bluuebunny/crossref_metadata_2025 huggingface dataset:
Cell proliferation during early development of the chick embryo otic anlage: Quantitative comparison of migratory and nonmigratory regions of the otic epithelium
Authors: Alvarez Ignacio S. , Martín‐Partido Gervasio , Rodríguez‐Gallardo Lucía , González‐Ramos Carmen , Navascués Julio
Published: January 2005

During development of the otic anlage, a certain proportion of epithelial cells migrate toward the mesenchymal compartment to form part of the acoustic‐vestibular ganglion. The migrating cells are observed only in the zone of the otic anlage that will make contact with the acoustic‐vestibular ganglion (so‐called ganglion zone). In Hamburger and Hamilton's stages 13 to 16, the number of epithelial cells that migrate is relatively low, but it becomes steadily higher from stage 17 on. In the otic anlage of chick embryos, between developmental stages 9 and 21 (48 to 94 hours of incubation), mitotic index, apical or basal localization within the epithelium of dividing cells, and orientation of the mitotic spindles were analyzed. These features in the ganglion zone were compared with observations in the rest of the otic epithelium, where migratory processes do not take place. In stages 13 to 15, when few epithelial cells are migrating, the mitotic index (MI) in the ganglion zone of the otic anlage is similar to that in nonmigratory regions. In more advanced stages, however, when cell migration becomes accelerated, the MI in the migratory zone of the otic wall is significantly higher than that in the rest of the otic epithelium. This suggests an intimate relationship between the migration of otic epithelial cells and a high rate of cell proliferation, the possible nature of which is discussed. Although the majority of mitoses in the otic anlage are located at the apical surface of the epithelium, from stage 13 onward, a few dividing cells are seen in the basal third of the epithelium. Furthermore, these basal mitoses appear exclusively in the migratory zone of the otic anlage, thus suggesting a possible relationship between epithelial cell migration and basal mitosis. During the developmental period prior to stage 18, no significant differences in mitotic spindle orientation are noted between migratory and nonmigratory zones of the otic anlage. In contrast, in stages of maximal otic epithelial cell migration (stages 19 to 21), the frequency of mitoses with the spindle axis oriented radially is significantly higher in the migratory zone. These findings point toward a close correlation between increased frequency of radial mitotic spindle orientation and intense cell migration, although the exact nature of this relationship is as yet unknown.
Morphology and distribution of neurons immunoreactive for substance P in the turtle retina
Authors: Cuenca Nicolas , Kolb Helga
Published: January 2005

Immunocytochemical staining procedures with the HRP‐complexed antibody to substance P have been carried out on the turtle retina. Examination by light microscopy of wholemount retinas has allowed us to evaluate the morphology and distribution of the substance P immunoreactive cell types. Two amacrine cell types and two or more ganglion cell types are stained in our hands. Type A amacrines are tri‐stratified wide‐field amacrines. They have their major dendrites in S1 and S3 of the inner plexiform layer and they emit fine dendrites from the major dendrites that end in varicose boutons in S5 on and around cell bodies in the ganglion cell layer. Some of the dendrites in S1 radiate out in axon‐like fashion for 1 mm across the retina. The type B amacrine cells are small to medium‐field in dendritic extent. They have smaller cell bodies than type A and a single or, at most, two primary dendrites that pass directly to S3 before branching profusely into an intricate net‐like dendritic field. The ganglion cells that are stained with substance P antibodies appear to be of several types but their exact morphologies are in doubt because only portions of their major dendrites are stained. Substance P immunoreactive axons are clearly seen to project from the cell bodies to the optic nerve head and axons are stained in the optic nerve itself.

The substance P‐stained ganglion cells occur in an irregular distribution that reaches a peak density in an elongated band parallel to and 1 mm below the visual streak. The type B amacrine cells reach a maximum density in the visual streak and are distributed in a highly regular mosaic decreasing in density in elliptical isodensity contours from the visual streak. In contrast the type A amacrine cells are rare or absent in the streak, being located in an irregular mosaic in peripheral retina.
On the number of purkinje cells in the human cerebellum: Unbiased estimates obtained by using the “fractionator”
Authors: Nairn J. G. , Bedi K. S. , Mayhew T. M. , Campbell L. F.
Published: January 2005

Stereological estimates of the numbers of Purkinje cell nucleoli in human cerebellar cortex have been obtained from systematic random samples of tissue by using the fractionator. The estimates are unbiased by fixation, section thickness, or sampling errors and are independent of any assumptions about cell shape, size, or spatial orientation. Twelve brains from aged subjects of both sexes were examined.

The average complement of nucleoli in four female brains (age range 71–93 years) amounted to 14.8 millions (with an observed coefficient of variation between subjects of 29%). For three male brains (76–91 years), the corresponding estimates were 15.7 millions (10%). No significant sex differences were found for these small samples. Five brains of unknown sex and age yielded values of 15.8 millions (18%).

