bluuebunny/crossref_metadata_2025 huggingface dataset:
Patterns of degeneration in the external cuneate nucleus after multiple dorsal rhizotomies
Authors: Rosenstein Jeffrey M. , Page Robert B. , Leure‐DuPree Alphonse E.
Published: December 2004

Unilateral, intradural dorsal rhizotomies (C3‐C8) were performed on adult rats to study the patterns of synaptic organization of ascending dorsal root fibers in the external cuneate nucleus (ECN). Animals were permitted to survive for periods of time ranging from 3hours to 12 days. Sham‐operated animals presented a morphology indistinguishable from that of normal, unoperated animals. In rhizotomized animals, degeneration was observed ipsilaterally at all survival periods. After postoperative survivals of 3 to 14 hours some terminal boutons displayed clumbing and diminution in numbers of synaptic vesicles and, in addition, degenerating myelinated axons were observed at this time. There was considerable degeneration in the neuropil between 24 and 48 hours postoperative. Two forms of degeneration occurred in axons and terminal boutons with comparable frequency: electron lucent degeneration and electron opaque degeneration. Reactive phagocytic glial cells contained degenerated masses, lipoid droplets, lysosome‐like structures and myelin fragments. After postoperative survivals of four to six days, lucent and opaque degenerating terminals were less numerous. Neurofilamentous degeneration was observed only occasionally. Unaltered synaptic membrane specializations were present and were usually abutted by glia. At 12 days postoperative, synaptic glomeruli and serial synapses were not seen. Invaginating dendritic spines were rarely seen. Bouton populations that remained unaltered were: small (0.3‐3.0 μm) boutons that contact dendritic shafts and somata, nodal synaptic boutons and boutons containing granular vesicles (80–100nm).
Development of outer segments and synapses in the rabbit retina
Authors: McArdle Craig Bryant , Dowling John E. , Masland Richard H.
Published: December 2004

The peripheral retina of rabbits aged 0 to 60 days was studied by electron microscopy. Ribbon and conventional synaptogenesis was studied with serial sections, and the density of synapses of the inner plexiform layer was measured on large (1,500μm2) montages.

Photoreceptor and bipolar ribbon synapses seem to develop similarly in that processes of the prospective dyad or triad contact the presynaptic ribbon‐containing terminal one at a time. No statistically significant difference in the lengths of ribbon lamellae was found at 11 and 30 days. Conventional synapses appear to result from the aggregation of synaptic vesicles on one side of junctions that first existed as symmetrical membrane densities without vesicles. The length of the synaptic membrane specialization remains constant between 0 and 30 days.

The density of inner plexiform layer conventional synapses remains at a low and roughly constant level from 0 to 9 days, after which there is an abrupt increase to a plateau at about 20 days. After nine days the density of ribbon synapses also increases, with an initially steep time course similar to that of conventional synapses. All subcategories of synapse studied (amacrine‐to‐amacrine, amacrine‐to‐bipolar, serial, and reciprocal) participate in the general increase between 9 and 20 days. Functional circuits of the inner plexiform layer thus seem to be assembled primarily during the second and third weeks of life.
Maturation of function in the developing rabbit retina
Authors: Masland Richard H.
Published: December 2004

Retinas isolated from rabbits aged less than eight hours to adult were maintained in a flowing physiological medium. The electroretinogram or activity of single ganglion cells were recorded, and receptive fields were studied using stimulation of the retina with focused light. Retinal activity was stable for at least eight hours of incubation.

Retinal ganglion cells are electrophysiologically active on the first day of life. They generate spontaneous bursts of action potentials at rates of 10 to 30 spikes/ sec, separated by silent intervals of one to six minutes. Maintained trains of action potentials follow elevation of the concentration of K+ in the incubating medium to 10 mM. Ganglion cells are also stimulated by acetylcholine, with apparent threshols equal to or lower than those of ganglion cells in adult retinas.

The first response of the retina to light is a small cornea‐negative transretinal potential at day 6, presumably PIII of the electroretinogram. Responses of the ganglion cells are seen at eight days, but the responses are weak and adapt quickly to repeated stimulation. Many unresponsive cells are present. By ten days 60% of ganglion cells respond to light, and examples of mature receptive fields are present. Immature receptive fields at ten days fall into two rough classes, one characterized by a large responsive area with no antagonistic surround, and a second in which the surround can suppress the response to illumination of the center but can not itself cause a discharge. Immature fields are progressively replaced by mature ones, and by 20 days the qualitative organization of receptive fields is indistinguishable from adult.
Cytoarchitecture of the tectum mesencephali in two types of siluroid teleosts
Authors: Schroeder Dolores M. , Vanegas Horacio
Published: December 2004

