bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of the human cervical spinal cord with reference to synapse formation in the motro nucleus
Authors: Okado Nobuo
Published: January 2005

Synaptic development in the motor neuropil of the cervical spinal cord was quantitatively studied by light and electron microscopy in human embryos and fetuses ranging from five to 19 weeks of ovulation age. The numbers of axodendritic synapses increase substantially at the end of the eighth week. However, axosomatic synapses rapidly proliferate between 10.5 and 13 weeks of ovulation age. The increases in both types of synapses generally coincide with the behavioral chages in human fetuses that have been reported by other investigators. Only synaptic boutons containing spherical vesicles (S‐type synapses) were found in the motor neuropil throughout the stages examined; no synapses with flattened vesicles (F‐type synapses) were encountered. The majority of these synaptic boutons contain only a small number of synaptic vesicles (fewer than 20), although the number tends to increase with maturation. There is no significant maturational change in the size of synaptic vesicles. The present study suggests that synapse formation in the motor neuropil of the human fetus cervical spinal cord may continue up to 19 weeks of ovulation age because immature types of synapse are found in all fetuses. Myelin formation probably begins by the 11th week.
Naturally occurring alterations of cortical layers surrounding the fissura prima of rat cerebellum
Authors: Griffin W. S. T. , Eriksson M. A. E. , Del Cerro M. , Woodward D. J. , Stampfer N.
Published: January 2005

We have regularly observed alterations in the three‐layered arrangement of cerebellar cortex surrounding fissura prima in normal adult and neonatal rats. In 90 of 110 rat brains analyzed, the cortical layers surrounding fissura prima were found to be altered from the four‐layered (neonatal) or three‐layered (adult) arrangement found in the majority of the remainder of cerebellar cortex. This common alteration extended long distances (as much as 320 microns) on either side of the midline, causing fissura prima to become more and more shallow from its lateral to medial extent. In sagittal sections at the lateral edge of the alteration in neonatal cerebellum, the external granular layer and pial cells disappeared, leaving an expanse of molecular layer lying between internal granular layer cells of lobules V and VI. Proceeding medially toward the midsagittal region, the cells of the internal granular layer of lobules V and VI were situated closer together and often merged. In such sections Purkinje cells did not usually remain in a monolayer, but were displaced, and clusters of these cells were sometimes found within the white matter. Various complex configurations of internal granular layer, molecular layer, and Purkinje cell groups surrounding fissura prima were commonplace in regions of cerebellum as far lateral as 320 microns on either side of the midsagittal plane. The greatest dorsoventral extent of such alterations measured was 400 microns. The presence of these previously unreported deviations is unrelated to experimental stress, as they occur spontaneously, possibly due to a vestigeal disorganization left in midline zones after early cell migration phases.
Segmental organization of sympathetic preganglionic neurons in the mammalian spinal cord
Authors: Rubin Eric , Purves Dale
Published: January 2005

We have used retrograde transport of horseradish peroxidase to determine the distribution of the preganglionic cell bodies whose axons join particular rami of the thoracic spinal cord in a series of guinea pigs, and in a small number of hamsters and cats. In contrast to other recent studies, our results show that the neurons sending axons to a ramus are confined to a single segment at the corresponding spinal level. This segmental organization supports the idea that the rostro‐caudal position of preganglionic cell bodies is one determinant of selective synapse formation between preganglionic axons and sympathetic ganglion cells.
Correlation between soma size and dendritic morphology in cat retinal ganglion cells: Evidence of further variation in the γ‐cell class
Authors: Stone Jonathan , Clarke Rosemary
Published: January 2005

The morphology of ganglion cells in the cat's retina has been examined in Golgi‐impregnated whole mounts. The α‐, β, and γ‐cell groups described by Boycott and Wässle ('74) were observed. Also observed were may cells with wide dendritic fields typical of γ‐cells, and medium‐sized somas more usually associated with β‐cells. It is suggested that these cells belong to the γ‐cells group, adding to the variety already described by Boycott and Wässle among γ‐cells.
Distribution of small and medium‐sized ganglion cells in the cat's retina
Authors: Stone Jonathan , Keens Jeremy
Published: January 2005

The distributions of small and medium‐sized ganglion cells in the cat's retina have been studied.

The soma size ranges of ganglion cells projecting to the superior colliculus and the A‐laminae of the dorsal lateral geniculate nucleus were determined by the retrograde transport of horseradish peroxidase. Confirming previous work, the results suggest a division of the overall soma population into large, medium and small ranges. The large somas are the cell bodies of α‐ or Y‐cells; the small somas are the cell bodies of γ‐ or W‐cells, most of which project to the superior colliculus; and the medium‐sized somas include the cell bodies of β‐ or X‐cells and of γ‐ or W‐cells, most of which project to the forebrain.

The small‐soma (collicular‐projecting) cells have a strongly streaky distribution, i.e., the isodensity lines in a map of their distribution are markedly elongated horizontally. These cells form the principal component of the visual streak, especially in nasal retina. The medium‐soma (forebrain‐projecting) cells also show some streakiness, i.e., their isodensity lines are also elongated horizontally, but less markedly than for small cells. The results also show differences between nasal and temporal retina in the distributions of medium‐sized and small somas.

