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PubMed2006

Activation of epidermal growth factor receptor mediates receptor axon sorting and extension in the developing olfactory system of the moth Manduca sexta.

During development of the adult olfactory system of the moth Manduca sexta, olfactory receptor neurons extend axons from the olfactory epithelium in the antenna into the brain. As they arrive at the brain, interactions with centrally derived glial cells cause axons to sort and fasciculate with other axons destined to innervate the same glomeruli. Here we report studies indicating that activation of the epidermal growth factor receptor (EGFR) is involved in axon ingrowth and targeting. Blocking the EGFR kinase domain pharmacologically leads to stalling of many axons in the sorting zone and nerve layer as well as abnormal axonal fasciculation in the sorting zone. We also find that neuroglian, an IgCAM known to activate the EGFR through homophilic interactions in other systems, is transiently present on olfactory receptor neuron axons and on glia during the critical stages of the sorting process. The neuroglian is resistant to extraction with Triton X-100 in the sorting zone and nerve layer, possibly indicating its stabilization by homophilic binding in these regions. Our results suggest a mechanism whereby neuroglian molecules on axons and possibly sorting zone glia bind homophilically, leading to activation of EGFRs, with subsequent effects on axon sorting, pathfinding, and extension, and glomerulus development.

Amino Acid Sequence↗
PubMed1983

Development of order in the rat trigeminal system.

The trigeminal system of the rat is characterized by a high degree of order. The pattern of the distribution of vibrissae follicles on the face is replicated at each synaptic station between face and somatosensory cortex (Belford and Killackey, '80). The present study details the development of the trigeminal nerve, its intrinsic organization, and its relationship with its peripheral and central targets. We have observed that at early embryonic ages (E12 and E13) the trigeminal ganglion neurons grow out in straight lines without crossing, and the distance between these neurons and their peripheral and central targets is very short. We have found that fibers reach the periphery before follicle formation is first detectable (E14). At all ages, the trigeminal fibers show a marked tendency to fasciculate. After the development of the pattern of vibrissae follicles on the face, the pattern of fasciculation within the nerve can be clearly related to the rows of vibrissae and the buccal pad. This peripherally related order in the nerve was experimentally verified by injecting horseradish peroxidase into the follicles of individual rows and selectively sectioning portions of the nerve. Further, we provide evidence that the discrete brainstem pattern reflecting vibrissae distribution develops after organization is detectable in the nerve and in a temporal sequence from lateral to medial, which replicates the developmental sequence of vibrissae follicles from ocular to nasal on the face. This sequence is detectable in both the distribution of afferent terminals as measured with succinic dehydrogenase histochemistry and of horseradish peroxidase back-labeled trigeminothalamic relay cells. We interpret our results as suggesting that a number of factors may play a role in the establishment of specific neuronal topographies in the rodent trigeminal system.

Afferent Pathways↗
PubMed1986

The early development of the optic nerve and chiasm in embryonic rat.

To establish the time course and major features of the development of the optic nerve and chiasm in the embryonic rat, the growth of axons from the retina to the brain has been studied by light and electron microscopy. On embryonic day 14 (E14), the first axons are generated by retinal ganglion cells. Fascicles of axons can be detected in the optic stalk at E14.5 and in the diencephalon by E15.0. In the vitreal retina and optic fissure, large extracellular spaces resemble the oriented channels previously described in the mouse. They form approximately 12 hours before the invasion of optic axons and contain hyaluronic acid. In the optic stalk and diencephalon of the rat, similar spaces are not present, but the timed autolysis of neuroepithelial cells could provide a pathway of minimal resistance for the earliest axons. Degenerating cells are prominent in the ventral stalk and rostral diencephalon prior to the arrival of the first optic axons that preferentially invade these regions. The role of pigment in the development of visual pathways is controversial. In one strain of rat, Manchester Hooded, the retinae are heavily pigmented, but little pigment is seen at any stage in the stalk; in albinos, pigment is absent from both retina and stalk. However, the distribution of axons within the developing optic stalk is very similar in both strains, suggesting that the reduction in size of the ipsilateral pathway observed in the albino rat compared with the Manchester Hooded is not due to a lack of pigment in the optic stalk early in development. Several factors previously reported to contribute to the development of retinotopic order in other species are also present in the rat. These include the sequence in which axons grow into the stalk, and fasciculation. Intermembranous contacts observed between growth cones and adjacent tissues suggest one mechanism by which fasciculation occurs. A small group of fascicles, which may represent the ipsilateral projection, diverges from the crossing fibers on E15.5, without evidence of being deflected by any glial or other structures.