The cytoarchitecture of the tectum mesencephali in the siluroid teleosts Bagrus and Ictalurus was studied by means of the Golgi method. These animals are known to have a restricted visual system and it seemed important to study whether this fact would affect the existence or the shape of the main neuron types which have been described for highly visual teleosts. It had been shown for a variety of teleosts that the retinotectal axons and terminals occupy almost exclusively the stratum opticum and the stratum fibrosum et griseum superficiale. The thickness of these strata in Bagrus and Ictalurus was found to be reduced. However, the main types of especially the vertically oriented neurons, such as the pyramidal, fusiform, large pyriform and periventricular neurons which have been described for highly visual species of teleosts, were also found in Bagrus and Ictalurus. Although their shape was somewhat distorted, these neurons, nevertheless, showed processes distributed to the same tectal layers as in highly visual teleosts and are accessible to horizontally distributed fiber systems such as marginal, telencephalotectal and commissural tectal fibers, as well as the retinotectal fibers. Nonvisual inputs appear to be considerably involved in the maintenance of the main neuron types in the siluroid tectum. For example, the pyramidal neuron's apical dendritic tree, which receives the excitatory input from the marginal fibers, is as well developed in siluroids as in highly visual teleosts.
Laminar differentiation of the hippocampus, fascia dentata and subiculum in developing rats, observed with the timm sulphide silver method
Authors: Zimmer Jens , Haug Finn‐Mogens Š.
Published: December 2004

The laminar staining of the rat hippocampal region with the Timm sulphide silver method is from studies on adult rats known to depend on the various fibersystems terminating in these laminae. In order to illustrate the development of these fibersystems the laminar differentiation of the Timm staining of fascia dentata, hippocampus and subiculum is presented for rats between 1 and 31 days old. Corresponding changes in cytoarchitectonics as revealed by thionin staining are briefly demonstrated.

Even on the first postnatal day there are indications of the mature, laminar staining pattern, and between three and nine days all the laminae corresponding to the terminal fields of the major afferent and intrinsic systems appear. After 12 days only minor additions to the laminar pattern develop, but there are adjustments of absolute and relative dimensions of layers and fields, and also the staining densities of individual laminae change.

These observations are in good correlation with the available information on both hippocampal neurogenesis and cytodifferentiation, and the few fiber tracing studies performed on the developing hippocampal region. Compared to the latter, which ideally marks only one system or one lamina per animal, the Timm method provides an excellent means for getting an overview of the general developmental situation at the different ages. Thus developmental gradients along septo‐temporal, medio‐lateral and basal‐apical axes are found, which should be heeded in future studies on hippocampal synaptogenesis.

The observations are discussed in relation to current models for neuronal growth and formation of nervous connections.
A comparative study of the immunohistochemical localization of basic protein to myelin and oligodendrocytes in rat and chicken brain
Authors: Hartman Boyd K. , Agrawal Harish C. , Kalmbach Sandra , Shearer William T.
Published: December 2004

Antisera to highly purified basic protein (BP)7 from rat and chicken brain were prepared and their purity and specificity demonstrated by double immunodiffusion and cross‐immunoadsorption. These antisera were used for immunohistochemical localization of BP in the brains of adult and developing rat and chick.

Myelin basic protein was exclusively localized to myelin or the myelin forming elements of the CNS. It was present in high concentrations in white matter and absent in areas free of myelin. Neuronal parikarya and dendrites were negative as were axons cut in cross section and at Nodes of Ranvier. The latter was best observed in cross sections of human spinal cord demonstrating also the immunoreactivity of the antibodies with human BP. The internodal distance in a fine (1.5 μm) rat cortical fiber was determined to be approximately 45 μm. Myelin basic protein was shown to extend into cranial roots, in contrast to myelin proteolipid protein which abruptly lost fluorescence as the nerves emerged from the brain.

During development, BP was first observed on the fourteenth day of incubation in chick and at birth in the rat. The protein appeared in oligodendrocyted and in association with fibers near these cells. Fluorescent processes were frequently observed connecting the oligodendrocytes with the fibers. As myelination progressed, the intensity of the immunohistochemical reaction decreased in the oligodendrocytes while the brightness in fibers increase. Eventually, the oligodendrocytes became undetectable. Fibers with immature myelin exhibited a beaded or varicosed appearance with the highest concentration of immunofluorescence in the outer portion of the varicosities. The varicosities were postulated to represent dilations in the newly forming sheath between intervals of compaction along the axon undergoing myelination. These dilations might represent areas of increased cytoplasmic volume which could serve as channels for transport and/or storage sites for myelin proteins prior to incorporation into the membrane. The varicosities became less prominent with the thickening of the myelin sheath and mature myelinated fibers became smooth. The process of synthesis of BP, transport of the protein to the varicosed fibers, and maturation of the myelin sheath was seen to progress in a more or less caudal to rostral direction as myelination of the CNS takes place. In the rat, this was accomplished over approximately a 30‐day period starting near the time of birth. In the chick, most of the myelination was accomplished in the three or four days immediately before hatching. At this time, innumerable oligodendrocytes were observed producing BP simultaneously in the major white fiber tracts. It is postulated that in chick some degree of oligodendrocytic cell death occurs normally during myelination.
Retinal projections in the tasmanian devil, Sarcophilus harrisii
Authors: Sanderson K. J. , Pearson L. J. , Haight J. R.
Published: December 2004

Retinal projections were mapped in Tasmanian devils which had one eye injected with 3H‐proline. The retinal fibers terminate in seven regions in the brain. These are (1) dorsal lateral geniculate nucleus (LGNd), (2) ventral lateral geniculate nucleus, (3) lateral posterior nucleus, (4) pretectum, (5) superior colliculus, (6) hypothalamus and (7) accessory optic system. The pattern of retinal input to six of these regions is similar to that seen in other marsupials.