It is suggested that the patterns of distribution of small and medium cells may be reflected in the topography of visual centres of the midbrain and forebrain, respectively.
Patterns of cortico‐cortical connections related to tonotopic maps in cat auditory cortex
Authors: Imig Thomas J. , Reale Richard A.
Published: January 2005

Topographic distributions of cortico‐cortical projections from the primary (AI), anterior (A), posterior (P), ventroposterior (VP), and second (AII) auditory fields were studied in relation to tonotopic maps in combined anatomical and electrophysiological experiments. Distributions of axon terminals were determined by autoradiographic labeling with tritiated proline and leucine. Each of fields A, AI, P, and VP is connected with the other three in the same hemisphere as well as with a number of other auditory cortical areas. Additionally, neurons in each of the fields studied were found to project to the lateral bank of the collateral fissure. In general, regions near the injection site receive more densely labeled projections than do more distant targets. Neurons in each field were found to project to one or more areas in the opposite hemisphere. Only similar portions of the best‐frequency representations in fields A, AI, P, and VP are interconnected. A single isotope injection generally produced multiple patches of labeling within each of several cortical fields. Within AI, projections from contralateral fields A and AI and from ipsilateral fields A and P terminate in patches which are often elongated in a direction parallel to the low‐to‐high best‐frequency gradient. A divergence in the projections from one field upon another is apparent in many experiments. Within fields A, AI, P, and VP, patches of label are distributed along a band of cortex oriented parallel to isofrequency lines.
Lumbosacral predominance of vestibulospinal fibre projection in the rat
Authors: Shamboul K. M.
Published: January 2005

The somatotopic organization of the vestibulospinal tract (VST) and the percentages of cells of the lateral vestibular nucleus (LVN) contributing fibres to different regions of the spinal cord of the rat have not been studied before. These problems are investigated using the technique of retrograde cellular degeneration. Varying degrees of spinal cordotomies were performed at upper cervical, thoracic, and lumbar segments in 75 adult rats of Wistar strain. The animals were killed after varying survival periods and the brain stems were processed in the usual way. Chromatolytic neurons were observed in the ipsilateral lateral vestibular nucleus, and no such neurons were seen contralaterally. Following lumbar lesions, reacting neurons were condensed in the caudal two thirds, while with cervical and thoracic lesions, such neurons occupied more cranial levels in the nucleus. It is concluded that vestibulospinal fibres projecting to lumbosacral segments arise from the caudal two thirds of the nucleus, while those projecting to cervical and thoracic segments come from the cranial two thirds, those to the cervicals arise from the most cranial levels. The dense lumbosacral projection was attributed to the role played by the vestibulospinal fibres in maintaining extensor tonus of antigravity musculature, especially in the rat, which can effectively stand on its hindlimbs and use its free forelimbs for handling and examining objects.
Representations of the body surface in postcentral parietal cortex of Macaca fascicularis
Authors: Nelson R. J. , Sur M. , Felleman D. J. , Kaas J. H.
Published: January 2005

The somatotopic organization of the postcentral parietal cortex of the Old World monkey, Macaca fascicularis, was determined with multi‐unit microelectrode recordings. The results lead to the following conclusions: (1) There are at least two complete and systematic representations of the contralateral body surface in the cortex of the postcentral gyrus. One representation is contained within Area 3b, the other within Area 1. (2) While there are important differences in the organization of the two representations, they are basically mirror‐images of each other. (3) Each representation maintains body‐surface adjacency by cortical adjacency in some mediolateral regions. In other regions, two types of discontinuities can be described: first, in which adjacent body surfaces are represented in separate cortical loci; second, in which adjacent cortical regions represent disparate body‐surface regions. The internal organization of each representation is better described as a composite of somatotopic regions (Merzenich et al., '78) than as a serial array of dermatomal bands, or as a “homunculus.” (4) While architectonic Area 2 responds to stimulation of deep body tissue, at least parts of Area 2 also respond to cutaneous stimulation. The organization of the cutaneous representation of the hand in Area 2 is basically a mirror‐image of the hand representation in Area 1. (5) Area 3a is activated by deep body tissue stimulation, suggesting the possibility of a fourth body representation within the traditional “S‐I” region of somatosensory cortex in macaques. In accord with a previous study in a New World monkey (Merzenich et al., '78), we suggest that the cutaneous representation in Area 3b be considered as SI proper, and that the cutaneous representation in Area 1 be termed the posterior cutaneous field. Furthermore, based on the orientation of the representations of the body surface, as well as other factors, we suggest that the representation in Area 3b is homologous to “SmI” (or “SI”) in non‐primates.
Neuronal morphology of the rabbit cochlear nucleus
Authors: Disterhoft John F. , Perkins Randolph E. , Evans Scott
Published: January 2005

