is readily visible. In such preparations it is evident that the apical dendrites of the pyramidal cells of layer VI form fascicles that pass into layer IV, where most of them gradually taper and form their terminal tufts. In contrast, the apical dendrites of the smaller layer V pyramidal cells come together in a more regular fashion. They form clusters that pass through layer IV and into layer II/III where the apical dendrites of many of the pyramidal cells in that layer add to the clusters. In horizontal sections taken through the middle of layer IV, these clusters of apical dendrites are found to have an average center‐to‐center spacing of about 30 μm, and it is proposed that each cluster of apical dendrites represents the axis of a module of pyramidal cells that has a diameter of about 30 μm and contains about 142 neurons.The MAP2 antibody reaction also reveals that some pyramidal cells in layers IVA and IVB have their cell bodies arranged into cones. There are about 118 such cones beneath 1 mm2of cortical surface and the apical dendrites of the pyramidal cells within them bundle together at the apex of each cone to pass into layer III. Surrounding the cones of neurons there are horizontally aligned, thin dendrites. The location of these dendrites coincides with the dark walls of the honeycomb pattern seen in layer IVA after cytochrome oxidase reactions, or after the parvocellular input from the lateral geniculate nucleus has been labeled. Thus the cones of pyramidal cells within upper layer IV fit into the pockets of the honeycomb pattern. Below the cones of pyramidal cells are the outer Meynert cells within layer IVB, and the cell bodies of these large neurons are disposed so that they preferentially lie beneath the neuropil between the cones of pyramids.It is suggested that pyramidal cell modules are a basic feature of the cerebral cortex, and that these are combined together by afferent inputs to the cortex to generate the systems of functional co

ISSN:0092-7317    

DOI:10.1002/cne.903060102

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe cerebral cortex of adult mammals contains several somatotopic representations of the body surface. Although the organization of the various somatosensory cortices of numerous species of adult animals has been elucidated, data on the somatosensory representations of fetal and neonatal animals are limited. As part of an investigation into the perinatal development of the somatosensory cortices, it was necessary to delineate the organization of the somatosensory cortices of the perinatal pig. This study presents the topographical organization of the primary somatosensory cortex (SI) of the perinatal pig.Multiunit microelectrode mapping methods were used to produce topographic maps of SI from barbiturate anesthetized pigs ranging in age from 7 days preterm to 2 months postpartum. It was demonstrated that the overall organization of this region of cortex was similar to that of other mammals: a somatotopic projection of predominantly the contralateral body surface was delineated in which the hindlimb is represented medially and the face laterally across the cortex. A disproportionately enlarged rostrum representation was mapped in detail, and multiple representations of the rostrum, face, and mouth were found. Several of these representations exhibited bilateral and ipsilateral input. The SI trunk and hindlimb representations were located on the medial wall of the hemisphere; these representations were small but their presence refutes speculation that ungulates do not have a complete body representation in SI.

ISSN:0092-7317    

DOI:10.1002/cne.903060103

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

年代:1991

数据来源: WILEY

摘要:

AbstractMultiunit microelectrode recording techniques were used to delineate the somatotopic organization of the secondary somatosensory cortex (SII) of the neonatal pig. Barbiturate anesthetized piglets ranging in age from 7 days preterm to 2 months postpartum were used. The SII area, located lateral to the rostral and middle suprasylvian sulci, was found to contain a complete somatotopic representation of the contralateral body surface with a significant proportion of bilateral input for all body regions except the forehoof and forelimb. The SII forelimb and hindlimb representations were found to possess a “striplike” orientation in a rostral to caudal sequence, and the trunk representation was located posterolateral to the hindlimb representation, giving SII an inverted appearance. Two apparently separate face representations were delineated; one posterolateral to the projection from the trunk and the other anterior to the forehoof region.Unlike SI, which possesses a disproportionately large representation of the rostrum, SII has no specialized representation of the rostrum. The overall organization of SII supports the contention that this cortical region provides a more generalized representation of the entire body surface than does

ISSN:0092-7317    

DOI:10.1002/cne.903060104

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

年代:1991

数据来源: WILEY

摘要:

AbstractSerially sectioned rabbit foliate taste buds were examined with high voltage electron microscopy (HVEM) and computer‐assisted, three‐dimensional reconstruction. This report focuses on the ultrastructure of the type III cells and their synapses with sensory nerve fibers. Type III cells have previously been proposed to be the primary gustatory receptor cells in taste buds of rabbits and other mammals.Within rabbit foliate taste buds, type III cells constitute a well‐defined, easily recognizable class and are the only taste bud cells observed to form synapses with intragemmal nerve fibers. Among 18 type III cells reconstructed from serial sections, 11 formed from 1 to 6 synapses each with nerve fibers; 7 reconstructed type III cells formed no synapses. Examples of both convergence and divergence of synaptic input from type III cells onto nerve fibers were observed. The sizes of the active zones of the synapses and numbers of vesicles associated with the presynaptic membrane specializations were highly variable. Dense‐cored vesicles 80–140 nm in diameter were often found among the 40–60 nm clear vesicles clustered at presynaptic sites. At some synapses, these large dense‐cored vesicles appeared to be the predominant vesicle type. This observation suggests that there may be functionally different types of synapses in taste buds, distinguished by the prevalence of either clear or dense‐cored vesicles. Previous investigations have indicated that the dense‐cored vesicles in type III cells may be storage sites fo

ISSN:0092-7317    

DOI:10.1002/cne.903060105

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

年代:1991

数据来源: WILEY

摘要:

AbstractCytoarchitectonic and neurochemical studies of the dorsal vagal complex in the caudal medulla oblongata of rats indicate the existence of distinct anatomical and functional compartments within its components. We applied morphometric methods to discern whether capillary networks differed quantitatively between subregions and zones of area postrema, nucleus tractus solitarii (NTS), and dorsal motor nucleus of the vagus nerve (DMN) of rats. Analysis of 11 subdivisions of area postrema identified both “true” (range in luminal diameter of 3–7.5 μm) and sinusoidal (luminal diameter>7.5 μm) capillaries that, together, made the capillary density for most of area postrema 75% greater than that found in NTS and DMN (526/mm2vs about 300/mm2). The rank order of true capillary density in area postrema along its rostracaudal axis was caudal>central

ISSN:0092-7317    

DOI:10.1002/cne.903060106

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe differentiated cytoarchitecture, neurochemistry, and capillary organization of the rat dorsal vagal complex prompted this comprehensive investigation of micro vascular physiology in 11 subdivisions of area postrema, 5 subnuclei of nucleus tractus solitarii (NTS), the dorsal motor nucleus of the vagus nerve, and 4 other gray matter structures in the dorsal medulla oblongata. Microvascular exchangeable volume (residual plasma volume), capillary blood and plasma flow, and unidirectional transfer constants for a tracer amino acid, [14C]α‐aminoisobutyric acid (AIB), varied considerably among the structures analyzed. Exchangeable volume, largest in area postrema medial zones (about 29 μl μl · g−1) and smallest in medullary gray matter (7–11 μl · g−1), correlated directly with subregional densities of capillaries and rates of tissue glucose metabolism. Capillary blood flow (range of 1,430–2,147 μl · g−1· min−1), plasma flow, and tissue glucose metabolism (range of 0.48–0.71 μmol · g−1· min−1) were linearly related in the dorsal vagal complex. The most striking quantitative difference among structures in this brain region were the rates of transcapillary influx and derived permeability X surface area (PS) products of [14C]AIB, which has physicochemical properties resembling those of hormones. PS products for AIB were negligible in most medullary gray matter regions (<1 μl · g−1· min−1, indicative of blood‐brain barrier properties), but were 20–59 × and 99–402 × higher in NTS subnuclei and area postrema, respectively. An extraordinary feature of the microcirculation in area postrema was the long‐duration transit of tracer sucrose and blood, a characteristic that would amplify the sensing ability of area postrema a

ISSN:0092-7317    

DOI:10.1002/cne.903060107

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

年代:1991

数据来源: WILEY

摘要:

AbstractIn order to examine the mode of outgrowth of the pyramidal tract in the rat, the ultrastructure of its pathway in the dorsal funiculus of the spinal cord was analysed. The analysis was performed by means of serial sections of the third cervical segment before and during the arrival of pyramidal tract axons, and focussed on the morphology and microenvironment of the growth cones. Growth cones appear as elongated terminal enlargements without side branches. Two zones could be discerned: the distal, usually lamellipodial fine granular zone, containing no organelles, except for an occasional clear vesicle; and the proximal organelle‐rich zone, which contains various organelles, such as agranular reticulum and vesicular structures. In addition, the proximal organelle‐rich zone contains round or elliptic structures, limited by two concentric membranes, that enclose reticular and vesicular elements. The electron density of these structures varied from as low as the surrounding growth cone matrix to as dark as lysosomal structures, suggesting their involvement in turnover processes.At embryonic day 20, the most ventral part of the dorsal funiculus, where the first pyramidal tract axons are due to arrive within two days, is populated by axons that are relatively small compared to those in the rest of the dorsal funiculus. At birth, the arrival of the first pyramidal tract axons is marked by the presence of numerous large growth cone profiles in between small axons in the most ventral part of the dorsal funiculus; no circumscript bundle separated from the ascending sensory fiber tracts is present yet. The growth cones descend, club‐shaped and 1 to 2 μm in diameter, without lamellipodia or filopodia. Within the same area a second growth cone type is present, which contains dense‐core vesicles and has spread‐out lamellipodia. Most of these growth cones are ascending and they probably belong to primary afferent or propriospinal fibers.At postnatal day 2, the pyramidal tract can be readily delineated from the adjacent fasciculus cuneatus where myelination has already started, but no glial boundary is present. The abundant growth cones are 1–2 μm wide and extend single unbranched lamellipodia, up to 15 μm long, which often enfold parallel axons or other growth cones. At postnatal day 4, growth cones are scarce in the tract. They measure 1 μm or less in diameter and each extends a single, straight lamellipodium or filopodium over 1 to 7 μm in the caudal direction.At all ages examined, most of the surface of the growth cones is in apposition to longitudinally oriented axons and growth cones. The caudally outgrowing growth cones also make contact with glial elements. These are predominantly oriented perpendicularly to the longitudinal axis and are not joined together into continuous arrays. Furthermore, growth cones form synaptic contacts with dendrites that extend into the dorsal funiculus from the adjacent spinal grey.These observations indicate that the morphology of growth cones changes during the formation of the pyramidal tract in the cervical spinal cord. It is proposed that the outgrowing axons are probably guided into their pathway by selective fasciculation on their precursors, and by local differences in oligodendrocyte and axon maturation within the dorsal funiculus. Furthermore, it is suggested that the leading growth cones of the pyramidal tract grow into the most immature region of the ascending sensory fiber tracts without actively fasciculating on the axons

ISSN:0092-7317    

DOI:10.1002/cne.903060108

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe ultrastructure of contacts between axonal growth cones and glial cells in the developing pyramidal tract was examined by serial sectioning at the third cervical spinal cord segment in 0‐, 2‐, and 4‐day‐old rats. Junctional specializations, composed of synapse‐like contacts and invaginations, were frequently observed at the contact zone between growth cones and glial elements. The synapse‐like contacts consist of clear, round vesicles of 43 ± 6 nm in the presynaptic growth cone, a pre‐ and a postsynaptic density, separated by a cleft of 12.1 ± 0.9 nm. The invaginations consist of small protrusions of the growth cone into the glial element. The invaginated glial membrane is coated. Within the glial element, close to the invagination, frequently organelles were observed that closely resemble endosomes and prelysosomes. Therefore, it is suggested that the invagination represents a stage in endocytosis or possibly phagocytosis of the protruding part of the growth cone by the glial cell. The junctional specializations are formed by growth cones and, less frequently, by axon shafts. The targets of these specialized contacts are, in general, immature glial cells located within the tract area. Occasionally, however, invaginations were also observed into myelinating oligodendrocytes, suggesting that the population of immature target cells includes oligodendrocyte precursors.With regard to the functional significance of these temporary growth cone‐glial contacts, several possibilities are discussed, including the suggestion that outgrowing pyramidal tract axons provide immature glial cells with chemical messages, which may influence the timing of glial cell matura

