bluuebunny/crossref_metadata_2025_split huggingface dataset:
A quantitative study of morphological changes accompanying the initiation and progress of myelin production in the dorsal funiculus of the rat spinal cord
Authors: Matthews Murray A. , Duncan Donald 
Published: December 2004

AbstractThe dorsal funiculus in cervical spinal cords of rats from 3 to 120 days postnatal was studied in order to document and quantitate glial cell development and axonal growth as related to the initiation and progress of central myelination. Within the dorsal funiculus are three major and distinct tracts, each having distinct developmental trends and adult characteristics in terms of fiber sizes and amount of myelin. These tracts are the cuneate and gracile fasciculi and the cortico‐spinal tracts.Glial cell counts and cross‐sectional surface area determinations of each tract at increasing ages show that the initial rate of glial population increase is similar. However, each tract is unique in terms of the age at which a maximum population density is reached and the rate at which the expected population dilution takes place. An electron‐microscopic examination indicates that oligodendrocytes constitute over 85% of the total glial population throughout the development period surveyed. As such, these cells are primarily responsible for the population density changes.The diameters of unmyelixgnated fibers, promyelin fibers and some myelinated fibers in these tracts were measured at 5, 10, 15, 20 and 120 days postnatal. This was done both for the purpose of relating glial population density changes with the initiation and decline of active myelination, and for determining whether or not a critical diameter for myelination exists in the CNS as was found in peripheral nerves (Matthews, '68). For each tract there is a characteristic sequence of events involving not only myelination, but also changes in diameter distribution just prior to the appearance of myelin and during the period of active myelin formation. These events coincide with the concentration and dilution of the glial population, but it is also evident that there is no critical and constant diameter in the CNS above which all axons are myelinated and below which all are unmyelinated. Myelin appears first on larger axons, but as the animal matures, it is found on progressively smaller axons until between 20 and 120 days, axons 0.2–0.4 μ in diameter acquire myelin. Thus, myelination begins with axons destined to be large and then extends down to those which enlarge very little prior to acquiring myelin and remain very small even in adult animals.Finally, from the determination, in adult rats, of the number of axons and oligodendrocytes in a defined volume of each tract and an estimation of internode length, the ratio of internodes to oligodendrocytes was calculated. The specific values obtained could vary by as much as ±50% and are only meant to serve as indicators of a trend. However, it is suggested that the number of internodes per oligodendrocyte may be inversely proportional to the length of the internode.
Histogenesis of the substantia nigra, ventral tegmental area of Tsai and interpeduncular nucleus: An autoradiographic study of the mesencephalon in the rat
Authors: Hanaway Joseph , McConnell Jo Ann , Netsky Martin G. 
Published: December 2004

AbstractThe origin of large neurons of the substantia nigra, ventral tegmental area of Tsai and interpeduncular nucleus was determined in three‐week‐old rats receiving a single injection of thymidine‐H3 during gestation. These neurons underwent final mitotic division on embryonic days 11 through 15 with maximal production on days 14 and 15. Glia and the smallest type of granular neurons were produced from day 11 through 22. Cells in the ventral angle of the neuroepithelium were not labeled one hour after injection of thymidine‐H3 in any of the series.Study of animals receiving a single injection of thymidine‐H3 during gestation and killed at serial intervals thereafter showed that neurons forming the substantia nigra migrated from the middle third of the basal neuroepithelium and moved between existing cells in radial patterns. Production of neurons specifically for each division of the substantia nigra was not observed either in cross‐section or rostrocaudally, nor was the destination of neurons related to their time of origin. The ventral tegmental area of Tsai and interpeduncular nucleus formed from neurons originating in the medial third of the basal plate and migrating almost to the ventral surface of the mesencephalon. The neurons then divided into two streams to create a pattern of an inverted fountain comparable to the distribution of neurons containing catecholamines. Some of these neurons may have contributed to the substantia nigra. The primordia in all three nuclear areas were first seen on embryonic day 18.
Patterns of neuronal differentiation in developing cultures of neonatal mouse cerebellum: A living and silver impregnation study
Authors: Allerand C. Dominique 
Published: December 2004

