bluuebunny/crossref_metadata_2025 huggingface dataset:
Role of target tissue in regulating the development of retinal ganglion cells in the albino rat: Effects of kainate lesions in the superior colliculus
Authors: Carpenter Paul , Sefton Ann Jervie , Dreher Bogdan , Lim Wei‐Leng
Published: January 2005

Kainic acid or ibotenic acid was injected unilaterally into the major target regions of the axons of retinal ganglion cells—the superior colliculus (SC) or dorsal lateral geniculate nucleus (DLG)—of rat pups ranging in age from postnatal day 0 to postnatal day 10 (PO – P10). While the collicular or geniculate neurons within the injection site died within 48 hours of the injection, damage to axons and terminals of extrinsic origin within the injection region was not apparent. The neuronal degeneration induced by the neurotoxins, observed at both the light and electron microscopic levels, resembled the neuronal degeneration that occurs in the colliculus during normal development. Macrophages were identified in the regions containing degenerating cells.

Two to three weeks after the injections of neurotoxin, massive injections of the enzyme, horseradish peroxidase (HRP), were made into the retinorecipient nuclei. After about 24‐hour survival time the numbers of retinal ganglion cells were estimated by counting the number of neurons containing HRP reaction products in sample areas distributed in a regular rectangular array across the entire retinal surface.

In the animals in which the neurotoxin was injected into the SC during the first 4 postnatal days, there was a substantial reduction (on average 41.5%; the range: 27.5–65.5%) in the normal number (mean value of 113,000—Potts et al.: Dev. Brain Res. 3:481–486, '82) of retinal ganglion cells surviving the period of naturally occurring ganglion cell death in the retinae contralateral to the injected SC. By contrast, injections of neurotoxins into the DLG and/or the optic tract of newborn rats did not result in a significant reduction in the numbers of retinal ganglion cells surviving the period of naturally occurring ganglion cell death. The period of sensitivity of retinal ganglion cells to the injection of neurotoxin into the colliculi extends from birth to about the end of the first postnatal week; the greatest sensitivity seems to be restricted to the first 3–4 postnatal days.

In the retinae in which the total number (and density) of ganglion cells was substantially reduced by the selective destruction of their target cells, the centroperipheral difference in the somal diameters of the ganglion cells (apparent in normal animals) was abolished, both amongst the whole population of ganglion cells and amongst the ganglion cells with the largest somata, relatively thick axons, and large‐gauge primary dendrites (Class I cells). The number and distribution of the Class I cells in the depleted retinae were, however, unaltered. The abolition of the centro‐peripheral difference in somal sizes results mainly from an increase in the somal size of the centrally located ganglion cells.
Afferent and efferent projections of the inferior area 6 in the macaque monkey
Authors: Matelli Massimo , Camarda Rosolino , Glickstein Mitchell , Rizzolatti Giacomo
Published: January 2005

The rostral part of the agranular frontal cortex (area 6) can be subdivided on the basis of its cytoarchitecture, enzymatic properties, and connections into two large sectors: a superior region, lying medial to the spur of the arcuate sulcus, and an inferior region, lying lateral to it. In this study we traced the afferent and efferent connections of the inferior region of area 6 by injecting small amounts of wheat germ agglutinin conjugated to horseradish peroxidase (WGA‐HRP) and fluorescent tracers (fast blue and diamidino yellow) into restricted parts of inferior area 6 and in physiologically determined fields of area 4.

There is an ordered topographic pattern of connections between inferior area 6 and area 4. The region near the spur of the arcuate sulcus (hand field) projects to the area 4 hand field while the lateral part of inferior area 6 (mouth field) is connected with the corresponding field in area 4. The organization of the connections between the two fields is, however, different. The hand fields in area 6 and 4 have direct reciprocal projections, whereas the mouth field in the postarcuate cortex relays information to area 4 via a zone intermediate between the arcuate and the central sulcus. This zone corresponds to the cytochrome oxidase area F4 (Matelli, Luppino, and Rizzolatti:Behav. Brain Res. 18: 125–137, '85). The inferior area 6 also has topographically organized connections with the supplementary motor area.

The inferior area 6 receives and sends fibers to a series of discrete cortical areas located in the lower cortical moiety (Sanides: The Structure and Function of the Nervous Tissue, Vol. 5. New York: Academic Press, pp 329–453, '72). These areas that form a broad ring around the central sulcus are the ventral bank of the principal sulcus and the adjacent area 46, the precentral operculum (PrOC), area SII (Jones and Burton: J. Comp. Neurol. 168:197–248, '76), the parietal operculum, and the rostral part of the inferior parietal lobule including the lower bank of the intraparietal suclus. Finall, the inferior area 6 has sparse but consistent connections with insular and cingulate cortices. The functional significance of this complex pattern of connections is discussed.
Immunoreactivity in Limulus. II. Studies of serotoninlike immunoreactivity, endogenous serotonin, and serotonin synthesis in the brain and lateral eye
Authors: Chamberlain Steven C. , Pepper John , Battelle Barbara‐Anne , Wyse Gordon A. , Lewandowski Thomas J.
Published: January 2005

