bluuebunny/crossref_metadata_2025 huggingface dataset:
Maturation of oligodendroglia and myelinogenesis in rat optic nerve: A quantitative histochemical study
Authors: Hirose Genjiro , Bass Norman H.
Published: May 2005

Microchemical techniques correlated with histologic observations were used to study rat optic nerve at 5, 10, 15, 20, 30, 40 and 50 days of postnatal development. Cell enumeration was accomplished by combining DNA as says with previously reported differential cell counts in electron microscopic montages (Vaughn, '69). At 5 days of age, the optic nerve contained unmyelinated axons, and its volume and total number of glia (DNA) were less than 40% of 50‐day‐old values. The cell population was composed of equal numbers of fibrous astrocytes and glial stem cells but contained only 7% oligodendrocytes. Between 5 and 20 postnatal days, mitotic proliferation of these stem cells resulted in a 3‐fold increase of DNA, while numbers of oligodendroglia increased 10‐fold. The cell population of the nerve at 20 postnatal days was similar to that found in the adult, with oligodendrocytes constituting 60% of the total cell population. Although these cells continuously formed myelin throughout postnatal development, their maximal rate of myelin lipid deposition (cerebrosides and cholesterol) occurred between 5 and 20 postnatal days. Hence, the most rapid rate of myelinogenesis in rat optic nerve occurred during the first three weeks of postnatal life and was synchronous with the mitotic proliferation and cellular differentiation of interfascicular oligodendroglia.
The ultrastructure of the cat olfactory bulb
Authors: Willey T. Joe
Published: May 2005

The fine structure of the olfactory bulb was investigated in the cat. Five types of bulbar neurons were identified on the basis of size, location, cytoplasmic organelles and synaptic complexes with the neuron perikaryon. The smallest diameter neurons were predominatly located in the glomerular and granule cell layers. Ultrastructural characteristics for these two neuron populations, viz., periglomerular and internal granule cells, were identical. Tufted cells, smaller in diameter than mitral cells, were located in the external plexiform and glomerular layers and possessed all the morphological characteristics of the mitral cells. Mitral cells were the largest bulbar neurons and were located in a single lamina. Stellate (short‐axon) neurons were found in the glomerular, external plexiform and granule cell layers.

Reciprocal synapses were observed in all laminae of the bulb except the primary olfactory nerve and deeper granule cell layers. Such synapses were found in the glomeruli, on tufted and mitral cells, in the neuropil of the external plexiform layer, and on the axon hillock and initial segments of the mitral cells. The morphology in the cat olfactory bulb corroborated bulbar ultrastructure described for other mammals.
Fluorescence histochemistry of monoamine‐containing cell bodies in the brain stem of the squirrel monkey (Saimiri sciureus). IV. An atlas
Authors: Di Carlo Vincenzo , Hubbard Jack E. , Pate Patricia
Published: May 2005

The topography of the various groups of catecholamine‐ and serotonin‐containing cell bodies in the squirrel monkey (Saimiri sciureus), as described in the preceding three papers of this series, is presented in an atlas of Nissl and myelin stained frontal sections. The major findings of this study are reviewed and discussed. These include: (1) evidence of fundamental similarities in the topographic distribution of the cell groups between the primate and the rat and of significant differences between the primate and the cat; (2) identification as the catecholaminergic cells of the locus caeruleus of a cellular group incorrectly identified in the literature as nucleus tracti mesencephalici nervi trigemini; (3) consolidation of several catecholamine‐containing cell groups as belonging respectively to the locus caeruleus (C4, C6, C7) and the substantia nigra (C8 and C9); (4) predominant distribution of the serotoninergic cell groups in the midline raphe region (with lateral extensions in some cases) and location within well defined nuclei, such as the nucleus raphe obscurus, nucleus raphe pallidus, nucleus raphe magnus, nucleus raphe pontis, nucleus raphe dorsalis and nucleus centralis superior.
The motor nucleus of the facial nerve in the opossum (Didelphis marsupialis virginiana). Its organization and connections
Authors: Dom Richard , Falls William , Martin George F.
Published: May 2005

The organization of the facial nucleus was studied in the opossum by localizing neurons which stin poorly for acetylcholinesterase activity following transection of identified facial rami. The caudal auricular representation is limited to the ventromedial extreme of the nucleus, whereas the neurons contributing to the cervical ramus are situated dorsally and medially. The zygomatic representation extends throughout the intermediate portion of the nucleus, apparently overlapping with that of the palpebral and rostral auricular muscles which is limited to the ventral extreme of the intermediate zone. The buccolabial area is particularly large in the opossum and encompasses most of the lateral facial enlargement.

