bluuebunny/crossref_metadata_2025 huggingface dataset:
The differentiation of the olfactory placode in Xenopus laevis: A light and electron microscope study
Authors: Klein S.L. , Graziadei P.P.C.
Published: January 2005

The origin and development of the olfactory neuroepithelium of Xeno‐pus laevis has been investigated with light microscopy and scanning and transmission electron microscopy.

The cranial ectoderm of the Xenopus laevis embryo consists of two layers: The inner layer is called the sensory or nervous layer (NL) and the outer layer is called the nonnervous layer of the ectoderm (NNE). Between stages 23 and 26, the presumptive olfactory region consists of two discretely arranged cellular populations: the cells of the olfactory placode proper derived from the NL and the cells of the overlying NNE. After stage 26 the placodal cells begin to move toward the body surface by migrating between the NNE cells. As the placodai cells migrate they sprout an apical process which reaches the body surface at approximately stage 28. The apical process contains free and membrane‐bound ribosomes, elongated mitochondria, and microtubules oriented parallel to the process. Centrioles and basal bodies are present in the apical cytoplasm and microvilli and cilia project from the process's surface. The structure and ultrastructure of the apical process identify it as the dendrite of an olfactory neuron. As the apical process reaches the epithelial free surface, a second process sprouts from the base of the cell. This process pierces the basal lamina at stage 29/30 to reach the underlying telencephalon. The basal process is considerably thinner than the apical one and contains only free ribosomes and mitochondria. Between the stages 29/30 and 32+ it elongates and displays at its distal end the characteristics of a growth cone. The structural and ultrastructural morphology of the basal process identifies it as the axon of the olfactory neuron. Thus the placodai cells which migrate superficially differentiate into the olfactory neurons. Many placodai cells do not migrate, however, butremain at the epi‐thelial base as basal cells.

As the placodal cells migrate to the body surface the NNE cells, originally confined to the surface layer (NNE), elongate and project processes toward the basal lamina. Beginning at stage 27 the apical surface of these cells becomes domed; the dome is filled with dense‐core vesicles and is covered with microvilli and globular material. The supranuclear cytoplasm of these cells contains free and membrane‐bound ribosomes, microtubules, and bundles of filaments. These cells can be characterized as the supporting cells of the olfactory neuroepithelium.

The results indicate that (1) the olfactory neurons and basal cells are derived from the cells of the nervous layer, (2) the supporting cells are derived from the cells of the nonnervous ectoderm, (3) the olfactory nerve emerges from the olfactory neuroepithelium at stage 29/30, and (4) the placodai cells begin to display the morphological features of the mature olfactory neurons before their axons reach their target, the olfactory bulb.
Different granule cell populations innervate superficial and deep regions of the external plexiform layer in rat olfactory bulb
Authors: Orona Edward , Scott John W. , Rainer Elizabeth C.
Published: January 2005

Studies on the morphological organization of the main olfactory bulb have indicated that there are subpopulations of granule cells with different dendritic patterns in the external plexiform layer (EPL). Small, extracellular injections of horseradish peroxidase (HRP) were made iontophoretically into superficial and deep parts of the EPL and the granule cell layer (GCL) in adult rats. Superficial EPL injections principally labeled superficial granule cell somata, whereas deep EPL injections labeled both superficial and deep granule cell somata. Injections in the superficial GCL labeled granule cell dendritic processes extending across the entire EPL. However, deep GCL injections labeled few granule cell dendrites in the superficial EPL, but labeled many such processes in the deep EPL. These results were the same in material processed with the Hanker‐Yates procedure, where the morphology of individual neurons could be studied, and in the more sensitive tetramethyl benzidineprocedure.

Serial reconstructions of individual granule cells were made from both HRP and Golgi‐Kopsch material. The distal dendrites of deep granule cells reached only as far as the deep EPL, where they branched extensively and had many dendritic spines. The dendrites of superficial granule cells, however, reached the most superficial part of the EPL where they ramified most extensively. The superficial granule cells typically had a higher spine density in the superficial part of the EPL than in the deep part. On the basis of these results, we conclude that the superficial granule cells predominantly innervate the superficial EPL and that the deep granule cells exclusively innervate the deep EPL. Granule cells are believed to exert inhibitory influences on the bulbar output neurons, the mitral and tufted cells, through reciprocal dendrodendritic synapses. Since the secondary dendrites of the tufted cells ramify in the superficial EPL and the dendrites of most mitral cells ramify in deep EPL, the superficial and deep granule cells may preferentially modulate the responses of tufted and mitral cells, respectively.
Afferent connections of the lateral agranular field of the rat motor cortex
Authors: Donoghue Johnp P. , Parham Carol
Published: January 2005