Serotoninlike immunoreactivity was examined by the fluorescein‐iso‐thiocyanate‐labeled secondary antibody technique in the lateral eye and brain of Limulus. Endogenous serotonin was measured with high‐perfor‐mance liquid chromatography and electrochemical detection. The synthesis of [3H]serotonin from [3H]tryptophan was measured in the presence and absence of reserpine. Fibers with serotoninlike immunoreactivity were found in the proximal stalks of the corpora pedunculata, in the neuropil of the central body, in the neuropils of the visual centers (lamina, medulla, and ocellar gnaglion), in the optic tract that connects the ocellar ganglion with the posterior medial medulla, and in the central neuropil of the brain. Immunoreactive somata were found in four groups in the brain. Up to 50 somata were scattered through each side of the dorsal medial group that lies centered on the dorsal surface within the curve of the centra body. These neurons innervate the central body neuropil and send processes into the central neuropil. Three of four reactive somata formed the ventral pole of each medullar group. These may provide the innervation of the proximal stalk of the corpora pedunculata. Five to ten reactive neurons were observed anteriorly in the ventral posterior lateral group #2 on each side that send processes into the central neuropil. Ten to 15 reactive somata were found on either side of the midline in the dorsal anterior part of the ventral medial group that contribute processes to the central neuropil. The remainder of the brain was not immunoreactive. No immunoreactive fibers or somata were found in the lateral eye or in the lateral optic nerve. Serotoninlike and substance P‐like immunoreactivities were not found to be colocalized anywhere in the brain. Significant amounts of endogenous serotonin were detected in the lamina and medulla whose neuropils are rich in immunoreactive fibers and in the central body and dorsal medial group that are also rich in immunoreactive somata and fibers. No endogenous serotonin was detected in either the lateral eye of the lateral optic nerve. The lamina, medulla, and central body and dorsal medial group also synthesized and stored [3H]serotonin from [3H]tryptophan. It is likely that serotonin is a neurotransmitter in the brain, but not in the lateral eye of the horseshoe crab. In particular, it appears that serotoninergic neurons may play a role in central visual processing.
Morphology of physiologically identified thalamocortical relay neurons in the rat ventrobasal thalamus
Authors: Harris Roger M.
Published: January 2005

The anatomical structure of physiologically identified neurons of the rat ventrobasal thalamus was studied in order to determine if there are morphologically distinct subsets of neurons that correlate with the somatosensory submodalities processed by these cells. Intracellular recordings were used to determine the modality and receptive field of a neuron, after which horseradish peroxidase was iontophoretically injected into the cell, allowing it to be histologically visualized. Computer‐assisted measurements of the labeled cells were made to quantitatively analyze the dendritic structure. Cells were divided into physiological groups stimulated by whiskers, glabrous skin, furry skin, noxious stimulation, or joint rotation. Qualitatively, all cells appeared similar, with the same types of branching patterns. Dendritic spines and long, sinuous appendages were found on all distal dendrites. Quantitatively, no statistically significant differences in dendritic structure were found between functionally defined groups with the aid of a number of parameters, including a fitted dendritic ellipse. There was a weak correlation between somal cross‐sectional area and receptive field size, suggesting larger cells processed larger receptive fields. In summary, the ventrobasal thalamus of the rat, in contrast to that of higher mammals, appears to contain only one major cell type and to have a very simple neuronal circuitry.
Retinal crowding alters the morphology of alpha ganglion cells
Authors: Kirby Michael A. , Chalupa Leo M.
Published: January 2005

It has been hypothesized that the dendritic field size of individual retinal ganglion cells is regulated early in development by interactions among neighboring cells (Wässle and Reiman, Proc. R. Soc. Lond. B. 200:441–461, 1978). An opportunity to test this hypothesis is provided by the consequences of prenatal enucleation that results in an increased density of ganglion cells in the remaining retina (Chalupa et al., Neuroscience 12:1139–1146, 1984). In the present study we compared dendritic field diameters of alpha ganglion cells in normal retinas to those of adult cats that were monocularly enucleated before birth (on embryonic days 42 and 51) and 6 days after birth. In each animal ganglion cells were labeled by central injections of horseradish peroxidase. The retinas were incubated according to a modified Hanker‐Yates procedure and whole‐mounted. All cells were sampled from the temporal retina along a corridor estalished by a line drawn through the optic disk and the area centralis. Alpha cells were differentiated into ON and OFF subtypes on the basis of their level of stratification in the inner plexiform layer (Peichl and Wässle, Proc. R. Soc. Lond. B. 212:139–156, 1981). Dendritic field and soma diameters were determined from complete cell drawings by calculating the mean of the two longest orthogonal diameters.

Our main findings are: (1) Early monocular enucleation does not disrupt the mosaics of ON and OFF alpha ganglion cells in the remaining retina of adult animals. (2) Within the retinal corridor sampled, the density of alpha cells was substantially greater than normal in the remaining retina of the prenatal enucleates at all eccentricities except the far periphery. (3) Except at the far periphery, the dendritic field diameters of the prenatally enucleated animals were significantly smaller than normal when compared at equivalent eccentricities. However, when compared at equivalent cell densities, dendritic field dimensions in the prenatally enucleated and normal animals were found to be similar. (4) In the prenatal enucleates the somas of these neurons were also significantly smaller than normal. (5) If the monocular enucleation was postnatal, however, the density and the dendritic field diameters of alpha cells did not differ appreciably from normal.

