bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ultrastructural basis of impulse propagation failure in a nonbranching axon
Authors: Smith Dean O. 
Published: January 2005

AbstractThe morphological basis of intermittent conduction failure in the excitor axon innervating the crayfish opener and stretcher muscles was investigated using the electron microscope. The connective tissue component of the sheath surrounding the axon was found consistently to be thinner in the region at which blocking occurs than in control regions located one cm either proximally or distally, at which blocking does not occur. Otherwise, in these regions differences in the width of the periaxonal spaces, the length or width of the mesaxons, the density of mitochondria, the width of the adaxonal glial cell layer, or the structure of the lamination of the sheath are not observed. Because of the thinner connective tissue component of the sheath in the joint region, neighboring axons are distributed more densely around the excitor, and the volume of the extracellular space is reduced. The possibility that the reduced extracellular space might allow excessive accumulation of potassium during repetitive discharge, causing conduction block, is discussed. Alternative mechanisms consistent with this morphology are also considered.
An X‐ray diffraction comparison of myelins from the human nervous system
Authors: Chandross Ronald J. , Bear Richard S. , Montgomery Royce L. 
Published: January 2005

AbstractEarlier small‐angle X‐ray diffraction studies have indicated that central and peripheral nerve myelins may be significantly different structurally, although relatively few examples for each system and for individual species have been examined. In order tounderstand better the intra‐ and inter‐system relationships, this study has developed more extensive information for a single species: six cases centrally and ten peripherally, featuring cranial nerves and a few others of the human nervous system. Peripheral myelin spacings (membrane pair thicknesses) are relatively similar, 184.4 ± 1.40 Å, and the ratios of diffraction peak height intensities of the second to fourth orders are also closelybunched: 1.85 ± 0.216. Central myelin spacings and intensity ratios are distinctly different and more variable: spacings 160.3‐165.8 A and intensity ratios 2.81‐4.46. It appears that within a given species or between closely related (e.g., mammalian) species peripheral myelins possess relatively invariant structures, though significant spacing declines are encountered for both systems as phylogenetic relationships become more distant. The observed greater variability of CNS structures within a singlespecies may correspond to known compositional differences between CNS regionsor result from observational difficulties. In any case there is a marked discontinuity between the myelin structures of CNS and PNS nerves.
Discontinuous transition of myelin structure at the junction between central and peripheral components of the eighth cranial nerve, as disclosed by X‐ray diffraction
Authors: Chandross Ronald J. , Adams Jerry B. , Bear Richard S. 
Published: January 2005

AbstractScanning along human acoustovestibular nerves from cross‐sections closely proximal to the brain to locations distinctly peripheral thereto, by means of small‐angle X‐ray diffraction, has disclosed transitional junctions at which the myelin structure typical of central nervous system (CNS) axons gives way to one characteristic of peripheral (PNS) fibers. The junctions correspond to regions along the nerves, previously recognized histologically, at which the satellite cells responsible for axon myelination change character, from the oligodendrocytes of the CNS to the Schwann cells of the PNS. Thus the structural discontinuity between the CNS and PNS myelins can be ascribed to differences in the biosynthetic processes of the respective satellite cells. Junctions of this kind are to be expected in all cranial and spinal roots near the locations where they leave the CNS.
Cortico‐cortical connections of somatic sensory cortex (areas 3, 1 and 2) in the rhesus monkey
Authors: Vogt Brent A. , Pandya Deepak N. 
Published: January 2005

AbstractThe connections of areas 3, 1 and 2 in the postcentral gyrus of the rhesus monkey are investigated using ablation‐degeneration techniques following both full depth lesions and lesions which involved fewer than six cortical layers. Analysis of the topographic and laminar organization of these connections reveal that each of these areas has a differential connection pattern both within the parietal lobe and with respect to motor cortex. Area 3 projects predominantly to area 1 via a horizontal, intracortical fiber system which courses through layers III and V without entering the white matter while other efferents of area 3 to areas 2, 3a and second somatosensory cortex (SII) are less dense and course through the white matter. There is no indication that area 3 efferents terminate in areas 4 or 5. In comparison to area 3, area 1 has a wider projection field. Its primary outflow reaches area 2 via a white matter course while moderately strong connections are directed to areas 3a, S II, 4 and supplementary motor cortex (M II) and a minor projection to area 5. Lesions involving the supragranular layers of area 1 demonstrate that efferents from these layers (II‐III) travel directly through the cortex to terminate in layer I of area 3 as well as entering the white matter before terminating in area 2 ventral to the tip of the intraparietal sulcus. Finally, area 2 projects primarily to area 5 via both an intracortical fiber system in layers III‐V as well as through the white matter. While area 2 also has connections with areas 1, 3a, S II, 6 and M II, it was not observed to project to area 3. In addition, layers I‐IV of area 2 ventral to the intraparietal sulcus send a number of horizontally oriented fibers mainly through layer IIIb to terminate in rostral area 7 (area PF of Bonin and Bailey, '47).Thus, the projections of these three subdivisions of the postcentral gyrus indicate that there is a strong and sequential outflow of connections from area 3 to areas 1 and 2, then from area 1 to area 2 and finally from area 2 to area 5 and rostral area 7. Each of these connections originates to a large extent from the supragranular layers. In contrast, connections of these areas in the opposite direction toward the central sulcus are less pronounced.
The retinotopic organization of area 17 (striate cortex) in the cat
Authors: Tusa R. J. , Palmer L. A. , Rosenquist A. C. 
Published: January 2005