Midbrain‐facial projections were identified from the superior colliculus, the midbrain tegmentum (particularly caudal ventromedial areas) and the red nucleus. The location of terminal degeneration in the facial nucleus following lesions within each of these areas was plotted and interpreted in light of facial organization. Of particular note is the fact that the fibers of rubral origin distribute preferentially to the zygomatic and, to some extent, buccolabial areas, whereas the ventromedial tegmental system distributes most strongly to the areas of caudal auricular, cervical, palpebral and rostral auricualar representation. The medial and intermediate regions of the facial nucleus receive a denser midbrain projection than does the lateral (buccolabial) area. In contrast, evidence was obtained for an extensive facial projection from the parvocellular reticular formation and the caudal spinal trigeminal nucleus which strongly favors the buccolabial enlargement. The possibility exists that the medial pontine and medullary reticular formation as well as portions of the dorsal column nuclei also have a facial projection. Spino‐facial fibers arise rostral to the cervical enlargement and show a predilection for the medial facial enlargement (cervical and caudal auricular areas). Although some systems distribute preferentially to specific areas of the facial nucleus, overlap is present suggesting considerable integration.
Astrocyte‐specific protein and neuroglial differentiation. An immunofluorescence study with antibodies to the glial fibrillary acidic protein
Authors: Bignami A. , Dahl D.
Published: May 2005

The topographical features of the neuroglial network in the mature rat CNS and the differentiation of fibrous neuroglia in the neocortex and hippocampus have been studied by immunofluorescence using antibodies to the glial fibrillary acidic (GFA) protein. In the mature brain and spinal cord the distribution and appearance of neuroglia as observed with immunofluorescence were similar to those described by Weigert ('95) using his method for astrocytic fibers. In the developing rat immunofluorescence started to appear on the surface of the neocortex in the first week after birth. In 9‐day‐old rats a continuous external glial membrane had formed by immunofluorescence. Immunofluorescence of the perivascular glial membrane appeared later. Blood vessels completely surrounded by a fluorescent membrane were not observed in the middle cortical layers before the eighteenth day of life. An unexpected finding in the hippocampus was the sudden appearance in the 8‐day‐old rat of a radial system of immunofluorescent fibers crossing the granular layer and extending in the molecular layer. The radial fibers were still present in the adult rat. However, they became widely spaced and thus less prominent than in the immature animal. In fetal rats immunofluorescent fibers first appeared in the medial wall of the lateral ventricles on the eighteenth post‐conceptionaly day. The radial system of glial fibers extending from the ventricles to the surface of the brain and characteristic of this stage of development was not stained by immunofluorescence.
Fine structure of dendritic and axonal growth cones in embryonic chick spinal cord
Authors: Skoff Robert P. , Hamburger Viktor
Published: May 2005

Our preliminary electron microscopic observations of embryonic chick spinal cord indicate that the majority of synapses in the cervical cord at the fourth and sixth days of incubation are found in the marginal layer rather than the mantle layer. These findings raise two basic questions about the type of connections in the marginal zone during the first week of development: are all these early synapses axondendritic, and are synaptic junctions present on axonal and dendritic growth cones? Since criteria for distinguishing between axonal and dendritic growth cones are scarce or nonexistent, serial section electron microscopy was employed to definitively identify the two types of terminals.

Two types of dendritic growth cones are present in the marginal layer during the first week of development. The first type is distinguished by a dendritic stalk which expands into a club‐shaped or bulb‐like terminal. A characteristic feature of this type of dendritic ending is the presence of numerous vesicles which vary in diameter from about 1000 Å to 2500 Å. Its cytoplasm has a floccular appearance and is frequently electron lucent. In contrast, the second type of dendritic terminal is electron dense, has a consistently homogeneous appearance, and usually lacks the large vesicles of the first type. The shape of the second type is a finger‐like process (filopodium) roughly of the same diameter as the main dendritic trunk. Evidence is presented that some dendritic growth cones observed in this study represent growing, motile processes rather than quiescent enlargements. Synapses on dendritic growth cones are quite numerous and, in addition, the first synapses on dendrites appear to form on growth cones. The hypothesis is put forward that synapses on dendritic growth cones. The hypothesis is put forward that synapses on dendritic growth cones are incorporated onto the dendritic trunk as the terminal continues to grow.

Axonal growth cones may be distinguished from dendritic growth cones on the basis of their overall morphology and their cytoplasmic components. An axonal growth cone is, in general, a larger and more irregular structure than the dendritic terminal. This irregularity is due to the large number of processes radiating away from the terminal enlargement or varicosity. While dendritic terminals almost always have finger‐like projections, processes of axonal growth cones are more often sheet‐like extensions of cytoplasm (folipodia). Another important difference between axonal and dendritic growth cones is that ribosomes in axonal varicosities are infrequently encountered and rarely aggregated into polysomes as in dendritic terminals. Axonal growth cones are occasionally observed to be presynaptic to a dendrite during the first week of development.
Ascending connections of a midbrain auditory area in a crocodile, Caiman crocodilus
Authors: Pritz Michael B.
Published: May 2005