AbstractOrganotypic explants of neonatal mouse cerebellum were cultured for periods up to 56 days in vitro. Living cultures were compared to those fixed and stained by the Holmes' reduced silver nitrate method. The explants consist of a heterologous neuronal population comparable to that found in situ. Since the differentiation of the cerebellum is actively in progress during the neonatal and postnatal periods, cultures derived from such tissue demonstrate the developmental phases that are present at the time of explantation.The in vitro. maintenance of neonatal mouse cerebellum allows the expression of those aspects of neuronal development which are intrinsic to the cell proper and primarily concerned with type‐specific differentiation, e.g., neurofibrillary development; axonal growth; myelination; and the acquiring of basic dendritic patterns. The secondary aspects of differentiation, which determine the adult state and which are characterized primarily by the increasing complexity of dendritic formation and of synaptic interactions, occur to a much lesser extent in vitro.The importance of recognizing transitional forms as normal and not peculiar to the in vitro situation is emphasized.
Hippocampal efferents to the ipsilateral entorhinal area: An experimental study in the rat
Authors: Hjorth‐Simonsen A. 
Published: December 2004

AbstractA hitherto undescribed pathway from the hippocampus to the entorhinal area has been found in the albino rat in experimental studies by the silver‐impregnation technique of Fink and Heimer ('67) and a modification there of by the present author ('70). Animals in which the hippocampal formation had been deprived of commissural and other afferents by a preliminary operation at the age of eight days were used to faciliate the search for the site of origin of the pathway. Lesions in various parts of the hippocampus showed the origin to be restricted to subfield CA3 in approximately the temporal third of the hippocampus. The axons run caudally in the stratum radiatum and stratum lacunosummoleculare, and terminate in the medial part of the entorhinal area in a distinct zone corresponding to layer IV of Lorente de Nó ('33, '34). By the aid of alternating series of sections impregnated with silver and incubated for acetyl‐cholinesterase, the zone of termination was shown to be identical with the acetyl‐cholinesterase positive band at the level of layer IV. In the dorso‐ventral sense the fibers exhibit a topical organization, terminal degeneration at different levels of the entorhinal area depending on the levels of CA3 damaged. The mean course of the fibers from each level of CA3 seems to be roughly horizontal. A hippocampoentorhinal neuron circuit is proposed.
The telencephalon and hypothalamus of the bluegill (Lepomis macrochirus): Evoked feeding, aggressive and reproductive behavior with representative frontal sections
Authors: Demski Leo S. , Knigge Karl M. 
Published: December 2004

AbstractBluegills were stimulated electrically while swimming free in an aquarium containing other bluegills, a mirro, gravel and food. Stimulation sites have been plotted on representative frontal sections for which a nomenclature system was developed. Nestbuilding was evoked in both sexes by stimulation near the area dorsalis telencephali pars centralis, while strong after‐responses were elicited from the ventral preoptic region. Stimulation in the preoptic region slightly rostral to the habenula simultaneusly inhibited aggressive behavior and evoked courtship. Feeding (snaping up prey, gravel or debris) and aggressive behavior (chasing and biting another bluegill) resulted from stimulation in the region surrounding the lateral recess of the third ventricle of the inferior lobe of the hypothalamus. In several cases feeding and aggressive responses alternated during stimulation; a similar pattern was observed as an after‐response to stimulation in the nucleus rotundus. These results are discussed with regrard to stimulation in the nucleus rotundus. These results are discussed with regard to possible anatomical systems controlling reproductive, feeding and aggressive behavior in fishes.
An electron microscopic study of synaptic morphology in the oculomotor nuclei of three inframammalian species
Authors: Waxman Stephen G. , Pappas George D. 
Published: December 2004

