bluuebunny/crossref_metadata_2025 huggingface dataset:
The organization of the dorsal root entry zone in cats and monkeys
Authors: Snyder Russell
Published: December 2004

In five adult cats and three adult monkeys the dorsal rootlets at cervical and various lumbar levels were examined by both light and electron microscopy. In both species, the rootlets could be divided into three anatomically distinct parts: a peripheral, a transitional, and a central zone. The anatomy of the peripheral and transitional parts of the cat were identical with those of the monkey. The peripheral part of the rootlet in both these species had many of the ultrastructural characteristics of a peripheral nerve: and, as in the peripheral nerve, the small caliber axons were randomly distributed throughout the rootlet. In the transitional part of the rootlet, where the anatomical characteristics change to those typifying the tracts of the central nervous system, the unmyelinated axons and small caliber myelinated axons become organized into bundles at the periphery of the fascicles of large myelinated axons. In the central part there were differences between the two species in the distribution of the unmyelinated axons. In the cat no reorganization of the fibers of the central part of the rootlet could be found: the rootlets entered the cord and passed through the dorsal part of Lissauer's tract, and the bundles of unmyelinated axons simply merged with the tract as they came into contact with it. In the monkey, however, the dorsal root enters dorsal to Lissauer's tract and as each part of the rootlet passed from transitional to central, the small caliber axons took a ventrolateral course within the rootlet. As the rootlet merged with the dorsal columns, these axons formed a single bundle on the ventral and lateral surface of the rootlet which then merged with Lissauer's tract. These results indicate that a “lateral division” of the dorsal root is present in the monkey, but not the cat.
The lateral reticular nucleus of the opossum (Didelphis virginiana). I. Conformation, cytology and synaptology
Authors: Andrezik Joseph A. , King James S.
Published: December 2004

When viewed in Nissl preparations, the lateral reticular nucleus (LRN) of the opossum can be divided into three subgroups: a medial internal portion, a lateral external portion and a rostral trigeminal division. Neurons within the internal division measure 13‐45 μ in their greatest dimension whereas those within the external and trigeminal portions measure 11‐32 μ and 14‐27 μ respectively.

Golgi impregnations reveal that many neurons in all three subdivisions display a radial dendritic pattern although some of the nerve cells within the external division have dendrites which orient mainly in a ventromedial to dorsolateral direction. The cell bodies of LRN neurons are relatively spine‐free. However, a small percentage of neurons exhibit clusters of sessile spines on proximal and more distal dendritic segments. No locally ramifying axons or axon collaterals were found within the LRN.

Synaptic terminals within the LRN were divided into four categories: (1) small terminals measuring 2.5 μ or less containing agranular spherical vesicles; (2) small terminals (2.5 μ or less) with agranular pleomorphic synaptic vesicles, i.e., a mixture of spherical and elliptical synaptic vesicles; (3) small terminals (2.5 μ or less) containing agranular spherical or pleomorphic vesicles with a variable number (4‐27) of dense core vesicles; and (4) large terminals (greater than 2.5 μ) which contain agranular spherical synaptic vesicles and a variable number of dense core vesicles (1‐17).

Dendritic diameters were measured from Golgi impregnations and correlated with cross‐sectioned profiles in electron micrographs to help determine the post‐synaptic distribution of synaptic endings. Small terminals containing agranular spherical or pleomorphic synaptic vesicles contact the soma and entire dendritic tree in each portion of the nucleus, whereas the small terminals containing dense core vesicles are usually located on distal dendrites or spines. Some large terminals make multiple synaptic contacts with a cluster of spines, others contact groups of small (distal) dendrites.

In order to identify two of the major afferent systems to the LRN, 15 adult opossums were subjected to either a cervical spinal cord hemisection or a stereotaxic lesion of the red nucleus. Two days subsequent to spinal hemisection, large terminals in the caudal part of the ipsilateral LRN exhibit either an electron dense or filamentous reaction. Their postsynaptic loci are spines and shafts of proximal dendrites or a number of distal dendrites and spines. In addition, small terminals containing spherical agranular synaptic vesicles undergo an electron dense reaction in the same areas. Their postsynaptic loci are proximal or distal dendrites. Two days subsequent to rubral lesions, small terminals containing agranular spherical synaptic vesicles undergo a dark reaction in rostral portions of the contralateral nucleus. They contact intermediate or distal dendrites and occasionally spines.
Fiber counts of regenerating peripheral nerves in axolotls and the effect of metamorphosis
Authors: Ehrlich D. , Mark R. F.
Published: December 2004

Counts have been made of myelinated and unmyelinated fibers in the sixteenth nerve root of the axolotl, before, during and after regeneration following nerve section. There is no loss of myelinated fibers. Many collateral sprouts are formed and eventually withdrawn. Regeneration during metamorphosis is similar but there is more sprouting. There is no fiber loss from cut nerves in metamorphosis. This suggests that rising thyroid hormone levels are not in themselves detrimental to nerves without peripheral connections. Other factors that may govern cell loss in limb development are discussed.
Amygdaloid and pontine projections to the ventromedial nucleus of the hypothalamus
Authors: McBride Russell L. , Sutin Jerome
Published: December 2004

Amygdaloid and pontine projections to the feline ventromedial nucleus of the hypothalamus (HVM) were studied with retrograde transport of horseradish peroxidase (HRP) and anterograde transport of tritiated amino acids. Following injections of HRP into HVM, amygdaloid neurons were labeled in the ipsilateral cortical and medial nuclei and the ventral portion of the parvocellular part of the basal nucleus. In experiments in which HRP was injected into the tuberal hypothalamus following stria terminalis lesions, it was determined that amygdaloid neurons projecting to HVM by way of the stria terminalis were located in the cortical and medial nuclei while those projecting through another route, presumably the ventral amygdalofugal pathway, were found in the rostral part of the medial nucleus and the parvocellular basal nucleus.

