bluuebunny/crossref_metadata_2025 huggingface dataset:
Topographic organization of the orientation column system in the striate cortex of the tree shrew (Tupaia glis). I. Microelectrode recording
Authors: Humphrey Allen L. , Norton Thomas T.
Published: January 2005

Microelectrode recordings were made in the binocular portion of the tree shrew striate cortex to determine how orientation selective cells are distributed topographically in area 17 of this species. Seventy‐five percent of the cells sampled were activated well by elongated visual stimuli and were quite selective for stimulus orientation. Ninety‐five percent of the orientation‐selective cells had orientation tuning ranges (Wilson and Sherman, '76) between ± 5° and ± 40° from their optimal orientation.

Orientation‐selective cells with the same or similar optimal orientations were distributed in cortex in a columnar manner (Hubel and Wiesel, '62), as determined from electrode penetrations nearly normal to the cortical surface. Penetrations parallel to the cortical surface revealed a highly ordered representation of optimal stimulus orientation, generally characterized by sequential changes in optimal orientation with electrode movement across the striate cortex. In addition, relatively consistent differences were observed in the rates and patterns of orientation shift on these penetrations depending on the direction of electrode movement across the cortex. Penetrations parallel to the 17–18 border yielded moderate‐to‐high rates of orientation change (mean slope = 434°/mm), with the changes genearlly progressing through a complete clockwise or counterclockwise cycle of 180° or more before a major reversal in the direction of orientation shift was encountered. In contrast, penetrations perpendicular to the border yielded low‐to‐moderate slopes (mean slope = 239°/mm). On these penetrations a more limited range of optimal orientations (<180°) was usually encountered, due to frequent reversals in the direction of orientation shift. Also, extended regions (100–200 μm long) of constant optimal orientation were observed in these penetrations. The different patterns of orientation change found on these orthogonal penetrations across the striate cortex indicate that the orientation column system in this species is anisotropically organized with respect to the 17–18 border. Further, the regions of constant optimal orientation frequently encountered on penetrations perpendicular to the 17–18 border suggest that the anisotropy is subserved by a system of elongated zones of iso‐orientation arranged approximately perpendicular to the 17–18 border.
Topographic organization of the orientation column system in the striate cortex of the tree shrew (Tupaia glis). II. Deoxyglucose mapping
Authors: Humphrey Allen L. , Skeen Leslie C. , Norton Thomas T.
Published: January 2005

The topographic organization of the orientation column system in tree shrew striate cortex was examined by using 2–deoxyglucose autoradiography to map the cortical sites of increased metabolic activity produced by visual stimulation with stripes of a single orientation. Awake experimental tree shrews (freely moving, restrained, or paralyzed) were given injections of deoxyglucose label and then stimulated with vertical, horizontal, or oblique stripes for 45–75 min. Autoradiographs of coronal sections through the striate cortex revealed regularly spaced radial zones of increased deoxyglucose uptake 150–350 μm wide, extending from the cortical surface to the white matter, separated by interzone regions of lower uptake. The radial zones were most densely labeled and distinct in layers I–IIIb and least distinct in layer IV, which was continuously and densely labeled throughout both the radial zone and interzone regions. These radial zones, which were not present in control animals that viewed many orientations, reflect the locations of cortical cells activated by a single stimulus orientation.

Reconstructions of the radial zones from serial sections produced maps of the distribution of increased deoxyglucose uptake across striate cortex. The maps reveal a highly organized system of narrow, parallel bands that are slightly wavy and have a mean spacing of 530 μm. The band pattern was confirmed in sections cut tangential to the cortical surface and was similar in animals stimulated with either vertical or horizontal stripes; the bands consistently abut the 17–18 border at nearly right angles and extend across the striate cortex in a generally posteromedial direction. These patterns of increased deoxyglucose consumption confirm the anisotropic distribution of orientation‐selective cells across the tree shrew striate cortex, suggested in the preceding microelectrode study (Humphrey and Norton, '80). The density distribution of label within the bands further suggests that the anisotropy is due to a system of parallel, somewhat wavy iso‐orientation lines arranged roughly perpendicular to the 17–18 border.
Axon reaction in dorsal motor vagal and hypoglossal neurons of the adult rat. light microscopy and RNA‐cytochemistry
Authors: Aldskogius Håkan , Barron Kevin D. , Regal Ronald
Published: January 2005

Qualitative light microscopical observations, morphometric measurements, and cytophotometric values for nucleolar and cytoplasmic RNA were compared in axotomized rat dorsal motor vagal and hypoglossal neurons. These data were correlated with consective cell counts and examination of the peripheral nerves.

Vagal neurons showed an early prominent chromatolysis, later accompanied by increased cytoplasmic basophilia. Morphometric data showed a transient slight cytoplasmic enlargement but no nucleolar hypertrophy. Nucleolar RNA was unchanged, but cytoplasmic RNA was elevated 7 to 84 days postoperatively. Cell counts demonstrated a final cell loss of about 70%.

Hypoglossal neurons showed a moderate chromatolysis. Nucleolar and cytoplasmic areas were enlarged for a short period. Nucleolar and cytoplasmic RNA were elevated about 3 to 14 days and about 3 to 28 days postoperatively, respectively. Cell counts demonstrated a loss of 25% at the longest postoperative survival period.