Albinism↗
PubMed1989

Immunohistological localization of the adhesion molecules L1, N-CAM, and MAG in the developing and adult optic nerve of mice.

The localization of the cell adhesion molecules L1, neural cell adhesion molecule (N-CAM), and myelin-associated glycoprotein (MAG) was studied immunohistologically at the light and electron microscopic levels and immunochemically in the developing and adult mouse optic nerve and retina. The neural adhesion molecule L1 is strongly expressed on the shafts of fasciculating unmyelinated axons at all ages studied from embryonic day 15 through adulthood. Growth cones of retinal ganglion cell axons were weakly L1-positive or L1-negative when contacting glial cells. Unmyelinated axons were not only L1-positive when contacting each other but also when contacting glia, whereas contacts between glial cells were L1-negative at all developmental unmyelinated retinal nerve fiber layer or in the unmyelinated optic nerve head became L1-negative when enwrapped by myelin in the optic nerve proper. At all stages of development N-CAM showed profuse labeling on fasciculating axons, growth cones, and their contact sites with glial cells as well as contacts between glial cells. In contrast to L1, axons remained N-CAM-positive when becoming myelinated. Sometimes, N-CAM was found in compact myelin. However, N-CAM was absent from glial surfaces contacting basement membranes at the interface to meninges, blood vessels, and the vitreous body of the eye. MAG was first detectable intracellularly in oligodendrocytes associated with the endoplasmic reticulum and Golgi apparatus before it became apparent at the cell surface. There it was present on oligodendrocytes prior and during the first stages of ensheathment of axons, both on cell body and processes. After formation of compact myelin MAG remained strongly expressed periaxonally and was only weakly detectable in noncompacted myelin including inner mesaxon and paranodal loops. None of the adhesion molecules was detectable on extracellular matrix, in the meninges, or on endothelial cells. Immunochemical analysis of antigen expression at different developmental stages was in agreement with the immunohistological data. We infer from these observations that L1 is involved in stabilization not only of axon-axon, but also axon-glia contacts, while the more dynamic structure of the growth cone generally expresses less L1. A differential expression of L1 along the course of an axon--being present on its unmyelinated, but absent on its myelinated part--further supports the notion that L1 may be involved in the stabilization of axonal fascicles but not of axon-myelin contacts.(ABSTRACT TRUNCATED AT 400 WORDS)

Aging↗
PubMed1990

Implantation of cultured sensory neurons and Schwann cells into lesioned neonatal rat spinal cord. II. Implant characteristics and examination of corticospinal tract growth.