Following HRP injection into lateral hypothalamus at the level of HVM, labeled neurons were seen in the magnocellular basal nucleus. After preoptic injections, neurons containing the HRP reaction product were in cortical and medial nuclei and magnocellular and parvocellular parts of the basal nucleus.

In addition to cells in the amygdala, rostral pontine neurons were labeled after HRP injections into HVM. The cells were located ipsilateral to the injection, mostly in the dorsal nucleus of the lateral lemniscus, lateral and dorsolateral to the brachium conjunctivum. The pontine cells labeled following HVM injections of HRP were different from those labeled following lateral hypothalamic and preoptic region injections. The pontine projection to HVM was confirmed using axoplasmic transport autoradiography. A mixture of tritiated leucine and tritiated proline was injected into the lateral pontine region labeled after HRP injections into HVM. Labeled axons ascending in the medial forebrain bundle terminated throughout the rostro‐caudal extent of HVM.
Interlaminar connections of rat visual cortex: An ultrastructural study
Authors: Butler Albert B. , Jane John A.
Published: December 2004

Thermal lesions were made in layers I, II, and upper part of layer III of rat visual cortex. The distribution of degenerating axons and axon terminals in layers IV, V, and VI was studied using electron microscopic techniques.

Following supragranular thermal lesions, the majority of degenerating axon terminals were found in layer V, with extension into the adjacent part of layer VI. Neural profiles postsynaptic to degenerating axon terminals were found in these layers in the following distribution: 81.7% on spines of small to medium size dendrites; 18.2% on dendrite shafts; and <1% on neuronal perikarya. Few degenerating terminals were found on or near apical dendrites. Degenerating terminals were identified on shafts of stellate‐type dendrites found in the upper part of layer V.

Degenerating axons oriented parallel to the cortical surface were found most often in deep layer IV and upper layer V. Degenerating axons were also seen in axon bundles coursing vertically through layer IV.

Approximately 10% of the terminals within a grid square have undergone degeneration; no clustering of degenerating terminals was found in vertical or transverse sections through layers V and VI.

We suggest that most axon terminals arising from pyramidal neurons in layers II and upper III synapse with spines and shafts of dendrite branches originating from pyramidal neurons in layer V and perhaps VI.
Retinofugal projections in the lepidosirenid lungfishes
Authors: Northcutt R. Glenn
Published: December 2004

Autoradiographic and silver methods indicate that the African and South American lungfishes, Protopterus and Lepidosiren, lack ipsilateral retinal projections. Contralaterally, the retina projects to the preoptic nucleus of the hypothalamus, to four discrete areas located in the lateral neuropil of the thalamus, to a superficial pretectal neuropil, to the upper half of the tectal neuropil, and to a laterally situated basal optic neuropil located in the rostral tegmentum. The overall pattern of the primary retinofugal projections is markedly similar to that of amphibians which suggests that lungfishes may be more closely related to amphibians than to actinopterygian fishes. Neotenic trends in both lepidosirenid lungfishes and urodeles may be expressions of parallelism, hence Latimeria and Neoceratodus must be examined to resolve this phylogenetic problem. A 300‐fold range in the size of the eye, indicated by the number of ganglion cells present, occurs among lungfishes, salamanders and frogs. This variation may have implications for recognizing the morphological expression of selection operating on the visual systems of lepidosirenids and amphibians.
Commissural connections of the dentate area in the rat
Authors: Hjorth‐Simonsen A. , Laurberg S.
Published: December 2004

The commissural connections of the area dentata were investigated with the Fink‐Heimer silver impregnation method and the commissural terminals in the hilus of the fascia dentata further studied by electron microscopy of anterograde degeneration.

The commissural endings in the molecular layer were found to terminate as previously reported by others. In addition it was shown that the hilus also receives a significant commissural input. The commissural afferents to both the molecular layer and the hilus terminate along the full rostro‐caudal extent of the area dentata, but with varying densities. The degeneration in the molecular layer is maximal dorso‐rostrally and declines in the caudo‐ventral direction, whereas the degeneration in the hilus varies inversely.