Retrograde axonal transport techniques were used to identify the afferent connections of the lateral agranular field (AG) of the rat frontal cortex. This cytoarchitectonically distinct cortical field forms the bulk of the primary motor cortex (MI) as defined by intracqrtical microstimulation studies (Donoghue and Wise, 1982). Following injections of horseradish peroxidase (HRP) or wheat germ agglutinin conjugated to HRP into AG1, retrogradely labeled cells are found in the forebrain, thalamus, and brainstem. Within the cerebral cortex labeled neurons are mainly present in the first somatic sensory area (SI), the second somatic sensory area (SII), and the medial agranular field, which lies medial and rostral to AG1. In SI, labeled cells are found primarily in a cytoarchitecturally distinct region called the dysgranular field of SI. Labeled neurons are present in layers II and III, Va, and the deepest part of layer VI in this field and in SII. Labeled cells are also present in layers Va and VI of the densely granular field of SI, which is the part of SI that is strongly activated by cutaneous inputs. Commissural inputs to AG/ arise from layers II‐VI of the contralateral AG1 and thalamic inputs arise from the ventrolateral, ventromedial, posterior medial, and central lateral nuclei. Additional afferent fibers originate from neurons in the basal forebrain, the ventral thalamus, the midbrain raphe nuclei, and the locus coeruleus. This combination of inputs to AG1 from somatic sensory and frontal cortical fields, thalamic motor centers, and several other subcortical areas implies that AG1 forms a subdivision of sensorimotor cortex that is important in centrally directed movements as well as those that are guided by somatic sensory feedback.
Olivocerebellar connections in sheep studied with the retrograde transport of horseradish peroxidase
Authors: Saigal R.P. , Karamanlidis A.N. , Voogd J. , Michaloudi H. , Mangana O.
Published: January 2005

We describe here the morphology of the inferior olive and the localization of labeled cells after HRP injections into various lobules of vermis and hemisphere of the cerebellum of the sheep. The medial part of the caudal half of the medial accessory olive projects to a medial zone in the anterior lobe, the simple lobule, and the lobules VII and VIII. The lateral part of the medial accessory olive projects to more lateral parts of these lobules with the exception of lobule VII. The group β projects in a differential manner to the lateral parts of the lobules VII and VIII and the medial parts of the lobules IX and X. The dorsomedial cell column projects to lobules VIII, IX, and X; the connections of the dorsal cap are restricted to lobule X.

Fibers from the caudal limb of the dorsal accessory olive terminate in the B zone, the simple lobule, and in lobule VIII. The rostral half of the medial accessory olive projects to lobule IX and to the hemisphere. The other projections of the accessory olives and the principal olive to the hemisphere are similar to those reported for the cat. An accessory cell group in the sheep, located between the principal and the dorsal accessory olive, has connections with the caudal vermis and the hemisphere.
The organization of forebrain afferents to the paraventricular and supraoptic nuclei of the rat
Authors: Sawchenko P. E. , Swanson L. W.
Published: January 2005

Axonal transport techniques were used to define the organization of projections from the forebrain to the paraventricular (PVH) and supraoptic (SO) nuclei of the hypothalamus in the adult rat. First, injections of a retro‐gradely transported fluorescent tracer, true blue, were placed in the region of the PVH, and the distribution of retrogradely labeled cells was charted. Then, the autoradiographic method was used to confirm the results of the retrograde transport experiments, to describe the route taken by inputs to the PVH and SO, and to determine the distribution of each projection within the various subdivisions of the nuclei that have been recognized previously on the basis of cytoarchitectonics, efferent projections, and immunohisto‐chemistry.

The results can be summarized as follows. First, direct projections to the PVH arise from all areas of the hypothalamus (except the SO, the medial and lateral mammillary nuclei, and the magnocellular preoptic nucleus), and from the subfornical organ and the bed nucleus of the stria terminalis. Second, every forebrain region projecting directly to the PVH appears to innervate cell groups in parvocellular parts of the nucleus that in turn project to the neurohemal zone of the median eminence, and to autonomic centers in the brainstem and spinal cord. In addition, each input has a unique distribution within the parvocellular division. Third, relatively few regions in the forebrain project directly to magnocellular neurosecretory parts of the PVH, and are thus in a position to influence directly the release of posterior pituitary hormones. These regions (each of which also projects to the parvocellular division) include the dorsomedial nucleus of the hypothalamus, the median preoptic nucleus, the subfornical organ, and the bed nucleus. Therefore, inputs from the hippocampal formation, amygdala, and lateral septum that have been shown to influence the magnocellular neurosecretory system appear to be relayed by way of short projections from other parts of the hypothalamus (including perhaps parvocellular parts of the PVH) and from the bed nucleus. Fourth, most of these cell groups innervate preferentially either oxytocinergic (dorsomedial and bed nuclei) or vasopressinergic (subfornical organ) parts of the magnocellular division of the PVH. Only the projection from the median preoptic nucleus appears to be distributed uniformly over parts of the magnocellular division in which oxytocin‐ and vasopressin‐con‐taining cells are concentrated. And fifth, each region that preferentially innervates either oxytocinergic or vasopressinergic neurons in the PVH also preferentially innervates the same cell type in the SO (which does not contain a distinct parvocellular division). The results indicate that the coordination of neuroendocrine and autonomic responses from the PVH is mediated at least in part by a complex series of neural inputs, each of which innervates more than one functional subdivision within the nucleus.
Birth dates of trigeminal motoneurons and metamorphic reorganization of the jaw myoneural system in frogs
Authors: Alley Keith E. , Barnes Maryann D.
Published: January 2005