The purpose of this study was to test the effectiveness of implants derived from peripheral neural tissue to serve as bridges following interruption of the developing corticospinal tract (CST). Implants prepared from purified populations of cultured dorsal root ganglion neurons (DRGNs) and Schwann cells (SCs) (Kuhlengel et al., J. Comp. Neurol. 293:63-73, 1990) were placed into thoracolumbar regions of neonatal rat spinal cord from which a 2-mm length of dorsal columns had been removed by suction. These cords were examined by a number of techniques 10 days to 6 months later. The implants, recognizable by their DRGN content, filled the vacated dorsal columns and survived the longest periods examined. The most effective method to maintain implant position was dorsal placement of collagen-coated Nitex filter. Implants were inserted either at the time of lesioning or 5 days later. The implant survival rate was better (72% vs. 50%) and meningeal scarring was less with immediate implantation, but delayed implantation resulted in better implant-cord fusion and the implant better filled the lesion cavity. DRGN/SC implants became well vascularized without leptomeningeal cells; this may explain why implant survival was not improved with leptomeningeal cell addition. Particularly well-differentiated implants (full extracellular matrix production and myelination) did not fuse as well with cord as did those less well differentiated. The addition of nerve growth factor to the Nitex filter collagen coating led to improved survival of DRGNs in implants. Electron microscopy showed that astrocytes populated the implant-cord junction region and migrated into implants. Typical SCs related to nonmyelinated and myelinated axons were present in implants. Close proximity of astrocytes and central myelin to SCs and peripheral myelin demonstrated good implant integration with cord. Clusters of SCs, astrocytes, and axons, all enclosed within a common basal lamina, were observed in implants. Immunostaining for GFAP and laminin confirmed our microscopy findings that SCs did not migrate from implant into host but that astrocytes left host tissue to enter implants. Neuroanatomical tracing of CST neurons with HRP-WGA showed that labeled fibers were not present in the implant but were fasciculated just beneath in gray matter. These fibers remained clustered in gray matter underneath the ventral dorsal columns caudal to the lesion. In lesioned but not implanted rats, labeled fibers were only diffusely distributed in gray matter. Delayed implantation led to more variation in fasciculation compared with immediate implantation.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

Glial process elongation and branching in the developing murine neocortex: a qualitative and quantitative immunohistochemical analysis.

Cells of astroglial lineage in the murine cerebrum undergo a succession of transformations during prenatal and early postnatal development. The bipolar radial cell, the earliest astroglial form to appear, provides a radially aligned, parallel array of fibers that serves as a guide to neuronal migration. The multipolar astrocyte is the representative of this lineage that persists in the adult cerebrum. The processes of the multipolar astrocytes form a complex reticulum, which is considered critical to the development, function, and maintenance of neural circuits. A monopolar radial cell appears to be transitional between the two. The shift from the radial glial fiber system to a diffuse glial network is achieved largely in the E17-P2 interval in the mouse. This phenomenon has been studied qualitatively and quantitatively by staining cerebral tissue with monoclonal antibody RC2, a specific and sensitive ligand for cells of astroglial lineage in the mouse. Elongation and branching of glial processes contribute to the glial transformation. Elongation of radial fibers occurs under the guidance of other radial glial fibers (fasciculated elongation) or independently of other fibers (nonfasciculated elongation). Fasciculated elongation results in an increase in the density of radial glial fibers that span the cortical layers. Nonfasciculated elongation appears to be associated with process branching. This is the initial event in transformation of the bipolar radial cells to monopolar radial or multipolar cells. Only nonfasciculated elongation is characteristic of processes of the monopolar radial cells and multipolar astrocytes. Branching of the processes of all three cell forms appears to occur both by bifurcation at the elongating tip and by sprouting from the fiber shaft. Elongating fibers are tipped by growth cones that are relatively simple in shape as compared to those observed at the tips of elongating axons. Growth cones at the tips of nonfasciculated fibers are more complex in form than those at the tips of radial fibers elongating in contact with other radial fibers.

Animals↗
PubMed1991

Pathfinding by growth cones of commissural interneurons in the chick embryo spinal cord: a light and electron microscopic study.