The commissural terminals in the hilus make asymmetrical contacts with dendritic spines and to a lesser extent with dendritic stems. Dark, but otherwise apparently normal terminals with the features of mossy fiber boutons, were encountered in low numbers in both decommissurated and control animals. The commissural projection to the dentate area originates in the opposite hilus and possibly the adjacent part of CA3 (CA3c). Fibers from middle dorso‐basal levels of the hilus to the opposite molecular layer are distributed more rostrally than ventrally relative to the level of the source of the fibers.
Cerebellar corticonuclear and corticovestibular fibers of the flocculonodular lobe in a prosimian primate (Galago senegalensis)
Authors: Haines D. E.
Published: December 2004

Efferent projections from the flocculonodular lobe and the ventral part of the uvula were studied in a prosimian primate (Galago senegalensis) utilizing the Fink and Heimer (1967) method. Corticonuclear and corticovestibular fibers of the flocculonodular lobe and ventral uvula are ipsilateral. Fibers from both the flocculus and nodulus appear to terminate in cell group y (of Brodal and Pompeiano, 1957) although there is little evidence of other projections beyond the vestibular complex. The cortex of the flocculus sends numerous fibers into ventral portions of the NL, central areas of the SVN, and rostral and ventral regions of the MVN and fewer fibers into dorsal and medial SpVN. Many fibers from the nodulus terminate in ventrocaudal NM, peripheral areas of the SVN, and dorsal and caudal MVN. Fewer fibers course into ventral areas of the ipsilateral NL and in approximately the dorsal half of the SpVN and in its ventrolateral area at caudal levels. The LVN receives few, if any, fibers from the flocculonodular lobe. When present they appear to end almost exclusively in those areas of the LVN which border the SVN, MVN, or SpVN. The ventral uvula sends fibers mainly to the dorsomedial SVN, throughout the dorsal SpVN and in its ventrocaudal area, and to a limited region of the ventrolateral MVN at caudal levels. A few fibers from the ventral uvula distribute to dorsolateral SVN, to central areas of the caudal SpVN, and to the ventral MVN at caudal levels.

Corticonuclear and corticovestibular fibers of the flocculus, nodulus and ventral uvula are (1) topographically organized with respect to their specific nuclei of termination and (2) have terminal fields in the cerebellar nuclei and vestibular complex which are partially coextensive (with the terminal field of one or both of the other lobules) and partially exclusive (to that particular lobule). Projections are seen into ventral portions of the ipsilateral NL from both floccular (hemisphere) and nodular (vermis) cortices. It is postulated that this may represent a direct route through which the flocculonodular cortex may assist in the regulation of eye movement since the primate NL, expecially its ventral part, sends fibers to certain of the contralateral oculomotor nuclei via the crossed ascending limb of the brachium conjunctivum (Carpenter and Strominger, 1964; Martin et al., 1974; Chan‐Palay et al.,1976).
Experimental evidence for climbing fibers in the avian cerebellum
Authors: Freedman S. L. , Voogd J. , Vielvoye G. J.
Published: December 2004

This study identifies climbing fibers in the cerebellar cortex following brain stem lesions. Antegrade nerve fiber degeneration was studied after electrolytic destruction of rhombencephalic structures in 24 domestic fowl. Direct damage to the cerebellum was precluded by a retropharyngeal surgical approach. Only lesions that include the inferior olivary nucleus were compatible with Fink‐Heimer staining of degenerating nerve fibers in the Purkinje cell and molecular layers. Degenerating axons were identified as climbing fibers from their trajectory in association with Purkinje cell soma and dendrites. Terminal nerve endings were observed only in the basal one‐third to one‐half of the molecular layer. The presence of climbing fibers in only the contralateral molecular layer was observed in autoradiographic preparations subsequent to unilateral injection of tritiated leucine into the inferior olivary nucleus of three hens. The morphology of the labeled and impregnated degenerating nerve fibers closely coincides with information provided by previous investigators using Golgi stained histological preparations and electron microscopy.
Scanning electron microscopy of the third ventricular floor of the rat
Authors: Paull W. K. , Martin H. , Scott D. E.
Published: December 2004

By utilizing a horizontal dissection technique the entire floor of the third ventricle has been examined. When viewed in toto the ventricular floor was seen to have an hourglass shape with the supraoptic and infundibular recesses equalling the widened portions. Consistent regional differences were also noted. The rostral half of the floor was densely ciliated while the caudal portion, containing ependymal elements of the underlying median eminence, possessed few cilia. The ciliated cells ended in an abrupt transition zone located about halfway along the floor. The rostral portion of the infundibular recess had many more apical blebs and microvilli than did the caudal areas. Supraependymal cells of both the phagocyte‐like and neuron‐like variety were observed in all of the animals examined. In some animals, complex, branching, interconnecting networks of fine calibered fibers interconnected neuron‐like cells that occurred singly and occasionally in clusters. Female rats examined at all phases of the estrus cycle demonstrated no cyclic alterations of the ependymal surface.
Orientation of slit pupil and visual streak in the eye of the cat
Authors: McIlwain James T.
Published: December 2004

