bluuebunny/crossref_metadata_2025_split huggingface dataset:
Methods of fixation and the morphology of synaptic vesicles
Authors: Valdivia Oswaldo 
Published: December 2004

AbstractCerebellar mossy, parallel, basket and Golgi axons were used to study the variables contributing to vesicle shape.It has been found that, when aldehydes are used as a primary fixative, synaptic vesicles can be either small round vesicles (less than 400 Å in diameter), large round vesicles (400–500 Å in diameter) or flat, with a ratio of large to small diameters of 2 or greater (500–600 Å × 250 Å). The proportion of round vesicles as well as the presence and the number of flat vesicles in each axon depend basically upon the osmotic pressure of the buffer. Concentration of aldehydes, duration of the fixation and dehydration, temperature of the fixative, etc. do not affect the synaptic vesicle shape. With buffers (phosphate and sodium cacodylate) of low osmolarity, mossy and parallel axons exhibit a round synaptic vesicle population and no flat vesicles are seen at all. With the same low osmolarity buffers, basket and Golgi axons have a synaptic vesicle population that is mainly round with a low proportion of flat vesicles. As the osmolarity of the buffers is increased, the number of flat vesicles in basket and Golgi axons increases. In mossy and parallel axons the flat vesicles are present with highest osmolarities but always in a lower proportion than in basket and Golgi axons.Quantitative observations indicate that each axon type, under given conditions of fixation, exhibits a mixed vesicle population with a characteristic vesicle ratio. Although this vesicle ratio is modified significantly with changes in the osmotic pressure of the buffer, each axon type exhibits a different and characteristic modification of its vesicle ratio. These observations show that the vesicle ratio and its changes in different conditions of fixation are useful parameters for classifying axon.
The relations of ependyma to neurons and capillaries in the hypothalamus: A Golgi‐Cox study
Authors: Bleier Ruth 
Published: December 2004

AbstractNumerous basal processes of ependymal cells extend peripherally into every cell group and area of the hypothalamus of the four species of mammals examined: mouse, rat, rabbit and cat. With Golgi‐Cox impregnation and Nissl counterstaining, ependymal cell processes appear to have a variety of forms and of intricate structural relationships with neurons and capillaries within the hypothalamus. It is proposed that hypothalamic ependymal cells and their processes function as a communication system between the cerebrospinal fluid of the third ventricle and neurons and capillaries within the hypothalamus. The role that such a system may play in the regulation of adenohypophysial function is discussed.It was also noted that in all hypothalamic cell groups, dendrites of some neurons extend to the ependymal layer.An unusual cell, resembling microglia forms, within the infundibular nucleus appears to be selectively impregnated by the Golgi‐Cox technique employed. The cell is characteristic of the infundibular nucleus and, with rare exceptions, is confined to that cell group. Some of these spider‐cells lie on the ependymal layer and also have endfeet extending to the ventricular surface of the ependyma.
The optic nerve of the Mallard duck: Fiber‐diameter frequency distribution and physiological properties
Authors: O'Flaherty Juan J. 
Published: December 2004

AbstractA correlative study of the anatomy and physiology of the axons of the optic nerve of the Mallard duck was carried out. The principal findings were:

Electronmicroscopy used in conjunction with phase contrast microscopy showed the nerve to have a fiber spectrum ranging from 0.3 μ to 6.0 μ with a mode at 1.15 μ.
No unmyelinated axons were found.
The cross‐sectional area of the nerve was estimated to be 4.38 mm2; assuming a mean fiber density of 350,000 fibers/mm2, the total number of axons in the nerve was estimated to be about 1,500,000.
The conduction velocities of the fibers were found to range from 21 m/sec to about 3 m/sec.
Different recovery cycles were found for each of the different compound action potentials.
Using a graphical method, a good correlation could be established between the fiber‐size spectrum and the configuration of the compound action potential.
Comparisons in the strucure of avian muscle spindes
Authors: Maier Alfred , Eldred Earl 
Published: December 2004