The pattern of retinal projections to the LGNd, while basically similar to that observed in other polyprotodont marsupials, is much simpler than that seen in the related native cat, Dasyurus viverrinus. The LGNd of Sarcophilus presents the simplest cytoarchitectural organisation of any marsupial examined so far. Each LGNd receives overlapping projections from both eyes. Suggestions of an intermittent lamination are seen in the LGNd contralateral to an eye injection of 3H‐proline. On the ipsilateral side there are two patches of label, a large lateral patch and a smaller medial patch, both of which occupy areas receiving contralateral input. The monocular segment, occupying the ventral 40%; of the nucleus, is more extensive than has been reported in any other polyprotodont marsupial.
A topographic map of sensory cell terminal arborizations in the cricket CNS: Correlation with birthday and position in a sensory array
Authors: Murphey R. K. , Jacklet Alice , Schuster Lesley
Published: December 2004

The development of a group of club‐shaped sensilla called clavate hairs, located on the cerci of the cricket (Acheta domesticus), was examined morphologically. The clavate hairs are located on the base of the cercus and are thought to inform the animal of its orientation with respect to gravity. There are two groups of clavate hairs distinguished from one another by the orientation of their sockets: a dorso‐medial group whose sockets are oriented perpendicular to the long axis of the cercus and a ventro‐medial group inclined 45–60° away from the perpendicular. The ventro‐medial group consists of a series of rows of sensilla running parallel to the long axis of the cercus.

By examining a cast‐off exoskeleton in the scanning electron microscope and comparing it with newly developed cuticle of the subsequent instar (Fig. 3), we showed how receptors were added to the ventro‐medial array of clavate hairs. The first ventral hair (#10, Fig.1) appeared in the second instar. Three more hairs were added in the third instar: two (#11 and #12) proximal to hair 10 forming the first row and one (#20) medial to 11 and initiating the second row. After the third instar one hair was usually added proximal to each row each time the specimen molted. Because of the regular positioning of hairs and their orderly addition to the array, it is possible to identify uniquely all of the hairs in the three largest rows of ventral hairs (Fig. 4).

We developed a simple method for staining the neuron associated with each hair. A hair was injured by cutting off its tip. A bubble of cobaltous acetate was then placed on the hair for 18–20 hours and only the neuron associated with the injured hair took up the stain.

The synaptic terminal arborizations of identified neurons examined in this manner were unique and reproducible from specimen to specimen (Fig. 6). Furthermore, there is a topographic order to the terminal arborizations. Within one row the oldest neurons project furthest into the nervous system and arborize over the greatest area, whereas younger neurons arborize in more restricted areas near the entrance of the cercal nerve. Thus it was concluded that birthday was corretated with the morphology of the synaptic arborization.

By staining neurons that were the same age but located in different rows, we determined that birthday was not the only variable influencing the morphology of the terminal arbors. The terminal arbors of neurons 11 and 20, both of which first appear in the third instar, were very different from one another. Thus another variable, presumably position on the body surface, was also correlated with the morphology of a neuron's terminal arborization. We concluded from these results that position on the cercus as well as birthday is encoded in the developmental program of these neurons and that the morphology of their terminal arborizations is a joint function of these two variables.
Differences between the peripheral and the central nervous system in permeability to sodium fluorescein
Authors: Malmgren Leslie T. , Olsson Yngve
Published: December 2004

Sodium fluorescein (SF) was used as a very small tracer (mol wt 376; 5 A° diameter) to examine diffusion barriers in peripheral nerves and to compare them to those in other regions of the nervous system. The technique involved immobilization of the tracer by rapid freezing, followed by freezedrying and vacuum embedding in paraffin. The localization of the SF was then determined in tissue sections using fluorescence microscopy.

Even at the highest doses of intravenously (IV) injected tracer, no extravasation could be detected in the cerebral cortex. On the other hand, SF penetrated very rapidly into peripheral ganglia and into the epineurium and perineurium of large peripheral nerves. The penetration of SF into the endoneurium of large nerves was, however, much more restricted with tracer detectable within the endoneurium only at high doses and long survival times. Even in such cases, the level of SF fluorescence was much lower within nerve fascicles than in the epineurium and the perineurium, and a sharp gradient in fluorescence intensity persisted at the inner border of the perineurium. The extent of extravasation into the endoneurium varied markedly between different fascicles of the same nerve and between different nerves in the same animal.