These results indicate that the morphology of retinal ganglion cells can be influenced by increasing the density of developing ganglion cells. The reduced size of dendritic fields and somas in the remaining retina of prenatally enucleated animals may reflect increased cellular interactions due to ganglion cell “crowding.” It is suggested that both intraretinal interactions and competition among axon terminals contribute to establishing the adult retinal ganglion cell organization.
Multiple cortical targets of one thalamic nucleus: The projections of the ventral medial nucleus in the cat studied with retrograde tracers
Authors: Minciacchi D. , Bentivoglio M. , Molinari M. , Kultas‐Ilinsky K. , Ilinsky I. A. , Macchi G.
Published: January 2005

The organization of the cortical projections of the ventral medial thalamic nucleus (VM) was studied in the cat with retrograde tracers. The extent of the VM‐cortical projections was first investigated with horseradish peroxidase injected in different cortical fields. The results obtained in the experiments indicated that (1) the main target of VM efferents is represented by a large territory anterior to the cruciate sulcus involving area 6 and the gyrus proreus and extending into the anterior part of the medial cortical surface. The afferents to these precruciate fields arise from throughout the VM. In addition, the lateral third of VM projects upon the lateral precruciate cortex that is coextensive with the precruciate part of area 4, whereas VM efferents do not extend into the posterior sigmoid gyrus. (2) A second major target of VM efferents is represented by the insular cortex in the anterior sylvian gyrus. (3) VM projections also reach the prepyriform cortex and the cingulate gyrus. An anteroposterior decrease of density was found in the VM‐cingulate projections. (4) Sparse VM projections reach the temporal cortex, the adjacent posterior sylvian and ectosylvian fields, and the anterior ectosylvian gyrus. (5) No VM projections were found either upon the visual areas 17 and 18 or upon the primary auditory cortex.

The interrelations between some VM‐cortical cell populations and their divergent collateralization were studied by using double retrograde labeling with fluorescent tracers. The results of these experiments demonstrated that a relatively high number (at least 20%) of VM cells projecting to the insula are also connected to the precruciate fields by means of axon collaterals. This finding indicates that VM is a highly collateralized structure of the cat's thalamus. Very few branched cells were found in the other combinations of cortical fields here examined (precruciate vs. posterior sylvian fields, lateral precruciate vs. proreal cortex, anterior vs. posterior cingulate fields). Altogether these data indicate that VM branched cells preferentially interconnect the two main cortical targets of the nucleus, i.e., precruciate and insular fields.

The results of the present study are discussed in regard to the literature on the VM projections in the rat and the previously available data in the cat, to the afferent VM organization in the cat, to the relationship between VM and the nucleus submedius, and to the anatomical and functional role of VM in relation to the so‐called “nonspecific” thalamocortical system.
Species differences in the distribution of substance p and tyrosine hydroxylase immunoreactivity in the olfactory bulb
Authors: Baker Harriet
Published: January 2005

These studies document species differences in the distribution of the peptide substance P and the catecholamine‐synthesizing enzyme tyrosine hydroxylase (TH) within a central nervous system region of a number of mammalian species including the mouse, rat, guinea pig, rabbit, cat, and two species of hamster (Chinese and Syrian). Substance P‐containing neuronal perikarya were observed in the main olfactory bulb (MOB) of both species of the hamster, but not in the MOB of the other species examined. In the accessory olfactory bulb (AOB), however, neuronal staining was observed in all species except the mouse. The number of stained somata and their intensity varied such that label was most prominent in the rat followed in decreasing order by the rabbit, guinea pig, cat, and hamster. The mouse displayed no perikaryal staining. Stained somata in AOB were found in the internal granule cell layer with dendritic processes ramifying through the internal plexiform layer to arborize within the mitral cell layer.

The distribution of substance P‐stained neurons in the MOB also differed between the two hamster strains. In the Syrian hamster, neurons were primarily juxtaglomerular. In the Chinese hamster, labeled perikarya were found in both the juxtaglomerular region and within the superficial aspect of the external plexiform layer (EPL). The mean longest diameter of the majority of substance P‐labeled neurons in both species was greater than 10 μm, suggesting that they were tufted cells. Those in the EPL of the Chinese hamster were the largest (17 μm). Species differences also were observed in the distribution of substance P‐positive axons and terminals within the MOB. Lable was distributed primarily in the internal granule cell layer of the Syrian hamster and the internal plexiform layer of the Chinese hamster.

Tyrosine hydroxylase staining was similar among species with the exception of the Syrian hamster. In the latter species, an additional large population of neurons was found within the external plexiform layer. In all other species, TH‐stained neurons were found scattered throughout the MOB and occasionally the AOB but were not numerous in the EPL. Although most TH neurons were larger than 10 μm, in all species a population of smaller TH cells was observed primarily in the glomerular layer, suggesting that most neurons labeled with TH are tufted cells but that some may be periglomerular cells.