Drastic alterations in oral behavior characterize metamorphosis of anu ran amphibians. Changes cascade through all components of the jaw appa ratus from bone to muscle to nerve. In this investigation, tritiated thymi dine autoradiography was used to determine the production schedule of the trigeminal motoneurons in the leopard frog, Rana pipiens. The time of origir of these neurons and their subsequent fate are of special interest given the breakdown of the larval jaw muscles and the de novo generation of adul muscle fibers during metamorphosis. Specifically, we wanted toalearr whether trigeminal motoneurons are added, deleted, or reused during meta morphic climax.

The entire complement of trigeminal motoneurons was produced over 4‐day span commencing at embryonic stage 13 and terminating at stage 20 Newly formed neurons are added to the primordial trigeminal nucleus in ar orderly pattern. Firstborn neurons settle in the ventrorostral region of the nucleus; cells with progressively later birth dates were added in a postero dorsal direction. No additional trigeminal motoneurons are generated dur ing larval maturation or at metamorphosis, thus indicating that the same population of neurons is present throughout the lifespan of the animal. From these observations we suggest that, during metamorphosis, the trigemina motoneurons that supply the larval muscles switch their allegiance to the newly formed adult jaw muscles. This change of peripheral targets can be viewed as a respecification of the trigeminal motoneurons.
On neuronal homology: A comparison of similar axons in Musca, Sarcophaga, and Drosophila (Diptera: Schizophora)
Authors: King David G. , Valentino Karen L.
Published: January 2005

Thoracic axons occurring in Musca and Sarcophaga are similar to those previously reported in the giant fiber pathway of Drosophila. Serial section reconstruction of both species has shown that the cervical giant fiber descending from the brain into the thoracic ganglion and the thoracic motor axon innervating the tergotrochanteral muscle follow courses matching those of similar axons in Drosophila. Likewise in both Musca and Sarcophaga a thoracic axon establishes axoaxonal synapses onto dorsal longitudinal muscle motor neurons. This axon is similar in both course and synaptic configuration to the peripherally synapsing interneuron in Drosophila. Although these similarities suggest that the three axon pairs are homologous in all three fly species, several differences are also observed. Thus this system of identified axons may be a useful model for investigating phylogenetic variation in specific neuronal form and connectivity.
A reevaluation of the functional organization and cytoarchitecture of the feline lateral posterior complex, with observations on adjoining cell groups
Authors: Updyke B. V.
Published: January 2005

The organization of the cat's lateral posterior complex was reevaluated and its cytoarchitecture described, Analysis of visual representations within the complex confirmed that the pulvinar, lateral zone (LPl), and interjacent zone (LPi) correspond to separate representations of the visual field and established that the zones exhibit heterogeneous connections as a result of retinotopic interconnections with extrastriate areas which represent varying amounts of the visual field. A common system of visual representation extending through layers with differing anatomical connections was identified within zone LPl. The concept of an “isorepresentation cord” was introduced to describe these variable correspondences between sensory representations and connectional relationships. Isorepresentation cords are conceived as holding in common representation of a common locus on a sensory surface without functioning as a unit with respect to connections. Visual representations wtihin the lateral posterior complex consist of many such cords arranged in orderly array.

Zone LPm (medial) was also delineated more accurately on the basis of its connections with the ectosylvian visual area. Analysis of termination patterns which occupy boundary regions adjacent to and between the principal zones further established the existence of a collection of cell groups which form a thin, irregular shell investing the principal zones. The identification of these additional cell groups and the recognition of connectional heterogeneity within the principal zones of the complex made it possible to identify and describe the subtle cytoarchitectural differences which characterize the subdivisions of the lateral posterior complex and their boundaries with adjoining nuclear groups.

The present findings are discussed with respect to the functions of the lateral posterior complex in interconnecting cortical visual and visuomotor areas, and with respect to the conceptual issues raised by variable correspondences between sensory representations and connectional relationships within thalamus.
The development of the cervical spinal cord of the mouse embryo. I. A Golgi analysis of ventral root neuron differentiation
Authors: Wentworth Lee E.
Published: January 2005