For the twelve brains examined, the total number of Purkinje cell nucleoli per cerebellum was found to be 15.4 millions (19%). Estimated numbers showed a significant positive correlation with cerebellar weights. The number of nucleoli in an individual cerebellum was obtained with high precision in as short a time as 4 hours.
Development of calcitonin gene‐related peptide (CGRP) immunoreactivity in relationship to the formation of neuromuscular junctions in Xenopus myotomal muscle
Authors: Benjamin Peng H. , Chen Qiming , de Biasi Silvia , Zhu Dingliang
Published: January 2005

Immunoreactivity (IR) to calcitonin gene‐related peptide (CGRP) has recently been found in chick motoneurons. Bath application of this peptide causes an increase in surface acetylcholine receptor (AChR) density and cAMP level in cultured chick muscle cells. These results suggest a role for this peptide in the formation of synaptic specializations. In this study, we examined the development of CGRP IR in larval Xenopus myotomal muscle in relation to synaptogenesis. Using an antiserum against CGRP, a monoclonal antibody against the p65 synaptic vesicle antigen and a fluorescence conjugate of α‐bungarotoxin, we followed the development of synaptic specializations with fluorescence microscopy in whole‐mount specimens. We found that the postsynaptic specialization in the form of AChR clusters was first detected in stage 22 (24 hour) embryos. The presynaptic specializations, including the synaptic vesicle clusters as evidenced by p65 antibody staining and CGRP IR, were first detected at stage 32 (40 hours). The appearance of these two presynaptic specializations followed the same time course. Subsequently, all three structures, the AChR clusters, CGRP IR, and synaptic vesicle clusters, were colocalized at the neuromuscular junction (NMJ). This shows that CGRP is unlikely to be involved in signaling the development of the postsynaptic apparatus. This premise is further examined in cultures of Xenopus myotomal muscle cells. CGRP at concentrations up to 1 μM did not affect the number of AChR clusters, nor did it interfere with the formation of clusters induced by polycation‐coated beads. In contrast, an extract from the basement membrane of Torpedo electric organ promoted the formation of AChR clusters and interfered with the clustering activity of the beads. These results suggest that CGRP, an integral component of the presynaptic specialization, is not involved in signaling synaptogenesis at the NMJ.
Corticotropin‐releasing factor immunoreactivity in monkey neocortex: An immunohistochemical analysis
Authors: Lewis David A. , Foote Stephen L. , Cha Choong I.
Published: January 2005

Corticotropin‐releasing factor (CRF) has been implicated in the patho‐physiology of certain human neuropsychiatric disorders that affect neocortical function. However, the anatomical organization of CRF‐containing structures in the expanded and highly differentiated primate neocortex has not been previously described. In this study, the distribution of CRF‐immunoreactive neurons and processes was characterized in the neocortex of New World squirrel monkeys (Saimiri sciureus). Substantial regional differences were present in the density, laminar distribution, and morphological appearance of CRF‐immunoreactive neurons. The greatest density of labeled neurons was present in anterior cingulate cortex. A wide range of intermediate densities of CRF‐immunoreactive neurons was evident in the association regions of the prefrontal, parietal, and temporal cortices. The lowest numbers of CRF‐immunoreactive neurons were observed in the primary visual and primary motor cortices. For example, the density of labeled neurons was nearly five times greater in the anterior cingulate cortex than in the precentral cortex.

CRF‐immunoreactive neurons were also distributed in at least four different laminar patterns. For example, in the agranular anterior cingulate cortex, labeled cell bodies were distributed throughout layers II, III, and V. In other regions, such as the posterior cingulate cortex, labeled neurons were present in layers II, III, and IV. In contrast, labeled neurons were predominantly present in layers II and superficial III of the visual cortex, whereas in the inferior temporal cortex, they were present predominantly in layer IV.

Regional and laminar differences were also present in the relative distributions of the two major morphological types (as defined by cell body shape) of CRF‐immunoreactive neurons. Vertically oriented oval neurons, which frequently had a single dendritic process arising from each somal pole, were most frequently found in layer III. In contrast, the labeled neurons in layers II and IV tended to have a round‐ or triangular‐shaped soma. In layer IV of some association cortices, these multipolar neurons were associated with a high density of rod‐like structures composed of large immunoreactive varicosities clustered together in vertical arrays. These structures were frequently found to be located immediately below the soma of pyramidal neurons. Comparison of these findings with Golgi impregnation studies strongly suggests that CRF is present in the soma and axonal cartridges of a subset of chandelier neurons.

The heterogeneous distribution and morphological diversity of CRF‐containing neurons suggest that CRF may mediate distinct functions in different regions and layers of monkey neocortex.
Embryonic development of four different subsets of cholinergic neurons in rat cervical spinal cord
Authors: Phelps Patricia E. , Barber Robert P. , Brennan Lynn A. , Maines Victor M. , Salvaterra Paul M. , Vaughn James E.
Published: January 2005

The developmental stage at which a neuron becomes committed to a neurotransmitter phenotype is an important time in its ontogenetic history. The present study examines when choline acetyltransferase (ChAT) is first detected within each of four different subsets of cholinergic neurons previously identified in the cervical enlargement of the spinal cord: namely, motor neurons, partition cells, central canal cluster cells, and dorsal horn neurons. By examining the temporal sequence of embryonic development of these cholinergic neurons, we can infer the relationships between ChAT expression and other important developmental events.