In conclusion, these data suggest that either substance P is present in the MOB of hamsters but is not found in juxtaglomerular neurons of the main olfactory bulb of the mouse, rat, guinea pig, rabbit, or cat, or that species differences exist in the level of substance P or in its processing from precursors. In either case, by using the same fixation and staining procedures, the peptides can be localized in some and not other species, whereas tyrosine hydroxylase staining is similar in all species examined.
Cerebellar nucleocortical projection with a survey of factors affecting the transport of radioactive tracers
Authors: Legendre A. , Courville J.
Published: January 2005

The nucleocortical projection has been studied with the method of anterograde transport of tritiated amino acids and autoradiography. It was observed that this projection is made up of a small number of fibers. Counts of silver grain aggregates in projection sites of the granular layer were compared with counts from material on the cuneocerebellar projection. As it had been concluded in previous studies that the projection is quantitatively important, several modifications of the experimental conditions were tested. Radioactive leucine of high or low specific activity as well as a mixture of amino acids were used. It was observed that labeling is always more intense with a high specific activity tracer. Variations of the aspect and density of the projection were observed with survival periods lasting from a few hours to several days. With survival times between 9 and 15 hours, round aggregates of silver grains measuring from 10 to 20 μm were observed in the granular layer of labeled regions. At longer survival periods, the terminal structures in the granular layer appeared as coarse linear aggregates. It is suggested that the latter represent preterminal labeled fragments while the round accumulations correspond to terminal rosettes. Maximum density of the labeling in the granular layer occured between 9 and 15 hours. At 2 days, the density was lowest, and at 5 or 6 days it was somewhat higher. Even under optimal conditions, the density of the nucleocortical terminals was low.
Comparative anatomy of the ventromedial mesencephalic tegmentum in the rat, cat, monkey and human
Authors: Halliday Glenda M. , Törk Istvan
Published: January 2005

The five component nuclei of the ventromedial mesencephalic tegmentum (VMT) were studied on Nissl stained serial sections of the brain stem of rat, cat, monkey (Macaca nemestrina) and human. Models of the VMT nuclei were constructed to compare their size, shape and disposition across species. For each nucleus ineach species the following were calculated: the volume, the number of neurons, the size distribution of neurons, the mean soma size and the packing density of neurons. The morphology of the cells in the different nuclei is also described.

The parabrachial pigmented nucleus (PBP) forms, on average, 51% of the VMT volume and cell number. The paranigral nucleus (PN) and the central linear nucleus (LC) formed 19% and 14% of the VMT volume and cell number respectively. The relatively small, but compact interfascicular nucleus (IF) was on average 9% of the VMT volume and cell number and the rostral linear nucleus (LR) formed its remaining 7%. However, in different species the relative prominence varies between species. Thus PBP is the largest of the VMT nuclei in the monkey, PN is particularly well developed in the human, IF contains a particularly large number of cells in the rat, and LR and LC are strongly developed in the cat.

This study presents a cytoarchitectonic description of the five nuclei in each species. The distinctive cytoarchitectonic appearance of each nucleus suggests that their functions may differ. This possibility, which is strengthened by evidence that the projections of the VMT nuclei are differential, may need to be considered in the interpretation of the results of experimental investigations using stimulation and/or lesion experiments in the VMT region and in the interpretation of pathological findings in the human brain.
Colonization of the bowel by the precursors of enteric glia: Studies of normal and congenitally aganglionic mutant mice
Authors: Rothman Taube P. , Tennyson Virginia M. , Gershon Michael D.
Published: January 2005

The terminal portion of the ls/ls mouse is congenitally aganglionic because the precursors of enteric neurons fail to enter this region. This animal was studied in order to gain insight into the origin of enteric glia and into the process by which the precursors of these cells colonize the gut. In control (CD‐1) mice, immunoreactivity of the glial marker, glial fibrillary acidic protein, appeared for the first time in the fetal bowel at day E16 and, in adults, was much more intense within intraenteric neural elements than in nerves outside the bowel. Glial fibrillary acidic protein developed in tissue cultures of fetal intestine explanted before the protein appeared in situ, and before the bowel became innervated by extrinsic nerves; thus, the precursors of cells able to elaborate glial fibrillary acidic protein must have been present, but unrecognizable, in the original explants. This explant assay demonstrated that these glial precursors were present in all regions of the bowel of control mice, but not in the presumptive aganglionic bowel of ls/ls mice. The nerves (of extrinsic origin) in the aganglionic tissue of ls/ls mice showed a high level of immunoreactive glial fibrillary acidic protein; nevertheless, their ultrastructure was typical of peripheral nerve, not enteric plexus, and they contained Schwann cells, not enteric glia. These observations support the view that enteric glia are derived from the single wave of neural crest colonists that populates the enteric nervous system before the gut receives its extrinsic innervation. These glial precursors, like neuronal precursors, tend to be excluded from the presumptive aganglionic ls/ls bowel. In contrast, Schwann cells grow into the abnormal ls/ls gut with the extrinsic innervation. The enteric microenvironment appears to promote the expression of glial fibrillary acidic protein in both enteric glia and Schwann cells; however, even within the bowel, Schwann cells retain their characteristic morphology. It is thus probable that the normal enteric nervous system contains supporting cells of separate lineages, enteric glia and Schwann cells.
Synaptic relationships between neurons containing vasopressin, gastrin‐releasing peptide, vasoactive intestinal polypeptide, and glutamate decarboxylase immunoreactivity in the suprachiasmatic nucleus: Dual ultrastructural immunocytochemistry with gold‐substituted silver peroxidase
Authors: van den Pol Anthony N. , Gorcs Tamas
Published: January 2005

