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Monoclonal antibody labels olfactory and visual pathways in Drosophila and Apis brains.

We employed a monoclonal antibody raised against Drosophila brain homogenate for a comparative immunocytochemical analysis of visual and olfactory pathways in brains of two insect species. On Western blots of Drosophila and Apis nervous tissue, antibody fb45 recognized an antigen with an apparent molecular weight higher than 180 kD. Application of the antibody to sections of Drosophila and Apis brain stained certain interneurons which conspicuously fasciculate in common tracts or neuropilar compartments. Both in Drosophila and in Apis, the antigen was also expressed on the perineural sheath and granular cell compartments in the majority of neuronal cell bodies. The antibody stained monopolar cells in the visual system of both species, and in Apis those fibers of the anterior superior optic tract which link the medulla with the mushroom bodies. In Drosophila, bundles of Kenyon cells of the mushroom bodies were stained. In worker bees and drones, the relay neurons of the median and lateral antennoglomerular tracts were labelled. Since the recognition of the antigen does not require fixation, the antibody can be employed to label selectively living neurons in dissociated cell culture. This opens up the possibility for future functional studies on the role of the antigen in vitro.

Animals↗

Prenatal exposure to ethanol alters the postnatal development and transformation of radial glia to astrocytes in the cortex.

Postmitotic neurons migrate from a zone(s) near the ventricles to the neocortex. During this migration, neurons associate with radial glia. After serving their role as guides for neuronal migration, the radial glia transform into astrocytes. Prenatal exposure to ethanol causes abnormal neuronal migration. We examined the effects of gestational exposure to ethanol on radial glia and astrocytes. Radial glia were stained immunohistochemically with the antibody RAT-401, and astrocytes were labeled with an antibody directed against glial fibrillary acidic protein (GFAP). The subjects were the offspring of rats fed an ethanol-containing liquid diet (Et), pair-fed a liquid control diet (Ct), or fed chow and water (Ch). During the first postnatal week, radial glial fibers (in Et-treated rats and controls) stretched from the ventricular surface through the developing cerebral wall to the pial surface. In the Et-treated rats, the radial processes were less dense and more poorly fasciculated than they were in the Ch- and Ct-treated rats. Moreover, by postnatal day (P) 5, there was a significant reduction in RAT-401 immunostaining in the Et-treated rats, particularly in the superficial cortex. A similar reduction in control rats did not begin until P10. In all three treatment groups, GFAP-immunoreactive astrocytes were in the cortex throughout the period from P1 to P45. In neonates, GFAP-positive cells were distributed in the marginal zone (layer I) and the intermediate zone (the white matter). The number of GFAP-positive cells in the cortical plate increased steadily with time so that, by P26, GFAP-immunoreactive astrocytes were distributed evenly through all cortical laminae. Interestingly, between P5 and P12, the number of astrocytes was significantly greater in Et-treated rats than in controls. Thus prenatal exposure to ethanol induces the premature loss of RAT-401-positive processes and the precocious increase in GFAP immunostaining. These ethanol-induced changes in glial development indicate that ethanol accelerates the transformation of radial glia into astrocytes. Moreover, the ethanol-induced premature degradation of the network of radial glial fibers may underlie the migration of late-generated neurons to ectopic sites.

Animals↗

Distribution of VIP mRNA and two distinct VIP binding sites in the developing rat brain: relation to ontogenic events.

The peptide neurotransmitter vasoactive intestinal peptide (VIP) has neurotrophic properties and influences neurobehavioral development. To assess the role of VIP during neural ontogeny, the present work traces the development of VIP mRNA with in situ hybridization and VIP receptors with in vitro autoradiography in rat central nervous system (CNS) from embryonic day 14 (E14) to the adult. VIP mRNA was not evident in the CNS until birth. Postnatally, it was expressed in several distinct brain regions, but its distribution bore little relation to that of VIP receptors. VIP receptors were present and expressed changing patterns of distribution throughout CNS development. The changing patterns were the result of 1) the transient appearance of GTP-insensitive VIP receptors in several regions undergoing mitosis or glial fasciculation and 2) the transient appearance of GTP-sensitive VIP receptors homogeneously distributed throughout the CNS during the first 2 postnatal weeks, the period of the brain growth spurt. At E14-16 VIP binding was dense throughout the brainstem and spinal cord, but limited in the rest of the brain. From E19 to postnatal day 14 (P14), while VIP binding was higher in germinal zones, it tended to be uniformly dense throughout the remainder of the brain. By P21 the adult pattern began to emerge; VIP binding was unevenly distributed and was related to specific cytoarchitectural sites. Since the expression of VIP in the CNS is limited to postnatal development but VIP receptors are abundant prenatally, we suggest that extraembryonic VIP may act upon prenatal VIP receptors to regulate ontogenic events in the brain.