The results indicate that axotomized adult mammalian extrinsic neurons—even those destined to die—accumulate RNA. This response contrasts with axon reaction in many axotomized mammalian intrinsic neurons which appear to undergo depletion of RNA.
The normal organization of the lateral posterior nucleus of the golden hamster
Authors: Crain Barbara J. , Hall William C.
Published: January 2005

As a first step in analyzing the influence of various afferent projections on the development of the hamster lateral posterior nucleus, its normal organization was studied using both light and electron microscopic techniques. Rostrolateral, rostromedial, and caudal subdivisions were identified. The rostrolateral subdivision receives dense projections from the ipsilateral superior colliculus and posterior neocortex, as well as sparser, more restricted projections from the contralateral colliculus and retina. The ipsilateral colliculus is by far the major source of medium‐sized (M)terminals with round vesicles. These terminals synapse around the shafts of large central dendrites to form distinctive synaptic clusters. The contralateral colliculus and retina contribute a few M‐terminals to the clusters. In contrast, axons from the posterior neocortex form very large (RL‐)terminals with round vesicles from the posterior neocortex form very large (RL)terminals with round vesicles which synapse onto numerous appendages of a single proximal dendrite, are surrounded by glial lamellae, and rarely participate in the clusters. Axons from all four sources also form small (RS)terminals with round vesicles which synapse on the shafts of small dendrites. Finally, F‐terminals with flat or pleomorphic vesicles form symmetric synaptic contacts both within and outside the clusters. The only identified projection to the rostromedial subdivision is from the ipsilateral posterior neocortex, which contributes RL‐ and RS‐ terminals. F‐terminals are also found, but neither M‐terminals nor synaptic clusters are present. The caudal subdivision also receives RL‐ and RS‐terminals from the ipsilateral posterior neocortex. Small inputs from the ipsilateral and contralateral colliculi are present, but their axons form only RS‐terminals. No M‐terminals or synaptic clusters are found.

These results indicate that a large neonatal superior colliculus lesion would eliminate the vast majority of the M‐terminals in the synaptic clusters of the ipsilateral lateral posterior nucleus. In subsequent studies (Crain and Hall, '80 a, b, c), we will examine how the remaining inputs from the retina, contralateral superior colliculus, and posterior neocortex contribute to the synaptic organization when it develops after such a lesion.
Clonal analysis of the avian neural crest: Migration and maturation of mixed neural crest clones injected into host chicken embryos
Authors: Bronner‐Fraser Marianne , Sieber‐blum Maya , Cohen Alan M.
Published: January 2005

Quail neural crest cells were grown in vitro at clonal density for 7 or 10 days. Mixed neural crest colonies and clones (containing both pigmented and unpigmented cells) were implanted into the trunk region of 2 1/2‐day‐old host chicken embryos by a previously described injection technique (Bronner and Cohen, '79). Here we describe the migratory behavior and subsequent phenotypic expression of the injected cells. Unpigmented cells and pigmented cells both migrated along the ventral neural crest pathway; there were, however, some differences in migratory behavior between the two cell types. After 3 days in vivo, unpigmented quail neural crest cells contributed to the sympathetic ganglion, adrenal medulla, and/or aortic plexus in the host. Many of the unpigmented cells became catecholamine‐containing neuroblasts. Unpigmented cells were never observed in the gonads or the gut, but localized only in regions normally populated by trunk neural crest precursors to neurons and supportive cells. Melanocytes derived from the same precursor, however, were often found in the gonads or gut, in addition to normal neural crest locations in the trunk. These results demonstrate that quail neural crest cells grown in tissue culture for 7 days or more retain the ability to migrate and contribute to normal neural crest structures when placed in the embryonic environment. Under the conditions described, a single neural crest cell gave rise to daughter cells expressing the melanotic phenotype (detected in tissue culture) and adrenergic phenotypes (detected after injection in vivo). This demonstrates that at least some single cells of the premigratory crest in the trunk region are pluripotent.
Ipsilateral projection from the subiculum to the retrosplenial cortex in the guinea pig
Authors: Sørensen Knud Erik
Published: January 2005

A projection from the subiculum to the retrosplenial cortex (area 29a and b) was studied by autoradiographic tracing of anterogradely transported proteins following injections of radioactive amino acids into ventral and dorsal parts of the subiculum. Only the dorsal parts of the subiculum projected to the retrosplenial cortex. The projection was exclusively ipsilateral, and topographically arranged along both the longitudinal septotemporal axis and the transverse plane of the subiculum. The termination in the retrosplenial cortex was confined to the relatively cell free superficial layer (lamina 1) and the underlying cell‐rich layers (laminae 3–4). Between these two terminations a narrow zone (lamina 2) was only weakly labeled. The projection constitutes an output route for hippocampal activity in addition to the fimbria‐fornix system and the subicular projections to the parahippocampal areas.
An analysis of the retinal afferents to the cat's medial interlaminar nucleus and to its rostral thalamic extension, the “geniculate wing”
Authors: Guillery R. W. , Geisert E. E. , Polley E. H. , Mason C. A.
Published: January 2005

The retinal afferents to the medial interlaminar nucleus and to its rostro‐dorsal extension at the edge of the pulvinar have been studied in cats by fiber degeneration and autoradiographic methods. Fiber degeneration following section of one optic nerve shows two distinct retinal inputs: One is coarse‐fibered and goes to the medial interlaminar nucleus itself; the second, which is fine‐fibered, goes to the rostral and medial borders of the medial interlaminar nucleus and continues into the pulvinar. The regions in receipt of these fine fibers have been called the “geniculate wing”.

