bluuebunny/crossref_metadata_2025_split huggingface dataset:
A study of the organization of apical dendrites in the somatic sensory cortex of the rat
Authors: Peters Alan , Walsh T. Myrick 
Published: December 2004

AbstractIn the parietal cortex of the rat, sections cut tangentially show that profiles of medium and large apical dendrites are grouped into clusters. The number of apical dendrites in each cluster is variable and the usual separation between individual clusters is about 50 μ. Despite these variations the pattern does not appear to be random. Reconstructions from one micron serial sections show that neurons giving rise to the ascending dendrites forming clusters are located at different levels in layer V. The cell bodies of these neurons are arranged vertically below their dendrites and show a tendency to form groups. All of the neurons have apical dendrites that ascend through the cortex with a few secondary branches occurring close to the base. The principal secondary branching begins in layer III and spreads obliquely up through layer I. Furthermore, beginning in the inferior region of layer III apical dendrites are added to the clusters at their peripheries. These are from layer III pyramids. It is clear that the superior aspects of the cluster arrangements must intermingle with those of the neurons in adjacent clusters. The neuropil surrounding the dendrites forming clusters appears to contain a few smaller dendrites. Small unmyelinated axons are the most frequent component of the surrounding neuropil and these form terminals which synapse on the spines and trunks of the clustered dendrites. There is no obvious function that can be ascribed to the clusters other than they may form a component of the columnar organization in cortex described in part by physiological techniques.
Dorsal root projections to the motor nuclei in the cat spinal cord
Authors: McLaughlin Barbara J. 
Published: December 2004

AbstractThe dorsal root projections to the motor nuclei of the L7 spinal cord segment were examined with light and electron microscopy in cats surviving dorsal rhizotomies of L6–S2 for periods of 2–15 days. Light microscopy demonstrated maximal Nauta‐Gygax and Fink‐Heimer degeneration around large neurons and their dendrites of the motor nuclei within the four to eight day period. Electron microscopy revealed axonal degeneration without any accompanying synaptic knob degeneration. Counts of the synaptic populations in the 12 and 15 day animals revealed that one particular synaptic type, the M knob, occurred less frequently and was smaller in size. In the normal animals the M knob, which was present up to 8 days postoperatively, was a large terminal containing rounded vesicles and making multiple synaptic contacts which had specialized subsynaptic densities. It was found primarily on proximal dendrites of large neurons and was often accompanied by a smaller flattened vesicle knob. All other synaptic knobs described in the normal animal were intact throughout all postoperative periods.The possibility that dorsal root afferents synapse farther out on the motoneuronal dendritic tree, as well as the possibility that few dorsal root terminals synapse on the motoneuronal surface, is discussed. The lack of any morphological evidence for presynaptic inhibition of dorsal root afferents in lamina IX is also discussed and possible alternative mechanisms are considered.
Propriospinal and supraspinal projections to the motor nuclei in the cat spinal cord
Authors: McLaughlin Barbara J. 
Published: December 2004

AbstractPropriospinal and supraspinal projections to the motor nuclei of L3–S1 were examined with light and electron microscopy in cats surviving complete transection of L2 for periods of 1–12 days. Light microscopy revealed maximal Nauta‐Gygax and Fink‐Heimer degeneration in the motor nuclei of L3–L5 at three days survival. Maximal degeneration in the motor nuclei of L6–S1 did not appear until six days post‐operatively. In the three and four day animals, electron microscopy revealed degenerating synaptic knobs, making axo‐dendritic and axo‐somatic contacts, and many phagocytosed degenerating synaptic knobs, in the motor nuclei of L3–L5; no synaptic degeneration was observed in the motor nuclei of more caudal segments. In the six to eight day animals, degenerating axo‐dendritic knobs and many phagocytosed degenerating knobs were found in the motor nuclei of S1; no synaptic degeneration and very few phagocytosed degenerating knobs were present in the motor nuclei of L3–L5 at these survival times. Because of the rapid phagocytosis of degenerating knobs in the motor nuclei of the early and late post‐operative animals, it was difficult to attribute the various degenerating knobs to a particular synpatic type.It is suggested that the synaptic degeneration seen in the motor nuclei near the transection of the earlier post‐operative animals is of mixed propriospinal and supraspinal origin, whereas the degeneration seen in the caudal motor nuclei of the later post‐operative animal represents supraspinal terminations.The contribution of dorsal root and long and short descending projections to the synaptic population about motoneurons is discussed.
The fine structure of the ependymal tanycytes at the level of the arcuate nucleus
Authors: Brawer James R. 
Published: December 2004