Aging↗

Early development of efferent projections from the chick tectum.

The early development of the uncrossed tectobulbar and the crossed tectospinal tracts was studied. These two projections arise from the same structure, the mesencephalon, and develop during the same time period, but follow divergent courses. We have traced the pathways followed by these projections and identified the positions at which axon guidance decisions are made. The first neurons differentiate either side of the entire rostrocaudal extent of the dorsal midline and initiate axons that extend dorsoventrally across the surface of the tectum. At the ventral edge of the tectum these axons turn abruptly and fasciculate to form a caudal descending projection to the hindbrain. These axons extend to the caudal hindbrain and do not project to the periphery along cranial nerve roots. We therefore consider this tract to be the tectobular, rather than the mesencephalic division of the trigeminal. While the tectobulbar projection is still developing, a second wave of axons is initiated, which arises from only the rostral part of the tectum. These axons grow beyond the tectobulbar turn point and continue toward the ventral midline, where they cross the floor plate, before turning caudally at the lateral edge of the main descending hindbrain tract, the ventrolateral tract. We discuss the development of these tracts with reference to possible guidance cues mediating their course.

Animals↗

Visualizing neurons one-by-one in vivo: optical dissection and reconstruction of neural networks with reversible fluorescent proteins.

A great many axons and dendrites intermingle to fasciculate, creating synapses as well as glomeruli. During live imaging in particular, it is often impossible to distinguish between individual neurons when they are contiguous spatially and labeled in the same fluorescent color. In an attempt to solve this problem, we have taken advantage of Dronpa, a green fluorescent protein whose fluorescence can be erased with strong blue light, and reversibly highlighted with violet or ultraviolet light. We first visualized a neural network with fluorescent Dronpa using the Gal4-UAS system. During the time-lapse imaging of axonal navigation, we erased the Dronpa fluorescence entirely; re-highlighted it in a single neuron anterogradely from the soma or retrogradely from the axon; then repeated this procedure for other single neurons. After collecting images of several individual neurons, we then recombined them in multiple pseudo-colors to reconstruct the network. We have also successfully re-highlighted Dronpa using two-photon excitation microscopy to label individual cells located inside of tissues and were able to demonstrate visualization of a Mauthner neuron extending an axon. These "optical dissection" techniques have the potential to be automated in the future and may provide an effective means to identify gene function in morphogenesis and network formation at the single cell level.

Animals↗

Neurochemical development of the hippocampal region in the fetal rhesus monkey. II. Immunocytochemistry of peptides, calcium-binding proteins, DARPP-32, and monoamine innervation in the entorhinal cortex by the end of gestation.

Material for the study came from one 126 day-old rhesus monkey fetus and two 3 day-old neonates. The immunocytochemical detection of somatostatin, neurotensin (NT), parvalbumin, calbindin D-28K, DARPP-32 as well as tyrosine hydroxylase (TH), dopamine-beta-hydroxylase and serotonin (5-HT), was carried out on serial cryostat sections of the entorhinal cortex. The authors reported in a previous paper the precocious differentiation of the entorhinal cortex in rhesus monkey fetuses and featured the conspicuous expression of calbindin D-28K, somatostatin, neurotensin, and the monoaminergic innervation during the first half of gestation. The present study shows distinct temporal profiles of neurochemical development during the second half of gestation: the dense neuropeptidergic innervation remained a constant feature; the three aminergic systems gradually increased in density; parvalbumin, unlike calbindin D-28K, was primarily expressed during the last quarter of gestation. Three other prominent features of the last quarter of gestation are illustrated: the refinement of the modular neurochemical organization of the lamina principalis externa, the delayed chemoanatomical development of the rhinal sulcus area, and the establishment of a distinct rostrocaudal pattern of neurochemical distribution. In correspondence with the cluster-like organization of the lamina principalis externa, the authors observed in the olfactory, rostral, and intermediate fields of the neonate monkey entorhinal cortex, a particular subset of pyramidal-shaped neurons: located in layer III, they were characterized by fasciculated apical dendrites ascending between the cellular islands of the discontinuous layer II and the coexpression of calbindin D-28K and DARPP-32. Besides, most of the other chemical systems displayed a distinct, area-specific, patchy distribution, except for the homogeneously distributed noradrenergic innervation. In the olfactory and rostral fields, TH positive dopaminergic fibers accumulated on the neuronal islands of layers II-III, and parvalbumin labeled fibers on those of layer III, whereas patches of 5-HT and NT-like reactive terminals were segregated between the cellular islands, overlapping the DARPP-32/calbindin D-28 K labeled dendritic bundles. At the opposite, in the intermediate field, 5-HT positive terminals overlapped the cellular islands of layer II and thin fascicles of dopaminergic fibers ran in the inter island spaces. The somatostatin-LIR innervation was apparently too dense to reveal a patchy distribution that existed at earlier developmental stages. In the caudal field, the patchy pattern was replaced by a predominant bilaminar type of distribution of NT, 5-HT, and TH-like positive afferents.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