AbstractA study of muscle spindles in several species of birds was made to determine if avian intrafusal (IF) fibes are separable into the nuclear bag and chain fiber types found in mammals, and whether prominent differences in spindle structure might exist among species. Van Gieson‐stained serial sections of the sartorius, a flexor muscle, and the antigravity adductor profundus muscle were examined in the chicken, quail, pigeon and canary. Avian IF fibers did not exhibit the pronounced “bag” of nuclei characteristic of mammalian nuclear‐bag fibers, although the non‐striated region at mid‐length was marked by a moderate excess of eccentric, vesicular nuclei. No consistent differentiation in pattern of nuclear aggregation or manner of fiber termination among fibers of a spindle was detected, nor was there unequivocal bimodality in cross‐sectional areas. These characteristics in bird spindles, therefore, do not afford trustworthy criteria for separation of types of IF fibers. The number of spindles per unit volume was particularly high in the canary and lowest in the chicken muscles. Spindles in the chicken were larger and more complex than canary spindles in respect to numbers of fibes per spindle, spindle length, and cross‐sectional area of intrafusal fibers at the equator. Values for the quail and pigeon ocupied an intermediate position. Relation of the differences in spindle structure to the size of the bird and to other factor is discussed, and some contrast between avian and mammalian spindles are pointed out.
Primary optic pathways in the echidna, Tachyglossus aculeatus: An experimental degeneration study
Authors: Campbell C. B. G. , Hayhow W. R. 
Published: December 2004

AbstractThe retinofugal axons of Tachyglossus aculeatus were found to project to two diencephalic nuclei, disparate in size and location and designated provisionally as LGNa and b, and to the pretectum and superior colliculus. The primary optic pathways of the echidna are crossed except for a few fibers which pass to the ipsilateral large diencephalic nucleus (LGNa). Further work is required before the homologies of the two diencephalic nuclei can be determined. In addition, entirely crossed projections were also found to a large number of optic nuclei including a medial terminal nucleus, four cell groups interstitial to the optic tract, and a nucleus located within the brachium of the superior colliculus which may represent a dorsal terminal nucleus. The latter nucleus may, however, actually be the nucleus of the optic tract which is displaced from its usual close association with the pretectal area. Only an inferior fasciculus of the accessory optic tract was found.
The contribution of the dorsal lateral geniculate nucleus to the total pattern of thalamic terminations in striate cortex of the virginia opossum
Authors: Benevento L. A. , Ebner Ford F. 
Published: December 2004

AbstractThese studies were carried out to show the manner of projection of the dorsal lateral geniculate nucleus and other thalamic nuclei to striate cortex in the Virginia opossum. In order to demonstrate these projections, lesions were made in the dorsal lateral geniculate nucleus, in the ventral lateral geniculate nucleus, in most of the thalamus on one side except for the dorsal lateral geniculate nucleus, and in the entire unilateral thalamus. Following various survival times, usually seven days, the brains were appropriately prepared and stained with procedure I of the Fink‐Heimer technique. Dorsal lateral geniculate neurons project in a topographical manner only to certain layers of striate cortex. These projections from the lateral geniculate are compared with the same system in other mammals, and it is concluded that it is similar in all mammals studied, except for the cat. In the cat the lateral geniculate projects beyond the border of striate cortex, but even in the cat the layers of termination within striate cortex are apparently similar. The ventral lateral geniculate nucleus does not project to visual cortex. Dorsal thalamic nuclei other dian the lateral geniculate project to peristriate cortex and to layers VI and I of striate cortex. The finding that thalamic nuclei, other than the lateral geniculate nucleus, project to striate cortex has never been described as part of the visual pathways in other mammals. It is suggested that these additional projections arise mainly from the lateral nuclear group of the thalamus in the opossum, and must be considered in relation to any response characteristics and organization of striate cells determined from physiological studies. These multiple thalamic projections can provide the substrate for more than one representation or “map” of sensory information in striate cortex.
Behavioral encephalization in the bullhead embryo and its neuroanatomical correlates
Authors: Armstrong Philip B. , Higgins Don C. 
Published: December 2004