AbstractThe location and retinotopic organization of visual areas in the cat cortex were determined by systematically mapping visual cortex in over 100 cats. The positions of the receptive fields of single neurons or small clusters of neurons were related to the locations of the corresponding recording sites in the cortex to determine the representations of the visual field in these cortical areas. In this report, the first of a series, we describe the organization of area 17. A single representation of the cat's entire visual field corresponds closely to the cytoarchitectonically defined area 17.This area has the largest cortical surface area (380 mm2) and the highest cortical magnification factor (3.6 mm2/degree2 at area centralis) of all the cortical areas we have studied. There was perfect agreement between the borders of area 17 determined electrophysiologically and cytoarchitecturally. This area contains a first order transformation of the visual hemifield in which every adjacent point in the visual field is represented as an adjacent point in the cortex. Some variability exists among cats in the extent and retinotopic representation of the visual field in area 17.
The retinotopic organization of lateral suprasylvian visual areas in the cat
Authors: Palmer L. A. , Rosenquist A. C. , Tusa R. J. 
Published: January 2005

AbstractThis is the second in a series of papers in which we describe our continuing efforts to define functional units of visual cortex based upon electrophysiological mapping of single and multiple unit activity in both awake and the nitrous oxide anesthetized cats. In the first paper (Tusa, Palmer and Rosenquist, '78), the extent and retinotopic organization of area 17 were described. In this paper, we describe the somewhat more complex organization of the visual cortex lying on the banks of the middle and posterior suprasylvian sulci. This region of cortex consists of six retinotopically organized units. These areas are arranged as three roughly mirror symmetrical pairs separated in each case by the fundus of the middle or posterior suprasylvian sulci. Some thalamo‐cortical autoradiographic material is presented which supports this parcellation of the cortex.
Expansion of the half retinal projection to the tectum in goldfish: An electrophysiological and Anatomical study
Authors: Schmidt John T. , Cicerone Carol M. , Easter Stephen S. 
Published: January 2005

AbstractThe topographical retino‐tectal projection of goldfish was electrophysiologically mapped at various intervals after surgical removal of the nasal half of the retina and pigment epithelium. The remaining projection was initially restricted to the appropriate rostral half of the tectum, even if the nerve was crushed and allowed to regenerate. But later, after 137 days or more, it showed a progressive expansion onto the foreign caudal half of the tectum. The magnification factor, the number of micrometers of tectum per degree in the visual field, doubled in the rostro‐caudal but not in the medio‐lateral direction. Analysis of the sequence of the expansion showed that a few fibers originally projecting nearest the denervated area were the first to spread over it. Then, progressively more fibers moved caudally until a nearly uniform representation of the half retina was established on the tectum. Radioautography also demonstrated that retinal fiber terminals had invaded the caudal tectum. The retinae of these fish were also examined histologically. The density of ganglion cells had not increased, but they consistently showed the axonal reaction. This was not found to be associated with any initial surgical trauma, but rather with the movement of their fiber terminals within the tectum. Frozen sections, through half retinal and normal eyes, were cut and photographed for comparison of ocular geometry. Operated eyes were normal except for a slight but consistent loss of ocular volume. Analysis of the optical geometry showed that recording with fish in air produced two effects: Myopia (10° blur circle, or less) and enlargement of the visual field by 15% to 20%.
Retinal fibers alter tectal positional markers during the expansion of the half retinal projection in goldfish
Authors: Schmidt John T. 
Published: January 2005