No previous Golgi studies have described early neuron differentiation in mammals near the time of neural tube closure. By leaving embryos in utero and varying the impregnation times, the cells of the cervical spinal cord of mice of 8–11 days of gestation (E8–E11, where E0 = day vaginal plug observed) were stained and analyzed in the present study. The early stages of ventral root motoneuron differentiation described earlier (Wentworth and Hinds, '78), using serial section electron microscopy, have been confirmed in this study and include preaxonic neuroblasts (stage 1–detached from the ventrical but still attached to the basal lamina), bipolar neuroblasts (stage 2), and unipolar neuroblasts (stage 3). Later stages of differentiation described in this study include young neurons with dendrites: secondary bipolar (stage 4) and multipolar neurons (stage 5). At E8 the neural tube is just closing and consists of undifferentiated ventricular cells. On E9 a few ventral root neuroblasts are differentiating in the cervical spinal cord. The majority of these cells are in the bipolar and unipolar neuroblast stages, although the most advanced cells observed had reached the secondary bipolar neuron stage of differentiation. By E10 a large cluster of ventral root motoneurons is differentiating in the ventrolateral cord. Some cells have reached the bipolar stage, a few cells are becoming multipolar, and a subdivision into dorsolateral and vrntromedial subgroups is beginning. By E11 the medial and lateral subdivisions are more obvious, and the most advanced cells are well‐differentiated multipolar neurons oriented either mediolaterally or dorsoventrally, although cells in the earlier unipolar and secondary bipolar stages are still observed.
The origin of postganglionic and sensory axons in the cervical sympathetic trunk of the cat: A horseradish peroxidase study
Authors: Wong Wai Chow , Leong Seng Kee
Published: January 2005

The composition of the cervical sympathetic trunk (CST) in the cat is still not completely understood. The present study investigates, by the horseradish peroxidase (HRP) method of tracing neuronal connections, the presence of postganglionic and sensory neurons projecting via the CST. Following sympathectomy at the midcervical level and the application of HRP crystals to the cut ends of the CST which had been isolated from the surrounding by a 1.5% solution of agar‐agar, labelled neurons were seen in the superior cervical (SCG), stellate (SG), inferior vagal ganglia (IVG), and spinal ganglia C8–T8. The maximum number of labelled nuerons was 536 in the SCG, 460 in the SG, 180 in the IVG, and 104 in spinal ganglia C8–T8.
Organization within the cranial IX–X complex in ranid frogs: A horseradish peroxidase transport study
Authors: Stuesse Sherry L. , Cruce William L. R. , Powell Katina S.
Published: January 2005

Cranial nerves IX and X in frogs have been described as originating from a nuclear group referred to as the IX–X complex. We studied the central nervous system components of this complex in Rana pipiens and R. catesbiana by labeling peripheral branches of cranial nerves IX and X and identifying the central nervous system contributions of these branches. Various peripheral nerves (IX and the cardiac, gastric, pulmonary, and laryngeal branches of X) were identified and soaked in horseradish peroxidase (HRP). One to 2 weeks later, the frogs were killed and processed for HRP by the tetramethylbenzidine method. Glossopharyngeal efferents originated from a small ventrolateral cell group found at the level of the IX root exit. Vagal efferents formed a single column of cells in a ventrolateral position from the level of the brainstem exit of the vagus nerve (approximately 2,000 μm above the obex) to 200 μm below the obex (values given are for an 80‐g frog). This cell group was separate from and just caudal to efferent cells of the glossopharyngeal nerve. Within the vagal portion of the column, cells projecting through the gastric branch were found throughout the rostral‐caudal extent of the nucleus. “Cardiac” cells tended to be more rostral than “pulmonary” cells, and both groups of cells were located in the middle of the nucleus. “Laryngeal” cells were located more caudally in the nucleus. This peripheral representation within the vagal nucleus corresponds more closely to the organization found in the mammalian nucleus ambiguus, rather than to the apparent lack of organization found in the mammalian dorsal motor nucleus.

Afferents of IX and X entered slightly rostral to the ventral roots of their respective nerves and descended in two tracts. The majority entered the tractus solitarius and descended in a medial position to cervical spinal cord. A portion of the afferents from the vagus nerve crossed the midline in the lower myelencephalon just dorsal to the central canal and ascended a short distance on the contralateral side. Within the solitary tract, vagal afferents were located in a ventrolateral position as they descended to below the obex. Glossopharyngeal afferents filled the remainder of the tract. A smaller portion of afferents from both IX and X did not enter the solitary tract but descended in the spinal tract of V and the dorsolateral funiculus of the spinal cord (Lissauer's tract) to thoracic levels. Afferents of IX also formed a rostral bundle which extended in the solitary tract to the caudal metencephalon.
Morphometry of spine‐free nonpyramidal neurons in rabbit auditory cortex
Authors: McMullen Nathaniel T. , Glaser Edmund M. , Tagamets Malle
Published: January 2005

A study of the morphometry and laminar distribution of spine‐free nonpyramidal neurons in electrophysiologically verified primary auditory cortex was carried out in adult rabbits. By using image‐combining computer microscopy, the locations of all impregnated neurons in 300‐μm Golgi‐Cox Nissl sections through the auditory cortex were determined. Spine‐free non‐pyramidal neurons constitute nearly 72% of the nonpyramidal neurons present. They are distributed in a band extending from 450 to 750 μm beneath the pial surface corresponding to laminae III and IV. A combination of dendritic stick, Fourier, and statistical analyses revealed a highly significant spatial orientation of their dendrite systems along a vertical axis parallel to the apical dendrites of pyramidal neurons. A significant tangential orientation of dendrites along a dorsal‐ventral axis was also found. A radial analysis of the dendrite systems revealed that the pronounced vertical orientation of spine‐free nonpyramidal neurons is due to (1) directed dendritic growth along the vertical axis, (2) decreased branching and rapid termination of tangentially oriented dendrites, and (3) increased branching of vertically growing dendrites. The radial analysis also revealed that the longest branches are those directed toward the white matter.
A study of axonal diameters and areas in lumbosacral roots and nerves in the rat
Authors: Suh Young Suk , Chung Kyungsoon , Coggeshall Richard E.
Published: January 2005