The torus semicircularis is a tonotopically organized auditory region in the midbrain of the crocodile, Caiman crocodilus (Manley, '71). Two distinct regions of the torus can be distinguished in Caiman: an external nucleus, which is continuous with the deep layers of the optic tectum, and a central nucleus. Ascending connections of the central nucleus were studied with the light microscope by means of the Fink‐Heimer procedure after unilateral, anodal stereotaxic lesions. Efferent axons leave the central nucleus in the lateral lemniscus to enter the tecto‐reuniens tract where they course as far rostrally as nucleus Z. At this level, this bundle bifurcates. The majority of these fibers turn medially and then pass through and probably synapse on interposed neurons of nucleus Z, prior to their termination in nucleus reuniens. The remaining axons continue ventrally past nucleus Z to enter the ventral supraoptic decussation where they travel anteriorly to a level just posterior to the optic chiasm. Here the fascicles cross the midline and swing caudally, still in the ventral supraoptic decussation, until they reach nucleus Z of the contralateral side. At this level, these fibers enter the tecto‐reuniens tract and turn medially, to pass through and perhaps end on the intercalated neurons of nucleus Z, prior to their termination in nucleus reuniens. The neuronal architecture of nucleus Z and that of the nucleus reuniens complex are described. The latter, a midline nuclear group, consists of two subdivisions: a pars centralis and a pars diffusa. Each of these subdivisions is segregated into two neuronal aggregates at the midline. Efferents of the central nucleus terminate massively in the pars centralis and, to a considerably lesser extent, in the pars diffusa of nucleus reuniens.

The results of this study are compared with similar ones in pigeons and mammals. Parallels in the fiber connections of midbrain auditory and visual areas and the segregation of these modalities in the mesencephalon and diencephalon are discussed.
Fluorescence histochemistry of monoamine‐containing cell bodies in the brain stem of the squirrel monkey (Saimiri sciureus). III. Serotonin‐containing groups
Authors: Hubbard Jack E. , Carlo Vincenzo Di
Published: May 2005

The distribution and cytological characteristics of the serotonin‐containing cell bodies in the brain stem of the squirrel monkey (Saimiri sciureus) are described using the fluorescence histochemical technique of Falck and Hillarp for the demonstration of monoamines. Eight groups of serotonin‐containing neurons were found, located predominantly in the midline raphe region of the brain stem within defined nuclei, such as the nucleus raphe obscurus, nucleus raphe pallidus, nucleus raphe magnus, nucleus raphe pontis, nucleus raphe dorsalis and nucleus centralis superior. Portions of some of the groups also extend laterally in the brain stem, particularly at the levels of the upper pons and midbrain. The appearance and distribution of the serotonin‐containing groups of cell bodies in the squirrel monkey were found to be somewhat similar to that described for the rat, but differed in at least one major respect from that reported for the cat.
The optic tectum of a perciform teleost I. General configuration and cytoarchitecture
Authors: Vanegas Horacio , Laufer Miguel , Amat José
Published: May 2005

Golgi techniques have been employed to study the cytoarchitecture of the optic tectum in the perciform teleost Eugerres plumieri. The stratum marginale (SM) contains abundant fine axons which contact the spiny dendritic tree of large pyramidal neurons of the stratum fibrosum et griseum superficiale (SFGS). Such arborizations arise from a robust, naked apical dendritic shaft. The pyramidal neurons also have a basal dendritic shaft and an axon, both of which ramify in overlapping horizontal fields within the stratum griseum centrale (SGC). The SGC contains fusiform neurons with apical and basal dendritic shafts which ramify horizontally at the SFGS and just above the stratum album centrale (SAC), respectively; an axon “a crosse” originates from the apical shaft. Also in the SGC is the soma of the small pyriform neuron; from it originates a slender dendritic stem which branches out at the SM. Other neurons of SGC and SAC are the small and the large multipolar neurons, and the large pyriform neuron. The large pyriform neurons send a thick dendritic stem which gives horizontal branches mainly at the SFGS, and from which an axon “a crosse” originates. The stratum periventriculare contains small pyriform neurons whose slender dendritic stem ramifies at the stratum opticum as well as at other strata. No axon was seen to originate from these neurons.
The optic tectum of a perciform teleost III. Electron microscopy of degenerating retino‐tectal afferents
Authors: Laufer Miguel , Vanegas Horacio
Published: May 2005

Axonal and terminal degeneration has been studied with the electron microscope in the optic tectum of the teleost Eugerres plumieri, at 7, 15 and 35 days after eye enucleation. The distribution of degenerating elements corresponds to that found in light microscopical studies; it is confined to myelinated axons and terminals in stratum opticum, stratum fibrosum et griseum superficiale, and stratum album centrale. No degeneration was seen in other strata. Early axonal degeneration includes increase in filaments, sometimes accompanied by axoplasmic densification, as well as formation of vacuoles and membrane bound bodies. Myelin appears normal in a large proportion of axons at seven days after eye enucleation. Degenerating terminals may show increased number of filaments as well as densification, but neither reaction is marked; they show characteristic vacuoles and membrane bound bodies. Increase in vesicle size was observed only in few degenerating terminals. At 15 days after enucleation, there is myelin breakdown, bizarre axoplasmic inclusions, and glial and perivascular cell ingestion of debris. At 35 days, no terminals are found, and various stages of axonal degeneration are present.
Cytological evidence for catecholamine‐containing sensory cells bordering the ventricle of the toad hypothalamus
Authors: McKenna Olivia C. , Rosenbluth Jack
Published: May 2005