AbstractThree physiological phases can be recognized in the encephali‐zation of motor control in the developing bullhead. These are in succession 1. the spinal phase, 2. the hindbrain phase and 3. the optic‐midbrain phase. During the spinal phase motility is limited to lateral flexions of the trunk and tail by the contractions of the somitic muscle. The flexions become amplified as additional somites participate in this activity. There is no evidence of any encephalic control. Random undulatory swimming characterizes the hindbrain phase. It emerges with the maturation of the Mauthner cell and its labyrinthine afferents. In the optic‐midbrain phase there is a superposition of a visual control on swimming, a control which comes on with the differentiation of the rods and cones of the eye and their projection by way of the optic tectum and the tecto‐bulbar tracts to the Mauthner cells. The response in this phase is directed, a negative phototaxis for a major share of this phase. However, toward the end of this phase the photomechanical properties of the retina come into play providing an adaptive mechanism in which the response, negative or positive, is determined by the photomechanical state of the retina. Thus the retina, an exteroceptor, serves as an analyzer. The photic response in the advanced embryos can be predicted if the adaptive state of the photomechanical apparatus is known.It is suggested that the spinal and hindbrain activities result from endogenous neural activating mechanisms. Spontaneous firing in the labyrinth transmitted to the Mauthner cells may spark the random swimming characteristic of the hindbrain phase. This provides an activity base for the directed optic responses. The Mauthner cells thus receive input from both the labyrinth and the retina, a case of heterogenous summation. The random motor activities in the spinal and hindbrain phases do not appear to have survival value. The optic midbrain responses are reactions to an environmental situation and appear to have survival value or “purpose.”
Quantitative cytoarchitectonic distribution of neurons, glia, and DNA in rat cerebral cortex
Authors: Bass Norman H. , Hess Helen H. , Pope Alfred , Thalheimer Caroline 
Published: December 2004

AbstractA new technique combining microfluorometric DNA assays with differential cell counts was used to quantitate the intralaminar distribution of neuronal and non‐neuronal cells (chiefly glial) in rat somatosensory cortex (Charles River 250 gm males, C D® strain). The intracortical amounts of DNA per unit fresh volume were calculated from the DNA contents of serial frozen slices of known volume sampled serially from the pial surface to white matter in frozen cortical cylinders; respective amounts per unit solids were calculated from predetermined dry weights of the slices. Cell counts were performed on serial horizontal sections from formalin‐fixed cylinders stained by Nissl's method. Neuronal DNA and glial DNA were calculated based on the percentages of the respective cells counted.Total DNA averaged 5.43 μg/mg dry weight (1.19 μg mm3 fresh volume). Values were highest in layers II and IV. Neuronal DNA paralleled total DNA in its intracortical distribution and showed distinct peaks in layers II and IV. Glial DNA showed an even distribution. Glia exceeded neurons only in layers I and VIc. The mean neuron/glia ratio was 2.5. This method gives a more precise estimate of the absolute numbers of neurons and glia than can be obtained by histological methods alone, since DNA assays eliminate the need to correct the histological counts for volume changes during fixation and staining.
Neuronal and synaptic organization of the normal dorsal lateral geniculate nucleus of the squirrel monkey, Saimiri sciureus
Authors: Wong‐Riley Margaret T. T. 
Published: December 2004