The orientation of the visual streak of the cat's retina was compared to that of the long axis of the slit pupil in the same eye. In five paralyzed, anesthetized cats, the retinal projection to the superior colliculus was mapped with electrophysiological techniques. The orientation of the visual streak was estimated from the projection in visual space of the collicular region of high magnification which corresponds to the central projection of the streak. The angle by which the streak was tilted from absolute horizontal was always within one or two degrees of the angle by which the pupil axis was tilted from absolute vertical. This relationship was confirmed in three of the animals in which small retinal lesions were placed a known distance from the histologically determined axis of the streak. From the visual coordinated of these lesions, an independent estimate of the streak's orientation was obtained. In each case, the tilt of streak axis from horizontal differed by no more than 0.5° from the tilt of the pupil axis from vertical. The results support the hypothesis that planes containing the long axis of the cat's slit pupil are perpendicular to planes containing the long axis of the visual streak of the same eye.
Afferent and efferent projections of the region in mouse sml cortex which contains the posteromedial barrel subfield
Authors: White Edward L. , DeAmicis Richard A.
Published: December 2004

Experiments using anterograde and retrograde tracing techniques have been used to identify projections to and from the region of mouse SmI cortex which contains the posteromedial barrel subfield (PMBSF, Woolsey and Van der Loos, '70). Microinjections containing horseradish peroxidase (HRP) and tritiated amino acids were placed unilaterally into the topographic center of the PMBSF. Brains were perfuse‐fixed and frozen sectioned. All sections were reacted for HRP and alternate sections were autoradiographed. Examination of sections cut tangential to the pial surface in the region of the injection site showed that diffusion of the injection was limited to cortex above and below the PMBSF in layer IV (i.e., PMBSF cortex). A “column” of HRP reaction product and developed silver grains was present in ipsilateral cortical area 40, in the face area of SmII. HRP positive cell bodies were mainly in layer III and VI of this “column.” A similar “column” was present in ipsilateral cortical area 6, in a region which in the rat corresponds to the vibrissal area of MsI (Hall and Lindholm, '74), but here HRF positive cells bodies were situated mainly in layer V. HRP labeled cells bodies were also present in layer V of ipsilateral cortical area 29c. The ipsilateral nucleus ventralis thalami pars lateralis and the nucleus posterior thalami contained many HRP positive cell bodies and were associated with dense aggregations of developed silver grains. Numerous silver grains were also present over portions of the ipsilateral caudate, reticular nucleus of the thalamus and ventral pontine nuclei, but no HRP positive cell bodies occurred in these regions.

HRP‐filled axons left the injection site and traveled via the corpus callosum to contralateral PMBSF cortex where HRF labeled cell bodies were present mainly in layers III and V. Usually only one or two labeled somata were located superficial or deep to a contralateral PMBSF barrel. A few HRF positive cell bodies were also present in layers II and III of contralateral pyriform cortex.

These results indicate that PMBSF cortex is reciprocally connected with ipsilateral cortical areas 6 and 40 and with the ipsilateral ventral and posterior nuclei of the thalamus. A small, homotopic callosal connection with contralateral PMBSF cortex has been demonstrated, and it is presumed that this projection is also reciprocal. PMBSF cortex projects to, but receives no projections from the ipsilateral caudate, reticular nucleus of the thalamus and the ventral pontine nuclei. Thus, many of the same projections of primary somatosensory cortex in higher animals, such as the monkey have been shown to occur in the mouse.
The morphology of the spinal cord efferent and afferent neurons contributing to the ventral roots of the cat
Authors: Light Alan R. , Metz Carol B.
Published: December 2004

Horseradish peroxidase was applied to proximal ventral roots of the coccygeal and sacral spinal cord of cats. Subsequent histochemical reaction resulted in extensive staining of spinal cord neurons that had processes in the ventral roots. This procedure was used to study four issues concerning ventral root neurons. (1) Extensive transverse dendritic arborizations were revealed for large and small neurons presumed to be α and γ motoneurons respectively. Dendrites from these neurons were found to project heavily into the ipsilateral white matter, both laterally and ventrally. Dendrites also projected extensively through the anterior commissure, attaining the contralateral grey and white matter. (2) Medially‐located efferent neurons were found to contribute the contralateral dendrites as well as some dorsally‐directed dendrites. Laterally‐located neurons projected dendrites extensively into the lateral and ventral white matter. (3) Stained neurons were found in the intermediolateral cell column, and were presumed to be preganglionic efferent neurons. Some of these neurons projected dendrites into the marginal zone of the dorsal horn, while others sent dendrites medially toward the central canal. (4) Stained fibers, presumed to be primary afferents, were found to enter from the ventral roots and course to the dorsal horn. Most of these fibers were small in diameter and distributed boutons predominantly to the substantia gelatinosa. A few large ventral root afferent fibers were observed that distributed boutons mostly to the nucleus proprius.
Transport of radioactivity from primary auditory neurons beyond the cochlear nuclei
Authors: Carpenter Malcolm B. , Batton Robert B. , Peter Philip
Published: December 2004

Transneuronal degeneration in secondary brainstem auditory nuclei has been described following cochlear lesions, and Marchi studies have revealed degeneration in the trapezoid body after such lesions. These findings support the view of some early neuroanatomists that primary auditory afferents project beyond the cochlear nuclei. Silver impregnation studies of degenerating cochlear afferents have failed to support this claim, leaving the question unresolved. Using [3H] amino acides auditory projections in the monkey were traced autoradiographically from labeled ganglion cells: (1) in all portions of the spiral ganglion, (2) in apical and middle turns of the cochlea and (3) primarily in the basal turn of the cochlea.