There has been debate as to whether there is a size difference between central and peripheral processes of dorsal root ganglion cells. In the present study, the mean areas of myelinated and unmyelinated fibers are measured as 27.8 μm2 and 0.55 μm2, respectively, in peripheral nerves and 13.72 μm2 and 0.14 μm2 in dorsal roots. Thus myelinated central processes of dorsal root ganglion cells have mean areas 50% less than the mean areas of the myelinated sensory axons in the same peripheral nerves, and the mean diameters of the central myelinated axons are 30% less than the peripheral myelinated axons. The mean areas of the unmyelinated sensory axons in the dorsal roots are 25% of the mean areas of the unmyelinated sensory axons in the same peripheral nerves. Thus the mean diameters of the central unmyelinated axons are 50% of the mean diameters of the unmyelinated sensory axons in the same peripheral nerve. These data indicate that both myelinated and unmyelinated central processes of dorsal root ganglion cells are smaller than the peripheral processes of these same cells for lumbosacral segments in the rat. It is shown that axonal tapering is not responsible for these striking differences. Finally, documentation of differences in myelinated fiber histograms from dorsal roots of different segments in the rat is provided.
Morphology of inspiratory neurons located in the ventrolateral nucleus of the tractus solitarius of the cat
Authors: Berger A. J. , Averill D. B. , Cameron W. E.
Published: January 2005

The morphology of 11 dorsal respiratory group (DRG) inspiratory neurons located in the ventrolateral nucleus of the solitary tract (vl‐NTS) was studied using the technique of intracellular labeling with the enzyme horseradish peroxidase (HRP). Six of these cells were cut in the transverse plane and had a mean somal diameter of 30.4 m̈m, while five others sectioned in the horizontal plane had a mean of 38.2 m̈m. These neurons produced an average of 6.2 primary dendrites (range: 4–10), many of which projected rostrally or caudally up to 1.0 mm from the cell bodies. These dendrites were oriented along the longitudinal axis; they ran parallel and ventral to the tractus solitarius. In general, all dendrites possessed numerous spines and appendages. Many axons could be traced for considerable distances within the medulla (in one instance, up to 8 mm). These axons were last discerned in the contralateral ventral medulla rostral to the level of their cell bodies. The axons of three neurons bifurcated in the ipsilateral medulla; one branch remained ipsilateral and projected caudally, while the other crossed the midline. A small number of counterstained cells of size similar to or larger than the HRP‐stained neurons formed a column that constituted the vl‐NTS. Based upon our observations of stained and counterstained cells, we conclude that the inspiratory neurons of the vl‐NTS are few in number and represent a morphologically homogeneous population. The primary orientation of the dendritic arbors of vl‐NTS inspiratory neurons appears to optimize the surface area available to receive synaptic contacts from sensory afferents emerging from the tractus solitarius.
Reconstructions of corticogeniculate axons in the cat
Authors: Robson J. A.
Published: January 2005

The terminal arbors of corticofugal axons to the dorsal lateral geniculate nucleus in the cat were filled with horseradish peroxidase and then partially reconstructed through serial sections. The results demonstrate that these arbors are far more complex than was suspected from previous studies of axon segments in individual sections. These axons branch profusely and spread widely within the nucleus. Within laminae A and A1 the terminal arbor of a single axon can be more than 800 μm wide compared with retinogeniculate axons whose terminal arbors range in width from 100 to 410 μm (Sur and Sherman, ′82).
Geniculocortical projection to layer I of area 17 in kittens: Orthograde and retrograde HRP studies
Authors: Kato Nobuo , Kawaguchi Saburo , Miyata Hirofumi
Published: January 2005

Using the orthograde and retrograde HRP methods, the distribution of geniculocortical (G‐C) afferent terminals in area 17 was examined in kittens and an adult cat. Following HRP injection in the entire dorsal lateral geniculate nucleus (LGNd), afferent terminals were labeled in layer I and deeper layers. The terminals in layer I in young kittens (less than 2 weeks old) were densely distributed throughout layer I, whereas in old kittens (over 1 month old) they were sparsely distributed in the outer half of layer I. When the HRP injection site was confined to the A laminae (lamina A and lamina A1), a few HRP‐labeled terminals in layer I were seen in young kittens but not in older kittens or an adult cat. Following HRP injection in layer I of area 17 in young kittens, relatively large neurons were labeled retrogradely. The labeled neurons were located chiefly in the C complex and partly in the A laminae.

