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Peters, Alan; Sethares, Claire
doi: 10.1002/cne.903060102pmid: 1710236
In 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.
Craner, Sandra L.; Ray, Richard H.
doi: 10.1002/cne.903060103pmid: 2040727
The 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.
Craner, Sandra L.; Ray, Richard H.
doi: 10.1002/cne.903060104pmid: 2040728
Multiunit 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.
Royer, Suzanne M.; Kinnamon, John C.
doi: 10.1002/cne.903060105pmid: 2040729
Serially 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.
Shaver, Steven W.; Pang, Judy J.; Wall, Katharine M.; Sposito, Nadine M.; Gross, Paul M.
doi: 10.1002/cne.903060106pmid: 2040730
Cytoarchitectonic 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/mm2 vs about 300/mm2). The rank order of true capillary density in area postrema along its rostracaudal axis was caudal > central < rostral, whereas the reverse order was true for sinusoidal capillaries. Dorsal (periventricular) and medial zones of area postrema throughout its rostrocaudal axis tended to have higher values for capillary density, volume, surface area, luminal diameter, and pericapillary space volume than lateral or ventral zones bordering NTS. Within 200 μm of obex, the ventral zone of rostral area postrema was distinct, having a relatively sparse capillary density that may indicate morphological specializations limiting blood‐tissue communication in this subregion. There were no quantitative differences in capillary dimensions between DMN and three subnuclei of NTS. These studies add to extant evidence that the dorsal vagal complex is differentiated for specific functions. Area postrema, especially, has topographical diversity in its capillary organization that likely corresponds to complex roles in neuroendocrine, autonomic, and chemosensory mechanisms.
Gross, Paul M.; Wall, Katharine M.; Wainman, Dan S.; Shaver, Steven W.
doi: 10.1002/cne.903060107pmid: 2040731
The 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 as it monitors the composition of the circulation.
doi: 10.1002/cne.903060108pmid: 2040732
In 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.
doi: 10.1002/cne.903060109pmid: 2040724
The 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.
Royce, G. James; Bromley, S.; Gracco, C.
doi: 10.1002/cne.903060110pmid: 2040725
The 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).
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