Labeling of the entire spiral ganglion resulted in profuse transport of isotope to parts of all cochlear nuclei [anteroventral (AVCN), posteroventral (PVCN), and dorsal (DCN) cochlear nuclei]. Labeled axons entering the trapezoid body (TB) projected ipsilaterally to: (1) the lateral trapezoid nuclei (LTN), (2) the lateral superior olivary nucleus (LSO), (3) the dorsal dendritic zone of the medial superior olivary nucleus (MSO), and (4) the pericollicular or cortical nucleus of the inferior colliculus (IC). Auditory fibers crossing the midline in the TB projected contralaterally to: (1) the medial trapezoid nucleus (MTN), (2) the ventral dendritic zone of the MSO, (3) the ventral nucleus of the lateral lemniscus (VNLL), and (4) the central nucleus of the inferior colliculus (CNIC). Selective labeling of cells in the apical and middle ganglionic turns of the cochlea resulted in a similar pattern of centripetal transport.

Selective [3H] uptake primarily by ganglion cells in the basal turn of the cochlea resulted in: (1) labeling of restricted parts of all cochlear nuclei, and (2) a considerable reduction of isotope transported beyond the cochlear nuclei. Labeled fibers in the TB were distributed sparsely in the ipsilateral LTN, LSO and dorsal dendritic zone of the MSO. Fibers in the TB were not labeled contralaterally in these animals.

Interpretation of these data considers the possibility of transneuronal isotope transport. The pattern of isotope transported beyond the cochlear nuclei does not correspond to the secondary projections of any individual cochlear nucleus, although it bears some resemblance to that of the AVCN. The current study suggests that some primary auditory afferents project beyond the cochlear nuclei.
Horizontal cells of the turtle retina. I. Light microscopy of golgi preparations
Authors: Leeper Harold F.
Published: December 2004

In Golgi preparations of turtle retina, four types of horizontal cells were observed and their morphological characteristics determined in vertical thick sections, whole mount preparations, and reconstructions from serial 1‐μm sections.

H1 consists of a nucleated, stellate cell body (H1CB) and an irregular, tuberous axon terminal (H1AT) connected by a slender axon. Both parts of these cells make contact with receptor cells. H1CB's appear to correspond to “L2‐type cells” while H1AT's correspond to “L1‐type cells” described in the physiological literature.

H2 and H3 are axonless stellate cells which are similar to one another in vertical profile and may occasionally appear similar in horizontal view. In general, the dendritic tree is more densely branched and the density of receptor cell contacts is higher for H2 than for H3. H2‐type cells may correspond to “R/G C‐type cells.”

H4 is also an axonless stellate cell type which is smaller than H2 or H3 at equivalent retinal locations.

The dendritic fields of H1CB's vary widely, but systematically, in size and shape over the retina. Their size is inversely related to receptor cell density, and the shape of the dendritic tree varies from roughly circular in the central area to elliptical in the periphery of the retina.
Development of the diencephalon in the rat. II. Correlation of the embryonic development of the hypothalamus with the time of origin of its neurons
Authors: Altman Joseph , Bayer Shirley A.
Published: December 2004

The development of the nuclei of the hypothalamus was examined in normal and X‐irradiated embryos from day 13 (E13) to the day before birth (E22). The diencephalic neuroepithelium was subdivided into three lobes (dorsal, medial, and ventral) and two lobules (superior and inferior). The hypothalamus is derived from the ventral lobe and the inferior lobule. The ventral neuropithelial lobe generates the neurons of most of the early arising hypothalamic structures, including those of the lateral tier nuclei associated with the medial forebrain bundle, and the heterogeneous intermediate tier nuclei. A specialized neuroepithelial region lining the diamond shaped ventricle produces the early neurohypophysial magnocellular neurons; the neurons of the paraventricular nucleus remain at the site, whereas the neurons of the supraoptic nucleus could be traced migrating laterally. The neurons of the late arising hypophysiotropic area of the posterior hypothalamus are derived from components of the inferior neuroepithelial lobule: the dorsomedial and ventromedial nuclei apparently from a shared matrix in the main portion of the inferior lobule; the tuberomammillary‐arcuate complex from its posteroventral recess. The triple‐decked and sequentially produced components of the mammillary system may arise from separate neuroepithelial sites. The autoradiographic results of the previous study (Altman and Bayer, '78a) showed that the structural and functional heterogeneity of the mature hypothalamus is paralleled by cytogenetic heterochronicity; the present embryonic observations indicate that many of the distinguishable components of the hypothalamus arise from a mosaic of heterogeneous neuroepithelial sites.
Projections from the subiculum to the deep layers of the lpsilateral presubicular and entorhinal cortices in the guinea pig
Authors: Sørensen Knud Erik , Shipley Michael T.
Published: December 2004