The topography of retinal representations and the degree of binocular overlap within the medial interlaminar nucleus and the wing have been studied by combining intraocular injections of 3H proline with local lesions of the injected eye, or with removal of the non‐injected eye. In the medial interlaminar nucleus three distinct laminae are recognizable and are particularly clearly shown in horizontal sections. Rostrally and medially, lamina 1 maps the contralateral nasal retina as a mirror reversal of lamina A. Posterior and lateral to this, lamina 2 maps the ipsilateral temporal retina as a mirror reversal of lamina A1. Lamina 3 lies closest to the optic tract and receives crossed afferents from the temporal retina. In this lamina, which is the smallest, vertical retinal dimensions map as in the other layers, but we were unable to determine the mapping of the horizontal dimensions.

In the geniculate wing, as in the other geniculate layers, vertical lines of the visual field are mapped as corresponding vertical diencephalic dimensions; horizontal retinal dimensions are mapped as horizontal lines in the wing, with central retinal areas represented furthest from the optic tract. In the geniculate wing the contralateral nasal and ipsilateral temporal retina are mapped with considerable binocular overlap. The crossed temporal retina has no demonstrable representation in the wing.
[14C] deoxyglucose mapping of first‐order projections activated by stimulation of lateral hypothalamic sites eliciting gnawing, eating, and drinking in rats
Authors: Roberts Warren W.
Published: January 2005

Rats having hypothalamic electrodes that elicited gnawing, eating; and drinking in free‐moving tests received intermittent electrical stimulation for 45 min following i.v. injection of [14C] deoxyglucose. Autoradiographs of regional brain glucose utilization were made by the method of Sokoloff et al. ('77). To maximize the detectability of first‐order neuronal effects and minimize potentially complex transsynaptic effects, baseline metabolism and synaptic transmission were reduced by light barbiturate anesthesia. Laterally asymmetrical increases in glucose utilization indicative of elicited activity were largely coterminous with the known projections of the lateral hypothalamus and some projections of adjoining areas, indication that most first‐order efferent were subthreshold. Although the majority of hypothalamic projections were similarly affected in control rats that received hypothalmic stimulation that elicited other responses, a number were activated significantly less than in the rats whose electrodes induced gnawing, eating, and drinking. Chief among these areas was a continuous descending pathway from the ventral tegmental area through the lateral tegmentum to the cuneiform and parabrachial nuclei. Smaller and/or less reliable increases above controls were found in the dorsomedial caudate‐putamen, the posterolateral zona incerta, the anterior lateral central gray, the caudal linear nucleus, the laterodorsal tegmental nucleus, the pontine tegmental nucleus, and a previously undescribed pathway lying medially between the pontine medial lemniscus and cerebral peduncle. These areas, especially the lateral tegmental and parabrachial zone, are the most likely candidates of the pathways and/or destinations of the directly excited efferents or fibers of passage that constitute the first link in the elicitation of gnawing, eating, and drinking by lateral hypothalamic stimulation. Since self‐stimulation and exploratory activity were elicited by control as well as experimental electrodes, they are probably dependent of other projections among those affected similarly in both groups.
The cytoarchitecture, cytology, and synaptic organization of the basilar pontine nuclei in the rat. II. Electron microscopic studies
Authors: Mihailoff Gregory A. , McArdle Craig B.
Published: January 2005

The basilar pontine gray in adult rats was subjected to electron microscopic examination in order to characterize: (1) certain general cytologic features, (2) the principle categories of presynaptic profiles, and (3) the postysnaptic targets of the various categories of presynaptic boutons. General cytologic features included the presence of neuronal somata exhibiting either a smooth contoured nucleus and central nucleous or an irregularly contoured nucleus with numerous invaginations and an eccentric nucleolus. In addition, dendritic protrusions with variable morphology were apparent as well as a class of dendrites and somata with a curious dense, granular matrix. Four general types of presynaptic profiles were distinguished and were classified as: round vesicle boutons, elongate vesicle, pleomorphic vesicle, and dense core vesicle boutons. The category of round vesicle boutons formed asymmetric synaptic contacts and included three subtypes. One group contained vesicles with diameters of 25–35 nm, a second group contained larger (40–60 nm) round vesicles, and a third group of much larger boutons (2.5–6.8 μm) exhibited the smaller round vesicles. Another general category of presynaptic profile contained distinctly elongated synaptic vesicles, formed symmetrical active sites, and ranged in size from 0.4–1.7 μm. A third category of synaptic end‐strucutures was distinguished by the presence of pleomorphic synaptic vesicles and microtubules and exhibited a distinctive pale or lucent matrix, while the fourth type was characterized by a mixed population of clear and dense core vesicles. Analysis of the distribution of such bouton types over the surface of pontine neurons revealed that: somata and proximal dendrites were contacted by round, elongate, and dense core vesicle boutons; intermediate and distal dendrites received synapses from all categories of boutons including the large endings with smaller round vesicles, while dendritic spines were contacted by round vesicle boutons (large and small), the large boutons, and elongate vesicle boutons. Synapses were also observed to occur between two vesicle‐containing profiles. In such situations, pleomorphic vesicle boutons were found to be postsynaptic to either elongate vesicle boutons or small boutons with round vesicles and at the same time were presynaptic to a dendritic profile.
Two visual pathways to the telencephalon in the nurse shark (Ginglymostoma cirratum). I. Retinal projections
Authors: Luiten Paul G. M.
Published: January 2005