The cytoarchitecture of the cochlear nucleus in young adult albino rabbits (Cuniculus oryctologus) has been examined in Nissl‐ and Golgi‐impregnated material to compare rabbit cochlear nucleus with other mammalian species. Cochlear nucleus was subdivided into anteroventral (AVCN), posteroventral (PVCN), and dorsal (DCN) regions, as in other mammals. AVCN was characterized by bushy cells and stellate cells. The “bushy” dendritic trees of adjacent bushy cells often overlapped. PVCN was characterized by octopus, elongate, and stellate cells. The dendritic trees of adjacent octopus cells extended in a parallel array across the auditory nerve fibers. DCN had molecular, fusiform and polymorphic layers. The fusiform cell layer was especially prominent, with the fusiform cells appearing visually to be the organizing elements in DCN. The large cells in DCN were the fusiform and giant neurons; the medium cells were the stellate and elongate neurons; the small cells were the cartwheel, small stellate, and granule cells. The cochlear nucleus of rabbit is essentially similar in cytoarchitectural organization to other mammalian species which have been studied. The detailed morphology of the various cell types seen in Golgi preparations is quite similar to that of cat (Brawer et al., '74), although some differences do exist.
Location of motoneurons supplying individual muscles in normal and grafted supernumerary limbs of Xenopus laevis
Authors: Rubin David I. , Mendell Lorne M.
Published: January 2005

The purpose of this study was to investigate innervation of transplanted supernumerary hindlimbs in the frog (Xenopus laevis). Motoneurons innervating identified muscles in normal and supernumerary limbs were located by the method of retrograde transport of HRP after intramuscular injection. In the lumbar spinal cord of normal Xenopus, motoneurons supplying medial hindlimb muscles, which are derived from the ventral muscle mass during development, are located at the medial end of the motor column; those innervating lateral, dorsallyderived muscles, lie at the lateral end of the motor column. In animals with supernumerary limbs, motoneurons supplying the transplant usually occupied the same mediolateral position as those supplying the same muscle in the normal limb. However, the rostrocaudal location of these motor pools exhibited greater flexibility. When the transplant was innervated by a rostral nerve of the lumbar plexus, motoneurons supplying gastrocnemius could be located in a region of the spinal cord whose motoneurons do not normally innervate this muscle. There is thus no rigid requirement that gastrocnemius motoneurons be located at specific segmental levels. Motoneurons supplying gastrocnemius in the normal limb on the experimental side showed normal rostrocaudal distributions, indicating little rearrangement of these motor pools. Dorsal root ganglion cells labeled after HRP injection could be concentrated in a ganglion which normally supplies little or no innervation to the injected muscle. The location of these cells confirmed the segmental source of sensory innervation of the extra limb; i.e., there was no stray innervation. Animals with supernumerary limbs exhibited little or no increase in the number of motoneurons on the extra limb side. In contrast, dorsal root ganglion cell populations exhibited a large increase on the experimental side.
Ultrastructure of the pyramidal basket cells in the dentate gyrus of the rat
Authors: Ribak Charles E. , Anderson Lynn
Published: January 2005

Light and electron microscopic preparations were used to examine the somata and dendrites of the large pyramidal basket cells in the dentate gyrus. Results from previous Golgi studies have shown that the somata of these neurons are located beneath the granule cell layer and that their axons are distributed around the granule cell somata, where they form basket endings. The results of the present study indicate that the morphology of the pyramidal basket cell differs in many ways from that of the granule cell, aside from the obvious difference of their greater size. The pyramidal basket cells display infolded nuclei and intranuclear rods and sheets, and these characteristics are not found in granule cells. The pyramidal basket cells also show a greater abundance of cisternae of granular endoplasmic reticulum and other perikaryal organelles. Furthermore, the somata and the smooth dendrites of these neurons form both symmetric and asymmetric synaptic junctions. The results of this study indicate that the pyramidal basket cells have distinct ultrastructural characteristics that are shared by other GABAergic neurons in the cerebral cortex. It is suggested that some of these characteristics may underlie the role played by these cells in providing GABA‐mediated, tonic inhibition of other neurons.
Cortical connections of the pulvinar nucleus in Galago
Authors: Raczkowski Denis , Diamond I. T.
Published: January 2005

In the first series of experiments, small amounts of HRP were injected into areas 17, 18, and 19 and each of the cytoarchitectonic areas of the temporal lobe. The resulting distributions of labeled cells fell into a number of distinctive classes. For example, after injecting the temporal anterior area (Ta), the labeled cells occupied a band on the ventral border of the inferior division of the pulvinar complex; after injecting the temporal ventral area (Tv), the labeled cells were concentrated in the medial extremity of the superior division. In spite of the distinctiveness of these different distributions, there was evidence that in areas that we know to contain a representation of the visual field, the injection of the same part of the field led to labeled cells in the same part of the pulvinar nucleus. Thus, when the representation of the center of the field was injected in areas 17 or 18 or Tm (the temporal middle area), labeled cells were found in the dorsal part of the rostral half of the inferior division. The distinctiveness of the different distributions did not obscure certain features common to all experiments: labeled cells were always found in both subdivisions of the pulvinar complex, and there was always continuity between the population of labeled cells in the inferior division and the population of cells in the superior division.

Wherever the site of the injection in the extrastriate region, some labeled cells were found in the caudal half of the inferior division. Since the caudal half of the inferior division corresponds approximately to the tecto‐recipient zone as defined earlier, the entire temporal lobe, except for the auditory areas, is visual cortex. Evidence was also found for an overlap in the striate cortex between the projections of the lateral geniculate body and the pulvinar nucleus. In conclusion, the pulvinar complex projects to a vast area of cortex, including all of the occipital lobe and most of the lateral surface of the temporal lobe. This entire region, which comprises a good part of the whole of the neocortex, can be regarded as visual cortex.