To investigate putative axonal guidance mechanisms used by commissural interneurons in the chick embryo spinal cord, we have examined growth cone morphology, the microenvironment through which the growth cones advance, and interactions between growth cones and their surroundings. Growth cones of both early and late developing commissural interneurons were examined. The growth cones were visualized by injection of either horseradish peroxidase (HRP) or the fluorescent dye Di-I. Unlabelled growth cones as well as HRP-labelled growth cones were also examined by electron microscopy. The early developing growth cones project circumferentially without fasciculation until they reach the region of the longitudinal pathway in the contralateral ventral funiculus (CVF). In their trajectory towards the floor plate, axons exhibited elaborate growth cones with filopodia and lamellipodia. They projected between processes of neuroepithelial cells within abundant extracellular spaces. Upon arrival at the ipsilateral ventral funiculus, growth cones did not appear to contact preexisting longitudinal axons. Within the floor plate, the growth cones were less complex and lacked long filopodia and exhibited bulbous or varicose shapes with short processes. Electron microscopic observations of the floor plate at this stage revealed that there was only a small amount of extracellular space and that the basal portion of the floor plate cells were directionally oriented (polarized) in the transverse plane. It is of particular interest that contacts between growth cones and the basement membrane in the floor plate were often observed. When the growth cones reached the contralateral ventrolateral region, they again exhibited an elaborate morphology. Close contacts between growth cones and the preexisting contralateral longitudinal axons were observed. Growth cones advancing in the contralateral longitudinal pathway exhibited various shapes and were observed to contact other axons and processes of neuroepithelial cells. Most of the later developing growth cones of commissural cells exhibited lamellipodial shapes irrespective of their location along the circumferential trajectory. Electron microscopic observations revealed that these late developing growth cones always contacted or fasciculated with preexisting axons and that the cellular environment through which they grow is oriented in such a way that the growth cones appear to be guided in specific directions. Growth cones entering the CVF exhibited more elaborated shapes with ramified lamellipodia that made multiple contacts with preexisting longitudinal axons. The present results indicate that differential axonal guidance mechanisms may be employed along the pathway followed by spinal commissural interneurons and that axons and growth cones projecting along this pathway at different developmental stages employ different mechanisms for pathfinding and guidance.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1991

Growth cones and axon trajectories of a sensory pathway in the amphibian spinal cord.

Central axons of sensory ganglion (SG) neurons of the Xenopus tail enter the spinal cord via the ventral roots and travel dorsally and rostrally following a diagonal course within the lateral marginal zone (LMZ) to reach the dorsolateral fasciculus (DLF) (Nordlander et al.: Brain Res., 440:391-395, 1988). Axons are dispersed as they cross the cord. At the DLF they turn and travel together rostrally, sharing the fascicle with axons of primary sensory neurons (Rohon-Beard cells) already present in the tract. In this paper we analyze the growth patterns of the central projections of SG axons in the tail by using HRP applied to proximal branches of tail spinal nerves. Growth cones of the diagonal route are variable in configuration, often bearing processes that spread within the LMZ. Once the DLF, growth cones change shape, becoming distinctly linear. While growth cones navigating the diagonal part of the route never contact or fasciculate with other diagonal SG axons, SG growth cones and axons of the DLF are more closely associated with their fellows. Measurements of the slopes of SG axons in the diagonal route indicated a limited range with a mean of 23 degrees with respect to the cord axis. On the basis of these observations, we conclude that 1) navigational patterns for growth cones of this pathway differ for the diagonal versus the DLF part of its course, and 2) fasciculation is not a mechanism used by SG axons to reach the DLF, but that instead, each axon is able to find its way independently.

Afferent Pathways↗
PubMed1991

Immunolocalization studies of putative guidance molecules used by axons and growth cones of intersegemental interneurons in the chick embryo spinal cord.