Zipper encodes a putative integral membrane protein required for normal axon patterning during Drosophila neurogenesis.

During the development of the central nervous system, Drosophila embryo axons become organized in a stereo-typed fasciculation pattern. We have found that the zipper (zip) gene, initially identified on the basis of a defective larval cuticle in zip mutant embryos, is possibly involved in the establishment or maintenance of the axon pattern during the late stages of neurogenesis. The zip wild-type gene is expressed in the developing nervous system. It codes for a putative integral membrane protein. Both the molecular features of zipper and its biological effect in the nervous system of mutants suggest that zipper is an essential component for cell surface interactions involved in axon patterning, and that the cuticle phenotype of zip mutants is dependent on the primary defects observed in the nervous system.

Amino Acid Sequence↗

Dtrk, a Drosophila gene related to the trk family of neurotrophin receptors, encodes a novel class of neural cell adhesion molecule.

We report the identification and molecular characterization of Dtrk, a Drosophila gene encoding a receptor tyrosine kinase highly related to the trk family of mammalian neurotrophin receptors. The product of the Dtrk gene, gp160Dtrk, is dynamically expressed during Drosophila embryogenesis in several areas of the developing nervous system, including neurons and fasciculating axons. gp160Dtrk has structural homology with neural cell adhesion molecules of the immunoglobulin superfamily and promotes cell adhesion in a homophilic, Ca2+ independent manner. More importantly, this adhesion process specifically activates its tyrosine protein kinase activity. These findings suggest that gp160Dtrk represents a new class of neural cell adhesion molecules that may regulate neuronal recognition and axonal guidance during the development of the Drosophila nervous system.

Amino Acid Sequence↗

Immediate post-dosing paralysis following severe soman and VX toxicosis in guinea pigs.

There have been numerous studies of the central nervous system (CNS) involvement in organophosphate (OP) poisoning showing status epilepticus and/or 'electrographic seizures'. Brain damage has been demonstrated as 'neuronal necrosis' primarily in the cortex, thalamus and hippocampus. To the authors' knowledge there have been no reports of partial/total paralysis following close upon OP exposure although delayed paralysis has been reported. This report summarizes the immediate, OP induced paralytic events recorded in guinea pigs during development of the Canadian reactive skin decontaminant lotion (RSDL). As part of the development work, supra-lethal cutaneous doses of OP were applied to large numbers of guinea pigs followed by decontamination with the RSDL or predecessor lotions and solvents. Soman (pinacolyl methylphosphonofluoridate; GD) challenges were applied to 1277 animals and S-(2-diisopropyl-aminoethyl) methylphosphorothiolate (VX) challenges to 108. The classic sequence of clinical signs--ptyalism, tremors, fasciculations, convulsions, apnea and flaccid paralysis before death--was seen in the 658 animals that died and in many of the survivors. Eighty-four of 688 survivors of GD and 4 of 39 survivors of VX showed random paralysis of various distal regions following recovery from an insult which produced convulsions and/or flaccid paralysis. Because the experiments were designed to assess the decontamination procedures, there were no apparent relationships between the amounts of OP applied and the sequellae recorded. The observations of paralysis were also incidental to the prime focus of the experiments. Because of this, only ten animals paralysed following GD exposure were examined for histological effects. The pathologist diagnosed 'encephalomalacia' and 'focal necrotic lesions' in the cerebral cortex and 'focal necrotic lesions' in one spinal cord. Of the 84 guinea pigs paralysed after GD challenge, one was not decontaminated and the decontaminants used on the remainder were sufficiently varied that there appeared to be no relationship between the type of decontaminant and the resulting paralysis.

Animals↗

In vitro and in vivo proposal of an artificial esophagus.