A laminar group of catecholamine‐containing cells bordering the infundibular recess of the toad hypothalamus has been studied by both fluorescence histochemical and electron microscopic methods. The perikarya of these cells form up to ten layers beneath the ependymal lining and send stout apical processes between the ependymal cells into the ventricle where they terminate as bulbous expansions. These cells fluoresce yellow‐green when studied by the method of Falck and Hillarp, indicating the presence of catecholamines. The fluorescence intensity is consistently greater in the bulbous ventricular endings than in the cell bodies and is greater in males than in females except when ovulation is induced. Electron microscopy shows that the ventricular bulb, apical process and cell body contain three distinctive cytoplasmic components: a population of dense cored vesicles (700 to 1500 Å in diameter), large aggregates of clear vesicles (440 to 600 Å in diameter) and mitochondria filled with crystalline inclusions. The nucleus is prominently lobulated. A slender process also extends from the base of the cell into the underlying neuropil; this basal process, however, contains only microtubules, a few vesicles of both types and a few mitochondria. The basal, lateral and apical surfaces of the cells form many synapses with neighboring processes. By and large these junctions are somatodendritic and are characterized by accumulations of either clear or a mixture of clear and dense cored vesiles against the perikaryal membrane. Axosomatic synapses in contrast occur only infrequently. The cytological characteristics of the cells suggest that their primary function may be to detect compounds in the cerebrospinal fluid and relay this information to neighboring neurons via the somatodendritic synapses.
Synaptic interactions of reticulospinal neurons and nerve cells in the spinal cord of the sea lamprey
Authors: Rovainen Carl M.
Published: May 2005

The reticulospinal system is the major descending pathway from the brain to the spinal cord in the sea lamprey, Petromyzon marinus. In order to determine the synaptic connections of this system and to gain a better understanding of its functions, individual cell bodies and axons of identified reticulospinal neurons were stimulated intracellularly while recording from spinal interneurons and motoneurons.

Stimulation of reticulospinal axons of the bulbar and vagal groups produced unitary composite EPSP's in lateral cells. Both components of these EPSP's followed repetitive presynaptic action potentials one‐to‐one at constant short latencies. The first component was due to electrical coupling between the cell and axon. The second component was due to chemical transmission because it was eliminated after extracellular Ca was replaced with Mg and because it changed in amplitude during repeated stimulation. Evidence is presented that the second component, as well as the first, is monosynaptic.

Both fast and slow motoneurons to myotomal muscle received a predominantly electrical synapse from the Müller axon I1. They also exhibited composite EPSP's after stimulation of M1, M3, some bulbar cells, and the Mauthner cell. Stimulation of ventral roots produced depolarizations in Müller axons which excited motoneurons. Polysynaptic EPSP's were observed in a fin motoneuron after stimulation of the contralateral axon M3 or I1.

Some edge cells exhibited a composite EPSP after stimulation of the bursting axon I2.

Morphologically mixed synapses with both chemical and electrical junctions were observed between Müller axons and unidentified dendrites.

The cells of origin of the bursting axons were the pair I2. Stimulation of these axons in situ produced either no movements or weak fin movements. No synaptic potentials were observed in motoneurons in the cord or in bulbar cells in the brain after stimulation of I2.

Intracellular stimulation of giant interneurons produced EPSP's in one pair of bulbar cells.

The conclusions drawn from this and the preceding study are as follows: (a) Connections of identified neurons in the lamprey are specific but do not always occur. (b) The majority of synapses from large axons to identified cells utilize dual electrical and chemical transmission. (c) Most unitary EPSP's are subthreshold. Thus, other sources of excitation, especially from smaller unidentified neurons, are required for activity.
Uptake of tracer proteins in the developing cerebellum, particularly by the growth cones and blood vessels
Authors: del Cerro Manuel
Published: May 2005

Tracer proteins ferritin (M. W. 500,000 daltons) and horseradish peroxidase (M. W. 40,000 daltons) were injected into the cerebella of suckling rats to study the uptake of macromolecules by growth cones and other structures in the developing nervous tissue. The animals were killed between 30 minutes and 6 hours after injection, and areas adjacent to, but excluding the injection site were studied by electron microscopy with optical microscopical controls.

At all time intervals both proteins were present in the extra‐ and intracellular compartments, although there was a clear time‐related increase of the concentration in the latter. Both tracers flowed through the intercellular gaps, permeated synaptic clefts, and concentrated in large amounts within the basal laminae of the pia mater and blood vessels. Upon crossing the laminae the markers were incorporated by pial and endothelial cells. The latter showed pinocytotic vesicles taking the marker at the abluminal surface and similarly labeled vesicles underneath the luminal surface or actually opening into the vascular lumina. Vessels of cerebella fixed by immersion showed similar uptake pattern and free tracer was found in the capillary lumina. These data indicate that a vesicle‐mediated transendothelial passage of proteins, from the parenchyma to the blood takes place under these experimental conditions.