ISSN:0092-7317    

DOI:10.1002/cne.903060109

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe primary objective of this study is to identify the totality of input to the centromedian and parafascicular (CM‐Pf) thalamic nuclear complex. The subcortical projections upon the CM‐Pf complex were studied in the cat with three different retrograde tracers. The tracers used were unconjugated horseradish peroxidase (HRP), horseradish peroxidase conjugated to wheat germ agglutinin (WGA‐HRP), and rhodamine‐labeled fluorescent latex microspheres (RFM).Numerous subcortical structures or substructures contained labeled neurons with all three tracing techniques. These labeled structures included the central nucleus of the amygdala; the entopeduncular nucleus; the globus pallidus; the reticular and ventral lateral geniculate nuclei of the thalamus; parts of the hypothalamus including the dorsal, lateral, and posterior hypothalamic areas and the ventromedial and parvicellular nuclei; the zona incerta and fields of Forel; parts of the substantia nigra including the pars reticularis and pars lateralis, and the retrorubral area; the pretectum; the intermediate and deep layers of the superior colliculus; the periaqueductal gray; the dorsal nucleus of the raphe; portions of the reticular formation, including the mesencephalic, pontis oralis, pontis caudalis, gigantocellularis, ventralis, and lateralis reticular nuclei; the nucleus cuneiformis; the marginal nucleus of the brachium conjunctivum; the locus coeruleus; portions of the trigeminal complex, including the principal sensory and spinal nuclei; portions of the vestibular complex, including the lateral division of the superior nucleus and the medial nucleus; deep cerebellar nuclei, including the medial and lateral cerebellar nuclei; and lamina VII of the cervical spinal cord.Moreover, the WGA‐HRP and rhodamine methods (known to be more sensitive than the HRP method) revealed several afferent sources not shown by HRP: the anterior hypothalamic area, ventral tegmental area, lateral division of the superior vestibular nucleus, nucleus interpositus, and the nucleus praepositus hypoglossi. Also, the rhodamine method revealed labeled neurons in laminae V and VI of the cervical sp

ISSN:0092-7317    

DOI:10.1002/cne.903060110

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe present study is devoted to a detailed analysis of the structural and synaptic organization of mormyrid Purkinje cells in order to evaluate the possible functional significance of their dendritic palisade pattern. For this purpose, the properties of Golgi‐impregnated as well as unimpregnated Purkinje cells in lobe C1and C3of the cerebellum ofGnathonemus petersiiwere light and electron microscopically analyzed, quantified, reconstructed, and mutually compared. Special attention was paid to the degree of regularity of their dendritic trees, their relations with Bergmann glia, and the distribution and numerical properties of their synaptic connections with parallel fibers, stellate cells, “climbing” fibers, and Purkinje axonal boutons.The highest degree of palisade specialization was encountered in lobe C1, where Purkinje cells have on average 50 palisade dendrites with a very regular distribution in a sagittal plane. Their spine density decreases from superficial to deep (from 14 to 6 per μm dendritic length), a gradient correlated with a decreasing parallel fiber density but an increasing parallel fiber diameter. Each Purkinje cell makes on average 75,000 synaptic contacts with parallel fibers, some of which are rather coarse (0.45 μm), and provided with numerous short collaterals. Climbing fibers do not climb, since their synaptic contacts are restricted to the ganglionic layer (i.e., the layer of Purkinje and eurydendroid projection cells), where they make about 130 synaptic contacts per cell with 2 or 3 clusters of thorns on the proximal dendrites. These clusters contain also a type of “shunting” elements that make desmosome‐like junctions with both the climbing fiber boutons and the necks of the thorns. The axons of Purkinje cells in lobe C1make small terminal arborizations, with about 20 boutons, that may be substantially (up to 500 μm) displaced rostrally or caudally with respect to the soma. Purkinje axonal boutons were observed to make synaptic contacts with eurydendroid projection cells and with the proximal dendritic and somatic receptive surface of Purkinje cells, where about 15 randomly distributed boutons per neuron occur.The organization of Purkinje cells in lobe C3differs markedly from that in lobe C1and seems to be less regular and specialized, although the overall palisade pattern is even more regular than in lobe C1because of the absence of large eurydendroid neurons. However, individual neurons have a less regular dendritic tree, there is no apical‐basal gradient in spine density or parallel fiber density and diameter, and there are no “shunting” elements in the climbing fiber glomeruli. Purkinje axonal boutons are not substantially displaced and have more but smaller boutons (on average about 70), which are not only contacting eurydendroid and Purkinje cells (about 40 boutons per cell), but also deeply located stellate neurons.As discussed in this study, none of the parameters analyzed is specifically and indissolubly correlated with the dendritic palisade pattern, and its functional significance consequently cannot be explained on the basis of a specific synaptic connectivity pattern. We suggest that palisade dendrites have a similar functional significance as their spines and may be considered as super‐ or giant spines, subserving optimal tuning of mormyrid Purkinje cells for specific spatio‐temporal patterns of parallel fiber activity. Comparison of different types of Purkinje cell organizations as encountered in vertebrates shows two extremes: on the one hand, the mammalian configuration, probably specialized for optimal interactions with climbing fibers, and, on the other hand, the mormyrid palisade pattern, probably specialized for optimal interacti

ISSN:0092-7317    

DOI:10.1002/cne.903060111

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

年代:1991

数据来源: WILEY