AbstractThe ependymal tanycytes of the third ventricle at the level of the arcuate nucleus were studied with the electron microscope. Criteria were discovered for identifying the tanycyte process as it courses through the arcuate neuropil, making it possible to describe the entire ependymal cell from the apical surface to the end foot. The apical membranes of the tanycytes are characterized by a lack of cilia and by numerous microvilli. The apical lateral membranes may be extensively interdigitated, and the junctional complexes between adjacent apical lateral membranes often lack maculae occludentes. The cells are well endowed with large Golgi apparatus. The endoplasmic reticulum is principally smooth. The tanycyte processes contain small paraxially oriented mitochondria and numerous paraxial microtubules as well as lipid droplets and accumulations of smooth endoplasmic reticulum in the form of concentric rings. Some of the tanycytes end on capillaries in the arcuate nucleus. These pericapillary ependymal sheaths contain irregular inclusions of varying densities. The ependymal tanycytes have been implicated as secretory cells involved in hypothalamic control of the anterior pituitary gland. This concept is discussed in relation to the present fine structural findings.
Ultrastructure of developing Xenopus retina before and after ganglion cell specification
Authors: Grillo M. A. , Rosenbluth J. 
Published: December 2004

AbstractThe neuroretina of Xenopus laevis was examined at embryonic stages 28 and 32 to determine whether the specification of the ganglion cells is accompanied by morphological changes detectable with the light and electron microscopes. Two changes were noted: an apparent increase in the length of polysome helices, and an apparent reduction in the number of pigment granules. The significance of these changes is discussed. In addition to the morphological features common to undifferentiated cells generally, the cells of the neuroretina also exhibit subsurface cisternae, granulo‐filamentous inclusions, and membranous organelles resembling the “spine apparatus.” These structures may be useful in identifying presumptive nerve cells in the proliferative state.
Cytology of the granular layer of the bulbar cochlear nuclei
Authors: Sobrino José A. , Gallego A. 
Published: December 2004

AbstractThe cytology of the granular layer of the cochlear nuclei was studied by aniline and Golgi staining methods. Four types of granule cell are described on the basis of the distribution of their processes and their size. Three types appear to be amacrine cells because they possess no process that has the morphological appearance of an axon. All of these cells are situated in the ventral portion of the granular layer. The granule cells of the fourth type have a distinct axonal process and are situated in the dorsal portion of the granular layer.
A retinohypothalamic projection in the rat
Authors: Moore Robert Y. , Lenn Nicholas J. 
Published: December 2004

AbstractA direct projection from the retina to the hypothalamus was demonstrated in the rat. Following injection of tritiated leucine or proline into the posterior chamber of the eye, labelled protein was shown autoradiographically in the suprachiasmatic nuclei of the medial hypothalamus, both ipsilateral and contralateral to the injected eye. The labelling of the nucleus was heaviest in its ventral portion but extended throughout the nucleus. No evidence for a projection to the supraoptic nucleus or any other hypothalamic nucleus was observed. All of the known terminal nuclei of the primary and accessory optic tracts were heavily labelled. The projection to the suprachiasmatic nucleus could not be clearly confirmed in material prepared using the Fink‐Heimer method for the demonstration of degenerating axon terminals. Electron microscopic study of the suprachiasmatic nucleus following orbital enucleation showed degenerating endings making synaptic contacts with small dendrites of the suprachiasmatic nucleus cells. These first appeared at three days after operation and were nearly gone by seven days. Thus, the retinohypothalamic tract in the rat appears to arise from the ganglion cells of the retina and to terminate on the smaller dendritic branches of the neurons of the suprachiasmatic nucleus.
The neuronal organization of the inferior colliculus of the adult cat. I. The central nucleus
Authors: Rockel A. J. , Jones E. G. 
Published: December 2004