AbstractThe fine structure and distribution of synapses in the oculomotor nuclei of three inframammalian species (spiny boxfish Chilomycterus schoepfi, grass frog Rana pipiens, American chameleon Anolis carolilzensis) were studied by electron microscopy. Oculomotor neurons in Chilomycterus are approximately 40 μ in diameter, and have one or a few large dendrites which extend in a ventro‐ lateral direction and ramify in the tegmental neuropil. Axons establish numerous en passant synapses and sometimes extend into indentations in the surfaces of the motoneurons. Approximately one‐sixth of synaptic profiles include regions of close membrane apposition (gap junctions). Presynaptic processes at these synapses contain electron‐lucent and dense core vesicles. Similar synapses occur on fine dendrites in the neuropil but are rare. Somatosomatic and dendroden‐ dritic close appositions are not present, so that electrotonic coupling between oculomotor neurons occurs via a presynaptic pathway. Synapses commonly arise at nodes of Ranvier. Rana oculomotor nucleus consists of motoneurons about 30 p in diameter with one or a few dendrites which ramify in the ventrolateral neuro‐ pil, and smaller and less common multipolar interneurons. The two neuronal types differ in their relationships with glial elements. The majority of synapses on large neurons exhibit distinct synaptic clefts. Close membrane appositions are present at approximately 8% of synaptic contacts on large neurons, but are rare on small diameter dendrites. Subsynaptic cisterns are present at some synapses, but were never observed subjacent to close appositions. Axosomatic synapses are uncommon on the smaller interneurons. A cryptlike extension of the cerebral aqueduct separates contralateral oculomotor nuclei in Anolis. Oculomotor neu‐ rons in dorsolateral and ventromedial divisjons of the nucleus are multipolar and approximately 25 p in diameter. Large areas of the cell bodies are covered by glial lamellae, and axodendritic synapses predominate. At 5% of synapses on somata and proximal dendrites, there are close appositions. Subjunctional dense bodies are present at other synapses. Previous electrophysiological studies have demonstrated electrotonic coupling between homonymous oculomotor neurons, and between neurons and presynaptic fibers in teleosts. The present results pro‐ vide morphological evidence for electrotonic transmission in the oculomotor nuclei of three diverse species of vertebrates.
Fiber systems of medial and anterior thalamus of macaque
Authors: Wright Sanford J. , Locke Simeon 
Published: December 2004

AbstractLesions were produced in the anterior limb of the internal capsule of three Macaca mulatta. The resulting median, paramedian, and lateral vertical bands of thalamic degeneration appeared to disregard nuclear boundaries and extend from the anterior tubercle to the habenula. A mediolateral gradient in the dorsomedial nucleus was related to a basal, middle and lateral disposition of lesions in the capsular fan. The possible significance of these observations as underscoring a more general theme of thalamocortical relationship was explored.
The role of the arcuate nucleus in the brain‐pituitary‐gonad axis
Authors: Brawer James R. 
Published: December 2004

AbstractRecent evidence indicates that the arcuate nucleus of the hypothalamus is involved in the control of gonadotrophin secretion. In the present work the neurons of the arcuate nucleus were studied in normal and castrated adult male rats with the electron microscope.The neurons of normal animals appear quite ordinary in many respects and contain the same types of organelles that are common to neurons in general. In addition, however, many neurons contain structures resembling the chromatoid bodies commonly found in developing spermatids. There are also some peculiar features of nuclear structure such as nucleolar association with the nuclear envelope and the fragmentation of the nucleolus.Arcuate neurons of castrated animals show two variations, the most obvious of which is the occurrence of whoreled formations of closely apposed concentric cisternae of the smooth endoplasmic reticulum. These whorled bodies appear in several different forms. The simplest consist of complete uninterrupted cisternal rings. Variations from the simple form involve anastomoses between adjacent cisternal shells, areas in which the regular layered structure is obliterated by confluence of cisternal rings, areas of irregular spacing in which varying amounts of cytoplasm are trapped between adjacent rings, and the presence of semicircular incomplete outer rings. As many as five whorled bodies have been observed in a single cell. The whorled bodies in such a group are continuous with one another and with the common endoplasmic reticulum.Whorled bodies appear four days after castration, and by two weeks about one tenth of the neurons exhibit them. Very few whorled bodies appear in castrated animals that received daily injections of 2 μg testosterone propionate per gram body weight. Castration produced no obvious qualitative changes in the ependymal cells or their processes.The second variation resulting from castration is the presence of large populations of dense core vesicles in some of the neurons of the arcuate nucleus. Dense core vesicles are sparse in the neurons of normal animals. The significance of these variations is discussed.There is evidence to suggest that the whorled bodies may be an indication of enhanced synthetic activity following release from gonadal steroid inhibition. In any case, the whorled bodies label the cells in which they occur as direct links in the brain‐pituitary‐gonad axis.
Corticobulbar projections of the marsupial phalanger (Trichosurus vulpecula). II. Projections to the mesencephalon
Authors: Martin George F. , Megirian David 
Published: December 2004