Experiments involving injection of high doses of SF adjacent to the nerve indicated relatively little movement of SF across the perineurium, which indicates that the observed accumulation of tracer within the endoneurium was the result of direct extravasation of SF from the endoneural blood vessels. Small nerve branches (< 100 μ in diameter) showed an earlier and more extensive penetration of SF into the endoneurium than large nerves like the sciatic, hypoglossal, or ventral tail nerve. This may be due to a diffusion of SF along the extracellular space of the endoneurium from nerve terminals where the perineurial barrier is open‐ended.

In experiments involving IV injection of a solution containing both green fluorescent SF and red fluorescent Evans Blue (Evans Blue‐serum albumin complex, EBA = mol wt 69,000), the distribution of SF could be directly compared at various sites and sacrifice times to that of EBA, a much larger tracer. SF appeared more rapidly and extensively than EBA in the various compartments in ganglia and peripheral nerve. The distribution of EBA was the same as is typically seen when this tracer is injected alone, indicating that there was no change in vascular permeability associated with IV injection of SF.

Since SF is of very small size, freely diffusible, nontoxic, and detectable at very low concentrations, it should be a useful complement to existing tracers. When tissues are processed according to the indicated procedure, one can obtain a very sensitive and reliable localization of this tracer which should be of value for studies in the nervous system concerning various pathological conditions associated with permeability alterations.
Tangential organization of thalamic projections to the neocortex in the mouse
Authors: Caviness Verne S. , Frost Douglas O.
Published: December 2004

Using the anterograde degeneration technique, we examine the tangential organization of a thalamofugal axon population (class I of Frost and Caviness, ′80) whose terminations are preferentially distributed to the middle tier (located in layers III and/or IV) of three radially separated tiers of thalamic projections to the neocortex. Less extensive data are also presented on the tangential organization of thalamofugal axon populations (class II of Frost and Caviness, ′80) that do not terminate preferentially in the middle tier, but that are otherwise heterogeneous with respect to their radial pattern of intracortical termination.

The projections of class I axons are distributed to all neocortical fields with the possible exception of fields 13, 25, and 35. The class I projections to a given cortical field (with the possible exception of the cortex of the second somatosensory representation) originate in only one thalamic nucleus. The class I projections of an individual thalamic nucleus form a cortical representation of the nucleus that constitutes a “first order line‐to‐line” (topologic) transformation of the nuclear volume. The ensemble of class I projections forms a cortical representation of the corresponding thalamic regions that constitutes a “second order line‐to‐line” (non‐topologic) transformation of the thalamic volume.

Class II axons project to all neocortical fields. Class II and class I projections contrast in that the class II projections of multiple thalamic nuclei overlap in the tangential plane of any given sector of the cortex. While the class II projections of the intralaminar nuclei and the widely projecting ventromedial nucleus are known to be topologically organized, the tangential organization of class II projections arising in other nuclei is incompletely understood.
Cytoarchitectonic sexual dimorphisms of the medial preoptic and anterior hypothalamic areas in guinea pig, rat, hamster, and mouse
Authors: Bleier Ruth , Byne William , Siggelkow Inge
Published: December 2004

A cytoarchitectonic analysis is presented of a configuration of cells which extends through the medial preoptic and rostral part of the anterior hypothalamus of the guinea pig, rat, hamster, and mouse. Within that configuration, called here the sexually dimorphic nuclear complex of the medial preoptic‐anterior hypothalamic area (SDNC‐MPAH), there is nearly continuous variation in cellular distribution or packing density as one pro‐ceeds rostrocaudally, as well as variations between females and males at corresponding levels. The major cell groups comprising SDNC‐MPAH are the medial preoptic nucleus (MP) and the preventricular portion of the periventricular nucleus (Pep) rostrally, and the anterior hypothalamic nucleus (AH), anterior portion of periventricular nucleus, (Pea), and bed nucleus of stria terminalis (ST) caudally. The most striking cytoarchitectonic dimorphisms usually involve MP and AH. In all four species examined, MP is larger and, except for the mouse, appears to be more densely cellular in the female than in the male. Most prominently in the rat and guinea pig, AH is densely cellular throughout in the female, including the subependymal zone, whereas in the male AH lies at a distance from the third ventricle, separated from the ependyma by a cell poor zone.

The significance of these findings may lie in the fact that the region exhibiting the sexual dimorphisms has been shown to be involved in the regulation of reproductive Functions which are sexually differentiated and developmentally influenced by the fetal or perinatal hormonal milieu in some species.
A quantitative anatomical study of the granule cell dendritic fields of the rat dentate gyrus using a novel probabilistic method
Authors: Desmond Nancy L. , Levy William B.
Published: December 2004

The granule cell dendritic fields of the adult rat dentate gyrus were analyzed quantitatively using a probabilistic method developed to correct dendritic length and segment number for dendrites cut during sectioning. Golgi‐impregnated, linearized hippocampi were sectioned serially in one of the three hippocampal planes. Three dendritic field parameters were quantified from camera lucida drawings of these dendritic fields: dendritic field spread, dendritic length, and the branching and termination patterns of dendritic segments.