ChAT was first detected reliably on embryonic day 13 (E13) by both biochemical and immunocytochemical methods, and it was localized predominantly within motor neurons. A second group of primitive‐appearing ChATpositive cell was detected adjacent to the ventricular zone on E14. These neurons seemed to disperse laterally into the intermediate zone by E15, and, on the basis of their location, were tentatively identified as partition cells. A third group of primitive ChAT‐immunoreactive cells was detected on E16, both within and around the ventral half of the ventricular zone. By E17, some members of this “U”‐shaped group appeared to have dispersed dorsally and laterally, probably giving rise to dorsal horn neurons as well as dorsal central canal cluster cells. Other members of this group remained near the ventral ventricular zone, most likely differentiating into ventral central canal cluster cells.

Combined findings from the present study and a previous investigation of neurogenesis (Phelps et al.: J. Comp. Neurol. 273: 459–472, '88), suggest that premitotic precursor cells have not yet acquired the cholinergic phenotype because ChAT is not detectable until after the onset of neuronal generation for each of the respective subsets of cholinergic neurons. However, ChAT is expressed in primitive bipolar neurons located within or adjacent to the germinal epithelium. Transitional stages of embryonic development suggest that these primitive ChAT‐positive cells migrate to different locations within the intermediate zone to differentiate into the various subsets of mature cholinergic neurons. Therefore, it seems likely that spinal cholinergic neurons are committed to the cholinergic phenotype at pre‐ or early migratory stages of their development. Our results also hint that the subsets of cholinergic cells may follow different migration routes. For example, presumptive partition cells may use radial glial processes for guidance, whereas dorsal horn neurons may migrate along nerve fibers of the commissural pathway. Cell‐cell interactions along such diverse migratory pathways could play a role in determining the different morphological, and presumably functional, phenotypes expressed by spinal cholinergic neurons.
Distribution of hyaluronic acid and chondroitin sulfate proteoglycans in the presumptive aganglionic terminal bowel of ls/ls fetal Mice: An ultrastructural analysis
Authors: Tennyson Virginia M. , Payette Robert F. , Rothman Taube P. , Gershon Michaed D.
Published: January 2005

The terminal colon of the ls/ls mouse is aganglionic because an intrinsic defect prevents its colonization by cells migrating from the neural crest. Previous studies showed that laminin, type IV collagen, and glycosaminoglycans accumulate in the region of the presumptive aganglionic ls/ls bowel through which crest‐derived cells would be expected to migrate. It was suggested that crest‐derived cells might fail to enter the abnormal bowel because they receive inappropriate signals from a defective extracellular matrix. This hypothesis was evaluated by analyzing the ultrastructure of the extracellular matrix in mutant and control gut. Tissue was fixed in the presence of ruthenium red before or after selective enzymatic digestion. Heparan sulfate proteoglycan (diameter ≅ 15 nm) and chondroitin sulfate proteoglycan (diameter ≅ 20‐50 nm) granules were found in both control and presumptive aganglionic gut. The heparan sulfate proteoglycan granules were primarily located within formed basal laminae, while chondroitin sulfate proteoglycan granules decorated plasma membranes and 5 nm hyaluronic acid microfibrils that formed a network in the extracellular matrix. At day E11.5, the mutant gut differed from the control in the following: (1) Hyaluronic acid microfibrils were longer and more numerous. (2) There were larger numbers of chondroitin sulfate proteoglycan granules associated with cell membranes and with hyaluronic acid microfibrils. By day E13 the spaces between mesenchymal cells of the outer wall of the control bowel contained a regular lattice of hyaluronic acid microfibrils studded with chondroitin sulfate proteoglycan granules. Instead of this lattice, tangles of excessively long hyaluronic acid microfibrils, coated more heavily than in the control with chondroitin sulfate proteoglycan granules, were found in the presumptive aganglionic gut. These results confirm that the extracellular matrix is abnormal in the presumptive aganglionic bowel of the ls/ls mouse; moreover, they also indicate that the defect involves not one, but several components of the extracellular matrix, as well as their distribution. The defective extracellular matrix is apparent at a time when crest‐derived cells would be expected to be migrating in the terminal bowel and is located in their path. The observations thus support the idea that a localized abnormality of the extracellular matrix interferes with the colonization of the terminal bowel by crest‐derived cells in the ls/ls mouse.
Infrahyoid and accessory motoneurons in the japanese monkey (Mascaca fuscata)
Authors: Ueyama Teizo , Satoda Takahiro , Tashiro Takashi , Sugimoto Tetsuo , Matsushima Ryotaro , Mizuno Noboru
Published: January 2005

The segmental and topographical organization of motoneurons innervating the infrahyoid (IH) and the spinal accessory (AC) Muscles was studied in the Japanese monkey (Macaca fuscata) with thje retrograde horseradish peroxidase (HRP) method after application of HRP to the peripheral nerve branches supplying the IH and AC inuscles. IH motoneurons constitute two distinct slender cell columns, a longer medial and a shorter lateral one. The medial cell column extends from the most caudal level of the hypoglossal nucleus to the lower levels of the sececond cervical (C2) cord segment. In the medial column, motoneurons supplying the sternohyoid and sternothyroid muscles are distributed at the medullary and C1 levels, while those innervating the omohyoid muscle are primarily distributed at the C2 level. The lateral cell column consists of motoneurons supplying the thyrohyoid muscle and extends from the most caudal level of the hypoglossal nucleus to the middle levels of the C1 cord segment. Axons of thyrohyoid motoneurons follow a dorsomedially directed bent emergent course, making a hairpin turn.