AbstractThe pattern of neocortical projections to the mesencephalon was studied in the marsupial phalanger (Trichosurus vulpecula). Lesions were placed in selected neocortical areas in 29 adult phalangers. After a one to two week survival time, the animals were perfused, the brains and spinal cords removed and processed by either the Nauta‐Gygax technique or the method of Fink and Heimer. The cytoarchictecture of the neocortex was studied also and those results pertaining to the ablated cortical areas are reported. The cortex just rostral to the orbital sulcus (motor area for the head and neck) contains numerous dark staining pyramidal neurons which measure up to 35μ at their widest dimension. Lesions within this region produce fiber degeneration within the ventral tegmental area, the nucleus linearis, the periaqueductal gray, the deeper layers of the superior colliculus and the lateral tegmental area. The frontal pole cortex contains very few large pyramidal neurons. Ablations of this cortex result in a similar pattern of fiber degeneration, although few, if any, degenerating fibers are present within either the superior colliculus or the lateral tegmentum.Cytoarchitecturally the cortex just caudal to the orbital sulcus (forelimb motor and some sensory cortex) is strikingly similar to the immediate preobital region. However, destruction of this region produces fiber degeneration within the nucleus of Darkschewitsch, the nucleus of the medial longitudinal fasciculus, the periaqueductal gray, the lateral and deep tegmental areas, the caudal pretectal nucleus and the red nucleus. The motor‐sensory hindlimb area also contains numerous large pyramidal neurons, but the internal granular layer is somewhat better developed than it is in the bulk of the forelimb region. Lesions within the motor‐sensory area for the hindlimb produce fiber degeneration within the same general regions as do ablations of the forelimb cortex, although more degenerating fibers are present within the red nucleus and fewer within the caudal pretectal nucleus.The somatic sensory face cortex (ventral and lateral to the motor‐sensory limb areas) is characterized by a particularly well developed internal granular layer. Lesions of this area produce axonal degeneration in both superficial and deep layers of the superior colliculus. The striate and peristriate areas can be distinguished from one another by the development of the internal granular layer. Lesions in these areas result in fiber degeneration which is limited to the superficial layers of the superior colliculus.The neocortex of the phalanger temporal pole cannot be distinguished by the development of any particular layer. Indirect evidence suggests that this cortical region projects to the nucleus of the inferior colliculus as well as to the deeper layers of the superior colliculus.
Topological analysis of the brain stem of the lamprey Lampetra fluviatilis
Authors: Nieuwenhuys Rudolf 
Published: December 2004