Granule cell dendritic fields resembled cones, their maximal extent occurring in the distal third of the molecular layer. The ratio of transverse to longitudinal dendritic field spread was greater than 1:1 for the dorsal leaf and crest regions, but close to or less than 1:1 for the ventral leaf.

The probabilities of segment branching and termination were highly similar for transversely and longitudinally sectioned tissue. The probability of branching varied among dendritic orders and across the molecular layer for the same order. The probability of termination did not vary greatly across orders. Most nonbranching segments terminated adjacent to the hippocampal fissure.

On the average, a granule cell had 2.23 first‐order dendrites that branched into a dendritic field containing seventh‐order dendrites. Total dendritic length, corrected for cut dendrites and projection errors, averaged 3,662 ± 88 μm. The somatic layer and proximal third of the molecular layer contained approximately 35% of this total length. The remainder, ca. 60%, was restricted to the distal two‐thirds of the molecular layer, the predominant termination zone of perforant path axons.

These data provide a quantitative characterization of the rat granule cell dendritic fields. Implementation of the probabilistic correction method overcomes methodological problems common to quantitative Golgi studies. These data permit a more precise relationship to be drawn between dendritic architecture and granule cell physiology.
Neurons of the lateral and basolateral amygdaloid nuclei: A golgi study in the rat
Authors: McDonald Alexander J.
Published: December 2004

Neurons in the lateral and basolateral nuclei of the rat amygdala were studied using Golgi‐Kopsch and rapid Golgi techniques. According to differences in perikaryal, dendritic, and axonal morphology, three main neuronal classes are recognized. Class I neurons, the predominant cell type in both nuclei, are large, spiny neurons that vary in size in different subdivisions of the lateral and basolateral nuclei. These neurons often have a pyramidal shape, exhibiting one or two thick “apical” dendrites and several thinner “basal” dendrites. Axons of class I neurons, which appear to pass out of the nucleus of origin, usually give off several collaterals that arborize modestly in the vicinity of the cell. Class II neurons are smaller, ovoid cells that comprise approximately 5% of impregnated neurons. These neurons are characterized by spine‐sparse dendrites and fairly dense local axonal arborizations. Class II neurons may be classified as multipolar, bitufted, or bipolar, depending on dendritic branching pattern. Another type of class II neuron, the amygdaloid chandelier cell, is recognized by virtue of its distinctive axon. The chandelier cell axon gives off numerous collaterals that form nestlike entanglements exhibiting clusters of axonal varicosities. Isolated chandelierlike axons of undetermined origin were observed forming multiple contacts with initial segments of class I axons. Several small, spherical class III neurons with short, varicose dendrites were observed. Axons branch profusely to form a dense tangle of collaterals in the vicinity of the cell. Both axons and dendrites establish numerous contacts with class I dendrites. This investigation, the first detailed Golgi study of the basolateral amygdala of the rat, reveals that the cytoarchitecture of this brain region in the rat is basically similar to that of the opossum and other mammals. Morphologic details described in this report should be useful in the interpretation of ultrastructural, immunocytochemical, and electro‐physiological studies of the basolateral amygdala.
Evidence for an orderly arrangement of optic axons within the optic nerves of the major nonmammalian vertebrate classes
Authors: Bunt Stuart M. , Horder T. J.
Published: December 2004

The pathways of selected optic axons were traced in representative urodele, anuran, teleost, reptile, and avian species by filling the fibers with HRP or by tracing, at the light and electron microscopic (EM) level, the degeneration caused by focal or optic nerve lesions.

In all species it was shown that fibers retain retinotopic neighborhood relationships throughout their transit of the optic nerve. Additionally, inanurans, it was found that a subset of large diameter, myelinated fibers take up a random arrangement in the nerve. It is argued that retinotopic fiber organisation is a reflection fo contact guidance of axons during fiber outgrowth in the embryo and that this organisation could account for the arrival of fibers in orderly arrays at central nuclei during normal embryonic development.
Axonal branching in the projections from precerebellar nuclei to the lobulus simplex of the rat's cerebellum investigated by retrograde fluorescent double labeling
Authors: Payne J. N.
Published: December 2004

The projections to lobulus simplex and Crus I of the cerebellum from various brainstem nuclei have been examined in adult rats by using the retrograde fluorescent double labeling technique. True blue was injected into the lobulus simplex on one side and nuclear yellow on the other and the brainstem was examined for labeled neurons. The lateral reticular nucleus, pontine tegmental reticular nucleus, and nucleus praepositus hypoglossi were similar to the equivalent nuclei in other species but all contained double‐ as well as single‐labeled neurons and it was concluded that these nuclei have neurons whose axons branch to both sides of the cerebellum. More neurons in the rostral part of the lateral reticular nucleus were bilaterally projecting than in the caudal and the significance of this in relation to its afferents is considered.