The central projections of the retina in the nurse shark were studied by anterograde transport of horseradish peroxidase and tritiated proline. With regard to efferent retinal fibres, both techniques gave completely identical results. Projections were found to pretectal area, dorsal thalamus, basal optic nucleus, and optic tectum, all at the contralateral side. The retinal target cells in the dorsal thalamus are restricted to the ventrolateral optic nucleus and the posterior optic nucleus. No evidence was found for an earlier‐reported projection to the lateral geniculate nucleus. The present findings show that the ventrolateral optic nucleus exhibits homological features of the dorsal lateral geniculate nucleus in other vertebrate groups, whereas the lateral geniculate nucleus of the nurse shark is much more comparable to the nucleus rotundus of teleosts and birds and would be more appropriately so named. The application of the HRP technique also allowed us to study afferents to the retina by retrograde transport of tracer. Retrogradely labeled cells were observed in the contralateral optic tectum and are apparently similar to those reported for teleosts and birds.
Connections of the corticomedial amygdala in the golden hamster. II. Efferents of the “olfactory amygdala”
Authors: Kevetter Golda A. , Winans Sarah S.
Published: January 2005

The anterior cortical (C1) and posterolateral cortical (C2) nuclei of the amygdala are designated the “olfactory amygdala” because they each receive direct projections from the main olfactory bulb. The efferents of these nuclei were traced after sterotaxic placement of 1—5 μCi tritiated proline in the corticomedial amygdala of male golden hamsters. Following survival times of 12, 24, or 48 hours, 20 μm frozen sections of the brains were processed for light microscopic autoradiography.

Efferents from C2 terminate in layers II and III of the olfactory tubercle and in layer lb of pars ventralis and pars medialis of the anterior olfactory nucleus. Fibers from this nucleus also project to layers I and II of the infralimbic cortex and to the molecular layer of the agranular insular cortex. More posteriorly, fibers from C2 teminate in layer I of the dorsolateral entorhinal cortex, and in the endopiriform nucleus.

From C1, efferent fibers travel in the stria terminalis and terminate in the precommissural bed nucleus of the stria terminalis and in the mediobasal hypothalamus. Efferents from C1 also innervate the molecular layer of C2, the amygdalo‐hippocampal area, and the adjacent piriform cortex.

Neurons in both C1 and C2 project to the molecular layer of the medial amygdaloid nucleus and the posteromedial cortical nucleus of the amygdala, the plexiform layer of the ventral subiculum, and the molecular layer of the lateral entorhinal cortex.
The structural organization of the ventral posterolateral nucleus in the rat
Authors: McAlliser J. P. , Wells J.
Published: January 2005

The structural plan of the ventral posterolateral nucleus (VLP) in the rat was analyzed by using a variety of techniques to study the pattern of distribution of the ascending afferent fibers and the synaptology of the neuropil within this somatosensory relay nucleus. Golgi stains, Fink‐Heimer methods, HRP labeling methods, and electron microscopy were all used in the analysis.

The neurons in VPL are aligned in rostrocaudal and dorsoventral rows that are roughly parallel to the curvature of the external medullary lamina (EML) and curve partially around the rostral pole of the ventral posteromedial nucleus (VPM). Golgi‐impregnated section reveal that the dendritic trees of the VPL neurons conform in general to the laminar pattern of VPL. Thick proximal dendrites extend about 25 μm from the cell bodies. Most proximal dendrites are aligned with the laminae of VPL but the distal dendrites spread over many laminae within VPL. The inputs from the dorsal column nuclei (DCN) end only on proximal dendrites as large, round‐vesicle terminals. About 20–25% of the small round‐vesicle terminals originate in the cerebral cortex and synapse only on the distal dendrites. The third type of synapse contains many flattened vesicles and is of unknown origin. No serial synapses or vesicle‐containing dendrites were observed. Input from the spinal cord projects to two segregated zones which are transitional between the ventral lateral nucleus (VL) and VPL rostrally and between the posterior thalamic complex (PO) and VPL caudally. Each transition zone contains neurons characteristic of both VPL and the adjacent region. Ascending afferent projections were demonstrated by the antegrade transport of HRP following injections into the ventral mesencephalon and by Fink‐Heimer stains of degeneration resulting from small lesions of the DCN. Both methods indicate that large‐caliber axons course parallel to each other and give off collaterals that diverge to widespread areas of the VPL. The widespread terminal fields that result do not conform to the laminar pattern of the nucleus. Small punctate lesions of DCN result in sparse degeneration that is also widespread in VPL. Structures which appear to be clusters of terminal arborizations of the ascending afferent input were also observed in VPL. These results suggest that somatotopy and modality separation in VPL may be determined either by intrinsic and/or corticothalamic morphological relationships and not by precise topographical ordering of sensory input.
The pontocerebellar system in the rat: An HRP study. II. Hemispheral components
Authors: Mihailoff G. A. , Burne R. A. , Azizi S. A. , Norell G. , Woodward D. J.
Published: January 2005