The somata of neurons and glial cells showed a high degree of incorproation, the protein being taken by pinocytosis and stored in lysosomes. The vesicles populating growth cones (“growth vesicles”) regularly contained marker although in variable proportions. At any given time most of the vesicles in the glial cones were labeled, while only some were labeled in the axonal and dendritic cones. Since pinocytotic activity was low in growth cones, labeling of the “growth vesicles” could be tentatively explained by postulating that they become passively labeled when they open into and coalesce with the membrane of the cone (as in Bray's, '73, model). If that were the case differential labeling between neural and glial cones could be an indication of a differential rate of membrane increment and therefore a differential rate of growth. Alternative possiblities are considered.
Uniformity of monkey striate cortex: A parallel relationship between field size, scatter, and magnification factor
Authors: Hubel David H. , Wiesel Torsten N.
Published: May 2005

This paper is concerned with the relationship between orientation columns, ocular‐dominance columns, the topographic mapping of visual fields onto cortex, and receptive‐field size and scatter. Although the orientation columns are an order of magnitude smaller than the ocular‐dominance columns, the horizontal distance corresponding to a complete cycle of orientation columns, representing a rotation through 180°, seems to be roughly the same size as a left‐plus‐right ocular dominance set, with a thickness of about 0.5–1 mm, independent of eccentricity at least out to 15°. We use the term hypercolumn to refer to a complete set of either type (180°, or left‐plus‐right eyes).

In the macaque monkey several penetrations were made at various eccentricities in various parts of the striate cortex subserving the fovea, parafovea and midperiphery. As observed many times previously, in any vertical penetration there was an apparently random scatter in receptive‐field positions, which was of the same order of magnitude as the individual receptive fields in that part of the cortex; the field size and the scatter increased in parallel fashion with eccentricity. The movement through the visual field corresponding to a 1 mm horizontal movement along the cortex (the reciprocal of the magnification factor) also increased with eccentricity, in a manner that was strikingly parallel with the increase in receptive field size and scatter. In parts of the cortex representing retina, at least out to about 22° from the fovea, a movement along the cortical surface of about 1 mm was enough to displace the fields so that the new position they collectively occupied half overlapped the old. Such an overlap was thus produced by moving along the cortex a distance about equal to the thickness of a left‐plus‐right set of ocular‐dominance columns, or a complete 180° array of orientation columns. It therefore seems that, independent of eccentricity, a 2 mm × 2 mm block of cortex contains by a comfortable margin the machinery needed to analyze a region of visual field roughly equal to the local field size plus scatter. A movement of 2–3 mm corresponds to a new visual field region and to several new sets of hypercolumns. The cortex thus seems remarkably uniform physiologically, just as it is anatomically.
Ordered arrangement of orientation columns in monkeys lacking visual experience
Authors: Wiesel Torsten N. , Hubel David H.
Published: May 2005

The main object of this study was to see whether ordered sequences of orientation columns are present in very young visually naive monkeys. Recordings were made from area 17 in two macaque monkeys three and four weeks of age, whose eyes had been closed near the time of birth. The first monkey was born normally, but one day elapsed before eye closure could be done. The second was delivered by Cesarean section and the lids sutured shut immediately. The results in these two animals were very similar; in both, highly ordered sequences of orientation shifts were present, and were in no obvious way different from those seen in the adult. For example, average values for the size of orientation shifts, for the horizontal component of the distance between shifts, and for the slopes of orientation vs. track distance curves, were all similar to adult values. This indicates that the ordered column system is innately determined and not the result of early visual experience. In these two monkeys and a third one, sutured at two days and examined at 38 days, most of the cells seemed normal by adult standards, with simple, complex or hypercomplex receptive fields, showing about the same range in orientation specificity as is found in adults. About 10–15% of cells showed abnormalities similar to those seen in monkeys binocularly deprived of vision for longer periods. Furthermore, all three deprived monkeys showed a decided lack of cells that could be influenced from both eyes, whereas a normal three‐week‐old control animal seemed similar to the adult, with binocular cells comprising over half of the total population. A monkey deprived by binocular closure from the third to the seventh week also showed a diminution in number of binocularly influenced cells, suggesting that the deprivation from birth resulted in a deterioration of innate connections subserving binocular convergence. To be sure that the abnormalities in the deprived animals represented a deterioration of connections, we recorded from 23 cells in a normal two‐day‐old monkey: here the ocular dominance distribution of cells was about the same as in the adult, and the response characteristics of the cells were normal by adult standards.
A retinotopic analysis of the central connections of the optic nerve in the frog
Authors: Scalia Frank , Fite Katherine
Published: May 2005