AbstractAlthough widely accepted, the theory, that neurones carry immutable cytochemical markers which specify their synaptic connections, is not consistent with plastic reorganizations. Half retinal fish were therefore tested for changed markers following expansion. Optic nerve crush at the time of the half retinal ablation resulted in regeneration of a normal, restricted projection; but nerve crush following expansion (many months later) resulted in reestablishment of the expanded projection, assessed both by electrophysiological mapping and by radioautography. Since this implied changed markers, the half retina and tectum were tested independently using the ipsilateral tectum and eye as controls. In normal fish, removal of one tectum and deflection of the corresponding optic tract toward the remaining tectum resulted in regeneration of a positionally normal but ipsilateral map. In experimental fish, after the half retina had expanded its projection to the contralateral tectum, its optic tract was deflected to the control tectum. After 40 days it had regenerated a normal, restricted map indicating that the retinal markers had not changed. Such restricted projections did not expand in the presence of the normal projection even after a year or more. Similarly, the optic tract from the normal eye was deflected to cause innervation of the tectum containing the expanded half retinal projection. After 40 days, the projection regenerated from the normal eye was similar to the expanded half retinal projection. Areas of the normal retina corresponding to the missing areas of the half retina were not represented. Tectal markers had been altered by the half retinal fibers. In a final group, tecta were denervated and tested at various intervals by innervation from ipsilateral half retinal eyes. After five months of denervation, the regenerating fibers were no longer restricted to the rostral tectum but formed an expanded projection initially. Apparently tectal markers are induced by the retinal fibers, changed during expansion, and disappear during long‐term denervation.
Excitation of marginal and substantia gelatinosa neurons in the primate spinal cord: Indications of their place in dorsal horn functional organization
Authors: Kumazawa T. , Perl E. R. 
Published: January 2005

AbstractElecrophysiological recordings were made from superficial parts of the spinal dorsal horn in monkeys, using dye‐filled micropipette electrodes to permit iontophoretic marking of the recording sites for subsequent histological recovery. Focal field potentials and unitary activity evoked by dorsal root volleys including slowly‐conducting components (both myelinated and unmyelinated) were found in the posteromarginal zone and the substantia gelatinosa (SG). Unitary potentials identified as being of the type recorded from cellular regions wee separated into categories according to which groups of slowly‐conducting fibers and which kinds of cutaneous stimulation evoked the discharge. Recording locations for units exicted by volleys in myelinated fibers conducting under 35 m/sec, by the types of skin stimulation activating either highthreshold mechanoreceptors (nociceptos) or cooling thermoreceptors, and giving no evidence of suprathreshold C‐fiber excitation were centered on the posteromarginal zone. In conrast, recording loci for units exhibiting a strong C‐fiber excitation and responses to cutaneous stimulation known to effectively excite C‐fiber polymodal nociceptors or C‐mechanoreceptors were centered in the SG. There appeared varying degrees of convergence of primary afferent input to the neuronal units, although most showed substantial specificity in their afferent excitation. On the bases of these esults and consideration of existing morphological daa, it is proposed that the marginal zone is a major synaptic termination region for the affeent fibers from high‐threshold mechanoreceptors, cooling thermoreceptors, and perhaps otehr receptors with fine myelinated peripheral fibers. The SG, on the other hand, is suggested to be the terminal region for all types of unmyelinated primary afferent sensory neurons, and to have the complex role of integrating and distributing this input.
The connections of the nucleus reuniens thalami: Evidence for a direct thalamo‐hippocampal pathway in the rat
Authors: Herkenham Miles 
Published: January 2005

AbstractThe afferent and efferent connections of the rat's midline nucleus reunions thalami (reuniens) were studied by experiments using the methods of retrograde cell marking by horseradish peroxidase (HRP) and anterograde fiber tracing by autoradiography. A microelectrophoretic deposit of tritiated amino acids in reuniens provided the first evidence of a direct thalamo‐hippocampal connection. Labeled reuniens efferents ascend to the genu of the corpus callosum and turn caudally in the cingulate fasciculus, from which fibers distribute to layer I of the anterior medial, cingulate, and retrosplenial cortices. A longer component of this system curves around the callosal splenium and forms a massive rostrally directed fiber sheet that innervates entorhinal and parahippocampal areas and Ammon's horn. Entorhinal afferents are localized to layers I and III, whereas the hippocampal afferent plexus is remarkably restricted to the stratum lacunosum‐moleculare of the CA1 field and the corresponding stratum of the ventral subiculum.Reuniens projects more sparsely and diffusely to many subcortical structures, a number of which lie in the limbic domain: the anterior olfactory nucleus, nucleus accumbens, olfactory tubercle, amygdala, claustrum, septum, preoptic area, medial and lateral hypothalamic regions, deep portions of the pretectum and superior colliculus, rostral levels of the ventral tegmental area and central gray substance and, perhaps, the median eminence.The efferent connections of reuniens were examined with HRP. HRP deposited in the nucleus labeled small to moderate numbers of neurons in many structures extending from the frontal cortex to caudal midbrain levels. The appearance of cell labeling in regions projected upon by reuniens suggests a reciprocity of connections between it and the medial cortex, septum, preoptic area, amygdala, medial and lateral hypothalamic regions, ventral tegmental area, central gray substance, pretectum, superior colliculus and the subiculum. Cell labeling in regions not receiving its efferents – the ventral thalamus, midbrain tegmentum, mesencephalic raphe, and parabrachial nuclei – may hold another clue to the future understanding of the role of the nucleus reuniens in limbic functions.
Early motoneuron formation in the cervical spinal cord of the mouse: An electron microscopic, serial section analysis
Authors: Wentworth Lee E. , Hinds James W. 
Published: January 2005