AbstractThe intrinsic organization of the central nucleus of the inferior colliculus has been studied in the adult cat by means of the Golgi and Nauta techniques. On the basis of cytoarchitecture and fiber connections, the central nucleus can be divided into: (i) a smaller, dorsomedial division consisting mainly of large cells and receiving fibers from the auditory cortex, lateral lemniscus and probably the central nucleus of the other side; (ii) a larger, ventrolateral division consisting mainly of medium and small cells but with some intermingled larger types. This part receives fibers from the lateral lemniscus only.The ventrolateral division has a pronounced laminar arrangement of cells, dendrites and axons. The laminae, although overlapping extensively, form an onion‐like series of concentric, curved shells, most of which are incomplete except for those closest to the center of curvature in the dorsolateral part of the nucleus. It is probable that these laminae provide a basis for the pronounced tonotopic organization of neurons in the nucleus. The thickness of the laminae is determined by the dendritic ramifications of two principal cell types which are fusiform or bi‐tufted. Other, multipolar and large cells have dendrites which lie across one or several laminae and may form a basis for interaction between laminae.Four axon types can be distinguished: Type I (lateral lemniscal) and type II (corticofugal) axons run parallel to the laminae but in opposite directions, though type II axons are confined to the parts of the laminae projecting into the large‐celled, dorsomedial division. Type III axons are widely ramifying and may arise within the central nucleus or be another form of afferent fiber. Type I and III axons end in dense clusters of terminals on principal cells but as single en passant terminals on multipolar cells. Type IV axons are the efferents of the inferior colliculus and run a recurrent course through the central nucleus giving off collaterals which sometimes end on the parent cell.
Observations on the fine structure of the central nucleus of the inferior colliculus of the cat
Authors: Rockel A. J. , Jones E. G. 
Published: December 2004

AbstractThe central nucleus of the inferior colliculus has been examined electron microscopically in the adult cat, particular attention being paid to its ventrolateral division in which the majority of lateral lemniscal afferents end.Two cell types can be recognized: one, which is the equivalent of the spiny principal cell of light microscopy, is distinguished by having its soma and large proximal dendrites covered by axon terminals. More distally situated dendrites have fewer terminals ending mainly on dendritic spines. These spines resemble those of the cerebral cortex and have a modified spine apparatus. The second type of cell is the equivalent of the small multipolar cell of light microscopy. It has spineless dendrites and these and the soma receive relatively fewer axon terminals. It has a very thin axon.Several types of axon terminal can be recognized. Type I terminals are large, contain spherical synaptic vesicles and end by means of asymmetrical synaptic contacts, on the somata and proximal dendrites of principal cells and on the smaller dendrites of multipolar cells. The extracellular space on one or both sides of the synaptic complex is often characteristically widened. Correlative experimental degeneration studies show that these are the terminals of lateral lemniscal fibers. Various forms of smaller terminal also make asymmetrical contacts and have spherical vesicles. One type has a high concentration of large, densecored vesicles as well.Two types of axon terminal end in symmetrical synaptic contacts. One contains large, homogeneously flattened synaptic vesicles; the other, which is more common, contains smaller, irregularly flattened or pleomorphic synaptic vesicles.In the dorsomedial division of the central nucleus, the terminals of corticofugal fiber have spherical synaptic vesicles and end in asymmetrical synaptic contacts upon large dendritic spines.
Growth of lobster giant axons: Correlation between conduction velocity and axon diameter
Authors: Govind C. K. , Lang Fred 
Published: December 2004