In order to examine the morphological substrates for neuronal connections between cells of the hypothalamic suprachiasmatic nucleus (SCN) that contain immunoreactivity for different neurotransmitters, a double ultrastructural immunocytochemical analysis was used. For double immunostaining, the first neuroactive substance antigen was labeled with goldsubstituted silver‐intensified peroxidase (GSSP), which results in a granular gold deposit of high electron and light opacity. The second antigen was labeled with peroxidase and a diaminobenzidine chromagen.

The GSSP reaction product greatly increased the visibility of immunoreactive structures, with both light and electron microscopy. Intensification with the GSSP method worked at all depths of thick tissue sections as determined with analysis of immunostained sections cut perpendicular to their flat surface, and with analysis of thick 80‐μm sections of brain tissue into which horseradish peroxidase (HRP) has been microinjected. On a nitrocellulose dot‐blot comparison of different substrates for HRP, the GSSP intensification compared favorably with tetramethylbenzidine, but unlike tetramethylbenzidine, the GSSP was stable in a wide range of buffers. In addition to diaminobenzidine, the GSSP reaction was used to intensify and stabilize both the Hanker‐Yates reagent and tetramethylbenzidine on the nitrocellulose model system.

Through the use of the GSSP reaction, five new synaptic relationships in the suprachiasmatic nucleus were revealed. By increasing the sensitivity of the peroxidase method by silver‐gold intensification, immunoreaction product could be found in dendrites at a greater distance from the perikaryon than in nonintensified material. Because of this greater sensitivity, the neuroactive substance contained in the cell of origin of a dendrite could sometimes be identified. Boutons immunoreactive for vasopressin‐associated neurophysin were found to make synaptic contact with postsynaptic dendrites that also contained vasopressin‐neurophysin immunoreactivity. Similarly, boutons containing gastrin‐releasing peptide immunoreactivity made synaptic contact with cells also exhibiting gastrin‐releasing peptide immunoreactivity.
Origin and ultrastructural identification of dorsal column nuclear synaptic terminals in the basilar pontine gray of rats
Authors: Kosinski R. J. , Azizi S. A. , Border B. G. , Mihailoff B. G. A.
Published: January 2005

The ultrastructural characteristics of HRP‐WGA‐labeled or degenerating axon terminals arising from neurons in the dorsal column nuclei (DCN) were identified within the contralateral basilar pontine nuclei (BPN) following unilateral HRP‐WGA injections or ablations of the DCN. The cells of origin of these projections were also identified through the application of the retrograde tracer HRP‐WGA.

Two groups of degenerating DCN‐pontine terminals were identified. Both formed asymmetrical synaptic contacts with dendritic shafts and/or dendritic appendages of pontine neurons. One group of degenerating terminals contained small, round synaptic vesicles, while the other exhibited a mixture of dense core and pleomorphic vesicles. The former group, which clearly represented the majority of degenerating terminals observed, was interpreted to progress from an early filamentous form of degeneration to a later electron‐dense variety and to originate from dorsally located DCN cells distributed primarily at the level of and just caudal to the area postrema. Other DCN‐labeled neurons were more ventrally located and were postulated to give rise to those degenerative boutons that contained a mixture of dense core and pleomorphic‐shaped vesicles. The present study also identified the cells of origin of two additional projections to the basilar pons: one from cells in the external cuneate nucleus and another from neurons of the medullary reticular formation.
Coincidence of patchy inputs from the lateral geniculate complex and area 17 to the cat's clare‐bishop area
Authors: Sherk Helen
Published: January 2005

Pathways from a variety of structures to the largest of the cat's suprasylvian visual areas, the Clare‐Bishop area, were found to be patchy. These inputs arose from the lateral geniculate complex, from area 18, from area 19, and, as noted by Montero (Brain Behav. Evol. 18:194–218, '81), from area 17. The Clare‐Bishop area was previously delineated on the basis of its uniform pattern of connections with cortex and thalamus (Sherk: J. Comp. Neurol. 247:1–31, '86) and found to incorporate pieces of several retinotopically defined areas (Tusa, Palmer, Rosenquist: Cortical Sensory Organization. Vol 2. Multiple Visual Areas. Clifton, NJ: Humana Press, pp. 1–31, '81). However, since individual patches did not correspond to particular retinotopically defined areas, other explanations of afferent patchiness were sought.

An obvious question is whether the patches originating from different sources are systematically related to each other. Two hypotheses were considered. First, different inputs—for example, from the lateral geniculate nucleus (LGN) and from area 17—might terminate in intermingled but mutually exclusive zones in the Clare‐Bishop area. Second, multiple patches of input might reflect duplicate representations of the corresponding visual field segment in the Clare‐Bishop area. Both hypotheses were tested by injecting the lateral geniculate complex and either area 17 or area 19 with different anterograde tracers. In each case the two injections involved regions of the visual field that coincided to some degree, ranging from near‐total overlap to almost complete exclusion. The first hypothesis predicted that the different labels in the Clare‐Bishop area would never be found to overlap, while the second hypothesis predicted that when injections were closely matched retinotopically, there would be extensive overlap between patches.