The earliest developing interneurons in the chick spinal cord can be divided into two groups: neurons in the ventral region whose axons pioneer the primitive longitudinal pathway (PL-cells) and neurons whose axons project circumferentially (C-cells) along the lateral marginal zone and join the ipsilateral or contralateral ventrolateral longitudinal pathways. To begin to examine the molecular cues for axonal pathway formation of these interneurons, we screened a variety of molecules from embryonic day (E) 2 to E6.5 [stage 14-30 of Hamburger and Hamilton (1951) J. Morphol. 88:49-92]. These include cell adhesion and related molecules (G4, F11, neurofascin, N-cadherin, TAG-1-like molecule), extracellular matrix (ECM) molecules (laminin, fibronectin, heparan sulfate proteoglycan, laminin-heparan sulfate proteoglycan complex, and collagen type IV), and receptors for ECM molecules (beta 1-class integrin). PL-cells first expressed neurofascin at stage 14+ before the onset of axonogenesis. When the PL-cells began to extend their axons at stage 15, they expressed G4 and avian TAG-1-like molecules, as well as neurofascin, on both cell bodies and longitudinal axons. In the following stages, PL-cells continued to strongly express neurofascin and G4 on their fasciculating axons, suggesting the involvement of these glycoproteins in growth and fasciculation. C-cells began to express G4 and TAG-1-like molecules on cell bodies and axons at stage 15-16 shortly after axonal growth. In the following stages, C-cells expressed several cell adhesion molecules differentially on their axonal segments. The proximal segment of C-axons in the circumferential pathway strongly expressed a TAG-1-like molecule, whereas the distal segment in the longitudinal pathway strongly expressed G4 and neurofascin. The commissural axonal segment in the floor plate expressed TAG-1-like molecule, neurofascin, N-cadherin, and beta 1-class integrin. The basement membrane around the spinal cord was enriched with ECM glycoproteins (laminin, fibronectin, heparan sulfate proteoglycan, and collagen type IV) during the stages examined (stage 15-27), and commissural C-cell axons became strongly integrin positive in the floor plate where they contacted the basement membrane. These data indicate that interneurons may use multiple molecules during axonal pathway formation, depending on cell type, pathway position, and developmental stage.

Animals↗
PubMed1993

Distinct subsets of sensory olfactory neurons in mouse: possible role in the formation of the mosaic olfactory projection.

The axons of the primary sensory olfactory neurons project from the olfactory neuroepithelium lining the nasal cavity, onto glomeruli covering the surface of the olfactory bulb. Neuroanatomical studies have shown previously that individual olfactory glomeruli are innervated by neurons that are dispersed widely within the nasal cavity. The aim of the present study was to test the hypothesis that phenotypically unique subsets of primary sensory olfactory neurons, scattered throughout the nasal cavity, project to a subset of glomeruli in specific olfactory bulb loci. Immunochemical and histochemical analyses in neonatal mice revealed that the plant lectin, Dolichos biflorus agglutinin, bound to a subset of mature primary sensory olfactory neurons which express the olfactory marker protein. This subset of neurons was principally located in the rostromedial and dorsal portions of the nasal cavity and projected specifically to a subset of glomeruli in the rostromedial and caudodorsal portions of the olfactory bulb. Analysis of Dolichos biflorus-reactive axons revealed that these axons coursed randomly, with no evidence of their selective fasciculation, within the olfactory nerve. It was only at the level of the rostral olfactory bulb that a significant reorganisation of their trajectory was observed. Within the outer fibre layer of the bulb, discrete bundles of lectin-reactive axons began to coalesce selectively into fascicles which preferentially oriented toward the medial side of the olfactory bulb. These data demonstrated that a phenotypically distinct subset of primary sensory olfactory neurons exhibits a topographical projection from the olfactory epithelium to the olfactory bulb, and suggests that these, and other subsets, may form the basis of the mosaic nature of this pathway. Moreover, it appears that the outer nerve fibre layer in the rostral olfactory bulb plays an important instructive role in the guidance and fasciculation of olfactory sensory axons.

Animals↗
PubMed1993

Organization of the proximal, orbital segment of the infraorbital nerve at multiple intervals after axotomy at birth: a quantitative electron microscopic study in rat.