The present experiments revealed that the G‐C afferents to layer I of area 17 in young kittens originate from relatively large neurons which are located chiefly in the C complex and partly in the A laminae and that these afferents give dense terminals covering the entire layer I. These findings contrast with those obtained in adult cats, in which the G‐C afferents to layer I originate exclusively from small neurons in the C complex and give sparse terminals to the outer half of layer I.
Asymmetry of the olfactory system in the brain of the winter flounder, Pseudopleuronectes americanus
Authors: Rao P. D. Prasada , Finger Thomas E.
Published: January 2005

Adult flatfishes exhibit grossly asymmetric external morphology. Even the olfactory apparatus is asymmetric, being larger on the upward‐facing side. We undertook the present study on the winter flounder, Pseudopleuronectes americanus, to examine whether the asymmetry of the peripheral olfactory system is maintained in its central organization. In winter flounder, the right olfactory organ, nerve, and bulb are larger than the contralateral counterparts. In addition, the right telencephalon is about 8% larger than the left. Horseradish peroxidase (HRP) and degeneration techniques were used to trace the central connections of the olfactory bulbs.

Neurons afferent to the olfactory bulb occur bilaterally in the telencephalon and mesencephalic tegmentum. Afferent neurons are also present at the junction between the posterodorsal bulb and telencephalon, in the basal preoptic region, nucleus of the posterior tuber, locus coeruleus, raphe nucleus, and the contralateral bulb.

Each olfactory bulb projects bilaterally to several restricted areas of the telencephalon, the posterodorsal neurons of the nucleus preopticus and the tuberal region, with ipsilateral connections being heavier in all areas. Corresponding to the differences in the peripheral olfactory apparatus, the central olfactory projections were also asymmetric. The right olfactory bulb projects to 2.6% of the ipsilateral telencephalon and 1.99% of the contralateral telencephalon. The left bulb projects to 1.8% of the ipsilateral and 0.6% of the contralateral telencephalic hemisphere. Thus the left telencephalon receives roughly equal olfactory input from the two sides, while the right telencephalon receives vastly more input from the right olfactory system. The asymmetry in the projections of the right and left bulbs may be due to differential postmetamorphic growth of the olfactory system on the two sides.
Efferent connections of the caudate nucleus, including cortical projections of the striatum and other basal ganglia: An autoradiographic and horseradish peroxidase investigation in the cat
Authors: Royce G. James , Laine Erick J.
Published: January 2005

Tritiated tracer was injected into the head of the caudate nucleus in cats. Following such injections, labeling is present within extensive regions of both the globus pallidus and entopeduncular nucleus, where it presents a mottled or meshlike appearance. These projections are topographically organized in that there is simple correspondence between the mediolateral, dorsoventral, and rostrocaudal origin of the caudate projection and its input to the globus pallidus and entopeduncular nucleus. Transported tracer is also present within the substantia nigra, where it is most abundant within the pars reticularis. However, distinct labeling also overlies cells of the pars compacta, and lesser amounts of labeling are present within the pars lateralis and within the retrorubral area.

Following injections of horseradish peroxidase into the caudate nucleus, and subsequent tissue processing by the tetramethylbenzidine (TMB) method of Mesulam ('78), labeled anterograde fibers are present in abundance within the globus pallidus, entopeduncular nucleus, and all subdivisions of the substantia nigra, thus confirming the autoradiographic findings. Also, it is especially obvious in this HRP material that, contrary to previous degeneration studies, both the rostromedial and caudolateral parts of the pars lateralis of the substantia nigra contain numerous anterogradely labeled fibers. Retrogradely labeled neurons are also present within the substantia nigra of these same tissue sections, where they are most abundant within the pars compacta, but lesser numbers of labeled neurons are also present within the pars reticularis, pars lateralis, retrorubral area, and ventral tegmental area on the ipsilateral side, and all of these same subdivisions of the substantia nigra on the contralateral side. Also, within the subthalamic nucleus in these experiments, there are anterogradely labeled fibers, as well as retrogradely labeled neurons, which are interpreted to represent a reciprocal connection between the subthalamic nucleus and the striatum.

In a separate series of experiments, horseradish peroxidase was injected into the motor cortex‐specifically into the anterior sigmoidal gyrus. Following such injections, labeled neurons representing afferents to the motor cortex are found in all subcortical nuclei commonly known as the “basal ganglia,” including the caudate nucleus, putamen, globus pallidus, entopeduncular nucleus, substantia innominata, nucleus of the diagonal band of Broca, medial septal nucleus, claustrum, and basolateral amygdaloid nucleus.
Direct connections of rat visual cortex with sensory, motor, and association cortices
Authors: Miller Michael W. , Vogt Brent A.
Published: January 2005

Each division of rat visual cortex, areas 17, 18a, and 18b, has connections with sensory, motor, and association cortices. These corticocortical connections were sampled using anterograde autoradiographic and retrograde horseradish peroxidase labeling techniques.

Area 17 is connected via reciprocal pathways with each division of visual cortex, the posterior one‐third of motor area 8, association area 7, and posteroventral area 36 of temporal cortex. It also receives projections from perirhinal areas 13 and 35.