A second series of experiments involved cortical injections of tritiated amino acids. The results showed that the projections from the thalamus to cortex were precisely reciprocated by descending projections from cortex to thalamus. The results also served as a way of confirming the results of the first set of experiments.
The pretectal region of the cat: A structural and topographical study with stereotaxic coordinates
Authors: Avendaño C. , Juretschke M. A.
Published: January 2005

Using Nissl and myelin staining methods, the structure of the pretectal region has been analyzed in the cat. From this study and a review of the literature, three groups of cell populations have been identified, each made up of several parts or nuclei: 1) Nuclei of the posterior commissure, including dorsal, lateral, and ventral divisions; 2) A dorsolateral group of nuclei, which includes the pars lateralis and pars medialis of the nucleus of the optic tract, and the nucleus olivaris; 3) An intermediate nuclear group (pretectal nuclei, “sensu stricto”) composed of the nuclei posterior, subopticus, anterior (with two portions, compacta and reticularis), and medialis.

Stereotaxic coordinates of this region were also determined and plotted both on coronal and horizontal sections. The combined use of several spatial planes has proven to be of great value in studying transitional regions such as the pretectal region.
Presence of the ruffed cell in the olfactory bulb of the catfish, Parasilurus asotus, and the sea eel, Conger myriaster
Authors: Kosaka Toshio , Hama Kiyoshi
Published: January 2005

The ruffed cell is present in the olfactory bulb of the catfish, Parasilurus asotus, and of the sea eel, Conger myriaster. Its morphological features have been studied by light microscopy, high‐voltage electron microscopy, and conventional electron microscopy.

The ruffed cell of the catfish is very similar to that of the goldfish in its location and in its structural features. It has a spheroidal or ovoid cell body about 15 to 30 μm in diameter. Several dendrites arise from the cell body to form a rounded dendritic field about 100 μm in diameter near the cell body. The initial unmyelinated portion of its axon (IP) consists of a shaft and many protrusions arising from it. The shaft, about 1 μm in diameter, extends for about 100 to 200 μm, where it acquires a myelin sheath. The protrusions intermingle with one another in a complex manner to form a rather discrete spheroidal field about 20 to 50 μm in diameter, located in the vicinity of the cell body.

In contrast, the ruffed cell of the sea eel differs rather significantly from that of the goldfish in its morphological features. The ruffed cell of the sea eel is of a bipolar type. One thick dendrite arises from the cell body and extends for about 50 to 100 μm, where it gives rise to many thread‐like dendritic branches. The IP arises from the cell body as a smooth thin process. However, about 30 to 70 μm distant from its origin, many elaborate protrusions arise from the axonal shaft. These intermingle with one another to form a spheroidal or ovoid field about 20 to 40 μm in diameter. Distal to this protrusion‐bearing part, the axon continues as a smooth, thin process.

In spite of these differences in structural features, the ruffed cell of the catfish and that of the sea eel are very similar in their synaptic features in the nest (the special synaptic field around the ruffed cell IP, composed of its protrusions, of granule cell dendrites, and of other neuronal processes); that is, synapses between the ruffed cell IP (its shaft and protrusions) and granule cell dendrites and serial synapses made by the ruffed cell IP, granule cell dendrites, and perinest cell dendrites.

These results suggest that the ruffed cell is generally present in the teleostean olfactory bulb, although its detailed structural features may vary from species to species. Moreover, the neuronal organization of the olfactory bulb seems to be fundamentally similar in various species of teleosts.
The sensitive period in the development of the trigeminal system of the neonatal rat
Authors: Belford Gary R. , Killackey Herbert P.
Published: January 2005

In previous studies we have described vibrissae‐related segmentation in the brainstem, thalamus, and cortex of the neonatal rat. Using succinic dehydrogenase (SDH) histochemistry, we delineated the time course in development of the normal segmentation at each level of the trigeminal system and the aberrant segmentation resulting from follicle damage at birth (Killackey and Belford, '79; Belford and Killackey, '79a, b). The present study examines the aberrant patterns that result from damage to the vibrissae follicles at different ages, comparing the patterns at the different levels of the trigeminal system.

The present study indicates a number of similarities between the central representations of the vibrissae. First, the patterns are similar within each of the three representations in the trigeminal nuclei for removal at a given age in a particular animal. These changes include a decrease in SDH density but a maintenance of normal row widths. Second, the patterns are similar within both the ventrobasal complex and layer IV of somatosensory cortex for removal at a given age in a particular animal. These changes include a fusion of individual clusters into bands, and a decrease in band width, but maintenance of normal SDH density. Third, the effects of damage to a row of vibrissae follicles at different ages are graded. Earlier damage produces more marked aberrations. Fourth, for all of the structures, the transition between bands and clusters occurs with damage at the same age. Further, the last age at which damage produces aberrant patterns is Day 3 for all of the structures. Thus, the data suggest that there is one sensitive period for pattern alteration in the entire central trigeminal system.
The organization of the lateral posterior nucleus in neonatal golden hamsters
Authors: Crain Barbara J. , Hall William C.
Published: January 2005

The present series of experiments was designed to study how synaptic relationships in the lateral posterior nucleus are altered after neonatal superior colliculus lesions. In this paper, we studied the lateral posterior nucleus with light and electron microscopic techniques at two critical stages: at the time of the initial neonatal tectal lesion and at the onset of the consequent proliferation of retinal axons.