The possibility of retinotopic organization in the optic nerve projections to the contralateral and ipsilateral diencephalon was studied by means of partial retinal lesions and staining for terminal degeneration by the Fink‐Heimer technique. A retinotopic pattern of projection was observed in the nucleus of Bellonci, the corpus geniculatum thalamicum and the posterior thalamic nucleus. The temporal quadrant of the retina, and, to a lesser extent, the ventral quadrant projected to the ipsilateral side as well as to the contralateral side. In each diencephalic region noted above, the temporal and dorsal quadrants of the retina were represented more posteriorly (posteroventrally), and ventral and nasal quadrants projected more anteriorly (anterodorsally). The areas of representation for the temporal and ventral quadrants were located superior (superoposterior) to those for the dorsal and nasal quadrants. In their overall configuration and orientation, the retino‐diencephalic maps show mirror‐image reversal with respect to the retino‐tectal projection. Since, in their areal extent, both the retino‐diencephalic maps and the retino‐tectal map are approximately parallel to the ventricular surface, their mirror‐image reversal appears to indicate a reversal in the polarity of developmental processes across the di‐mesencephalic junction.

The retinotopic organization within the optic tract in the diencephalon and tectum was also analyzed. In the optic tract, the quadrants of the retina are reassembled such that the dorsal and nasal quadrants are widely separated in, respectively, the ventral and dorsal edges of the tract; the temporal and ventral quadrants are systematically represented in intermediate levels in the tract, the temporal quadrant above the dorsal, and the ventral quadrant below the nasal. When the optic tract bifurcates to encircle the tectum, the fibers from the ventral and nasal quadrants enter the dorsomedial arm and the fibers from the temporal and dorsal quadrants enter the ventrolateral arm of the optic tract. The paths taken by optic fibers in traversing the tectum to reach their areas of termination were reconstructed. Many optic fibers show an alignment parallel to an anteroventral posterodorsal axis as they cross the surface of the tectum, but the OS vs IS characterization of the fibroarchitecture of the tectum appears to be an oversimplification.
The structure of the inferior lobe of the teleost hypothalamus
Authors: Demski L. S. , Evan A. P. , Saland L. C.
Published: May 2005

Electron microscopic and Golgi studies on the inferior lobes of sunfish and goldfish are described. The inferior lobe consists primarily of a nucleus ventricularis of densely packed cells surrounding the lateral recess of the third ventricle, and a peripherally situated nucleus diffusus consisting mostly of scattered neurons. A cell‐sparse zone of dense neuropil is located between the two cellular areas. Neurons of both nuclei have spiny dendrites and axons which originate from basal dendrites. In some cases axons are found to send a collateral into the cell‐sparse zone. Neurons of the nucleus diffusus possess collaterals that extend a considerable distance within the nucleus itself. The ultrastructure of cells of both nuclei reveals cytoplasmic organelles typical of most neurons. Synapses containing dense‐cored and clear vesicles are present on the spines and shafts of the dendrites of both neuronal types. In only rare cases synapses were observed on the soma of neurons of the nucleus ventricularis. Possible anatomical substrates involved in the control of feeding and aggression in teleosts are considered in light of the present findings. Morphological similarities of the inferior lobes and related areas in various fishes and amphibians are discussed and their possible significance for the understanding of the evolution of hypothalamic mechanisms is considered.
Distribution of ultrastructural tracers in crustacean axons
Authors: Nordlander Ruth H. , Masnyi Jerry A. , Singer Marcus
Published: May 2005

Ruthenium red and horseradish peroxidase were used to compare the uptake of exogenous molecules into crayfish motor axons and their sheaths in severed and intact peripheral nerves. Both tracers penetrated the axonal sheath and were subsequently seen lining small vesicles and tubules in the axoplasm. Tracer appeared to enter the axon via pinocytotic vesicles. There were no perceptible quantitative or qualitative differences in ruthenium red uptake between intact and severed axons. However, counts of tracer‐filled vesicles in axons exposed to peroxidase showed that at least three times as much tracer penetrated the severed as opposed to the intact axons.
Scanning electron microscopy of the subarachnoid space in the dog. III. Cranial levels
Authors: Allen Delmas J. , Low Frank N.
Published: May 2005

Young dogs were anesthetized by intrathoracic injection of sodium pentobarbital and perfused with buffered aldehydes. Lining tissue samples from the cranial subarachnoid space were prepared for scanning electron microscopy (SEM) by postfixing in buffered OsO4. Samples were then dehydrated, dried in a Critical Point Drying System, and coated with carbon and palladiumgold. Specimens were viewed in a Cambridge S4 scanning electron microscope. After thorough scanning, selected samples were routinely prepared for transmission electron microscopy (TEM) and viewed in a Philips EM‐200 transmission electron microscope.