AC motoneurons supplying the sternocleidomastoid (SC) and trapezius (TZ) muscles form a single slender cell column extending from the most rostral level of the pyramidal decussation to the middle levels of the C6 cord segment. SC motoneurons are distributed from the most rostral level of the pyramidal decussation to the middle levels of the C3 cord segment, while TZ motoneurons are distributed from the upper levels of the C2 cord segment to the lower levels of the C6 cord segment. At the levels of the C2 and C3 cord segments, both SC and TZ motoneurons are distributed in the AC cell column; the cluster of SC motoneurons is located dorsomedial to that of TZ motoneurons.
Autoradiographic localization of progestin‐concentrating cells in the brain of the zebra finch
Authors: Lubischer Jane L. , Arnold Arthur P.
Published: January 2005

The production of song in passerine birds is under the control of steroid hormones, and brain regions involved in song production have been shown to contain androgen and/or estrogen receptors. Studies to date, however, have not considered the possible role of progestins in this behavior. As one approach to this question, the autoradiographic method was used to investigate the distribution of progestin‐concentrating cells in the brain of the adult male zebra finch (Poephila guttata) after injection of the radiolabeled synthetic progestin [17α‐methyl‐3H]‐promegestone. In the telencephalon, identifiable groups of progestin‐accumulating cells were found in the hyperstriatum dorsale, at the medial edge of the lobus parolfactorius, and in the medial septum. In the diencephalon, labeled groups of cells were found in the preoptic area, through much of the medial hypothalamus‐‐including nucleus periventricularis magnocellularis, nucleus medialis hypothalami posterialis, and area infundibularis‐‐and in the medial spiriform nucleus and dorsomedial thalamus. In the myelencephalon, labeled cells are described at the dorsal edge of the medulla and scattered lateral to nXII. These findings offer no support for the hypothesis that progestin acts on any of the known song regions, but do suggest areas of progestin action in the avian central nervous system outside of the known song system. Not surprisingly, these include many areas of the medial hypothalamus and other midline structures.
Projections ascending from the spinal cord to the brain in petromyzontid and myxinoid agnathans
Authors: Ronan Mark , Northcutt R. Glenn
Published: January 2005

The course of projections ascending through the rostral spinal cord to nuclei in the brains of petromyzontid and myxinoid agnathans was examined with silver staining of anterograde degeneration and horseradish peroxidase histochemistry. As in jawed vertebrates, the ascending spinal projections of lampreys and hagfishes appear to be organized into two major systems, the spinal lemniscal and dorsal column pathways. The spinal lemniscal pathway, extending rostrally along the ventrolateral margin of the spinal and medullary central gray, consists of a spinoreticular and possibly a spinovestibular projection in both aganthan groups. In Pacific hagfish, spinal lemniscal fibers reach the ipsilateral mesencephalic tectum, but no spinal projection to the thalamus was evident. The spinal lemniscus of lampreys ascends to the region of the isthmus and may extend into the mesencephalic tegmentum. Anterograde and retrograde tracing methods indicate that a very small population of cells in the far rostral cord of lampreys may project to the optic tectum and diencephalon; however, spinotectal and spinothalamic projections, if present, are limited in extent. The dorsal column pathway in agnathans, consisting in part of primary spinal afferents, ascends in the dorsal funiculus of the cord. The dorsal column fibers of agnathans, like those of some other anamniotes, continue beyond the spinomedullary junction through the length of the hindbrain, possibly conveying ascending somatosensory input to the sensory nuclei of the alar medulla.
Neurons of the lateral entorhinal cortex of the rhesus monkey: A golgi, histochemical, and immunocytochemical characterization
Authors: Carboni A. A. , Lavelle W. G. , Barnes C. L. , Cipolloni P. B.
Published: January 2005

This study identifies the neuronal types of the rhesus monkey lateral entorhinal cortex (LEC) and discusses the importance of these data in the context of the connectional patterns of the LEC and the possible role of these cells in neurodegenerative diseases. These neuronal types were characterized with the aid of Golgi impregnation techniques. These characterizations were based upon their spine densities, dendritic arrays, and, where possible, axonal arborizations. The cells could be segregated into only spinous and sparsely spinous types. The most numerous spinous types were pyramidal neurons. Other spinous types included multipolar, vertical bipolar and bitufted, and vertical tripolar neurons. The sparsely spinous neuronal types consisted of multipolar, horizontal bipolar and bitufted, and neurogliaform cells.