At birth, the lateral posterior nucleus is very immature. Very few synapses are present and no degenerating terminals were found 6 hours after a tectal lesion. Thus, very few, if any, tectal axons have established connections in the nucleus by this time and the optic tract terminals which proliferate as a result of a neonatal tectal lesion are not simply taking over vacated postsynaptic sites.

Optic tract terminal proliferation begins 4 to 6 days after removal of the superior colliculus and parallels the development of the normal retinal projections to the superior colliculus and to the dorsal and ventral lateral geniculate bodies (So et al., '78). Thus, the proliferation appears to be an example of increased synapse formation during normal development rather than a case of true “axonal sprouting”.

At 6 to 7 days of age, when optic tract terminal proliferation is beginning, the neuropil is still very immature. The terminal types found in the adult nucleus cannot be identified and synaptic clusters have not yet formed. Thus, following neonatal tectal lesions, the lateral posterior nucleus must undergo most of its development not only in the absence of one of its normal projections, but also in the presence of at least one anomalous projection.
Innervation of the urinary bladder in higher primates
Authors: Rockswold Gaylan L. , Bradley William E. , Chou Shelley N.
Published: January 2005

Stimulating electrodes were placed on the terminal branches of the pelvic nerves to the urinary bladder and the pudendal nerve to the sphincters in seven Rhesus monkeys and two chimpanzees. The proximity of the electrodes to these structures assured organ specificity. Evoked responses produced by stimulation of these terminal nerve branches were recorded in the fascicles and rootlets of the lower thoracic, lumbar, and sacral nerve roots. During identifical stimulating and recording conditions, the amplitude as well as presence or absence of the evoked responses recorded was variable within the various roots. The amplitude of the evoked responses or their absence depended on the number of fibers within a particular fascicle which conducted impulses to the urinary bladder or the urethral and anal sphincters. By this method, it was determined that there was segregation or compartmentalization of the nervous innervation to the urinary bladder and sphincters within the spinal roots.

In addition, the segmental spinal cord origin of the innervation of the urinary bladder was determined for the Rhesus monkey and chimpanzee. In the Rhesus monkey, the pelvic nerves to the urinary bladder arose from the first and second sacral segments and to a much lesser extent from the seventh lumbar segment. In the chimpanzee the sacral segments one to four gave rise to innervation of the urinary bladder.
Innervation of the external urethral and external anal sphincters in higher primates
Authors: Rockswold Gaylan L. , Bradley William E. , Chou Shelley N.
Published: January 2005

Stimulating electrodes were placed on the terminal branches of the pudendal nerve to the external urethral and external anal sphincters. The proximity of the electrodes to the sphincters assured organ specificity. Evoked responses produced by stimulation of these terminal nerve branches were recorded in the fascicles and rootlets of the lower thoracic, lumbar, and sacral nerve roots. By this method, the segmental spinal cord origin of the innervation of the external urethral and anal sphincters was determined for the Rhesus monkey and chimpanzee. The data indicated that the pudendal nerves to the urethral and anal sphincters in the Rhesus monkey arose from the sixth and seventh lumbar spinal segments and the first and second sacral spinal segments which are homologous to the S‐1 and S‐4 segments found to give innervation to these structures in the chimpanzee. The primate experiments thus indicate that the spinal origin of the pudendal nerve was more rostrally located by one segment or more than was the origin of the pelvic nerves to the urinary bladder.
Use of carbon labeling to demonstrate the role of blood monocytes as precursors of the ‘ameboid cells’ present in the corpus callosum of postnatal rats
Authors: Ling E. A. , Penney Don , Leblond C. P.
Published: January 2005

Cells with features suggestive of ameboid motion and phagocytic properties are observed in the rat corpus callosum during the first few days of life. These cells, herafter referred to as ‘ameboid cells’, have been investigated in several ways.

An electron microscopic study of the corpus callosum in 5‐ to 7‐day‐old rats indicated that most ‘ameboid cells’ were typical macrophages, but some displayed features of monocytes, while others appeared to be transitional between the two types. These observations raised the possibility that blood monocytes were the precursors of ‘ameboid cells’.

This possibility was tested by injecting a suspension of carbon particles into the circulation of rats of various ages to label and trace monocytes. Within 15 minutes after injection, carbon particles were seen between cells in blood smears as well as in the lumen of capillaries, but not between cells and axons in corpus callosum. By a half hour, a few of the circulating monocytes, and with time, up to half of them, contained carbon particles. Five days after injection, carbon particles were observed in cells of the corpus callosum identified as ‘ameboid cells’ of the monocytic and macrophagic type. Such carbon‐containing cells were seen in many of the animals injected at the age of 0–1 day, in few of those injected at 3–5 days, and in none of the older animals. Since free carbon had not been observed in corpus callosum spaces, it was concluded that ‘ameboid cells’ did not pick up carbon locally. The alternative was that blood monocytes, after ingesting carbon particles in the circulation, migrated to the corpus callosum and settled as ‘ameboid cells’.