The results supported the second hypothesis: the better the retinotopic match between injections, the greater the overlap found between labeled geniculate and cortical input in the Clare‐Bishop area. However, the multiplicity of patches seen in some experiments, and the close spacing between some patches, suggested that an additional, nonretinotopic mechanism also contributes to patchiness in the projections to the Clare‐Bishop area.
Frontal eye field as defined by intracortical microstimulation in squirrel monkeys, owl monkeys, and macaque monkeys: I. Subcortical connections
Authors: Huerta Michael F. , Krubitzer Leah A. , Kaas Jon H.
Published: January 2005

Intracortical microstimulation was used to define the borders of the frontal eye fields in squirrel, owl, and macaque monkeys. The borders were marked with electrolytic lesions, and horseradish peroxidase conjugated to wheat germ agglutinin was injected within the field. Following tetramethyl benzidine histochemistry, afferent and efferent connections of the frontal eye field with subcortical structures were studied. Most connections were ipsilateral and were similar in all primates studied. These include reciprocal connections with the following nuclei: medial dorsal (lateral parts), ventral anterior (especially with pars magnocellularis), central lateral, paracentral, ventral lateral, parafascicular, medial pulvinar, limitans, and suprageniculate. The frontal eye field also projects to the ipsilateral pretectal nuclei, subthalamic nucleus, nucleus of the posterior commissure, superior colliculus (especially layer four), zona incerta, rostral interstitial nucleus of the medial longitudinal fasciculus, nucleus Darkschewitsch, dorsomedial parvocellular red nucleus, interstitial nucleus of Cajal, basilar pontine nuclei, and bilaterally to the paramedian pontine reticular formation and the nucleus reticularis tegmenti pontis. Many of these structures also receive input from deeper layers of the superior colliculus and are known to participate in visuomotor function. These results (1) reveal connections that account for the parallel influence of the superior colliculus and the frontal eye field on visuomotor function; (2) suggest that there has been little evolutionary change in subcortical connections, and therefore function, of the frontal eye fields since the time that these lines of primates diverged; and (3) support the conclusion that the frontal eye fields are homologous in New and Old World monkeys.
Changes in the numerical density of synaptic contacts with long‐term potentiation in the hippocampal dentate gyrus
Authors: Desmond Nancy L. , Levy William B.
Published: January 2005

Long‐term potentiation (LTP) in the rat dentate gyrus is a multifaceted phenomenon, including synaptic potentiation; simultaneous synaptic depression at neighboring, unconditioned synapses; and a change in the amount of cell firing produced by a specified amount of synaptic current (see Levy and Desmond: In G. Buzsaki and C. Vanderwolf (eds): Electrical Activity of The archicortex. Budapest: Akademiai Kiado, pp. 359–373, ′85b). This study presents long‐term anatomical modifications that seem related to excitatory synaptic modification. These anatomical alterations appear early and persist for at least 60 minutes following conditioning stimulation.

Each animal received test pulse stimulation delivered alternately to the angular bundles before and after brief, unilateral high‐frequency conditioning stimulation that is typical of many LTP paradigms. Anataomical preparation followed standard procedures. Double‐blind scoring procedures quantified the number of asymmetric synapses in the dentate molecular layer. These counts were converted to the number of synapses per unit volume using stereological corrections that combined geometrically derived theory and modest serial sectioning. Multivariate analysis of variance evaluated the statistical significance of changes in synapse density.

Across all three groups of animals, conditioning stimulation does not significantly change the density of synaptic contacts across the entire molecular layer. There is a trend for a decreased density of synaptic contacts in the middle molecular layer, the region activated by the conditioning stimulation. Here the density of concave spine profiles increases significantly in all three groups of animals with conditioning stimulation. This increase accompanies significant decreases in the density of nonconcave, simple and ellipsoid, spine profiles. No significant changes in the density of shaft synapses occur with LTP‐inducing conditioning stimulation.

These data suggest that the concave spine profiles are a correlate of LTP‐inducing stimulation and may be the potentiated synapses. We hypothesize that with synaptic potentiation there occurs an interconversion of spine synapses such that some nonconcave spine profiles become concave spine profiles. Such an interconversion apparently begins shortly after the conditioning stimulation and persists for at least 60 minutes.
Comparative aspects of the primate posterior cingulate cortex
Authors: Armstrong Este , Zilles Karl , Schlaug Gottfried , Schleicher Axel
Published: January 2005