AbstractThe conduction velocity and axon diameter of medial and lateral giant axons in lobsters was followed during growth from early juvenile (13 mm) to adult (250 mm) forms. In both axons, conduction velocity increased more than 4‐fold in the growth period examined. Correlated with the increase in conduction velocity is an increase in axon diameter and the relationship between these two parameters is expressed by the equation CV = krx, where x equals 0.5 for the lateral and 0.7 for the medial giant axons. The sheath surrounding the giant axons also increases in size during growth with that of the medial giant axon being considerably thicker than that of the lateral giant axon. The significance of the increase in axon diameters is to increase conduction velocity and thereby reduce the latency of the escape response mediated by these giant axons.
The efferent connections of the feline nucleus cuneatus
Authors: Hand Peter J. , Van Winkle Thomas 
Published: December 2004

AbstractNucleus cuneatus projections to nucleus ventralis posterolateralis pars medialis (VPLm) and other thalamic as well as midbrain and medullary nuclei were studied in cats using the Fink‐Heimer I silver technique. Single electrolytic lesions of very small size were made stereotaxically in different zones of nucleus cuneatus under electrophysiological control. All zones studied projected to contralateral VPLm in a pattern of discrete terminal arborizations or clusters, which were organized in onionskin‐like dorso‐ventral laminae.The clusters of degeneration varied in size and density according to their dorsoventral location within VPLm. Those in dorsal areas were smaller in diameter (50–125 μ) and contained less dense amounts of degeneration than clusters (150–300 μ) in more ventral regions. The clustered terminal arborizations mirrored the organization of the VPLm neuronal clusters, themselves.Terminations within VPLm were topographically organized, but were completely inverted, i.e. dorsal nucleus cuneatus projected to ventral VPLm and ventral to dorsal, lateral to medial, and medial to lateral VPLm. A ventral zone of nucleus cuneatus, which contained “deep” units, projected to a separate dorsal zone of VPLm. In addition to its classical connection with VPLm, nucleus cuneatus projected to the following contralateral brainstem or thalamic nuclei: medial and dorsal accessory olives, external nucleus of the inferior colliculus, ventrolateral part of the superior colliculus, nucleus ruber, medial geniculate nucleus pars magnocellularis, suprageniculatus, medial and lateral divisions of the posterior thalamic nuclear group, zona incerta, and Fields of Forel. Very sparse amounts of degeneration were also present within nuclei ventralis posteromedialis (caudal pole) and ventralis posterolateralis pars lateralis. The brainstem and thalamic projections of the dorsocaudal part (cell nest region) of the cuneate nucleus were more restricted than those of its rostral and ventral regions. The clusters of both the VPLm neurons and cuneate terminations within VPLm provides an anatomical basis for the functional characteristics of synaptic security, fine grain somatotopia and modality specificity so prominent in the dorsal column nuclei‐medial lemniscal system.
Structure of the Purkinje cell membrane in staggerer and weaver mutant mice
Authors: Landis Dennis M. D. , Reese T. S. 
Published: December 2004

AbstractThe structure of the plasma membrane of Purkinje cell dendrites was examined in weaver and staggerer mutant mice. Purkinje spines in weaver mice have clusters of intramembrane particles which resemble those at normal synapses with parallel fibers, even though no parallel fibers are formed in this mutant. There are very few spines in the staggerer, and these manifest normal intramembrane structure at contacts with climbing fibers. The spines which would normally be involved in synapses with parallel fibers are never formed in the staggerer, and the intramembrane structures which would have been associated with these spine synapses are also lacking. Thus, during postnatal cerebellar development in the mutants, acquisition of intramembrane specializations requires Purkinje spine formation but can occur independently of the development of parallel fibers.
Efferent projections of the main and the accessory olfactory bulb in the tree shrew (Tupaia glis)
Authors: Skeen L. C. , Hall W. C. 
Published: December 2004