In the hope of obtaining a direct confirmation of this conclusion, blood cells obtained from carbon‐injected Lewis rats were centrifuged in a Percoll gradient to obtain a fraction which contained 70–80% monocytes, less than 2% granulocytes, and 20–30% lymphocytes. Carbon was present in up to half on the monocytes and 1% of the granulocytes, but not in the lymphocytes; and it was calculated that over 99% of the carbon‐labeled cells were monocytes. The cell fraction was then introduced into the blood circulation of 2‐ to 3‐day‐old syngeneic Lewis rats, and the animals were sacrificed 5 days later. Occasional carbon‐labeled cells appeared not only in liver, spleen and connective tissue, but also in the corpus callosum, where they were identified as ‘ameboid cells’ of the monocytic and macrophagic type. Even though such cells were infrequent, their presence conclusively demonstrated that at least some ‘ameboid cells’ of the corpus callosum were derived from circulating blood monocytes.
Uptake, intra‐axonal transport and fate of horseradish peroxidase in embryonic spinal neurons of the chick
Authors: Chu‐Wang I‐Wu , Oppenheim Ronald W.
Published: January 2005

Horseradish peroxidase (HRP) was injected in ovo into the ventral muscle mass of the hind limb of 5‐ to 7‐day‐old chick embryos or into the gastrocnemius muscle of 8‐ to 18‐day embryos and localized histochemically.

HRP is extensively incorporated via endocytosis into axonal growth cones or presynaptic terminals in the proximity of the injection site. Much of the tracer is taken up in vesicles and small vacuoles. Most of these are smooth‐surfaced and only a few are bristle‐coated. A small amount of the tracer is also incorporated into the axon terminal through the openings between the axolemma and an intricate membrane channel. The majority of the tracer‐laden vesicles and vacuoles rapidly fuse with one another to become large vacuoles, some of which are transformed into multivesicular bodies (MVBs). In axon shafts, many labeled vacuoles and MVBs are transferred to tubule‐like organelles, which appear to be the primary carrier for transporting the tracer back to the cell bodies in the lumbar spinal cord. HRP arrives in the sensory ganglia about 0.5–1 hour earlier than in the motoneurons of the lateral motor column. The maximal rate of the retrograde axoplasmic transport is about 3.5 mm/hour. After arriving in the cell bodies, HRP is transferred from tubule‐like organelles to discrete vacuoles of various sizes and appearance. Lysosomal dense bodies and HRP‐labeled vacoules can be distinguished ultrastructurally. A fusion of HRP‐labeled vacuoles with lysosomal dense bodies or Golgi vesicles was occasionally observed and the density of HRP‐labeled vacuoles diminished after 2 to 3 days. Most of the HRP‐labeled organelles were found to contain acid phosphatase activity. Therefore, the complete disappearance of HRP by 4 days postinjection is most likely related to lysosomal degradation.

Neuronal cell bodies diffusely labeled with HRP were only observed prior to day 6. After day 6, despite various attempts to injure the peripheral axons, only granularly labeled cell bodies were found. This difference may imply that ‘mature’ neurons have a more efficient mechanism for the sequestration of ‘free’ HRP in the cytoplasmic matrix into membrane‐bounded organelles.

A mature‐like retrograde transport mechanism appears to exist at the earliest stages of axonal growth in vivo.
The estrogen‐sensitive neural system in the brain of female cats
Authors: Rees Howard D. , Switz Genevieve M. , Michael Richard P.
Published: January 2005

Estrogens participate in the regulation of gonadotropin secretion and in the control of sexual and aggressive behavior. To elucidate the neuroanatomical substrate for these actions in the female cat, the topographical distribution of estrogen‐concentrating cells in the brain was studied by autoradiography. One hour after the intravenous injection of 1 mCi (3 μg) of 3H‐estradiol in three adult ovariectomized cats, radioactivity was concentrated in the nuclei of neurons in several brain areas. Within the telencephalon, high concentrations of moderately to heavily labeled cells were found in the lateral and posterior septal nuclei (n.), bed n. of the stria terminalis (medial division), medial and central amygdaloid n., and amygdalo‐hippocampal area. There were also many less strongly labeled cells in the ventral dentate gyrus. Within the diencephalon, many heavily labeled cells were distributed in the medial and periventricular preoptic n., anterior hypothalamic area, and infundibular, ventromedial, and periventricular hypothalamic n. In the brain stem, some labeled cells were located throughout the periaqueductal gray, and in the laminar spinal trigeminal n., n. of the solitary tract, n. incertus, marginal n. of the superior cerebellar peduncle, rostral linear n., and interfascicular n. Although minor differences were noted, the topographical distribution of estradiol‐concentrating cells in the femal cat brain agreed closely with that reported in other vertebrate species.
Ordinal position and afferent input of neurons in monkey striate cortex
Authors: Bullier Jean , Henry Geoffrey H.
Published: January 2005