AbstractCells of the ventrolateral region of the cervical spinal cord were reconstructed from serial thin sections in order to provide direct evidence concerning the early stages of motoneuron differentiation. Analysis of 321 sections from the spinal cord of a mouse embryo on the tenth day of gestation (E10) was performed. At E10 the general appearance of the ventrolateral region is that of a pseudostratified columnar epithelium. It consists primarily of radially oriented ventricular cells, while the remaining cells are either rounded mitotic cells (located at the neurocoel) or cells differentiating into either accessory root or ventral root motoneurons. The following early stages of motoneuron differentiation have been distinguished: anaxonic primitive bipolar cells (stage 1); primitive bipolar cells with an axon (stage 2); unipolar cells (stage 3); and secondary bipolar cells (stage 4). The earliest morphological change in the differentiation of both types of motoneurons appears to be the withdrawal of the apical process from the neurocoel and the migration of the Golgi apparatus, centrioles and cilium along the apical process toward the nucleus (anaxonic primitive bipolar cell). The nucleus then appears to migrate peripherally and the basal process (which never completely withdraws) to transform into an axon (primitive bipolar cell with an axon). Subsequent stages have only been identified in accessory root motoneurons; it appears that ventral root motoneurons are not as advanced in their differentiation at E10. In the unipolar stage the apical process has completely withdrawn, and the nucleus appears paler and rounder than that of earlier cells. Finally, in the secondary bipolar stage the cell is oriented dorsoventrally with an axon directed dorsally and a dendrite ventrally from the opposite pole of the cell. During differentiation of accessory root motoneurons, the Golgi apparatus, centrioles and cilium are found first in the apical process, then at the base of the axon, and finally at the base of the dendrite. The translocation of these organelles occurs secondary to the initial formation of first the axonal and then the dendritic process.
Qualitative and quantitative study of synaptic displacement in chromatolyzed spinal motoneurons of the cat
Authors: Chen D. H. 
Published: January 2005

AbstractQualitative and quantitative cytological evidences show a reduction in number and percentage of coverage of terminals on chromatolyzed spinal motoneurons 4 to 90 days after severance of their axons in the ventral root. The reduction in number and percentage of boutons on the surface membrane is due to detachment of synapses. This detachment is associated with changes in specialized regions (synaptic complexes: Conradi, '69) of synapses which involve disappearance of both pre‐ and postsynaptic membrane thickenings and widening of the synaptic cleft (width of 400‐1,400 A). The separation of terminals from surface membrane is also associated with the presence of reactive astrocytes and microglia. Most areas of surface membrane bared of synaptic contact are occupied by astrocytic processes. The astroglial responses coincide with the loss of synapses. Microglial cells, although extending to neuronal surface membrane, cover only a small portion of it. An extensive separation of boutons by microglia is not observed. Most microglia are seen located at some distance from surface membrane and are frequently separated by sheets of astrocytic processes. Synaptic restoration occurs by about 90 days after axotomy. Some motoneurons show good recovery, while others show only a limited amount.
Afferent projections to the rat locus coeruleus as determined by a retrograde tracing technique
Authors: Cedarbaum Jesse M. , Aghajanian George K. 
Published: January 2005

AbstractAfferent connections to the rat locus coeruleus (LC), which contains exclusively noradrenergic neurons, have been traced using the technique of retrograde transport of horseradish peroxidase (HRP). In order to ensure accurate placement of adequate amounts of HRP in the LC, a microiontophoretic delivery technique coupled with single cell recording was employed. The use of electrophysiological “landmarks” as aids in placing the injections is described. Following HRP injections into the LC, forebrain structures containing labelled neurons included the insular cortex, the central nucleus of the amygdala, the medial, lateral and magnocellular preoptic areas, the bed nucleus of the stria terminalis, and the dorsomedial, paraventricular and lateral hypothalamic areas. In the brainstem reactive neurons were observed in the central grey substance, the reticular formation, the raphe, vestibular, solitary tract and lateral reticular nuclei. In particular, the areas of catecholamine cell groups A1, A2 and A5 appeared to contain many reactive cells. Labelled neurons were also observed in the fastigial nuclei and in the marginal zones of the dorsal horns of the spinal cord. This pattern of afferent innervation supports suggestions for a role for the LC in behavioral arousal mechanisms and autonomic regulation.