The individual neurons in the pontine nuclei, inferior olivary nucleus, and cuneate nuclei only appear to project to one side and the recent evidence for axonal branching of pontine neurons in the cat is discussed.
Fine structural studies on a type of somatostatin‐immurioreactive neuron and its synaptic connections in the rat neostriatum: A correlated light and electron microscopic study
Authors: Takagi H. , Somogyi P. , Somogyi J. , Smith A. D.
Published: December 2004

Somatostain‐immunoreactive neurons in the rat neostriatum were studied by correlated light and electron microscopy using the peroxidase‐antipe‐roxidase immunocytochemical technique. Immunoreactivity was localized in neuronal perikarya and processes. The perikarya were of spindle or fu‐siform shape (average length 16.9 μm) and were found in all parts of the neostriatum. From each neuron there arose two to four straight immuno‐reactive dendritelike processes, which could frequently be traced as far as about 130 μm from their perikaryon. Immunoreactive varicose axonlike processes were occasionally found, some of which were proximal axons of identified immunoreactive cells. Nine of the light microscopically identified neurons showing somatostatin‐immunoreactivity were studied in the elec‐tron microscope; two of them had proximal axons with varicosities. Each neuron had an oval or elongated nucleus, which was always indented. These morphological features correspond well to those of certain “medium‐size aspiny” neurons classified by Golgi studies. Although the immunoreactive endproduct was diffusely located throughout the neuron, it was character‐istically located in the saccules and large granules (diameter 133 nm) of the Golgi apparatus, and large immunoreactive vesicles of similar size to those in the Golgi apparatus frequently occurred in all parts of axon. Very little synaptic input was found on the perikarya and dendrites of somato‐statin‐immunoreactive neurons. The perikarya and proximal dendrites re‐ceived both symmetrical and asymmetrical synaptic input, while the distal dendrites usually received boutons that formed asymmetrical contacts.

The somatostatin‐immunoreactive boutons contained pleomorphic elec‐tron‐lucent vesicles (diameter 39.3 nm) and a few large immunoreactive granular vesicles; these boutons always formed symmetrical synapses. Their postsynaptic targets were dendritic shafts, spines, and unclassified dendritic profiles. On the other hand, the varicosities of identified proximal axons of somatostatin‐positive neurons did not form typical synapses, since they lacked clusters of small vesicles, but some of them were in direct apposition (via membrane specializations) to unlabelled perikarya or dendrites.

It is concluded that somatostatin is a useful marker for a particular type of neuron in the neostriatum. The presence of somatostatin immunp‐reactivity in synaptic boutons is consistent with the view that somatostatin could be a neurotransmitter in the neostriatum.
Numbers of axons in lateral and ventral funiculi of rat sacral spinal cord
Authors: Chung Kyungsoon , Coggeshall Richard E.
Published: December 2004

The present study determines the numbers of myelinated and unmye‐linated axons in the ventral and lateral funiculi of rat sacral spinal cord. On average, there are 55,000 myelinated and 110,000 unmyelinated axons in the lateral funiculus and 26,000 myelinated and 9,000 unmyelinated axons in the ventral funiculus at these levels. These figures combined with data from earlier studies of the posterior funiculus and the tract of Lissauer give approximate figures of 88,500 myelinated and 131,500 unmyelinated axons for the entire white matter of one side of the rat sacral spinal cord. Thus unmyelinated axons predominate in the white matter of the rat sacral spinal cord.

The majority of axons, particularly the unmyelinated axons, are located in the lateral funiculus. The axons are concentrated in the dorsalateral part of the lateral funiculus, and so the dorsal part of the lateral funiculus, of ten referred to as the dorsolateral funiculus, contains more than half the fibers in the white matter of the spinal cord. A small nick in the dorsal and lateral part of the lateral funiculus, which is often done for various experimental reasons, could thus remove 40% of the axons in the white matter of rat sacral spinal cord.

The data reported in the present paper will serve as a basis for future studies on the white matter of the isolated spinal cord.
Midbrain nuclei projecting to the medial medulla oblongata in the monkey
Authors: Chung Jin Mo , Kevetter Golda A. , Yezierski Robert P. , Haber Lawrence H. , Martin Richard F. , Willis William D.
Published: December 2004

To identify the midbrain nuclei that project to the medial part of the lower brainstem in the monkey, labeled cells were mapped in the midbrain following the injection of horseradish peroxidase into the medial medulla oblongata. After the general distribution of labeled cells was observed in three animals with large injections, more discrete injections of HRP were made in different locations in six additional animals. The small injections were centered in the nucleus raphe magnus, nucleus reticularis giganto‐cellularis, or nucleus medullae oblongatae centralis. The five labeled mid‐brain nuclei were the periaqueductal gray, nucleus cuneiformis, deep layers of the superior colliculus, nucleus of Darkschewitsch, and the interstitial nucleus of Cajal. In addition, the parvocellular division of the red nucleus and the posterior pretectal nucleus contained large numbers of cells when the injection spread into the inferior olive. No major differences in the distribution of labeled cells between different injection sites were found with the exception that the superior colliculus did not contain any labeled cells when the injection was restricted to midline structures. The functional implications of these anatomical findings are discussed in relation to the descending control of pain.
A system of rat spinal cord lamina 1 cells projecting through the contralateral dorsolateral funiculus
Authors: McMahon S. B. , Wall P. D.
Published: December 2004

The aim of these experiments was to sample the properties of lamina I neurones with long ascending projections. Recordings have been made from 136 units at the LA/5 level, with ascending axons reaching C2. More than 80% of the units projected via the contralateral dorsolateral white matter and only 10% via the contralateral ventral quadrant. None projected via the dorsal columns. Receptive fields were typically 1–2 cm2 and although a substantial number of units responded to a limited range of intense stim‐uli, a greater number of units were fired by both low‐ and high‐threshold stimulation. In contrast to cells of deeper laminae, the majority of units were excited following activation of descending pathways in the dorsolateral funiculus.