Although much is known of the central consequences of infraorbital nerve (ION) transection at birth, little is known about the effects of this lesion on the organization of the ION itself. To advance our understanding of how deafferentation alters the developing trigeminal neuraxis, 19 newborn rats were subjected to left ION section and perfused 1, 2, 4, 7, 17, or 90 days later. Left IONs were removed in the orbit proximal to the nerve injury site, and axon numbers, types, and fasciculation patterns were assessed with light and electron microscopic methods. Complete axon counts demonstrated that the axotomized ION contained an average (+/- SD) of 13,945 +/- 10,335, 14,112 +/- 3,501, 16,531 +/- 1,904, 9,045 +/- 1,465, 7,018 +/- 4,212, and 8,672 +/- 1,030 axons at the above-listed ages, respectively. These values are well below the 33,059 axons in the normal adult ION (Jacquin et al. [1984] Brain Res. 290:131-135) and the 42,219 axons in the newborn ION (Renehan and Rhoades [1984] Brain Res. 322:369-373). The axotomized ION also contained lower than normal percentages of myelinated axons (26.7% +/- 6.3% on postnatal day 90 vs. 59.7% +/- 6.2% in normal adults). Unmyelinated fibers constituted the vast majority of the remaining fiber types; degenerating fibers never accounted for > 1.6% of all the axons. The number of fascicles making up the axotomized ION overlapped significantly with those found in the normal newborn and adult ION. We conclude that 1) extensive, though variable, axon elimination occurs proximally within one day of the lesion; 2) the 74% reduction in fiber number seen at 90 days is not reliably achieved until postnatal day 7; 3) the higher than normal proportion of unmyelinated axons in the injured ION may underly many of the known effects of neonatal ION injury on the developing whisker-barrel neuraxis; 4) gross changes in ION fasciculation patterns are not prerequisite to injury-induced pattern alterations in the developing trigeminal system.

Animals↗
PubMed1994

Distribution of TAG-1/axonin-1 in fibre tracts and migratory streams of the developing mouse nervous system.

The axonal cell adhesion molecule, TAG-1/axonin-1, stimulates axonal growth and supports neurite fasciculation in vitro. Using a polyclonal antiserum raised against chick axonin-1, which shares 75% of its sequence with TAG-1 of the rat, we have mapped the distribution of TAG-1/axonin-1 throughout the developing nervous system of the mouse. Although absent from proliferating neuroepithelia and from non-neuronal cells, immunoreactivity for TAG-1/axonin-1 is expressed by stage-specific subpopulations of differentiating neurons from embryonic day 10 to postnatal day 15. It stains their axons and the surface of their parent somata during the early phases of axogenesis. In agreement with a putative role of TAG-1/axonin-1 as an axon-bound growth substrate, immunoreactivity is found in developing spinal and cranial nerves, in corticothalamic projections, as well as in subsets of fasciculating long projecting tracts of the central nervous system, such as the dorsal funiculi of the spinal cord, the lateral olfactory and optic tracts, the fasciculus retroflexus, and the predorsal bundle. High levels of immunoreactivity characterise the development of the cerebellar molecular layer, the corpus callosum, anterior and hippocampal commissure, and of crossed projections in the spinal cord and at several levels of the brainstem. Intense immunoreactivity in fine collaterals of cutaneous afferents, including their growth cones that are in contact with the embryonic skin, suggests a role of TAG-1/axonin-1 in target recognition. While staining is weak on the somata of radially migrating neurons such as cortical neurons and cerebellar granule cells, strong immunoreactivity is associated with neural somata and processes of the three tangential migrations that form the precerebellar nuclei, indicating a possible involvement of TAG-1/axonin-1 in contacts between these neurons and the processes they migrate upon.

Aging↗
PubMed2006

Effect of octanol:water partition coefficients of organophosphorus compounds on biodistribution and percutaneous toxicity.

Knowledge of partition coefficient (log P) data can play a critical role in understanding the pharmacokinetic and pharmacodistributive properties of toxic organophosphorus (OP) compounds. Using a recently published gas chromatographic method, the octanol:water log P values for the compounds tabun (GA), sarin (GB), cyclosarin (GF), and O-ethyl-S-(2-diisopropylaminoethyl) methylphosphonothiolate (VX) were determined to be 0.384 +/- 0.033, 0.299 +/- 0.016, 1.038 +/- 0.055, and 0.675 +/- 0.070, respectively. Based on these data, the log P value of the fluorophosphonate fragment, common to GB, soman (GD), and GF, was determined to be -2.256 +/- 0.273. The predictive value for absorption and distribution of the determined log P values was compared to measured values. The time to onset of local fasciculations (47.3, 29.0, 8.8, 8.5, and 6.3 min, respectively) in guinea pigs exposed percutaneously to equilethal doses of GA, VX, GF, GB, or GD was used as an indicator of dermal penetration. There was a good correlation (r = 0.95) between the measured log P value and the rate of onset of local fasciculations. Assuming a direct correspondence, equilibrium tissue:blood log P may be estimated from octanol:water log P. Comparison of the estimated and directly measured tissue:blood log P revealed a correlation of 0.8 for GD in liver, muscle, and adipose tissue. Our results demonstrate the use of log P data to both predict absorption and determine the distribution of OP compounds in tissues. This facilitates further estimates of in vivo OP effects from in vitro experiments.