AbstractThe projections of the main and the accessory olfactory bulb in the tree shrew (Tupaia glis) have been analyzed with anterograde degeneration and autoradiographic methods for identifying axonal projections, and with the horseradish peroxidase method for identifying the distributions of neurons from which these projections originate. The cytoarchitectonic features of the paleocortical areas which receive projections from the main and the accessory olfactory bulb have also been described.The efferent projections of the accessory olfactory bulb are distributed to the bed nucleus of the accessory olfactory tract, the medial amygdaloid area, the posteromedial cortical amygdaloid area, and to the caudal portion of the bed nucleus of the stria terminalis. In contrast, the efferent projections of the main olfactory bulb are distributed to the anterior olfactory nucleus, the tenia tecta, the olfactory tubercle, the pyriform cortex, the anterior cortical amygdaloid area, the posterolateral cortical amygdaloid area, and to the lateral entorhinal cortex. These observations are consistent with the notion that the olfactory system can be divided into at least two major subsystems: one related to the vomeronasal organ and accessory olfactory bulb, and another related to the main olfactory organ and main olfactory bulb.The paleocortical areas receiving olfactory projections have three basic layers: a superficially positioned plexiform layer (layer I), a pyramidal cell layer (layer II), and a polymorphic cell layer (layer III). The projections of both the main and the accessory olfactory bulb terminate in the outer portion of the plexiform layer (sublamina la). Sublamina Ia contains the distal segments of dendrites which originate from a heterogeneous population of neurons located in layer II and, to a lesser extent, layer III.Although the efferent projections of the main and the accessory olfactory bulb are segregated, evidence for a more refined topographical organization within these projections was not obtained. However, the distribution of retrogradely labeled neurons in the main olfactory bulb, following injections of horseradish peroxidase into its various paleocortical targets, indicates that the olfactory projections to these areas may not all originate from the same population of cells.
Response of the three main types of glial cells of cortex nad corpus callosum in rats handled during suckling or exposed to enriched, control and impoverished environments following weaning
Authors: Szeligo F. , Leblond C. P. 
Published: December 2004

AbstractThe cell populations of the occipital cortex were examined in young rats subjected to different sensory experiences. In one series recently weaned animals were reared in enriched, impoverished or control environments. The enriched environment was obtained by keeping the animals among “toys” and other rats; the impoverished environment, by rearing the animals one pr cage in a darkened, quiet room; and the control environment, by housing the animals three per cage under animal room conditions. Six recently weaned rats were kept ini each environment for 30 days and ten, for 80 days. In a second series suckling rats for 15 minutes per day during the first ten days after birth; twelve rats were studied, six handled and six unhandled controls. In the two series, the animals were sacrificed under anesthesia by perfusion with mixed aldehydes. Semithin epon sections of occipital cortex ere stained with toluidine blue; neurons and the three main types of glia were enumerated. In addition, the thickness of the cortex was measured and the glial cells of corpus callosum counted in the animals exposed to the three environments for 80 days.Under the influence of the enriched environment, the occipital cortex enlarged, the number of oligodendrocytes increased over the controls by 27‐33% in the 30‐ and 80‐day groups and the number of astrocytes, by 13% in the 80‐day grup. Within the cortex, only certain layers showed the increase in glial numbers. In the corpus callosum, however, the numbers of glial cells did not differ from those in controls. In the animals exposed to the impoverished environment, neither the size of the cortex nor the number of oligodendrocytes and astrocytes differed from controls.The animals subjected to handling also showed evidence of cortical enlargement, but the only significant change in glial cells was a 12% increase in astrocytes.It is concluded that handling and enrichment produce changes in anatomical indices of neural function including depth of cortex and numbers of glial cells. The glial response was specific to the type of manipulation since astrocytes were predominantly affected by handling and oligodendrocytes, by enrichment. The effect of handling on astrocytes may be attributed to the stimulation being applied at a time of astrocyte proliferation, whereas the effect of the enriched environment on oligodendrocytes occurred at a time of active production of these cells. The differences in cell numbers were explained by changes in the rate of cell population growth; since the impoverished did not differ from the control animals, the changes probably consisted of growth acceleration in the enriched animals rather than dimiution in the impoverished ones.