The projection of basilar pontine neurons to the cerebellar hemispheres was studied in pigmented rats by means of the retrograde transport of horseradish peroxidase. Injections of horseradish peroxidase were restricted to the lateral aspects of the lobulus simplex (11 cases), crus I (26 cases), crus II (23 cases), and paramedian lobule (18 cases). The main focus of labeled neurons following lobulus simplex injections of horseradish peroxidase was located in the ventral pons, at rostral levels. Interestingly, the majority of labeled cells were distributed ipsilateral to the injection site. After crus I injections, however, labeled neurons were most evident contralaterally, although labeled ipsilteral cells were conspicuous rostrally. The majority of labeled cells were characteristically distributed along the medial, ventral, and lateral perimeters of the pontine gray. This pattern of labeling contrasts with that in cases of crus II injections, in which the main focus of labeled somata occupied more central regions of medial and ventral portions of the pons. Similarly, the pattern of labeling following injections into the paramedian lobule largely avoided the medial and lateral perimeters of the pontine gray, while numerous labeled somata occupied the central region of the pons. In addition to the pontine regions described above, labeled cells were observed in various cases in the dorsal peduncular region, the lateral and dorsolateral areas, and the nuclear reticularis tegmenti pontis (NRTP) where three separate zones of labeling could be discerned in various cases.

Several general organizational features were derived from these studies. Although specific quantitation procedures were not applied, the number of ipsilaterally labeled neurons was impressive in some cases, as was the mirror‐image location of certain ipsi‐ and contra‐lateral cell clusters. It was also noted that certain, similarly located clusters of labeled pontine neurons were present in cases in which injections were made into different cerebellar lobules, at least raising the possibility that some pontine neurons might give rise to divergent projections to multiple cerebellar locations. Moreover, it was evident that the location of certain clusters of labeled neurons was congruent with terminal zones of various pontine afferent systems, particularly those of the sensorimotor cortex. Combining the latter finding with the preceeding notion regarding pontocerebellar divergence suggests a mechanism by which sensorimotor information might be transmitted to several different cerebellar locations.
Spinothalamic projections in a lizard, Varanus exanthematicus: An HRP study
Authors: Hoogland Piet V.
Published: January 2005

In the present study HRP injections have been placed in various thalamic areas in order to investigate spinothalamic projections in the lizard Varanus exanthematicus. It appeared that the spinal cord projects to three different thalamic areas: nucleus dorsomedialis, nucleus ventrolateralis, and an area that includes both the nucleus dorsolateralis and nucleus intermediodorsalis. Spinal neurons projecting to nucleus dorsomedialis are localized bilaterally at the medial side of the dorsal horn. Following injections in nucleus ventrolateralis, labeled neurons were found bilaterally in area VII and VIII, whereas nucleus dorsolateralis and nucleus intermediodorsalis receive a bilateral input mainly from areas V and VI.
Morphology and number of neurons in two species of polychaetes
Authors: Hulsebosch C. E. , Bittner G. D.
Published: January 2005

Neurons of the ventral nerve cord (VNC) in the polychaete species Clymenella torquata and Nereis virens were ultrastructurally distinguished from glial cells by the smaller diameter and elongated shape of glial nuclei in adult organisms. In contrast to neurons, ß‐glycogen‐like particles and densely packed microfilaments were found in glial cytoplasm. Using these and other criteria glials cells were distinguished from nerve cells in histologic preparations.

All neuronal nuclei were counted in specified regions of the CNS of both polychaetes. In both species, the number of neuronal nuclei in various CNS regions remained constant in animals of very different body size. Since Clymenella has a set number of ganglia in the VNC and a set number of body segments, the total number of CNS neurons remains constant in adult members of this species. Since adult Nereis adds VNC ganglia in newly forming body segments, the total number of CNS neurons continuously increases, but the total number of CNS neurons in a ganglion does nto change after it is formed.
The organization of thalamic projections to the parietal cortex of the Virginia opossum
Authors: Donoghue John P. , Ebner Ford F.
Published: January 2005

The thalamic projections to somatic sensory‐motor (SSM) cortex and adjacent cortical areas of the Virginia opossum were studied using anterograde and retrograde axoplasmic transport techniques. Large injections of horseradish peroxidase and/or tritiated amino acids were made in the parietal cortex to identify all of the thalamic nuclei that are interconnected with this large cortical area. Very restricted injections were then made in physiologically identified subdivisions of SSM cortex, in the remaining posterior portion of parietal cortex, and in the anteriorly adjacent postorbital cortex.