From the extracellular recording of single units in the monkey striate cortex and electrical stimulation at two selected sites in the optic radiations it was possible to estimate (1) the ordinal position of striate neurons (i.e., whether they received a monosynaptic, disynaptic or polysynaptic input from the thalamus) and (2) the nature of the afferent input to these neurons (i.e., whether it came from the magnocellular or parvocellular subdivision of the lateral geniculate nucleus (LGN)). Based on receptive field properties six major classes of striate neuron were identified—three which lacked orientation specificity (the ON‐center, the OFF‐center, and the ON/OFF or nonoriented (N‐0) receptive fields) and three with orientation specific responses (the S, the C, and the B categories of receptive field). Units lacking orientation specificity were concentrated in laminae 4A, 4Cβ and 6 while, for the cells with orientation specificity, C cells were found in laminae 4B and 6, B cells in 2/3 and 5, and S cells predominantly in laminae 2/3, 4Cα, and 5.

The results of electrical stimulation indicated that cell‐to‐cell transmission time in the monkey striate cortex is 1.5 msec, and latency measures showed that cells with a monosynaptic drive from the thalamus were confined to laminae 4 and 6 while disynaptically driven cells were found principally in upper lamina 4 (4A and 4B). No cell class was identified exclusively with a given ordinal position and there were many types of potential first‐order neurons.

The conduction time from one stimulating electrode to the next in the optic radiation was used to identify the afferent input to each striate neuron. The input to color‐coded neurones was found to come exclusively from parvocellular layers while the C cells and two subclasses of the S cell (S2 and S3) were driven predominantly by the magnocellular subdivision. For other cell types (those with ON‐center, N‐0, and S1 receptive fields) the input came from either type of LGN neuron.

The laminar distribution of neurons receiving a direct input from the magnocellular and parvocellular streams is in accord with the results of anatomical studies into the site of termination of the LGN input. The cell types receiving these direct inputs vary in the two streams so that the parvocellular input terminates on cells with ON‐center and N‐0 receptive fields in lamina 4Cβ while the magnocellular input goes to cells with S, ON‐center, N‐0, and C receptive fields in lamina 4Cα and the lower part of 4B.

Consideration is given to the influence of these results on models for neural processing in monkey striate cortex and a comparison is drawn with the results of similar studies in the cat.
Effects of undernutrition on myelination in rat corpus callosum
Authors: Lai Mabel , Lewis Paul D.
Published: January 2005

Rats were undernourished by halving the mother's food intake from the sixth day of pregnancy onwards and through lactation. Subsequently, the young animals were maintained up to 48 days on half the normal diet. The effects of this regime of treatment on myelination in the corpus callosum were investigated by light and electron microscopy.

In comparison with controls, the percentage of axons myelinated at 15, 21, and 48 days was reduced in undernourished rats. The number of lamellae constituting the myelin sheath was also reduced at 15 and 21 days, but at 48 days no difference was seen between control and treated rats, suggesting that a catch‐up in myelination had occured. A linear relationship between myelin sheath thickness and axonal diameter was observed in both groups of animals. However, a long‐term effect on axonal growth was suggested by findings in the 48‐day undernourished animals; in comparison with controls, axonal diameter was reduced, relative to myelin sheath thickness.
Excitation and inhibition of marginal layer and interstitial interneurons in cat nucleus caudalis by mechanical stimuli
Authors: Hubbard J. I. , Hellon R. F.
Published: January 2005

In cats anesthetized with urethane, the caudal medulla was stabilized in preparation for intracellular recording from interstitial neurons in the descending tract of the trigeminal nerve and from neurons in lamina I of nucleus caudalis. Glass micropipets (10–50 M ohms) were advanced from the surface to a maximum depth of 350 μm. When DC potential shifts occurred, it was found that mechanical stimuli to the face generated bursts of positive‐going spikes, followed in some cases by inhibitory postsynaptic potentials (IPSPs). Subdermal electrical stimulation of the face in each receptive field almost always enabled the same neuron to be driven electrically.

Recordings were classified as from primary afferent fibers or from interneurons. Primary fibers had a purely positive spike, with a latency varying by no more than 0.05 msec, and could follow stimulation at 500 Hz. The mean latency for the fibers was 1.87 ± 0.06 msec (n = 75), and their absolute refractory period was 0.42 ± 0.02 msec (n = 36).

Recordings were classed as from interneurons if there was an IPSP or the latency was at least 4 msec, with a variation of latency of at least 0.5 msec. Responses thought to be monosynaptically driven had a mean latency of 2.09 ± 0.07 msec (n = 32) and could follow pairs of stimuli at a mean minimum interval of 0.70 ± 0.06 msec (n = 20). Responses thought to be polysynaptically driven had a mean latency of 7.9 ± 1.08 msec (n = 49) and a mean interstimulus interval of 2.96 ± 0.84 (n = 20). Most responses were generated by brushing the face (n = 87), some by pressure on the face (n = 25), and a few by pinching the skin of the face (n = 6).

Interneuron responses were most commonly recorded in the first 200 μm of the descending tract, and this position was confirmed by the injection of pontamine sky blue and the examination of frozen sections. The recordings were thought to be from dendrites of marginal and interstitial cells or the somas of interstitial cells.