AbstractThe normal cellular architecture and synaptic organization of the dorsal lateral geniculate nucleus (LGN) of Saimiri sciureus has been studied with light and electron microscopic techniques. Golgi preparations reveal at least four types of neurons: type I and II are large and medium‐sized cells; type II cells have grape‐like dendritic protrusions, while type I cells do not. Type III small neurons have very long dendrites that cross laminar borders freely; and type IV very small neurons resemble glial cells. The last type may correspond to small, spindle‐shaped or round, neurons which show somato‐dendritic synapses under the electron microscope. Types I and II neurons are regarded as geniculocortical relay cells. Types III and IV are good candidates for interneurons. A serial dorsal to ventral interlaminar dendritic overlap is noted throughout the LGN. With the electron microscope, several types of axonal profiles can be seen: large axons with round vesicles (RL's), small axons with round vesicles (RS's), and intermediate axons with flattened or pleomorphic vesicles (F's). The RL's are retinal terminals; some of the RS's are corticogeniculate fibers; while the F's are believed to be intrageniculate in origin. The F type is then subdivided into F1 and F2; F1 being darker and containing more evenly dispersed synaptic vesicles than F2. There is also a distinct class of presynaptic dendrites, Fd, which contains pleomorphic vesicles and has a light cytoplasmic density similar to that of the F2 profiles. It is possible that some or all of the F2 processes may prove to be dendritic. Somato‐dendritic synapses arise from very small neurons and form a part of the normal synaptic organization in the LGN. The RL and RS axons form asymmetrical synaptic contacts, whereas the F (F1, F2 and Fd) processes mainly form symmetrical ones. Non‐synaptic filamentous contacts are also found. The rules of synaptic connectivity are such that the RL and RS terminals are never synaptic to either the RL or the RS terminals, and presynaptic to other dendrites. If the F profiles contact each other, the F1 axon is never the post‐synaptic element. The RL and F processes synapse upon any part of the perikaryal and dendritic surfaces, whereas the RS terminals do not contact the soma.
Central projections of the spiral ganglion of the squirrel monkey
Authors: Moskowitz Norman , Liu Jung‐Ching 
Published: December 2004

AbstractFor establishing the relationships of the central projections of the spiral ganglion with the cytoarchitectural regions of the cochlear nuclear complex in a primate species, 23 squirrel monkeys, Saimiri sciureus were utilized. Restricted lesions of the cochlea were confirmed histologically and the resulting degeneration was traced to the cochlear nuclei in sections prepared with Nauta (′57) and Fink‐Heimer (′67) technics. By following the course of degeneration, the cochlear root fibers can be seen to bifurcate into ascending and descending branches. The ascending branches from the apical through basal turns of the spiral ganglion terminate in a rostro‐lateral to caudo‐medial gradient in the anteroventral cochlear nucleus. The descending branches from the apical through basal segments of the spiral ganglion terminate in a ventral to dorsal pattern in the posteroventral and dorsal cochlear nuclei. Ascending branches terminate chiefly on large and small spherical cells and globular cells in the anteroventral region. Terminals of descending branches are associated with globular, multipolar and octopus cells of the posteroventral nucleus and cells of the central and granular layers of the dorsal cochlear region.
Electron microscopic distribution of axoplasmic transport
Authors: Hendrickson Anita E. 
Published: December 2004

AbstractLight and electron microscopic radioautography have been used to localize the rapid and slow components of axoplasmic flow within the monkey lateral geniculate nucleus (LGN). Three days after an intravitreal injection of H3 leucine, 53% of the silver grains found in the LGN were localized to retinal synaptic terminals and 27% were over retinal axons. By 30 days post‐injection, 66% of the grains were localized to retinal axons while retinal synaptic terminals now contained 21% of the grains. At both 3 and 30 days LGN neurons postsynaptic to the radioactive retinal axons showed higher levels of labeling than LGN neurons in the layers not receiving afferents from the injected eye. These data indicate that the rapid phase is mainly confined to the synaptic terminal while the slow phase is mainly localized in the axon. This differing distribution of radioactivity may now be utilized as the basis of a neuroanatomical tracing method.
Mode of cell migration to the superficial layers of fetal monkey neocortex
Authors: Rakic Pasko 
Published: December 2004