The results show that the parietal cortex is reciprocally connected with a number of thalamic nuclei. Different combinations of these thalamic areas project to specific subregions within the parietal field. All parts of the SSM cortex, which occupies the anterior four‐fifths of parietal cortex, receive input from the ventrobasal complex (VB), the ventrolateral complex (VL), the central intralaminar nucleus (CIN), the central lateral nucleus (CL), and the ventromedial nucleus (VM). We could detect no segregation of VL and VB inputs in any part of SSM cortex. Projections from all of these thalamic nuclei, except VM. show at least some degree of topographic organization. Anterior‐posterior strips of SSM cortex receive input from clusters of thalamic neurons that extend dorsoventrally and rostrocaudally through VB and VL. The posterior one‐fifth of the parietal cortex (the posterior parietal area) receives input from VL, the posterior nuclear complex, and the lateral complex, as well as input from CL, CIN, and VM. Postorbital cortex receives input mainly from intralaminar, midline, and medial thalamic nuclei. We conclude that the projection field of VB in the parietal cortex coincides precisely with the first somatic sensory area (SI) as defined by single unit studies (Pubols et al., '76). The VB projection field also delineates the area of the first motor (MI) representation. Thus, there is no separation of SI and MI cortex in the opossum. The posterior parietal area lies outside of SSM cortex and has thalamic connections similar to the posterior parts of parietal cortex in other mammals.
Widespread corticostriate projections from temporal cortex of the rhesus monkey
Authors: Van Hoesen Gary W. , Yeterian Edward H. , Lavizzo‐Mourey Risa
Published: January 2005

The corticostriate projections of temporal areas TA, TE, TF, TG, 35, and 28 were studied in the rhesus monkey with the use of autoradiography. Widespread projections were observed to rostral as well as caudal parts of the striatum for all areas except area 28. For example, areas TA and TG have sizable projections to the medial or periventricular part of the head of the caudate nucleus, as well as to the medial part of the tail of this structure and the dorsally adjacent putamen. Areas TE and TF also were observed to send strong projections to the head of the caudate nucleus. In addition, they project to the rostral putamen. Both have projections to the tail of the caudate nucleus and caudal putamen.

The widespread distribution of temporostriate axons to the rostral striatum suggests strongly that previous silver impregnation studies have not only underestimated the strength of the temporal cortical contribution to the corticostriate system, but also failed to identify the major projection zone of temporostriate axon terminals. For example, while all temporal cortical areas contribute projections to an organized topography in the tail of the caudate nucleus and the ventrocaudal putamen, they were observed consistently to have larger projections to the head of the caudate nucleus and rostral putamen.

These results add to a growing body of evidence which demonstrates the existence of widespread nonmotor cortical input to the basal ganglia, and an organization of this input far greater in complexity than that demonstrated by earlier suppressive silver impregnation methods.
Matching populations of amacrine cells in the inner nuclear and ganglion cell layers of the rabbit retina
Authors: Vaney David I. , Peichl Leo , Boycott B. B.
Published: January 2005

In rabbit retina, neurofibrillar methods stain two populations of amacrines whose cell bodies are located on either side of the inner plexiform layer: on in the ganglion cell layer and the other at the inner margin of the inner nuclear layer. The stained amacrines in the ganglion cell layer have the distinctive cytology of ‘coronate’ amacrines described from Nissl‐stained retina (Vaney, 1980a) and account for about 85% of the displaced amacrines in the rabbit retina. The coronate amacrines have a streak topography similar to that of the ganglion cells; they comprise about 32% of the neurons in the ganglion cell layer although their proportion increases with eccentricity from the visual streak. The cytology of the neurofibrillar stained amacrines in the inner nuclear layer resembles that of the displaced amacrines and their densities are almost equal. The cell bodies of the stained amacrines are smaller than those of the displaced amacrines but larger than most others in the inner nuclear layer; they account for some 2% of the neurons in the amacrine sublayer. Although the cell bodies of both populations are distributed rather evenly, the mosaic of the inner nuclear layer cells is more regular than that of the ganglion layer cells. We propose that the two populations of amacrines stained by neurofibrillar methods correspond to the acetylcholine synthesizing cells labelled by Masland and Mills (1979).
Neurotropic influence of mesenchymal limb target tissue on spinal cord neurite growth in vitro
Authors: Pollack Emanuel D. , Muhlach William L. , Liebig Veronica
Published: January 2005

Peripheral nerve fiber outgrowth from developing spinal cord is proposed to be under the influence of the limb bud target which, at the time of nerve fiber invasion, is in an essentially premuscular, mesenchymal condition. Thus, the true target for elongating spinal nerve fibers in early development is mesenchyme rather than differentiated skeletal muscle. Spinal cord explants derived from stage V larval Rana pipiens were cultured in a defined medium in the presence or absence of mesenchymal limb tissue or limbconditioned medium (LCM). Analysis of quantified neuritic outgrowth under these conditions demonstrated a dependency on the target tissue for enhanced nerve fiber density and oriented growth. The characteristics of neuritic growth in the presence of limb mesenchyme or LCM changed from the relatively sparse and straight outgrowth of control cords to dense, wavy arborizations. Areas of the cord explants nearest the limb tissue exhibited the greatest increases in nerve fiber density and morphologic complexity. Additionally, an inverse relationship existed between growth enhancement and the cord‐to‐target distance. Regulation of directed nerve growth in vitro is suggested to result from a diffusible, target‐originated growth factor that binds to the attachment substratum as a concentration gradient guidance pathway with implications for mechanisms of in vivo nerve growth.
Development of the pyramidal tract in the hamster. II. An electron microscopic study
Authors: Reh Thomas , Kalil Katherine
Published: January 2005