Projections from the subiculum to retrohippocampal areas were studied by reduced silver impregnation of anterograde degeneration and by autoradiographic tracing of transported proteins following injections of radioactive amino acids. The subiculum was found to project to the presubiculum and to the medial and lateral parts of the entorhinal area. The projections are exclusively ipsilateral, and arranged in a dorso‐ventral topographical order with the terminations confined to the deep cortical layers. The projections form part of multisynaptic chains within the hippocampal region and must also be implicated in output routes for hippocampal activity additional to the fimbria‐fornix system.
A light microscopic and electron microscopic study of the superficial layers of the superior colliculus of the tree shrew (Tupaia glis)
Authors: Graham J. , Casagrande V. A.
Published: December 2004

Histochemical, Golgi, and electron microscopic methods were used to study the superficial layers of the superior colliculus of the tree shrew. Following horseradish peroxidase injections in the dorsal lateral geniculate nucleus (LGd) and the pulvinar (Pul), retrogradely labeled somata were found in the upper two‐thirds and the lower third of the stratum griseum superficiale (SGS), respectively, as has been described by Albano et al. ('79). In tissue prepared with Golgi methods, somata, similar in location and shape to those projecting to the LGd, had narrow, vertically oriented dendritic arbors, which were confined to the upper two‐thirds of the SGS. Cells located in the lower third of the SGS had larger somata, similar to those projecting to the Pul, and wider dendritic arbors, which were confined to the lower two‐thirds of the SGS. Electron microscopic comparison of the number of degenerating terminals following enucleation and striate cortex lesion indicated that within the SGS terminals from the retina overwhelmingly outnumbered those from the cortex. In both types of material, degenerating terminals were observed throughout the SGS. However, the majority of the degenerating optic terminals were located in the upper SGS, whereas most of the degenerating striate terminals were found in the lower SGS. Thus, cells that project to the LGd and those that project to the Pul differ not only with respect to location, size, and dendritic morphology, but also with respect to the proportion of retinal and striate afferents which terminate in the region of their dendritic trees.
Morphological effects of monocular deprivation and recovery on the dorsal lateral geniculate nucleus in galago
Authors: Casagrande V. A. , Joseph Rhawn
Published: December 2004

The effects of monocular lid‐suture deprivation on development were evaluated by measurement of cell sizes in the lateral geniculate nuclei of six deprived and three normally reared galagos. In all animals autoradiographic demonstration of the retino‐thalamic projections from one eye was used to define the lamination and distinguish the monocular from the binocular segment of the nucleus. Our results indicate that monocular deprivation significantly affects cell growth in both the binocular and monocular geniculate segments, with the greater change occurring in the binocular segment, suggesting that both visual experience and binocular competitive interactions influence geniculate cell growth in these primates. In animals forced to use their deprived eye for 2 months or more by reverse suturing, disparity of cell sizes is reduced in the monocular segment, while differences in binocular segment cell sizes are maintained. Our results also show that monocular deprivation with or without later reverse suture has an unequal influence on different geniculate layers, such that cells in laminae 4 and 5 are not as severely affected as the remaining layers. This differential influence could relate either to the unique pattern of projection of these layers to cortex or to functional differences between layers.
Second somatic sensory area in the cerebral cortex of cats: Somatotopic organization and cytoarchitecture
Authors: Burton H. , Mitchell G. , Brent D.
Published: December 2004

The cortex of the anterior ectosylvian gyrus and adjoining ectosylvian and suprasylvian sulci was explored with tungsten microelectrodes to determine the distribution of responses to light cutaneous stimulation in barbiturate‐anesthetized cats. Recordings were spaced between 125 and 250 μm and, in several cases, nearly all of the somatic areas in this cortex were explored in the same brain. Four somatic sensory areas were identified on the basis of response properties, sequences of receptive fields, and cytoarchitecture.

The largest area, which occupied the rostral and medial two‐thirds to three‐fourths of the exposed, relatively flat portion of the anterior ectosylvian gyrus, was called the second somatic sensory area (SII). Receptive fields in SII were primarily from the contralateral side of the body; they were well defined and somatotopically organized into an erect representation of the body. The top of the head was located next to similar representation of the periphery in a portion of the first somatic sensory area (SI)

Individual distal digits and toes occupied discrete components of the SII map. Another representation for the distal forelimb and hindlimb was noted medially along the lateral bank of the anterior suprasylvian sulcus. Receptive fields and response properties in this region were equivalent to those seen in SII proper. However, only a crude anteroposterior, fore‐ to hindlimb topographical organization was noted, but with more distal parts of the limbs generally located closer to the fundus of the sulcus in this medial representation. As the cytoarchitecture in this medial region was similar to the rest of SII it was considered a medial subdivision of SII. A third, topographically organized zone was located lateral to SII largely within the upper bank of the anterior ectosylvian sulcus and adjoining lateral crest of the anterior ectosylvian gyrus. Large, stockinglike, contralateral receptive fields were common; ipsilateral components to the receptive fields were present. Some individual digit receptive fields were located in the rostral part of the forelimb zone within the anterior ectosylvian sulcus. This lateral somatic area is probably equivalent to a fourth somatic sensory area (SIV) recently identified by Clemo and Stein (1982). Posterior to the hindlimb zones of SII and medial to SIV was another region that responded to cutaneous plus auditory stimulation. There was no detectable topography in this area; nearly all of the receptive fields were large, frequently bilateral, and often involved the whole body or all four extremities. This area's cytoarchitecture was comparable to previous descriptions of the suprasylvian fringe (Rose, 1949). The location and physiology of these four areas were discussed in reference to previous controversies regarding the topography of the body representation in SII and the location of an acallosal zone in this region of cortex.
Studies of effects of kainic acid lesions in the dorsal lateral geniculate nucleus of rat
Authors: Woodward William R. , Coull Bruce M.
Published: December 2004