The functional role of these units is not obvious, but the location of the ascending projection and the influence of descending pathways does not support the notion that the output of lamina 1 constitutes a simple “pain pathway”.
Qualitative and quantitative development of the visual cortex in man
Authors: Sauer B. , Kammradt G. , Krauthausen I. , Kretschmann H.‐J. , Lange H. W. , Wingert F.
Published: December 2004

Anatomical parameters derived from an analysis of 35 male brains, ranging in age from 137 days after conception (DAC) to 99 years, were studied in reference to the development of the human visual cortex (area 17). Distinct structuring of laminae V and VI of area 17 is present at 137 DAC, contrasting with the relative undifferentiation of area 18 at this time. Both the differentiation of the visual cortex into the fundamental six laminae of Brodmann and the emergence of the stripe of Gennari occur between 180 and 190 DAC. At this time, sublamina IVa emerges as a separate entity, external to a transient, trilaminated cortical complex of which the two internal components form sublamina IVc while the external component becomes a part of sublamina IVb (stripe of Gennari). Lamination in area 18 follows a different time course than area 17, appearing at about 160 DAC and achieving a definite six‐layered structure at the 185th DAC. The widths of the laminae in both areas continue to fluctuate after the 190th DAC while the cellular density appears to decrease. The fresh volume of the visual cortex was determined from stained serial sections of the brain, following adjustment for artifactual shrinkage. Approximations of values utilizing the 3‐, 4‐, and 5‐parametric logistic functions reveal that maximum growth of this area occurs at birth, with area 17 attaining 50% of its maximum volume. The maximum volume is reached at the 300th DAC and it apparently begins to decrease in the first decade. The visual cortex develops at a considerably faster rate and reaches its maximal volume much earlier than does the whole brain, cerebellum, or hippocampal formation.
The superior vestibular nucleus: An intracellular hrp study in the cat. I. Vestibulo‐ocular neurons
Authors: Mitsacos Ada , Reisine Harvey , Highstein Stephen M.
Published: December 2004

Superior vestibular neurons were penetrated with horseradish perox‐idase (HRP)‐loaded glass microelectrodes in anesthetized cats. Responses to electrical stimulation of the oculomotor complex and the vestibular nerves were characterized and selected neurons were injected with HRP. Neurons antidromically activated by oculomotor complex stimulation were generally monosynaptically excited by the ipsilateral vestibular nerve. Notable was the absence of strong commissural inhibition by stimulation of the contra‐lateral vestibular nerve. Light microscopy of antidromically identified injected cells demonstrated that these cells are predominantly located at the central levels of the superior vestibular nucleus along the incoming vestibular nerve fibers but a few are found at more caudal levels. Cell bodies, elongated or pyramidal, are mainly medium‐sized to large (30–50 μm). Dendritic trees extend in a plane at an acute angle to the collaterals of the vestibular nerve fibers. Dendrites remain within the nuclear territory and generally display an isodendritic branching pattern. Dendritic spines and appendages are mainly distributed on secondary and distal dendrites. A few terminal enlargements similar to growth cones are observed in these neurons.

Axons of these neurons project rostrally via the medial longitudinal fasciculus, while a minor projection via the brachium conjunctivum is also found. Axon collaterals, when present, originate in the nucleus itself and in the pontine reticular formation.
Gradients of cellular maturation and synaptogenesis in the superior colliculus of the fetal rhesus monkey
Authors: Cooper Michael Lee , Rakic Pasko
Published: December 2004