Administration, Cutaneous↗
PubMed1977

Alteration of structure and penetrability of the vitelline envelope after passage of eggs from coelom to oviduct in Xenopus laevis.

The vitelline envelope (VE) that surrounds an egg released from the ovary into the coelom of Xenopus laevis differs markedly, in structure and penetrability, from the VE surrounding an oviposited egg. In a coelomic egg, the filaments that form the VE are arranged in distinct fascicles or bundles. The exterior surface of the VE is irregular in contour and is permeated by channels. In an oviposited egg, the filaments are evenly dispersed and lack a fasciculated arrangement; the exterior surface is smooth and no channels are present. The fascicular arrangement of fibrils in the coelomic VE is maintained only at neutral pH, and is not visibly altered by the cortical reaction. VEs from coelomic eggs retain their fasciculated morphology after isolation from the egg. In an in vitro test system, sperm penetrated VEs isolated from oviposited eggs, but failed to penetrate VEs isolated from coelomic eggs. The structural transformation of the VE from the coelomic type to the oviposited type occurs in the first 1-cm segment of the oviduct, prior to addition of jelly to the egg. Neither intact jelly, solubilized jelly, nor jelly extracts were capable of altering the structural organization of coelomic VEs, suggesting that the structural transformation of the VE is effected by some oviducal factor other than jelly.

Animals↗
PubMed2003

Intracellular fibroblast growth factor produces effects different from those of extracellular application on development of avian cochleovestibular ganglion cells in vitro.

In an avian coculture system, the neuronal precursors of the cochleovestibular ganglion typically migrated from the otocyst and differentiated in response to soluble fibroblast growth factor (FGF-2), which had free access to FGF receptors on the cell surface. Free FGF-2 switched cells from a proliferation mode to migration, accompanied by increases in process outgrowth, fasciculation, and polysialic acid expression. Microsphere-bound FGF-2 had some of the same effects, but in addition it increased proliferation and decreased fasciculation and polysialic acid. As shown by immunohistochemistry, FGF-2 that was bound to latex microspheres depleted the FGF surface receptor protein, which localized with the microspheres in the cytoplasm and nucleus. For microsphere-bound FGF-2, the surface receptor-mediated responses to FGF-2 appear to be limited and the door opened to another venue of intracellular events or an intracrine mechanism.

Animals↗
PubMed1992

Miniature endplate potentials induced by ammonium chloride, hypertonic shock, and botulinum toxin.

Intracellular recordings were made at the neuromuscular junction (NMJ) of the mouse diaphragm to study alteration of miniature endplate potential (MEPP) amplitude and rise time after different treatments. Following either hyperosmotic shock or 3 to 5 min of incubation in 10 to 50 mM ammonium chloride (NH4Cl) (replacing NaCl, a treatment which is known to raise intracellular pH) MEPP frequencies increased and the amplitudes of MEPPs decreased. These treatments as well as type A botulinum toxin (BoTx) gradually prolonged the rising phase of some MEPPs, which increased their time-to-peak (slow-MEPPs; Vautrin and Kriebel: Neuroscience 41:71-88, 1991) and increased eventually their amplitude. Fasciculation after hyperosmotic shock or during NH4Cl challenge was blocked by D-tubocurarine and was due to large slow-MEPPs that reached threshold for the muscle fiber action potential. The development of fasciculation provided the time course for the development of giant-MEPPs. Increased frequency of giant MEPP is accompanied by a block of the nerve-evoked muscle contraction. Effects of BoTx on spontaneous release were functionally antagonized either by NH4Cl or hyperosmotic shock. NH4Cl delayed BoTx blockage of bell-MEPPs. Data suggest that BoTx alters the formation of transmitter packets gradually but similarly to other treatments which increase incidence of skew-MEPPs.