The IPSPs which followed spike potentials could only follow stimuli at 10 Hz or less. The failure appeared to be at a primary afferent synapse upon an inhibitory interneuron.

Collision tests between mechanically evoked and electrically evoked responses showed long‐lasting inhibition of the response to electrical stimulation after collision. Presynaptic inhibition exerted on the primary afferent excitation was suggested as the explanation.
Normal dendritic morphology of frog spinal motoneurons: A Golgi study
Authors: Bregman Barbara S. , Cruce William L. R.
Published: January 2005

Normal dendritic morphology of frog (Rana pipiens) lumbar motoneurons was studied using Golgi silver impregnation. Branching characteristics and quantitative measurements of dendrites were obtained using computeraided serial reconstruction of a typical lumbar motoneuron over seven adjacent 80‐μm transverse sections. Dendrites were classified based upon site of dendrite origin from the soma and distribution of the dendritic array within the spinal cord.

Eight possible sites of dendritic origin from the soma were identified. Two dendrites, D1 and D2, are planar dendrites which arise from the dorsal aspect of the soma. They are moderately complex, reaching branch order 5–6, and are oriented predominantly in the transverse plane. Input to these dendrites is primarily segmental via dorsal root projections.

Three dendrites, D3, D4, and D5, arise laterally from the soma and extend through the lateral funiculus toward the subpial region. Two dendrites, D6 and D7, arise ventrally. D6 extends ventrolaterally and is a simple dendrite reaching branch order 3–4. D7 aborizes extensively in the ventral funiculus and in the central gray, reaching a branch order of 8–9. This dendrite extends rostrally and caudally over a distance of at least 560 μm. Another dendrite (D8) arises from the medial aspect of the soma and projects toward the central canal.

Four sites (D1, D2, D6, and D7) almost invariably give rise to dendrites. Dendrites arise at D4 in 66% of the cells examined. Dendrites are found at D3, D5, and D8 much less frequently (6–21%). Total dendritic length (12,043 μm) and lengths of the individual dendrites, branch length versus branch order, and number of branches at increasing radii were examined, and Sholl analysis was performed.
The Purkinje neuron: I. A Golgi study of its development in the mouse and in culture
Authors: Hendelman W. J. , Aggerwal A. S.
Published: January 2005

The development of the Purkinje neuron was studied in organotypic culture and compared to that occurring in the intact animal, using a modified Golgi‐Cox method. The post‐natal sequence of development in the intact animal occurred in five distinct stages beginning with (1) an immature state (0–3 days), (2) a stage of perisomatic dendritic processes (4–6 days), and then (3) a stage characterized by the presence of spines on the soma region (7–10 days). This stage of somatic spines has not been delineated previously in Golgi studies of the Purkinje cell during its development. There was no evidence that the lateral somatic processes resorb; rather they continue to grow and develop into dendritic branches. It is proposed that by a process of perikaryal translocation, the soma region becomes transferred “downward,” resulting in an elongation of the primary, apical dendrite (stage 4, 11–14 days). Beyond 15 days (stage 5) the dendritic branches grow to the pial surface and the neuron has its full complement of secondary, tertiary, and spiny branches. In culture, the development parallels that occurring in the intact animal during the first 10 days (stages 1, 2, 3) despite the absence of extracerebellar afferents and the special conditions of the culture. However, there is an overall absence of lamination of the cortex, the Purkinje neurons do not align, and the development process is modified because of the failure of the process of perikaryal translocation in culture. The resultant mature neuron has an altered morphology characterized by the presence of several dendrites and spines attached to the soma, and also lacks the complete development of the smaller dendritic branches.
Development of excitatory innervation in the lobster claw closer muscle
Authors: King J. A. , Govind C. K.
Published: January 2005

The development of excitatory innervation to the claw closer muscles of 1st (larval), 4th (juvenile), and adult stage lobster was examined by thin serial section electron microscopy. This was possible since neuromuscular terminals of the excitatory axon are distinguishable from those of the inhibitory axon by the shape of their synaptic vesicles in all three stages. In the adult cutter claw closer muscle, innervation of a dorsal and a ventral fiber which is supplied by the fast closer excitor (FCE) and slow closer excitor (SCE) axons respectively, was qualitatively as well as quantitatively similar. Consequently no attempt was made to distinguish between innervation by FCE and SCE axons in the subsequent analysis of 1st, 4th, and adult stage claw closer muscles. Excitatory innervation in the 1st larval stage is limited to four discrete locations in the entire cross‐sectional area of the closer muscle. It subsequently spreads to each individual muscle fiber in the adult, thus demonstrating the tremendous proliferation of innervation during development. Concomitantly the mean size of synapses increases significantly from the 1st stage to the 4th stage to the adult lobster. This increase in synaptic size may occur by both the fusion and enlargement of existing smaller synapses. In contrast, the mean size of presynaptic dense bars and their mean number per synapse remained fairly constant in each of the 1st, 4th, and adult stages. However, a relatively greater proportion of adult synapses possessed two or more dense bars compared to their larval and juvenile counterparts. Development of innervation of the lobster claw closer muscle therefore consists of a substantial proliferation of axonal tissue and enlargement of synaptic size.