We undertook a qualitative and quantitative electron microscopic study of the growth and development of the pyramidal tract in the hamster to investigate the mode of growth of the axons, the possibility of fiber degeneration during development, and the process of myelination. By calculating the total fiber number as the product of axon density and tract area for several postnatal ages, we found that the pyramidal tract grows through the medulla as a compact bundle containing nearly twice the number of fibers as the mature tract. During the second postnatal week there is a substantial loss of axons followed in the third and fourth weeks by a more gradual loss such that by 34 days after birth the total number of axons reaches the adult value.

Myelination in the hamster pyramidal tract begins at 7 days and continues at a very slow rate until the third postnatal week, when a dramatic increase in myelin formation occurs. By 34 days after birth the number of myelinated axons is approximately 80% that of the adult. As has been reported for other CNS tracts, there does not seem to be a “critical diameter” of an axon that absolutely determines the presence or absence of myelin on a fiber. However, all axons above 0.5 μm in diameter are myelinated at approximately the same rate, while those under this diameter are myelinated much more slowly and even in the adult make up only a small percentage of the total myelinated fibers.
Neurotensin immunoreactivity in the superficial laminae of the dorsal horn of the rat: I. Light microscopic studies of cell bodies and proximal dendrites
Authors: Seybold Virginia S. , Elde Robert P.
Published: January 2005

Although neurotensin perikarya have been identified in the superficial laminae of the dorsal horn, little is known regarding the cytoarchitecture of these neurotensin‐containing neurons. Immunohistochemical staining of 75‐μm sections in several planes through colchicine‐treated rat spinal cords revealed morphologic features of neurotensinlike immunoreactive (NLI) perikarya and proximal dendrites.

Populations of NLI neurons were identified in the outer one‐third of lamina II, the inner one‐third of lamina II, and outer lamina III. The NLI neurons in lamina II had elongated perikarya and the dendrites emerged from the rostral and caudal poles of the cell body. The proximal dendrites of NLI cells in inner laminae II were shorter and contained more spines than outer lamina II NLI cells. The NLI cells in outer lamina III did not exhibit polarity and the proximal dendrites were generally shorter than those of NLI cells in lamina II. The lamina II cells appear similar to islet cells (Gobel, 1975), while the lamina III cells have many of the characteristics of the II/III border cell described by Gobel (1978). Interestingly, the inner lamina II NLI cells occurred in clusters with NLI cells in outer lamina III. The periodicity of these clusters suggests a neurochemical dimension for the organization of the superficial laminae of the dorsal horn.
Brain neurons which project to the spinal cord in young larvae of the zebrafish
Authors: Kimmel Charles B. , Powell Susan L. , Metcalfe Walter K.
Published: January 2005

A small number of brain neurons project to caudal levels of the spinal cord in the larva of the teleost Brachydanio rerio. These cells were identified in animals 6 days after fertilization by backfilling with horseradish peroxidase following transection of the cord at the level of the cloaca. In preparations with the most labeled cells a total of 30–40 were present on each side of the midline. They were located within three regions of the brainstem: the midbrain nucleus of origin of the medial longitudinal fascicle (mlf), the hindbrain reticular formation, and the hindbrain vestibular nucleus. A total of 15 classes of cells could be distinguished by soma positions, dendritic fields, and axonal pathways. For some of these classes only one or two cells were usually present on each side of the brain. Most of the labeled cells contributed axons to the mlf ipsilateral to the soma; however, the Mauthner cells and three new types of hindbrain reticulospinal cells have decussating axons that enter the contralateral mlf.

The observed distribution of labeled reticulospinal cells is similar to that previously described for large reticular cells in adult teleosts and to the system of identified Mauthner and Müller cells in the lamprey.
Lesion‐induced synaptogenesis in the dentate gyrus of aged rats: II. Demonstration of an impaired degeneration clearing response
Authors: Hoff Steven F. , Scheff Stephen W. , Cotman Carl W.
Published: January 2005

Previously we reported that a delayed onset in the reinnervation of the outer two‐thirds of the dentate molecular layer occurred in aged rats after an entorhinal lesion. Several factors associated with formation of new synaptic contacts and removal of degenerative debris may affect the reinnervation process. In this study the appearance and removal of degeneration was analyzed and evaluated with respect to the delayed reinnervation process in aged rats. After a complete lesion of the entorhinal cortex, 85–90% of the input to the outer two‐thirds of the ipsilateral molecular layer is lost. Electron‐dense and electron‐lucent degeneration are present throughout the outer two‐thirds of the denervated molecular layer. In both aged and young adult rats, the electron‐lucent degeneration disappears by 10 days postlesion. The predominant electron dense degeneration, however, is removed at a different rate by young adult and aged rats. Young adults demonstrate a biphasic degeneration removal process, with almost half of this degeneration rapidly lost by 10 days postlesion, and nearly all by 60 days post‐lesion. Aged animals in contrast, have lost only 16% of the dense degeneration at 10 days postlesion, with about 30% of the degeneration remaining at 60 days postlesion. The impaired removal of the degeneration from the denervated zone appears to be reciprocally related to the reinnervation response in both age groups and may be related to the normal astrocyte hypertrophy and elevated corticosteroid levels in aged rats.
The ultrastructure of identified locust motor neurones and their synaptic relationships
Authors: Watson A. H. D. , Burrows M.
Published: January 2005