These cells were further classified with the aid of histochemical stains and immunocytochemical markers. Nicotinamide adenine dinucleotide phosphate‐diaphorase (NADPH‐d) histochemistry stained multipolar, bipolar, and bitufted neurons. Stain for cytochrome oxidase (CO) was found in pyramidal and nonpyramidal cell types. Immunocytochemical techniques revealed several nonpyramidal neurons that contain somatostatin (Som) or substance P (SP). This study complements previous analyses of the neuronal components described in the LEC and adds further information about the distribution of selected neurochemicals within this cortex.
Estradiol‐concentrating forebrain and midbrain neurons project directly to the medulla
Authors: Corodimas Keith P. , Morrell Joan I.
Published: January 2005

The location and number of estradiol (E2)‐concentrating neurons afferent to the dorsal medulla were determined by combining retrograde fluorescent tract tracing with steroid hormone autoradiography. Injections of Fluoro‐Gold were made into the medulla of 80 day old, ovariectomized, and adrenalectomized female rats. After 7 days survival to allow for retrograde transport, females were injected with [3 H] estradiol; they were then perfused and their brains processed for steroid hormone autoradiography. Following a 4hyphen;12 month exposure period, autoradiograms were developed and microscopically analyzed for the presence of E2‐concentrating neurons that project to the medulla.

Numerous E2‐concentrating neurons were identified that send axons directly to the medulla; the majority were found in the bed nucleus of the stria terminalis, paraventricular nucleus of the hypothalamus, central nucleus of the amygdala, and the central gray. Of the E2‐concentrating neurons in the bed nucleus of the stria terminalis, 12.7% also projected to the medulla. E2‐concentrating neurons that sent axons to the medulla were also identified in and ventromedial to the lateral parvicellular subdivision in the caudal half of the paraventricular nucleus of the hypothalamus (69.4%). Over one‐third of the E2‐concentrating neurons found in the central nucleus of the amygdala coursed to the medulla. The central gray was the only mesencephalic brain region that contained E2‐concentrating neurons that projected to the medulla (41.9%).

The medulla‐bound E2‐concentrating forebrain and midbrain neurons identified in the present study may influence autonomic tone via direct projections.
Musculotopic organization of the facial motor nucleus in macaca fascicularis: A morphometric and retrograde tracing study with cholera toxin B‐HRP
Authors: Welt Carol , Abbs James H.
Published: January 2005

Morphometric and retrograde tracing methods were used to determine the location and number of motoneurons innervating individual facial muscles in Macaca fascicularis. Intramuscular injections of the cholera toxin B subunit‐horseradish peroxidase conjugate produced discrete labeling patterns in the ipsilateral facial motor nucleus with good definition of somata and their processes. The facial nucleus extended rostrocaudally in the pons for about 2 mm, varying in shape and cross‐sectional area along this axis. Motoneurons were clustered in subnuclei, but their boundaries were not sharp and they were not segregated by fiber bundles. The length, number, and area of subnuclei varied with rostrocaudal location.

Retrograde labeling patterns revealed that individual muscles were innervated by longitudinal columns of motoneurons with each muscle region represented at all rostrocaudal levels of its column. The columns began at different rostrocaudal levels and varied in length. Columns for closely related muscles, such as the orbicularis oris and mentalis of the lower lip, tended to overlap, whereas columns for disparate muscles, such as the perioral and orbital, did not overlap. The dendritic processes of most motoneurons branched extensively among several different columns or subnuclei. Some dendrites extended outside of the nucleus into the surrounding tegmentum.

Mean soma diameter (10.4‐42.2 μm) was distributed unimodally, reflecting the absence of gamma motoneurons and lack of muscle spindles in the facial muscles. Large and small motoneurons were found in all regions of the nucleus, but the largest ones were located caudally and innervated muscles of the upper and lower lip. The perioral muscles also had more neurons, longer columns, and a lower cell density than the other muscle groups examined. These features may reflect the functions of the perioral muscles in facial expression and vocalization.
Neurogenesis of the magnocellular basal forebrain nuclei in the rhesus monkey
Authors: Kordower Jeffrey H. , Rakic Pasko
Published: January 2005

The time of origin of the neurons that comprise the magnocellular basal forebrain nuclei in rhesus monkeys was determined by using [3H] thymidine autoradiography. Thirteen pregnant animals received an injection of [3H] thymidine between embryonic days 27 (E27) and E50 of their 165 day gestation, and their offspring were sacrificed during the early postnatal period. Neurons within this region were generated in a biphasic pattern. An initial burst of [3H] thymidine‐labeled magnocellular neurons was first observed throughout short quiescent period, cells of the remaining anterior basal forebrain (inclusive of magnocellular neurons comprising the vertical limb of the diagonal band and the anteromedial and anterolateral regions of the nucleus basalis) were generated between E36 and E45 with a peak of neurogenesis seen on about the same time, but the peak period of neurogenesis in this region occurred slightly earlier (E36 and E40) and was completed by E43. During the second phase of neurogenesis, neurons within the posterior division of the basal forebrain were generated first, with their genesis virtually completed between E33 and E36. The genesis of all neurons comprising the magnocellular basal forebrain nuclei was completed by E48 of gestation. A general caudal to rostral gradient of neurogenesis was observed within this telencephalic region. In contrast, a neurogenic gradient was not discerned in the radial direction. The present data demonstrate that neurons comprising the basal forebrain magnocellular nuclei in monkeys are generated early in gestation with two peak times of neuronal genesis. These nuclei are among the earliest to be generated in the entire telencephalon, which, like neurons of the thalamus and cortical neurons giving rise to cortical‐cortical connections, places them in a strategic position to potentially influence their target neurons within the cortical mantle that are generated later in gestation.
Timing and patterns of astrocyte migration from xenogeneic transplants of the cortex and corpus callosum
Authors: Zhou Hai Feng , Lee Lawrence Hou‐Chung , Lund Raymond D.
Published: January 2005