Area 18a has reciprocal connections with areas 17 and 18b, a patch in posterior somatosensory area 3, and dorsal auditory area 41. Like area 17, area 18a receives afferents from and projects to the posterior one‐third of motor area 8. The connections of area 18a with association cortices are extensive; these regions include parietal areas 7, 39, 40, and 14, posteroventral and dorsal area 36, and perirhinal cortex.

Area 18b is connected with areas 17 and 18a, a patch in medial area 3, and dorsal area 41. There are reciprocal projections between area 18b and posterior area 8. As for association cortex, area 18b projects to frontal area 11, area 7, posteroventral and dorsal area 36, and perirhinal cortex. In addition, area 18b receives input from and projects efferents to the dorsal claustrum.

Most of the interconnections among areas 17, 18a, and 18b originate from neurons in layers II, III, and V and end in terminal fields in layers I–III and V. In contrast, projections of other sensory, motor, and association cortices to visual cortex originate mainly from neurons in layer V and to a lesser extent from layer II. The reciprocal pathways from visual cortex terminate predominantly in the supragranular layers. In conclusion, these corticocortical pathways provide the basis for cortical visuosensory and visuomotor integration that may aid the rat in the coordination of visually guided behaviors.
Dendritic and axonal organization of mitral and tufted cells in the rat olfactory bulb
Authors: Orona Edward , Rainer Elizabeth C. , Scott John W.
Published: January 2005

The output cells of the main olfactory bulb, the mitral and tufted cells, can be categorized into subclasses on the basis of their intrabulbar dendritic and axonal characteristics. Their form was studied in rats following labeling by iontophoretic injection of horseradish peroxidase into the external plexiform layer (EPL). The fact that these extracellular injections labeled small numbers of neurons permitted reconstruction of individual cells. The injection depth within the EPL determined the type of cells labeled. Secondary dendrites of each cell type lay in one of three partially overlapping zones in the EPL. The deepest zone contained the secondary dendrites of one group of mitral cells (Type I), which had the deepest and longest dendrites of the output cells. An intermediate zone of the EPL contained the secondary dendrites of middle tufted and a second class of mitral cells (Type II). The superficial zone, adjacent to the glomerular layer, contained the relatively short, asymmetric dendritic fields of external tufted cells. The few labeled internal tufted cells had secondary dendrites in either the intermediate or deep zones. Every cell type, except the Type I mitral cells, had axon collaterals in the internal plexiform and upper granule cell layers. No cell types had axons re‐entering the EPL. These results for output cells combined with our previous observations on granule cells point to a functional sublaminar organization of the EPL that has not previously been proposed.
Organization of the cat's optic tract as assessed by single‐axon recordings
Authors: Mastronarde David N.
Published: January 2005

The organization of the cat's optic tract was assessed from recordings of single axons during vertical electrode penetrations. To analyse both the order and the scatter of axons in the optic tract, units were pooled from electrode tracks that had evidently passed through nearly equivalent parts of the tract. Receptive field elevation, the most strongly ordered parameter, was primarily organized horizontally, increasing from posteromedial to anterolateral tract. Azimuth tended to increase from dorsal to ventral, but was only half as well organized vertically as elevation was horizontally. Axon type was also organized vertically, at least among axons that were identified as X or Y (contralateral axons of less than 20° eccentricity). Axons of ON‐center X‐type were located mostly in the dorsal quarter, OFF‐center X‐type in the dorsal two‐thirds, and Y‐type (ON‐ and OFF‐center) in the ventral two‐thirds of the tract. Another difference between the horizontal and vertical axes was revealed by estimates that axons of one type, from one retinal locus, spread about twice as far vertically as horizontally in the tract.

Torrealba et al. (1982) have proposed that the sequential addition of ingrowing axons to the pial surface is a major source of the order in the tract. The differences between horizontal and vertical order seen here suggest an extension of this proposal: the sequential addition of axons to the ventral surface generates the vertical order, while some other process arranges axons horizontally, along the ventral surface, according to receptive field elevation (or some similar one‐dimensional retinal coordinate).
Topographic organization of connections between the main olfactory bulb and pars externa of the anterior olfactory nucleus in the hamster
Authors: Schoenfeld Thomas A. , Macrides Foteos
Published: January 2005