AbstractThe investigations of His, Herrick, Johnston and many others have led to the doctrine that the central nervous system fundamentally consists of a number of longitudinally arranged zones or columns, some of which are delimited from each other by distinct ventricular sulci. In order to facilitate the study of this basic morphological pattern in the brain stem, a procedure has been developed, making it possible to survey in one figure the neuronal structures and their relationship to the ventricular grooves in this region. Essentially this procedure involves two steps: first the cell masses and large individual cells are projected upon the ventricular surface, and next the ventricular surface is flattened out, i.e., subjected to a one‐to‐one continuous topological transformation. Such a topological analysis was carried out on the brain stem of the lamprey, Lampetra fluviatilis, and yielded the following results: The sulcus limitans of His extends throughout the rhombencephalon, but does not enter the midbrain. The rhombencephalic basal plate can be clearly divided into a medial somato‐motor, and a lateral viscero‐motor zone. The somato‐motor zone consists of a rostral extension of the spinal motor column and three reticular nuclei. Rostrally this zone is continuous with the tegmentum mesencephali, which contains another reticular nucleus and the superficial and deep nuclei of III. The reticular nuclei contain groups of large cells. On either side seven of these large cells, three in the midbrain, one in the isthmus and three in the hindbrain, are significantly larger than the others, and are designated as Müller cells. The viscero‐motor zone is confined to the hindbrain. It consists of a continuous chain of discrete cell masses: the motor nuclei of V, VII, IX and X. This zone contains in addition the large Mauthner neuron, which is situated between the nuclei of V and VII.In the rhombencephalic alar plate, separate viscero‐sensory and somatosensory zones could not be recognized. The delimitable nuclei in this region all belong to the somato‐sensory octavo‐lateralis complex. The latter complex extends rostrally into the very small cerebellum which, apart from a zone of periventricular gray and a nucleus cerebelli, harbours the motor nucleus of IV. The sensory centers of the midbrain, i.e., the torus emicircularis and the tectum are caudally continuous with the gray substance of the alar plate of the hindbrain. Large, presumably primary sensory, elements occur in the caudal and ventral part of the rhombencephalic alar plate. Such “dorsal cells” are also present in the spinal cord, but a midbrain equivalent, i.e., nucleus mesencephalicus of V, is entirely lacking.
Primary optic pathways in the duckbill platypus, Ornithorynchus anatinus: An experimental degeneration study
Authors: Campbell C. B. G. , Hayhow W. R. 
Published: December 2004

AbstractThe retinal efferent axons of Ornithorhynchus anatinus project, as in the echidna, to two diencephalic nuclei disparate in size and location and designated provisionally as LGNa and LGNb, and to the pretectum and superior colliculus. The primary optic pathways of the platypus are crossed except for a small number of fibers which project to the ipsilateral LGNa and b. The optic input to the superior colliculus enters via a sheet of retinal fibers which runs over the surface of the colliculus and distributes terminal endings to the stratum griseum superficiale. A similar situation exists in the echidna, birds and reptiles, but is not known to be present in therian mammals. No interstitial nuclei were found in the optic tract as are present in the echidna. In addition, no nucleus which could possibly be identified as a dorsal terminal nucleus of the accessory optic system was found in the platypus. Such a nucleus is present in the echidna. Projection of optic axons to a medial terminal nucleus of the accessory optic system is present, although discrete inferior and superior accessory optic fasciculi are not. The primary optic pathways of the platypus appear to be less complex than those of the echidna, possibly due to a more limited use of vision.
The structure of the ventral part of the lateral geniculate nucleus. A cyto‐ and myeloarchitectonic study in the cat
Authors: Jordan Hans , Holländer Horstmar 
Published: December 2004

AbstractThe cyto‐ and myeloarchitectonic organization of the ventral nucleus of the lateral geniculate body (LGV) were investigated by means of several histological series sectioned in different planes. Twenty‐one hemispheres of normal adult cats were used. The shape of the nucleus and its anatomical relationships with the optic tract, the dorsal nucleus of the lateral geniculate body (LGD) and the zona incerta were established. The LGV is club‐shaped with a broad main part and a slender stalk, which is twisted around the rostrolateral aspect of the optic tract. Caudolaterally the LGV is covered by the optic tract and dorsomedially it is apposed to the LGD. Rostromedially it merges with the thalamic reticular nucleus and ventromedially its stalk is continuous with the transition zone between the reticular nucleus and the zona incerta. Cell sizes were also measured. Five subdivisions of the nucleus were identified and their spatial interrelationships were determined: LGVa, LGVd and LGVe being composed of small cells exclusively, LGVb and LGVc containing both small‐ and medium‐sized nerve cells. LGVa and LGVb are situated at the rostral part of the nucleus both fusing rostrally with the reticular nucleus of thalamus. LGVd occupies the caudal end of the nucleus. LGVe is situated along the contact zone with the optic tract and is combined with LGVc. LGVb is located between LGVa, LGVc and LGVd.