Kainic acid has been described as a highly specific neurotoxin that when injected locally into the nervous system destroys neuronal perikarya but spares axons of passage and terminals in the vicinity of the injection site. The effects of injection of this agent into the rat dorsal lateral geniculate nucleus on geniculocortical and corticofugal pathways have been examined. Neuronal perikarya were absent from injected geniculates, and products of neuronal degeneration were observed in the external stratum of the optic radiation and in layer IV of striate cortex. Furthermore, no visually driven units could bu found in physiological recordings from ipsilateral visual cortex, and no orthograde axonal transport of radioactivity to cortex was de tectable by autoradiography. These observations are consistent with the complete destruction of the geniculocortical pathway. On the other hand orthograde axonal transport appeared normal in corticogeniculate and cor‐ticotectal neurons on the injected side. In addition to silver grains appearing over the geniculate and superior colliculus label was observed over corti cofugal axons in the internal stratum of the optic radiation. It is noteworthy that axons of the corticofugal pathways are clearly segregated from geniculocortical axons over a part of their course through white matter. Corticogeniculate neurons on the injected side were able to transport D‐aspartate but not nuclear yellow retrogradely to cell bodies in layer VI. These results are consistent with the notion that cortical neurons terminating in and passing through the kainate lesion site survive but suggests, however, that corticogeniculate neurons may be functionally altered by these lesions.
Efferent projections of the posterior lateral line lobe in gymnotiform fish
Authors: Maler Leonard , Sas Emilia , Carr Catherine E. , Matsubara Joanne
Published: December 2004

The posterior lateral line lobe (PLLL) of gymnotoid fish has efferent projections to two midbrain regions: the nucleus praeeminentialis dorsalis (n.P.d.) and the torus semicircularis dorsalis (T.Sd.). Both ipsilateral and contralateral connections are present; the n.P.d. receives nearly equal input from both sides while the T.Sd. receives a stronger contralateral input. The PLLL projection to n.P.d. merely maps medial PLLL to ventral n.P.d. and lateral PLLL to dorsal n.P.d., thus preserving the separate topography and relative orientation of the four electrosensory maps found in the PLLL. Only PLLL pyramidal cells (basilar and nonbasilar pyramids) contribute to this projection. The four PLLL electrosensory maps converge onto T.Sd. so that they map the dorsal body surface onto medial T.Sd. and the ventral body surface onto lateral T.Sd. Pyramidal cells, spherical cells, and multipolar cells contribute to this projection.

A small commiusural connection links homologous segments of the PLLL; these fibers arise from polymorphic cells of the PLLL.
Cortical and subcortical projections of the middle temporal area (MT) and adjacent cortex in galagos
Authors: Wall John T. , Symonds Laura L. , Kaas Jon H.
Published: December 2004

Projections of the middle temporal visual area, MT, and of visual cortex adjoining MT were investigated with autoradiographic methods in the prosimian primate, Galago senegalensis. Ipsilateral cortical targets of MT included area 17, area 18, cortex caudal to MT, cortex ventral to MT, and parietal‐occipital cortex dorsal to MT. This pattern of projections suggests that extrastriate cortex contains a number of visual subdivisions in addition to MT. Contralateral projections were to MT and parietal‐occipital cortex. Projections from MT to areas 17 and 18 connected regions representing similar parts of the visual hemifield while the location of callosal projections in MT matched the location of the injection site in the other hemisphere. Label in area 17 wac concentrated in layers I, III, and VI whereas other cortical areas were most densely labeled in the granular and supragranular layers. Subcortical projections of MT included the reticular nucleus of the thalamus, the lateral posterior nucleus, the superior pulvinar, the inferior pulvinar, the superior colliculus, and the pontine nuclei. The projection pattern to the superior and inferior pulvinar nuclei suggests that MT projects in a topographic manner to two subdivisions within each of these structures.

Injections in cortex just outside of MT labeled area 18, inferotemporal cortex, parietal‐occipital cortex, and, to a lesser extent, MT. The projections to inferotemporal cortex clearly distinguish the bordering cortex from MT. Contralateral cortical terminations were in locations corresponding to the injection site. Subcortical targets were generally similar to those seen after MT injections, although additional projections were observed depending on the location of the injection.

Comparison of these results from the prosimian galago with studies in New and Old World monkeys indicates there are substantial similarities in projections. Thus, some of the cortical and thalamic subdivisions described for monkeys appear to exist in prosimians.
Dendritic organization of the human spinal cord: The motoneurons
Authors: Schoenen J.
Published: December 2004

The dendritic organization of motoneurons was analyzed with the Golgi stain and a morphometric method in the immature and adult human spinal cord. Each motoneuronal column was found to be characterized by a specific orientation of dendritic trees and by a distinct pattern of dendritic bundling.