The organization of connections between the main olfactory bulb (MOB) and pars externa (pE) of the anterior olfactory nucleus was studied in hamsters by using wheat germ agglutinin‐horseradish peroxidase as both an anterograde and a retrograde neuronal tracer. Bulbar efferents of pE project exclusively to the contralateral MOB. A topographic organization is evident in these efferents, such that distinct sectors of pE project predominantly to certain sectors of the contralateral MOB and lightly to other sectors. The predominant projection to any bulbar sector in the coronal plane is repeated at nearly all rostral‐caudal levels, i.e., the pE efferents to the contralateral MOB terminate within long strips or wedges that show a sector‐to‐sector topographic organization with respect to the medial‐lateral and dorsal‐ventral axes but not the rostral‐caudal axis of the MOB. Afferents to pE arising in the ipsilateral MOB also show a sector‐to‐sector topographic organization. Injections into restricted sectors along the circumference of pE label all classes of output neurons (mitral cells and internal, middle, and external tufted cells) in restricted sectors of the ipsilateral MOB, and the sectors that have retrograde neuronal labeling are homotopic to those in the contralateral MOB that have dense anterograde terminal labeling. External tufted cells are not labeled and the other classes of MOB output neurons do not have prominent topographic patterns of labeling in cases with injections caudal to pE. The somata of external tufted cells that project to pE are predominantly in the deep part of the glomerular layer; most of the external tufted cells that He more superficially in the glomerular layer do not appear to have projections extrinsic to the MOB. These results indicate that both the afferent and efferent connections of pE with the MOB are topographically organized and provide a short synaptic pathway between homotopic sectors of the two main olfactory bulbs.
The effects of a lengthy period of environmental diversity on well‐fed and previously undernourished rats. I. Neurons and glial cells
Authors: Bhide P. G. , Bedi K. S.
Published: January 2005

Male rats undernourished from the 16th day of gestation until 25 postnatal days of age were raised either in enriched (EC) or isolated (IC) environmental conditions between about 35 and 115 days of age. A parallel set of well‐fed rats was raised in identical environments. At the end of this period all rats were killed by perfusion with 2% phosphate buffered glutaraldehyde.

Body and forebrain weights and forebrain lengths and widths were determined for each animal. The left cerebral hemisphere was embedded in paraffin‐wax and serially sectioned. Three of these coronal sections (defined by subcortical landmarks) taken from the occipital cortex region were used for cortical depth measurements.

Small pieces of cortical tissue taken from area 17 of the right cerebral hemisphere were embedded in resin and cut to yield 0.5 μm thick sections through the entire depth of the cortex. These sections were used to estimate the nuclear diameters and numerical densities of neurons and oligodendrocytes as well as neuronal perikaryal volumes.

Two‐way analysis of variance tests on data combined from both nutritional groups revealed significant main effects of nutrition on body weight, forebrain weight, forebrain width, and forebrain length × width values. Environment had significant main effects on forebrain weight, forebrain length, forebrain length × width values, and on neuronal numerical density. The interaction between nutrition and environment was not significant for any of the measurements carried out. These results suggest that 80 days of environmental diversity beginning at about 35 days of age can produce morphological changes in the brains of both well‐fed rats and rats undernourished during early life. These changes seem to be similar in direction and magnitude in the two nutritional groups.
Cerebellar cortical efferent fibers in the North American opossum, Didelphis virginiana. II. The posterior vermis
Authors: Klinkhachorn P. S. , Haines D. E. , Culberson J. L.
Published: January 2005

The projection pattern of corticonuclear and corticovestibular fibers from vermis lobules VI–X of the North American opossum, Didelphis virginiana, was studied using a modification of the Fink and Heimer (1967) technique.

The evidence suggests that corticovestibular projections in opossum are ipsilateral and exit the cerebellum via the juxtarestiform body. Lobules VI and VII contribute few, if any, corticovestibular projections. Corticovestibular fibers from lobule VIII are sparse to moderate and those from lobules IX and X are numerous. The main targets of corticovestibular fibers are the superior and spinal vestibular nuclei with some input to the medial vestibular nucleus, particularly from lobules IX and X. Although degenerated axons course through the lateral vestibular nucleus, they do not appear to terminate therein.

Corticonuclear fibers from lobules VI–X are ipsilateral and terminate in the caudal and caudoventral one‐third of the medial cerebellar nucleus (NM). Fibers from lateral areas of some vermal lobules appear to enter contiguous parts of the immediately adjacent posterior interposed nucleus. Although each lobule projects into a specific area of caudal and caudoventral NM when the terminal fields for lobules VI–X are superimposed, it is apparent that they are largely coextensive. This is in contrast to the pattern seen in projections from the anterior vermis. The results further indicate that zones A and B are present in lobules VI–X of opossum.
Localizing spinal‐cord‐projecting neurons in neonatal and immature albino rats
Authors: Leong Seng Kee , Shieh Jeng Yung , Wong Wai Chow
Published: January 2005

According to results from the horseradish peroxidase (HRP) method of tracing neuronal connections, the spinal cords of neonatal and immature rats receive a large number of descending projections from the first cervical cord segment, various brain‐stem nuclei, and deep cerebellar and diencephalic nuclei. All these projections are present at birth, though at this age some of them are not fully established. Thus, only a few cells in the trigeminospinal, solitariospinal, tectospinal, and cerebellospinal groups were labeled after HRP injection in the lumbosacral or cervical cord segments in neonatal animals. They were clearly labeled in older, immature animals. The labeled neurons in other descending pathways appeared to be equal in density in neonatal, immature, and adult rats. This visual impression was stregthened by the counts of neurons in the interstitial nucleus of Cajal, which showed no significant difference in the number of labeled neurons in the three age groups. However, counts of labeled cells in the lateral vestibular nucleus and nucleus of the posterior commissure showed that there is a steady rise in the number of labeled neurons as the animals increase in age.