The timing, pattern, and pathway of astrocyte migration were investigated in vivo by transplantation of CD‐1 mouse cerebral cortex E13‐14 or corpus callosum P2‐3 into neonatal rat cortex. A monoclonal antibody specific for a mouse astrocyte surface antigen M2 was used to identify the location of the grafts and the migrated donor astrocytes. Within the host cortex, astrocytes from cortical grafts began migration at post‐transplantation day PTD 7. Over the next 4 days, the most distant displaced donor cells were found progressively further away from the grafts, migrating at a rate of about 220 μm/day. After PTD 11, the migration rate for the farthest displaced donor cells slowed to 25 μm/day, and the cells appeared to stop at about PTD 16 at a distance of 1,100 μm from the edge of the graft. Astrocytes had a faster migration speed in the white matter and covered a longer distance (5 mm) than those in the gray matter, extending on occasion into the contralateral hemisphere. The patterns of astrocyte migration differed depending on local cues around the transplant. Donor astrocytes that had been implanted into the host cortex migrated toward the host cortical surface, sometimes ín several radial lines. Astrocytes from grafts, especially callosal grafts, placed in the subcortical white matter migrated along the host fiber tracts. Many astrocytes transplanted into the hippocampus formed laminar patterns close to the hippocampal neuronal layers. These results suggest that the direction, pattern, and speed of astrocyte migration are influenced by local substrates in the host brain.
Transient patterns of GAP‐43 expression during the formation of barrels in the rat somatosensory cortex
Authors: Erzurumlu Reha S. , Jhaveri Sonal , Benowitz Larry I.
Published: January 2005

The development of the rat barrel field cortex was investigated with an antibody to the axonal membrane‐specific phosphoprotein GAP‐43 in order to examine the developmental pattern of afferent projections, and with cytochrome oxidase histochemistry and Nissl stains to reveal the morphogenesis of cortical barrels.

On the first two days after birth, GAP‐43 immunostaining in the cortical plate was light and diffuse, then became intense in the presumptive layer IV of the parietal cortex on PND3 (day of birth = PND0). Immunoreactive densities were visible as small, focal patches within the centers of prospective barrels. These densities increased in size and intensity over the next few days and then diminished abruptly. On PnD7, the distribution of GAP‐43 was coextensive with barrels, as defined by cytochrome oxidase histochemistry and Nissl staining. GAP‐43 virtually disappeared from the barrels after PND7. From the second postnatal week, GAP‐43 immunostaining was evident in the septa between barrels and in the dysgranular regions of SI cortex. This pattern of GAP‐43 distribution was complementary to the pattern of cytochrome oxidase activity, and persisted into maturity.

In an attempt to identify possible source(s) of GAP‐43 positive afferents in the developing barrels, we examined the effects of altering the sensory periphery on the distribution of GAP‐43 immunostaining in the cortex. Rat pups had row C whiskers cauterized on PND0 and were sacrificed on PND3 or PND5. Whereas immunopositive densities corresponding to intact whiskers developed in a normal, punctate pattern, cortical representation of the lesioned whiskers formed a continuous band of labeling that was evident as early as PND3.

We argue that the disjunctive expression of GAP‐43 in the barrel field reflects the pattern of distribution of afferents (most likely from the ventrobasal thalamic nucleus) to the barrel field cortex, and that this pattern may be instructive in the formation of barrels as cytoarchitectonic units. The rapid alteration in patterns of immunostaining following whisker lesions lends further support to the conclusion that the “barrel template” is conveyed to the neocortex by incoming afferents. The possible significance of the transient expression of GAP‐43 in the maturing barrel field is discussed.
Human photoreceptor topography
Authors: Curcio Christine A. , Sloan Kenneth R. , Kalina Robert E. , Hendrickson Anita E.
Published: January 2005

We have measured the spatial density of cones and rods in eight wholemounted human retinas, obtained from seven individuals between 27 and 44 years of age, and constructed maps of photoreceptor density and between‐individual variability. The average human retina contains 4.6 million cones (4.08–5.29 million). Peak foveal cone density averages 199,000 cones/mm2 and is highly variable between individuals (100,000–324,000 cones/mm2). The point of highest density may be found in an area as large as 0.032 deg2. Cone density falls steeply with increasing eccentricity and is an order of magnitude lower 1 mm away from the foveal center. Superimposed on this gradient is a streak of high cone density along the horizontal meridian. At equivalent eccentricities, cone density is 40–45% higher in nasal compared to temporal retina and slightly higher in midperipheral inferior compared to superior retina. Cone density also increases slightly in far nasal retina. The average human retina contains 92 million rods (77.9–107.3 million). In the fovea, the average horizontal diameter of the rod‐free zone is 0.350 mm (1.25°). Foveal rod density increases most rapidly superiorly and least rapidly nasally. The highest rod densities are located along an elliptical ring at the eccentricity of the optic disk and extending into nasal retina with the point of highest density typically in superior retina (5/6 eyes). Rod densities decrease by 15–25% where the ring crosses the horizontal meridian. Rod density declines slowly from the rod ring to the far periphery and is highest in nasal and superior retina. Individual variability in photoreceptor density differs with retinal region and is similar for both cones and rods. Variability is highest near the fovea, reaches a minimum in the midperiphery, and then increases with eccentricity to the ora serrata. The total number of foveal cones is similar for eyes with widely varying peak cone density, consistent with the idea that the variability reflects differences in the lateral migration of photoreceptors during development. Two fellow eyes had cone and rod numbers within 8% and similar but not identical photoreceptor topography.
Branching patterns of corticospinal axon arbors in the rodent
Authors: Kuang Rong Zhen , Kalil Katherine
Published: January 2005