Ventromedial motoneurons have a pyramidal dendritic tree with numerous, short longitudinal branches and elongated dorsal branches. The latter form thick bundles oriented toward the ventral gray commissure. Longitudinal dendrites form a narrow‐meshed dendritic plexus, containing abundant microbundles. Motoneurons of the ventromedial column have fewer primary dendrites and a lower ramification index than other motoneurons. Central motoneurons are predominantly oriented longitudinally. The meshes of the rostrocaudal dendritic plexus are looser and the microbundles are finer. Most transverse dendrites run laterally and participate in dendritic bundles which penetrate into the ventrolateral funiculus. The rostrocaudal dendritic domain of ventrolateral motoneurons is the largest dendritic domain of all spinal neurons. The longitudinal dendritic network contains fine microbundles and appears wide‐meshed. Transverse dendrites form lateral or media dendritic bundles depending upon the position of their perikaryon. Dorsolateral motoneurons differ from other motoneurons by their multipolar organization with a slight preponderance of dorsoventral dendritic spread. Rudimentary lateral dendrite bundles are restricted to marginal neurons.

The longitudinal plexuses of motoneuronal dendrites and the verticotrans verse dendrite bundles of the ventromedial column are well developed in the 26–28‐week‐old fetus. In contrast, the horizontotransverse dendrite bundles of central and ventrolateral motoneurons can only be recognized from 36 weeks on.

The possible specific functions of the various types of dendrites bundles are examined and a laminar dendroarchitectonic schema of the human cord is proposed.
Brainstem projections of sensory and motor components of the vagus nerve in the rat
Authors: Kalia Madhu , Sullivan J. Michael
Published: December 2004

The sensory and motor connections of the cervical vagus nerves and of its inferior ganglion (nodose ganglion) have been traced in the medulla and upper cervical spinal cord of 16 male Wistar rats by using horseradish peroxidase (HRP) neurohistochemistry. The use of tetramethyl benzidine (TMB) as the substrate for HRP permitted the visualization of transganglionic and retrograde transport in sensory nerve terminals and perikarya, respectively. The vagus nerve in the rat enters the medulla in numerous fascicles with points of entry covering the entire lateral aspect of the medulla extending from level +4 to ‐ 6 mm rostrocaudal to the obex. Fascicles of vagal sensory fibers enter the dorsolateral aspect of the medulla and travel to the tractus solitarius (TS) which was labeled for over 8.8 mm in the medulla. The caudal extent of the TS receiving vagal projections was found in lamina V of the cervical spinal cord (C1 to C2). Sensory terminal fields could be visualized bilaterally in the nucleus of the tractus solitarius (nTS), area postrema (ap) and dorsal motor nucleus of the vagus nerve (dmnX). The ipsilateral projection to the nTS and the dmnX was heavier than that found on the contralateral side. The area postrema was intensely labeled on both sides. Motor fibers from HRP‐labeled perikarya in the dmnX travel ventromedially in a distinct fascicle and subsequently subdivide into a number of small fiber bundles that traverse the medullary reticular formation in the form of a fine network of HRP‐labeled fibers. As these fibers from the dmnX approach the ventrolateral aspect of the medulla they are joined by axons from the nucleus ambiguus (nA), nucleus retroambigualis (nRA) and the retro facial nucleus (nRF). These latter fibers form hairpin loops in the middle of the reticular formation to accompany the axons from the dmnX exiting from the medulla in a ventrolateral location. HRP‐labeled perikarya, in contrast to transganglionically transported HRP in sensory terminals in the nTS, were visualized on one side only, thus indicating that motor control via the vagus nerve is exerted only by motor neurons located ipsilaterally. Sensory information on the other hand, diverges to many nuclear subgroups located on both sides of the medulla.
An intracellular HRP study of the rat globus pallidus. I. Responses and light microscopic analysis
Authors: Park M. R. , Falls W. M. , Kitai S. T.
Published: December 2004

A study of the intracellularly recorded responses of rat globus pallidus neurons to activation of striopallidal fibers was combined with light microscopic examination of the morphology of these same neurons using intracellular horseradish peroxidase.

The response to stimulation of caudate‐putamen is an inhibitory post‐synaptic potential with observed latencies ranging from 5.1 to 9.8 msec. These values correspond to conduction velocities of 0.4 to 0.8 m/second for striopallidal fibers. Comparison with extracellular controls shows no excitatory component to the response.

All recovered and analyzed neurons (n = 11) were of the large type of pallidal neuron known from Golgi studies but with the addition that two subtypes could be recognized. Large neurons located medially in the nucleus had dendritic fields with large dorsoventral extent (ca. 1 mm) when compared to their mediolateral and rostrocaudal dimensions (ca. 0.4 mm) and these neurons emitted no axon collaterals. Large neurons located laterally in the nucleus had disklike dendritic fields with both dorsoventral and rostrocaudal dimensions being on the order of 1 mm but with a minor axis of approximately 100 μm. The axons of these neurons possessed collaterals. As a consequence of their disk‐shaped dendritic field, neurons belonging to the laterally placed subgroup and occupying the narrow (ca. 100 μm thick) striopallidal border zone known to receive a distinct input from neostriatum have dendrites restricted to that zone.