AbstractGolgi and electronmicroscopic methods were used to define the shapes and intercellular relationships of cells migrating from their sites of origin near the ventricular surface across the intermediate zone to the superficial neocortical layers of the parietooccipital region in the brains of 75‐ to 97‐day monkey fetuses. After mitotic division in either ventricular or subventricular zones, the cells enter the intermediate zone and assume an elongated bipolar form oriented toward the cortical plate. The leading processes, 50 to 70 μ long, are irregular cytoplasmic cylinders containing prominent Golgi apparatus, mitochondria, microtubules, ribosomal rosettes, immature endoplasmic reticulum and occasional centrioles. They usually terminate in several attenuated expansions, the longest one oriented toward the cortical plate. The trailing processes are more slender, relatively uniform in caliber and display few organelles.Throughout the 3500 μ pathway across the intermediate zone the migrating cells are apposed to elongated, radially oriented, immature glial processes which span the full thickness of the cerebral wall. Most of the perikarya of these glial cells in the younger specimens lie in the ventricular or subventricular zones, but in older fetuses of this series many are found in the intermediate zone. The main characteristics of these fibers are: elongated cylindrical form contaiing numerous microtubules; electronlucent cytoplasmic matrix; short lamellate expansions protruding at right angles from the segment of the fiber which runs through the intermediate zone; and terminal endfeet joined at the pial surface to form a continuous sheet coated externally with basement membrane. It is suggested that glial radial fibers provide guidelines for cell migration through the complex mixture of closely packed cell processes and cell bodies that compose the developing cerebral wall. Strong surface affinity between radial fiber and migrating cell is suggested in regions where both follow precisely the same curving course from subventricular to intermediate zones and also in areas where large extracellular spaces separate other cells and processes but in which migrating cells and radial fibers remain closely paired nonetheless. Specific affinity between them is implied in the failure of migrating cells to follow any of the myriad differently‐oriented processes they encounter. Several generations of postmitotic cells appear to migrate along the same radial fiber, a developmental mechanism that would allow for the vertical cell columns of adult neocortex.
Olfactory structures of the forebrain in the reeler mutant mouse
Authors: Caviness V. S. , Sidman R. L. 
Published: December 2004

AbstractPrior studies in the reeler mutant mouse have drawn attention to cytoarchitectonic anomalies in the neocortex and hippocampus of the forebrain and in the cerebellar cortex. In the present study cresyl violet and Loyez stained serial sections were used for light microscopic analysis of the olfactory structures in the forebrain of the mutant. The olfactory bulb and accessory bulb, both targets of afferents form the peripheral nervous system, are normal. By contrast, the laminate structures to which the olfactory bulbs project — the anterior olfactory nucleus, piriform cortex, olfactory tubercle, and cortical nucleus of the amygdaloid complex — are all abnormal in their cytoarchitecture. All of these structures share in common a segregation of cell populations according to size such that the larger cells lie in a deep position close to central fiber bundles. Small, polymorphic cells occupy a superficial zone, and there is no cellsparse external plexiform layer in the mutant. We adopt the view that the relationship of pyramidal cell to complex, external plexiform layer is the cardinal geometric principle defining a normal cortex, and suggest that derangement of this relationship may be the common denominator in the reeler cortical phenotype. The developmental mechanism influenced by the reeler locus and leading to the fundamental cortical geometry in normal or mutant animals may reside in the early interaction of afferent fibers and pyramidal cells.
Afferent connections to the diencephalon in the marsupial phalanger and the question of sensory convergence in the “Posterior Group” of the thalamus
Authors: Rockel A. J. , Heath C. J. , Jones E. G. 
Published: December 2004

AbstractThe various afferent pathways terminating in the thalamus of the marsupial phalanger have been investigated with the Nauta techniques, with a view to determining the extent of overlap and convergence of these pathways. If this had proved to be extensive, it would have lent support to the views of some authors that, in primitive and generalized mammals, the relay nuclei are in the process of differentiating out of a single archetypical, multi‐modal nucleus.However, the amount of overlap between the various afferent pathways in this animal is no greater than in the cat and monkey; in the case of the ventral nuclear complex, despite the presence of a common sensory and motor cortical representation, the overlap between the somatic sensory and cerebellar pathways is probaly less than in the higher mammals. The question, therefore, arises as to whether differentiation of certain thalamic nuclei may precede that of the cortical area with which they are connected.The results furnish evidence for the homologies of the posterior group of thalamic nuclei in other mammals, but the limited amount of overlap of afferent pathways occurring in the posterior group is not necessarily indicative of its being the common precursor of all the sensory relay nuclei.