Despite extensive study of corticospinal connections in a variety of species, little is known about the detailed morphology of corticospinal axon arbors. Results in previous studies of primates based on intra‐axonal filling with horseradish peroxidase (HRP) staining of a limited sample of fibers suggest that corticospinal arbors branch widely to multiple motoneuronal pools. To determine whether this pattern of corticospinal connectivity is present in nonprimate species as well, we studied the branching patterns of corticospinal axon arbors in a rodent species, the golden hamster. The axons were labeled by iontophoretic ijection of Phaseolus vulgaris‐leucoagglutinin (PHA‐L) into small regions of the forelimb and hindlimb sensorimotor cortex, and immunohistochemistry with the peroxidase‐antiperoxidase (PAP) method was used to reveal fine details of terminal arbors within the cervical and lumbar enlargements of the spinal cord. As in higher mammals, corticospinal connections are topographically organized. Moreover, corticospinal axons arising from somatosensory cortx project primarily to the dorsal horn, whereas those from motor cortex terminate most heavily in the ventral horn. This differential projection pattern, not previously demonstrated in rodents, implies functional differences between somatosensory and motor components of the corticospinal pathway. Reconstruction of corticospinal arbors in the ventral horn showed that in both cervical and lumbar spinal cord segments, axons branch widely into interneuronal regions. A surprising number appear to extend into motoneuron cell groups, and some of these axons branch into multiple motoneuronal pools. Widely divergent corticospinal axons that branch to multiple motoneuron pools have been shown to mediate activity in functionally related muscle groups of the primate forearm. The present results suggest that in other species, such as the rodent, a similar divergence of corticospinal arbors may also function to facilitate activity in subsets of muscles.
Shapes and distributions of the catecholamine‐accumulating neurons in the rabbit retina
Authors: Tauchi Masaki , Madigan Nancy K. , Masland Richard H.
Published: January 2005

Rabbit retinas were fixed with mixed aldehydes and examined for the fluorescence of catecholamines. Labeled cell bodies were present in the layer of the amacrine cells. A band of fluorescent processes was present in layer 1 of the inner plexiform layer. Weaker labeling was present in two deeper strata, one near the middle of the inner plexiform layer (presumably layer 3) and one at the juction of layers 4 and 5. Immunohistochemistry showed tyrosine hydroxylase (TH) to be present in the same cells and the same strata of the inner plexiform layer as the endogenous catecholamines. Exposing the retina to exogenous dopamine or norepinephrine resulted in stronger labeling in the middle and deep levels of the inner plexiform layer. At the same time a second population of amacrine cell bodies became visible.

Catecholamine fluorescence contained in the amacrine cell bodies was used as a guide to their injection with Lucifer yellow CH. The filled dendritic arbors revealed two main types of cells. The type 1 cells are monostratified at the most distal level of the inner plexiform layer. They have relatively uncomplicated, radially branching dendritic trees. They are the cells densely stained by immunohistochemistry with antibodies against. TH. The type 2 cells are tristratified, with minor branching in layer 1 of the inner plexiform layer and major branching in the two deeper sublayers. The descending dendrites follow a complicated course, and it is not uncommon for intermediate dendrites to cross between strata more than once.

The relationship of the cells to their dendritic plexuses was further studied in retinas in which the aldehyde‐induced fluorescence of catecholamines was photoconverted to a diaminobenzidine product. The type 1 cells were found to dominate the plexus of dendrites in layer 1 of the inner plexiform layer. The catecholaminergic plexuses in the middle and deep levels of the inner plexiform layer are formedf by dendrites of the type 2 cells.

The position of every type 1 cell was mapped in retinas stained with antibodies directed against TH. In one retina we counted 5,613 type 1 cells, distributed evenly across the retina. In another retina, all of the catecholamine‐accumulating cells were counted. There were 9,058 with a distribution that peaks in the visual streak. The type 1 cells appear to be the dopaminergic cells previously studied by others and thought to regulate the flow of information from rod bipolar cells to ganglion cells. The low density and wide spread of type 2 cells suggests that they, too, perform a generalized control function, presumably a novel one that dictates their intricate, tristratified shape.
Structural and functional organization of a diencephalic sensory‐motor interface in the gymnotiform fish, Eigenmannia
Authors: Keller Clifford H. , Maler Leonard , Heiligenberg Walter
Published: January 2005

The diencephalic nucleus electrosensorius (nE) of gymnotiform fish comprises a series of finely tuned neuronal filters for control of the jamming avoidance response (JAR) and probably other electromotor tasks as well. The nE receives electrosensory input from the dorsal torus semicircularis (TSd) and octavolateral input from the ventral torus (TSv). The nE, in turn, projects to various hypothalamic and thalamic nuclei, including the prepacemaker nucleus (PPn), which can modulate the frequency of electric organ discharges (EODs) via its unique input to the medullary pacemaker nucleus.