Cytoarchitecturally defined cortical areas of the posterior cingulate gyrus differ morphometrically among the major taxonomic divisions of primates. Prosimians and anthropoids have different laminar proportions in the isocortical regions (areas 30, 23, and 31); anthropoids have relatively larger outer main laminae and granular layers than prosimians. In the granular retrosplenial cortex (area 29), however, prosimians and anthropoids differ only in the proportion of the molecular layer to the rest of the cortex. On the other hand, the proportions of the inner and outer main laminae of area 29 differ between the infraorder divisions of Anthropoidea, the catarrhines, and the platyrrhines. The platyrrhines (New World monkeys) have apparently specialized by increasing the outer main lamina of area 29, which contains afferent and intracortical connections. Among all primates, the amount of neuropil in each cortical region changes as a function of brain weight, but within each area, the neuropil maintains a constant ratio between the outer and inner laminae. These observations suggest that neuropil ratios are conservative features in primates and that evolutionary changes more frequently involve shifts in volumetric proportions. Furthermore, the platyrrhine‐catarrhine differences in area 29 likely evolved after the prosimian‐anthropoid differences were established in the isocortical cingulate regions.
A forebrain atlas of the lizard gekko gecko
Authors: Smeets Wilhelmus J. A. J. , Hoogland Piet V. , Lohman Anthony H. M.
Published: January 2005

An atlas of the forebrain of the lizard Gekko gecko has been provided, which will serve as the basis for subsequent experimental tracing and immunohistochemical studies. Apart from a strongly developed medial cortex and septal area, the Tokay gecko shows all the main features of the forebrain of the lacertid‐type lizards. When its convenience as an experimental animal is also taken into account, this species seems to be very suitable for studying the limbic system in reptiles. The atlas comprises topographical reconstructions of the telencephalon and diencephalon and a series of transverse sections of which the levels have been indicated in the reconstructions. The results obtained in the Gekko are briefly compared with those found in other lizards studied.
Callosal connectivity of areas V1 and V2 in the newborn monkey
Authors: Dehay C. , Kennedy H. , Bullier J.
Published: January 2005

The callosal connectivity of areas V1 and V2 in the newborn monkey has been investigated with the neuroanatomical tracers wheat germ agglutinin conjugated to horseradish peroxidase and free horseradish peroxidase. In the adult, callosal projecting neurons in cortex subserving the lower parafoveal visual field were found to extend from the V1/V2 border for a distance of 1—2.5 mm into V1 and 8 mm into V2. In the newborn, the tangential extent and total number of callosal projecting neurons were the same as in the adult.

Within area V1, callosal projecting neurons in the adult and newborn were limited to supragranular layers. In the adult, axon terminals of callosal projections were located in layers 4B and 5 and were exluded from layer 4C. In the newborn, axon terminals were more extensively distributed than in the adult and invaded layer 4C.

In area V2, the laminar distribution and the patchy location of callosal connections in regions of high cytochrome oxidase activity were similar in the newborn and adult animals. In both newborns and adults, the patchy distribution of callosal projections persisted when the neuroanatomical tracers were injected over extensive regions of the contralateral striate and extrastriate cortex.

In the adult, area V1 and V2 project contralaterally to two heterotopic sites located in the fundus of the lunate sulcus and the superior temporal sulcus. This was also found to be the case in the newborn. In the adult the terminals of these heterotopic projections were focused in layer 4. This was not the case in the newborn, where after injection limited to the contralateral V1/V2 border they were more evenly distributed among the different cortical layers Following extensive contralateral injection of tracer, terminals in cortex anterior to V2 were focused over layer 5 and the bottom of layer 4.
Innervation of extraocular muscles in the rabbit
Authors: Murphy E. H. , Garone M. , Tashayyod D. , Baker R. B.
Published: January 2005

The innervation of extraocular muscles in the rabbit was studied by using the methods of horseradish peroxidase (HRP) histochemistry, gross dissection, and quantitative morphology. Subdivisions of the oculomotor complex that innervate the superior rectus, inferior rectus, medial rectus, and inferior oblique and levator palpebrae are described, and our results are in agreement with previous accounts of the projections of this nucleus. Our analysis of the innervation of the lateral rectus and retractor bulbi muscles, however, differs from previous descriptions. The axons of approximately 80% of neurons in the abducens nucleus are in the VIth nerve and innervate the lateral rectus muscle, and approximately 15–20% are internuclear neurons both surrounding and intermingling with the motor neurons of the abducens nucleus. The interneurons project to the medial rectus subdivision of the contralateral oculomotor complex via the medial longitudinal fasciculus (MLF). Neurons in both the abducens and the accessory abducens nucleus innervate the retractor bulbi muscles via the VIth nerve. All neurons in the accessory abducens nucleus innervate the retractor bulbi muscles, but gross dissection revealed that the retractor bulbi is also innervated by the IIIrd nerve. The bases for differences between our data and previously published descriptions are discussed.

The trochlear nucleus of the rabbit has not been previously studied by methods of axonal trbansport. The body of the nucleus, its caudal tail, the trajectories of axons entering the trochlear nerve, and soma size distributions are described. The trochlear nucleus contains approximately 900 neurons; most are motoneurons the axons of which travel in the trochlear nerve and decussate in the anterior medullary velum. Approximately 3% of trochlear motor neurons innervate the ipsilateral superior oblique muscle. Their soma size is significantly smaller than that of contralaterally projecting neurons. For comparative purposes, the innervation of extraocular muscles by the trochlear nerve was also investigated in several rodents and carnivores. In all animals studied, the percentage of trochlear neurons innervating the ipsilateral superior oblique muscle was strikingly uniform (2—4%).