This study depicts the surface morphology of the meningeal linings of the cranial subarachnoid space. The cranial pia mater possesses natural gaps or fenestrations between cells. SEM reveals a more complex morphology of arachnoid trabeculae than previously interpreted from light and transmission electron microscopy. Many free cells are observed on the meningeal linings of the subarachnoid space. The present study establishes that these free cells are macrophages by means of definitive TEM correlates. Microvillous‐like processes extending between macrophages and the pial surface are present. The frequency and the nature of these thin processes suggest the possibility of a plasmalemmamediated system of communication.
Surface fine structure of supraependymal elements and ependyma of hypothalamic third ventricle of mouse
Authors: Bleier Ruth
Published: May 2005

The ependymal surface of the hypothalamic third ventricle of the adult female and male mouse was examined with the scanning electron microscope. The material was dried with the critical point method. Supraependymal cells, exhibiting a variety of forms, lie among the cilia of the rostrodorsal two‐thirds of the ventricle. The cell bodies are usually between 8 and 10 μ in diameter and have dividing pseudopodial processes which may be broad or narrow, flat or stout, smooth or varicosed. The textured surfaces of the cells seen in this material appear to have no cilia, microvilli or membraneous folds though they may have small bleb‐like protrusions. Some cells and adjacent cilia bear clusters of friable‐looking material that may be secretory.

In several female mice, mounds of debris, that could be degenerating cells or secretory material, were seen in intimate association with clusters of cells. The cells' processes extend over and through the surface of the mound.

While some supraependymal cells may be neurons or glia, it is suggested that many of the cells seen may be morphological variants of one cell line, mononuclear phagocytes.

Sausage‐shaped structures at the end of long cilia‐like stalks are described and their possible identity discussed.
The connections and laminar organization of the optic tectum in a reptile (Iguana iguana)
Authors: Foster Robert E. , Hall William C.
Published: May 2005

The goals of this study were: (1) to describe the total pattern of projections from the optic tectum of Iguana iguana and Pseudemys scripta; and (2) to describe the contributions of particular lamina of the Iguana's optic tectum to this total pattern. Lesions were made in the optic tectum of the Iguana which damaged either all or only certain tectal laminae and, for comparison with the Iguana, lesions in the turtle's optic tectum were made which involved all laminae. The anterograde degeneration resulting from these lesions was stained with the Fink‐Heimer ('67) method. The total pattern of projections from the optic tectum in the Iguana and the turtle is similar to that reported for representatives of other vertebrate classes. That is, the optic tectum gives rise to ipsilateral ascending projections to pretectal nuclei, to nucleus rotundus and to nucleus geniculatus lateralis pars ventralis of the diencephalon and, in addition, to a contralateral ascending pathway which courses via the supraoptic decussation to the contralateral diencephalon. Tectotectal connections and several descending pathways were also recognized in each species. The descending pathways include ipsilateral tectobulbar and tecto‐isthmi pathways and a contralateral predorsal bundle.

Lesions which damaged only certain tectal laminae in the Iguana revealed a laminar organization of the efferent projections. A lesions restricted to the superficial retinal‐recipient layers, stratum griscum et album superficiale, resulted in degeneration in only nucleus isthmi pars magnocellularis and nucleus geniculatus lateralis pars ventralis. A lesion which involved both the retinal‐recipient layers and stratum griseum centrale resulted in degeneration in only one additional structure, nucleus rotundus. A small lesion involving the deep periventricular layer as well as the superficial layers produced degeneration in the predorsal bundle and the ipsilateral tectobulbar tract as well as in the structures receiving input from the more superficial layers. These results are compared to the results of similar analyses of the superior colliculus in mammals.
Unmyelinated preganglionic fibers in frog ventral roots
Authors: Vance W. Hugh , Clifton Guy L. , Applebaum M. L. , Willis William D. , Coggeshall Richard E.
Published: May 2005

It has been suggested that the preganglionic visceral fibers in the frog are unmyelinated. To obtain further evidence for this suggestion: (1) the percentages of unmyelinated fibers and the myelinated fiber histograms were done for all frog ventral roots, (2) the number of unmyelinated fibers were counted on either side of a chronic section of the seventh ventral root and (3) compound action potentials were obtained for roots 7–10. The results are that slightly more than 80% of the unmyelinated fibers in the seventh ventral root arise in the spinal cord and are presumably unmyelinated preganglionic efferents. Furthermore, a C fiber volley could be followed from the seventh ventral root into caudal parts of the sympathetic chain. Thus this data provides confirmation for the idea that many frog preganglionic fibers are unmyelinated. This study also shows that 24% of the ventral root axons in the frog are unmyelinated and that, on the basis of percentages of unmyelinated fibers and myelinated fiber histograms, there are five categories of frog ventral roots.
Hippocampal innervation by serotonin neurons of the midbrain raphe in the rat
Authors: Moore Robert Y. , Halaris Angelos E.
Published: May 2005