Action Potentials↗
PubMed2002

Ion channel and striational antibodies define a continuum of autoimmune neuromuscular hyperexcitability.

Neuromuscular hyperexcitability is a characteristic of Isaacs' syndrome. Autoantibodies specific for voltage-gated potassium channels (VGKC) or ganglionic nicotinic acetylcholine receptors (AChR) are markers of this disorder. To determine the frequency of these ion channel antibodies and of related neuron- and muscle-specific antibodies in patients with acquired neuromuscular hyperexcitability, we tested serum specimens from 77 affected patients (35 neuromyotonia, 32 cramp-fasciculation syndrome, 5 rippling muscle syndrome, and 5 focal neuromuscular hyperexcitability) and 85 control subjects. Among study patients, 14% had coexisting myasthenia gravis, and 16% had an associated neoplasm. We found that 35% had VGKC antibodies, 12% ganglionic AChR antibodies, 16% muscle AChR antibodies, and 10% striational antibodies. Overall, 55% had serological evidence of neurological autoimmunity compared to 2% of control subjects. Patients with neuromyotonia were more frequently seropositive (71%) than patients with cramp-fasciculation syndrome (31%). We conclude that acquired neuromuscular hyperexcitability consists of a continuum of clinical disorders with a common autoimmune pathogenesis.

Autoantibodies↗
PubMed2001

Immunoelectron microscopic localization of the neural recognition molecules L1, NCAM, and its isoform NCAM180, the NCAM-associated polysialic acid, beta1 integrin and the extracellular matrix molecule tenascin-R in synapses of the adult rat hippocampus.

We have investigated the possibility that morphologically different excitatory glutamatergic synapses of the "trisynaptic circuit" in the adult rodent hippocampus, which display different types of long-term potentiation (LTP), may express the immunoglobulin superfamily recognition molecules L1 and NCAM, the extracellular matrix molecule tenascin-R, and the extracellular matrix receptor constituent beta1 integrin in a differential manner. The neural cell adhesion molecules L1, NCAM (all three major isoforms), NCAM180 (the largest major isoform with the longest cytoplasmic domain), beta1 integrin, polysialic acid (PSA) associated with NCAM, and tenascin-R were localized by pre-embedding immunostaining procedures in the CA3/CA4 region (mossy fiber synapses) and in the dentate gyrus (spine synapses) of the adult rat hippocampus. Synaptic membranes of mossy fiber synapses where LTP is expressed presynaptically did not show detectable levels of immunoreactivity for any of the molecules/epitopes studied. L1, NCAM, and PSA, but not NCAM180 or beta1 integrin, were detectable on axonal membranes of fasciculating mossy fibers. In contrast to mossy fiber synapses, spine synapses in the outer third of the molecular layer of the dentate gyrus, which display postsynaptic expression mechanisms of LTP, were both immunopositive and immunonegative for NCAM, NCAM180, beta1 integrin, and PSA. Those spine synapses postsynaptically immunoreactive for NCAM or PSA also showed immunoreactivity on their presynaptic membranes. NCAM180 was not detectable presynaptically in spine synapses. L1 could not be found in spine synapses either pre- or postsynaptically. Also, the extracellular matrix molecule tenascin-R was not detectable in synaptic clefts of all synapses tested, but was amply present between fasciculating axons, axon-astrocyte contact areas, and astrocytic gap junctions. Differences in expression of the membrane-bound adhesion molecules at both types of synapses may reflect the different mechanisms for induction and/or maintenance of synaptic plasticity.

Animals↗