Gross dissection of the extraocular muscles revealed in the rabbit a muscle, innervated by the trochlear nerve, for which we propose the name “tensor trochleae.” In the rabbit, this muscle is innervated by approximately one‐third of the trochlear motor neurons. This tensor trochleae muscle slip was observed in no other mammal in which we made gross dissections, and it has only previously been described, as an anomalous muscle, in humans. It is hypothesized that its function, in the rabbit, is to retract the muscle enclosed in the trochlea during superior oblique activation.
Descending pathways to the spinal cord in the himé salmon (landlocked red salmon, oncorhynchus nerka)
Authors: Oka Yoshitaka , Satou Masahiko , Ueda Kazuo
Published: January 2005

Distribution and morphology of the cells of origin of the descending spinal pathways and their axonal courses were studied in the himé salmon, using retrograde labelling with cobaltic lysine and horseradish peroxidase (HRP). Following application of the tracers to the cut end of the spinal cord or injection of the tracers at the 10th to 15th spinal segment, neurons mainly labelled via the axons of passage were distributed in the mesencephalon and the rhombencephalon. Mesencephalic cell groups consisted of the nucleus pretectalis, the nucleus fasciculi longitudinalis medialis, and the nucleus ruber. The former two cell groups sent their axons to the fasciculus longitudinalis medialis. The axons of the nucleus ruber formed a separate loose bundle, the “tractus rubrospinalis.” The rhombencephalic cell groups consisted of the rhombencephalic reticular formation, the Mauthner cells (one cell for each side), and the octavolateral area. The rhombencephalic reticular formation could be further subdivided into the nucleus reticularis superior, nucleus reticularis medius, and nucleus reticularis inferior. The axons of these cell groups joined the fasciculus longitudinalis medialis and the “tractus bulbospinalis.” The Mauthner cell had two main gigantic dendrites, and its giant axons formed a conspicuous fiber of Mauthner throughout the rhombencephalon down to the spinal cord. The octavolateral area could be subdivided into the nucleus vestibularis magnocellularis, nucleus tangentialis, nucleus vestibularis descendens and nucleus intermedius. The axons of the nucleus vestibularis magnocellularis and nucleus intermedius entered the fasciculus longitudinalis medialis and/or the tractus bulbospinalis. Those of the nucleus vestibularis descendens and nucleus tangentialis formed the “tractus vestibulospinalis”. The descending spinal pathways of the himé salmon were compared with those of other fishes and other vertebrates. The significance of these descending spinal pathways in the control of locomotion and sexual behavior is also discussed.
Ascending pathways from the spinal cord in the himé salmon (landlocked red salmon, oncorhynchus nerka)
Authors: Oka Yoshitaka , Satou Masahiko , Ueda Kazuo
Published: January 2005

The ascending pathways from the spinal cord of the himé salmon were anterogradely labelled by the cobaltic lysine method, and their courses and terminations were examined. Following application of the cobaltic lysine to the cut end of the spinal cord or injection of the cobalt at the 10th to 15th spinal segment, labelled axons were traced from the spinal cord to various regions in the rhombencephalon and the mesencephalon. The axons ascending from the dorsal funiculus gave off many terminals as they ascended to the lower medulla. This terminal area may be homologous to the nucleus funiculi dorsalis of other vertebrates, although cytoarchitectural differentiation of the area is not evident. The dorsal funicular fibers also formed some terminals in the vagus and glossopharyngeal motor nuclei and the nucleus fasciculi solitarii. The axons arising from the anterolateral funiculus ascended as the common trunk of the lemniscus spinalis. The lemniscus spinalis fibers distributed many axon terminals on their way through the lower medulla, and most probably made synaptic contacts with the peripheral dendrites of the cells of origin of the reticulospinal pathways throughtout its rostrocaudal extent. They also projected to all the medullary cranial nerve motor nuclei (V, VI, VII, IX, and X). The rostral continuation of the lemniscus spinalis fibers entered the lemniscus lateralis and gave a rostrocaudally elongated terminal area in the nucleus lateralis of the torus semicircularis. The tractus spinocerebellaris branched from the common trunk at the level of the Vth nerve entry. The tractus spinocerebellaris terminated in the granular layers of the eminentia granularis and the valvula cerebelli, and sparsely in the corpus cerebelli as well.
Differentiation and maturation of the sensory hair bundles in the fetal and postnatal vestibular receptors of the mouse: A scanning electron microscopy study
Authors: Mbiene J.‐P. , Sans A.
Published: January 2005

By means of scanning electron microscopy, the differentiation and maturation of sensory hair bundles have been studied in the ampullar cristae of the mouse during development from gestational day 13 (GD13) to postnatal day 10 (PD10). Two gradients of ciliary differentiation were demonstrated, one from the apex to the base and the other from the center to the periphery. The different hair bundles that appeared on the crista during the fetal period originated in an initial ciliary stage found in regions undergoing differentiation, which was visible at the apex of the crista starting on GD14. This stage of ciliary development is gradually followed by a juvenile one at GD15. Starting on GD18, the maturation of hair bundles in the central apical area differed from that in the peripheral areas and prefigured the regional specialization of the crista found in the adult stage. In the discussion, we suggest that when the vestibular epithelial cells begin to exhibit ciliary differentiation, they are simultaneously contacted by nerve fibers.