The organization of the brainstem serotonin neuron projection to the hippocampal formation was analyzed in the rat. This projection arises in the raphe nuclei of the midbrain. Following destruction of the midbrain raphe nuclei, chiefly nucleus centralis superior, there is a 72% decrease in hippocampal serotonin content. Injection of tritiated amino acid into the midbrain raphe nuclei results in transport of tritiated protein to the hippocampal formation and this transport is blocked in animals pretreated by intraventricular administration of 5,6‐dihydroxytryptamine (5,6‐DHT). Autoradiographic analysis indicates that the transport reaches the hippocampal formation primarily via two major pathways, the cingulum and the fornix. Cingulum fibers terminate predominantly in the dorsal hippocampus whereas the fornix distributes throughout the entire hippocampal formation. Some fibers reach the ventral hippocampus from the entorhinal area. Within the hippocampus there is dense labeling in a restricted lamina of the CA1 stratum lacunosum‐moleculare with moderate labeling in stratum radiatum. Stratum oriens is sparsely labeled in CA1 and moderately so in CA2 and CA3. Stratum radiatum and stratum lacunosum‐moleculare are moderately densely labeled in CA2 and CA3. The area dentata is sparsely to moderately labeled in the molecular layer and heavily labeled in a thin lamina of the hilar zone immediately beneath the granule cell layer. The remaining hilar zone is moderately labeled. All of the discrete labeling of the hippocampus and area dentata described above is absent in animals pretreated with 5,6‐DHT. These observations indicate that serotonin neurons of the midbrain raphe provide a highly organized innervation of the hippocampal formation in the rat.
Cellular architecture and topographic organization of the inferior colliculus of the squirrel monkey
Authors: FitzPatrick Kathleen A.
Published: May 2005

The inferior colliculus of the squirrel monkey is made up of a large central nucleus, bordered by the smaller external and pericentral nuclei. The majority of cells in the central nucleus exhibit a pronounced laminar arrangement due to the orientation of their dendrites. In medial sections of the nucleus these laminae lie in a dorsorostral to ventrocaudal direction. More laterally the layers assume a horizontal orientation and at the far lateral edge of the central nucleus come to lie in a ventrorostral to dorsocaudal orientation.

A single tonotopic representation of audible frequencies is present in the central nucleus. A regular progression of best frequencies from low to high is encountered as a microelectrode advances from dorsocaudal to ventrorostral in the sagittal plane. Penetrations in more medial regions of the central nucleus encounter neurons whose best frequencies represent a higher range of frequencies than those in the lateral parts. The orientation of the isofrequency laminae determined physiologically appears congruent with the orientation of the dendritic laminae.

The relative volume of the central nucleus devoted to each octave from 250 Hz to 32 kHz was determined. Frequencies up to eight kHz command successively larger amounts of collicular tissue. The octave band from 8 to 16 kHz is represented by the greatest amount of collicular tissue. Disproportionate representation of frequency may be the consequence of innervation density along the basilar membrane.
Architectonic map of neocortex of the normal mouse
Authors: Caviness Verne S.
Published: May 2005

The neocortex of the normal mouse has been subdivided into architectonic fields on the basis of its cellular and fiber patterns. The map of medial, retrohippocampal, frontal and insular regions is little different from that of Brodmann as modified in minor ways by Krieg. The map of parietal, occipital and temporal regions follows closely the major rearrangements introduced to Brodmann's map by Krieg. Krieg's map has been modified to give individual status to the barrel fields and to designate occipital fields around the full circumference of field 17, and temporal fields circumferentially around field 41.
Monkey retinal ganglion cells: Morphometric analysis and tracing of axonal projections, with a consideration of the peroxidase technique
Authors: Bunt Ann H. , Hendrickson Anita E. , Lund Jennifer S. , Lund Raymond D. , Fuchs Albert F.
Published: May 2005

This paper presents evidence on the retinal distribution and certral projections of retinal ganglion cells of various cell body sizes in the adul macaque monkey. The ganglion cell sizes have been determined by computer assisted measurement of camera lucida drawings at various eccentricities of both flat mounted and sectioned retinae. The pattern of projections of individual ganglion cells to the dorsal lateral geniculate nucleus and superior colliculus has been studied using retrograde axonal transport of horseradish peroxidase. Following peroxidase injections into the parvocellular laminae of the geniculate, virtually every ganglion cell was labeled within a circumscribed zone of the retina known to project to the region of the geniculate immediately surrounding the injection needle tip. After magnocellular injections, only the largest cells of the peripheral retina and approximately 26% of the ganglion cells of the parafovea were labeled. Peroxidase injections into the superior colliculus produced labeling of scattered ganglion cells of all sizes in the retina, although no labeled cells were found within the centralmost 10° eccentricity. From these observations it is concluded that all ganglion cells of the macaque retina project to the parvocellular layers of the dorsal lateral geniculate, but that only the largest ganglion cells of the more peripheral retina and not all cells of the parafovea project to the magnocellular laminae. In contrast, only scattered ganglion cells, although these are of all sizes, appear to project to the superior colliculus.

Two major problems with the peroxidase tracing technique are described:

The extent of stainable peroxidase activity around the injection site appears to be larger than the area of injected tracer actually available for uptake by axons to produce labeled cells.

Cut or damaged axons appear to incorporate peroxidase sufficiently to produce labeling of the cell body.