Four subdivisions of the nE can now be recognized: 1) The beat‐related area (nEb)‐‐‐a rostral cluster of tightly packed cells which receives TSd input and projects to the inferior lobe, anterior tuberal nucleus, anterior thalamic nucleus, central posterior thalamic nucleus, and PPn. The nEb contains neurons responsive to beat patterns caused by jamming stimuli. Stimulation of the nEb with L‐glutamate, however, fails to induce any EOD‐frequency shift. 2) The area causing EOD‐frequency rises (nE↑)‐‐a horizontal band of cells at the dorsal aspect of the caudal nE which receives TSd input and projects to the PPn and vicinity and to the cerebellum; nE↑ stimulation induces slow EOD‐frequency rises characteristic of the JAR. Responses of these cells to jamming stimuli are not yet known. 3) The area causing EOD‐frequency falls (nE↑)‐‐a horizontal band of cells at the ventral aspect of the caudal nE which receives TSd input and projects only to the PPn and vicinity; nE↑ stimulation induces slow EOD‐frequency falls characteristic of the JAR. The responses of these cells to jamming stimuli are not yet known. 4) The acousticolateral region (nEar)‐‐‐a complex medial region of the nE which receives input predominantly from the ventral torus and projects to the inferior lobe, anterior tuberal nucleus, central posterior thalamic nucleus, PPn, and cerebellum; the sensory and motor properties of this region are not known in detail, although auditory and mechanosensory responses have been recorded here. Projections to the PPn and its vicinity suggest direct control of electromotor behaviors by the nE, whereas thalamic and hypothalamic projections may provide a substrate for electrosensory influences on neuroendocrine and motivational control centers.

The optic tectum projects strongly to the pretectum and various other diencephalic nuclei in the vicinity of the nE, but it does not innervate the nE itself. Accordingly, ablation of the tectum does not affect the performance of the JAR.
Anatomical studies of dorsal column axons and dorsal root ganglion cells after spinal cord injury in the newborn rat
Authors: Lahr Stephen P. , Stelzner Dennis J.
Published: January 2005

The response of dorsal column axons was studied after neonatal spinal overhemisection injury (right hemicord and left doral funiculus). Rat pups (N = 11) received this spinal lesion at the C2 level within 30 hours after birth. The cauda equina was exposed 3 months later in one group of chronic operates (N = 5) and in a group of normal aduits (N = 2), and all spinal roots from L5 caudally were cut bilaterally; 4 days later the spinal cord and medulla were processed for Fink‐Heimer impregnation of degenerating axons and terminals. In a second group of chronic operates (N = 6) and normal adult controls (N = 4) the left sciatic nerve was injected with a cholera toxin‐HRP conjugate (C‐HRP), followed by a 2–3 day transganglionic transport period, and then the spinal cord and medulla were processed with tetramethylbenzidine histochemistry. Both control groups have a consistent dense projection in topographically adjacent regions of the dorsal funiculus and gracile nucleus. However, there is no sign of axonal growth around the lesion in either group of chronic experimental operates. Instead, there is a decreased density of projection within the dorsal funiculus near the lesion site. Many remaining C‐HRP labeled axons in the experimental operates have abnormal, thick varicosities and swollen axonal endings (5–10 μm × 10–30 μm) within the dorsal funiculus through several spinal segments caudal to the lesion. Ultrastructural analysis of the dorsal funiculus in three other chronic experimental operates reveals the presence of numerous vesicle filled axonal profiles and reactive endings which appear similar to the C‐HRP labeled structures.

Transganglionic labeling after C‐HRP sciatic nerve injections (N = 4) and retrograde labeling of L4, L5 dorsal root ganglion neurons after fast blue injections of the gracile nucleus (N = 6) both suggest that all dorsal column axons project to the gracile nucleus in the newborn rat. Dorsal root ganglion (DRG) cell survival following the neonatal overhemisection injury was also examined in the L4 and L5 DRG. DRG neurons that project to the gracile nucleus were prelabeled by injecting fast blue into this nucleus at birth two days prior to the cervical overhemisection spinal injury. Both normal littermates (N = 9) and spinally injured animals (N = 12) were examined after postinjection survival periods of 10 or 22 days. Comparison of the percentage and number of labelled and unlabeled DRG neurons in the L4 and L5 ganglia in control and experimental operates reveals no sign of cell loss after neonatal dorsal colomn axotomy.

We conclude that dorsal column axons do not grow around damage to their normal pathway in the newborn rat during a period when previous studies show adjacent corticospinal axons are able to grow around the same type of spinal injury and when the spinal environment normally permits growth of the still elongating corticospinal tract axons to occur.