Motor neurones in the thoracic ganglia of the locust were impaled with microelectrodes and identified according to the muscle they innervated and their other physiological properties. They were then labeled by intracellular injection of horseradish peroxidase and processed for electron microscopy. The nature and distribution of synapses on each motor neurone was examined and, by the use of reconstructions from serial sections, their spatial relationships revealed. The metathoracic fast extensor tibiae and mesothoracic tergosternal flight motor neurones have both output and input synapses on their neuropilar branches. These synapses are involved in serial, reciprocal, and recurrent relationships showing that the structural equivalent of a physiological synapse may be complex. The metathoracic slow extensor tibiae and anterior fast flexor tibiae motor neurones apparently have only input synapses within the neuropile.
Amygdalopetal projections in the cat. I. Cortical afferent connections. A study with retrograde and anterograde tracing techniques
Authors: Russchen Fokje T.
Published: January 2005

The cortical afferent connections of the amygdaloid complex of the cat have been studied by means of retrograde tracing of horseradish peroxidase and the fluorescent substances bisbenzimid and nuclear yellow. Subsequently, anterograde tracing experiments were carried out in order to define more precisely the termination areas of the corticoamygdaloid fibers.

The results of the present study indicate that the main and accessory olfactory bulbs, the anterior olfactory nucleus, the prepiriform cortex and discrete regions of the medial frontal lobe, the insular and temporal cortices, as well as the perirhinal and entorhinal cortices and the ventral subiculum project to the amygdaloid complex. The main termination sites of these projections are the central, basolateral, and lateral amygdaloid nuclei. Neocortical regions project to the lateral nucleus and the lateral division of the lateral central nucleus. The mesocortical regions project predominantly to the basolateral nucleus and a medial division of the lateral central nucleus. In addition, area 35 distributes fibers to the lateral nucleus and the entorhinal cortex projects to the cortical nuclei of the amygdaloid complex. Fibers from the infralimbic area only reach the region of the medial central nucleus. Of the allocortical regions the prepiriform cortex distributes its fibers to the lateral, basolateral, and cortical nuclei, whereas the ventral subiculum projects to the medial division of the lateral central nucleus and the cortical nuclei.

In the neocortical and most of the mesocortical regions the cells which project to the lateral and basolateral amygdaloid nuclei lie in layer III, whereas the cells which project to the central nucleus are located in layer V.
Retinotopic and temporal organization of the optic nerve and tracts in the adult goldfish
Authors: Bunt Stuart M.
Published: January 2005

In order to investigate the role of the different factors controlling the pathways and termination sites of growing axons, selected optic fibers were traced from the eye to the tectum in adult goldfish either by filling them with HRP, or by severing a group of fibers and tracing their degeneration in 2μm plastic sections stained with toluidine blue. Some fish received more than one lesion and others received both lesions and HRP applications. Two major rearrangements of the optic fibers were identified, one at the exit from the eye, the other within the optic tracts.

Near the eye the optic fibers appear to be guided by the conformation of the underlying tissue planes that they encounter. The most recently added fibers, from the peripheral retina, grow over the vitread surface of the older fibers toward the blood vessel in the center of the optic nerve head. Behind the eye the fibers follow this blood vessel until it leaves the side of the optic nerve, and the fibers from peripheral retina are left as a single group on the ventral edge of the optic nerve cross section. As a consequence of this pattern of fiber growth the fibers form an orderly temporal sequence in the optic nerve, with the oldest fibers from the central retina on one side of the nerve and the youngest from peripheral retina on the other. In addition, the fibers are ordered topographically at right angles to this central‐to‐peripheral axis, with fibers from ventral retina on each edge of the nerve, dorsal fibers in the center, and nasal and temporal fibers in between. This arrangement of the optic fibers continues with only a little loss of precision up to the optic tracts. A more radical fiber rearrangement, seemingly incompatibe with the fibers simply following tissue planes occurs within the optic tracts.

Each newly arriving set of fibers grows over the surface of the optic tracts so that the older fibers come to lie deepest in the tracts. This segregation of fibers of different ages ensures that the rearrangement is limited to each layer of fibers. The abrupt reorganization of the fibers occurs as the tracts split around the nucleus rotundus to form the brachia of the optic tracts. The fibers are then arranged with temporal fibers nearest the nucleus rotundus and nasal fibers on the opposite edges of the brachia. From this point the fibers grow out over the tectal surface to their termination sites with only minimal rearrangements. Therefore the optic fiber rearrangements show evidence of several different sorts of constraints acting on the fibers at separate points in the optic pathway, each contributing to the final orderly arrangement of the fibers on the optic tectum.