Light (LM) and electron microscopic (EM) qualitative and quantitative analyses were employed to determine the tempo and spatial gradients of Synaptogenesis and cellular differentiation in the superficial superior collic‐ulus (SC) of the rhesus monkey between embryonic (E) days E47 and E84. 3y E47, a majority of the neurons of the prospective superficial gray layer (SGS) have arrived at their final positions and contribute to a uniform band of small, darkly Nissl‐stained neurons at the outer surface of the SC. By E54, cells in the middle of the rostral pole of the superficial SC become considerably larger, paler staining, and less densely packed than the more medially or laterally located cells. These regional differences, which extend posteriorly through about the middle of the SC at this age, are evident on both the LM and EM levels and were confirmed by a quantitative EM analysis of the cytodifferentiation and Synaptogenesis in the SGS. Several overlapping EM probes made across the medial, middle, and lateral regions of the SGS at each of three coronal levels reveal consistently more developed neuropil and smaller amounts of extracellular space in the middle region than in the medial and lateral portions of the more anterior SC. Further the densities of synapses, both in terms of synapses/μm2 of totalcross‐secti area and synapses/μm2 of neuropil alone, are also higher in the middle than the peripheral regions. Most of the middle‐peripheral differences found in the mid‐E.50s are still evident by the early E60s, but have disappeared by midgestation (E80s). The present results are interpreted to indicate that the middle region of the SGS at a given transverse level begins to mature significantly earlier than the medial or lateral areas. Since our previous 3H‐thymi‐dine analysis (Cooper and Rakic, 1981 a) failed to reveal significant regional variation in the time of neuron origin in the superficial SC, the observed spa‐tiotemporal gradients of neuronal maturation in the primate SGS probably do not arise from underlying gradients of cellular proliferation.
Somatosensory properties of the inferior olive of the cat
Authors: Gellman Reuben , Houk James C. , Gibson Alan R.
Published: December 2004

We examined the somatosensory properties of 391 neurons in the inferior olive in 20 cats that were anesthetized with barbiturate or decere‐brated. A response consisted of a single spike with a variable number of wavelets followed by a long refractory period. Neurons responsive to natural somatosensory stimuli were recorded in all olivary subdivisions. The dorsal accessory olive (DAO) contained the highest proportion of responsive units (96%), compared with 66% for the medial accessory olive (MAO) and 43% for the principal olivary (PO) nucleus. Within the rostral DAO we found a refined cutaneous map of the entire contralateral body surface. In the caudal DAO responsiveness to manipulation of deep tissues became prominent, and both individual limbs and bilateral pairs were represented. In the medial region of the PO responsiveness to taps predominated and bilaterally symmetrical fields were frequent. The lateral PO was unresponsive under the conditions of these experiments. The MAO was distinguished by a greater complexity of receptive field and by a preponderance of deep over cutaneous modality. The lateral part of caudal MAO contained cells with interesting spatial patterns of excitation and inhibition, whereas most cells in the rostral MAO had purely excitatory fields. A teleceptive area receiving visual and auditory input was recognized in the medial MAO and nearby structures such as the dorsal cap. Contact and proprioceptive signals arriving via climbing fibers may provide the cerebellum with information necessary to relate the body to external objects.
Early prenatal development of the human precommissural septum
Authors: Brown Jerry William
Published: December 2004

The development of the septum was studied in human embryos and fetuses ranging from 8 to 24.5 weeks of menstrual age (22.2 to 216 mm crown‐rump length). Neuroblasts migrating from the ventricular layer of the ventromedial hemispheric wall form a narrow intermediate layer that constitutes the primordial septum (8 weeks). Only a primordial nucleus of the diagonal band is identifiable within the gradually enlarging primordial septum at early stages. By 10 weeks the primordial septum is subdivided into medial and lateral zones. At 11.5 weeks well‐defined medial nuclei and the nucleus of the diagonal band are evident within the medial zone. Differentiation within the lateral zone occurs by 12.5 weeks with the appearance of nucleus lateralis pars interna. Nucleus dorsalis is developing in the lateral zone by 14.5 weeks and, by 15.5 weeks, well‐defined nuclei are present throughout the lateral zone. Further neuronal maturation and conforma‐tional changes result in the nearly adult appearance of the septum in older fetuses. Although a definite mediolateral differentiation‐gradient occurs, individual nuclei appear to differentiate along their own longitudinal gradient. Evidence presented suggests that the earliest fibers within the primordial septum are related to the tuberculum olfactorium and the medial forebrain bundle, that septohippocampal fibers appear at 10 weeks, hippocamposeptal fibers by 11.5 weeks, and that, later, stria terminalis fibers develop. The suggested developmental relationships of the septum with the hypothalamus (and brainstem), tuberculum, hippocampus, and amygdala emphasizes its role as an internode in the limbic system.
Rat ciliary neurotrophic factor (CNTF): Gene structure and regulation of mRNA levels in glial cell cultures
Authors: Carroll Patrick , Sendtner Michael , Meyer Michael , Thoenen Hans
Published: December 2004

The structure of the rat ciliary neurotrophic factor (CNTF) gene and the regulation of CNTF mRNA levels in cultured glial cells were investigated. The rat mRNA is encoded by a simple two‐exon transcription unit. Sequence analysis of the region upstream of the transcription start‐site did not reveal a typical TATA‐box consensus sequence. Low levels of CNTF mRNA were detected in cultured Schwann cells, and CNTF mRNA was not increased by a variety of treatments. Three‐week‐old astrocyte‐enriched cell cultures from new‐born rat brain contained easily detectable CNTF mRNA. In astrocyte‐enriched cultures, upregulation of CNTF mRNA levels was observed after treatment with IFN‐γ. CNTF mRNA levels were down‐regulated in these cells by treatments that elevate intracellular cyclic AMP and by members of the fibroblast growth factor (FGF) family. The implications of these results for potential in vivo functions of CNTF are discussed. © 1993 Wiley‐Liss, Inc.