Artificial materials and autologous tissues used for esophageal reconstruction often induce complications like stenosis and leakage at long-term follow-up. This study evaluates the possibility to obtain in vitro an implantable tissue-engineered esophagus composed of homologous esophageal acellular matrix and autologous smooth muscle cells (SMCs). Acellular matrices obtained by detergent-enzymatic method did not present any major histocompatibility complex marker and expressed bFGF as protein, showing angiogenic activity in vivo on the chick embryo chorioallantoic membrane (CAM). Moreover, they supported cell adhesion, and inasmuch as just after 24 h from seeding, the scaffold appeared completely covered by SMCs. To verify the biocompatibility of our constructs, defects created in the porcine esophageal wall were covered using homologous acellular matrices with and without cultures of autologous SMCs. At 3 week from surgery, the patches composed of only acellular matrices showed a more severe inflammatory response and were negative for alpha-smooth muscle actin immunostaining. In contrast, the cell-matrix implants presented ingrowth of SMCs, showing an early organization into small fascicules. Collectively, these results suggest that patches composed of homologous esophageal acellular matrix and autologous SMCs may represent a promising tissue-engineering approach for the repair of esophageal injuries.

Animals↗

Trochlear nerve regeneration in Xenopus laevis larvae.

The trochlear nerve of Xenopus laevis larvae was sectioned in the orbit, and the nerve distal to the section was removed, so that it could not serve to guide the return of the regenerating nerve to the superior oblique muscle (SOM). In a second series, in addition to removing the distal nerve segment, the SOM was removed or damaged. The regeneration pattern of the trochlear nerve fibers was recorded in situ at 1 to 5-day intervals with the aid of methylene blue staining. The early growth or regenerating fibers was multidirectional; only some fibers encountered the SOM by day 6 or 7; others reached nerves, inappropriate muscle, and other tissues. Ultimately, the fibers that reached the SOM persisted and were reinforced, while those that reached other locations were withdrawn. By 20 days or so, the regenerated trochlear nerve usually had an appearance that was close to that of an uncut nerve. In the second series, in which the SOM was removed or damaged, the multidirectional character of the growth persisted through 20 days after section. these data suggest that: 1) Trochlear nerve regeneration is not guided by cues that closely control fiber growth along a direct path to the SOM, and 2) The SOM acts as a trap for regenerating trochlear nerve fibers, promoting the maintenance and the fasciculation of the trochlear nerve fibers that reach it, and the degeneration of the fibers that do not.

Animals↗

The corpus callosum as an evolutionary innovation.

The corpus callosum (CC) is the major interhemispheric fibre bundle in the eutherian brain and has been described as a true evolutionary innovation. This paper reviews the current literature with regard to functional, developmental and genetic concepts that may help elucidate the evolutionary origin of this structure. It has been suggested that the CC arose in the eutherian brain as a more direct and, therefore, more effective system for the interhemispheric integration of topographically organized sensory cortices than the anterior commissure (AC) and hippocampal commissure (HC) already present in nonplacental mammals. It can also be argued, however, that the ability of the CC to integrate the newly evolving motor cortices of placental mammals may have played a role in the evolutionary fixation of this structure. Investigations into the developmental mechanism involved in the formation of the CC and their underlying patterns of gene expression make it possible to formulate a tentative hypothesis about the evolutionary origin of this commissure. This paper suggests that changes in the developmental patterns of the expression of certain regulatory genes may have allowed a first group of callosal pioneering axons to cross the cortical midline. These pioneering fibres may have used the axons of the HC to find their way across the midline. Additional callosal fibres may then have fasciculated with these pioneers. Once the CC had formed in this way, more complex systems of axonal guidance may have evolved over time, thus enabling a gradual increase in the size and complexity of the CC.

Animals↗

Organization of the nervous system in the pygmy cuttlefish, Idiosepius paradoxus ortmann (Idiosepiidae, Cephalopoda).

The idiosepiid cuttlefish is a suitable organism for behavioral, genetic, and developmental studies. As morphological bases for these studies, organization of the nervous system was examined in Idiosepius paradoxus Ortmann, 1881, using Cajal's silver technique and immunohistochemical staining with anti-acetylated alpha-tubulin antibody. The nervous architecture is generally identical to that described in Sepia and Loligo, but some features characterize the idiosepiid nervous system. The olfactory system is highly developed in the optic tract region. The dorsolateral lobes show large neuropils, connected with each other by a novel well-fasciculated commissure. Each olfactory lobe is subdivided into two lobules. The neuropils of the anterior and the posterior chromatophore lobes are very poorly developed. Neuronal gigantism is not extensive in the brain; enlarged neuronal cells are visible only in the perikaryal layer of the posterior subesophageal mass. The giant nerve fiber system is of the Sepia type; the axons are not markedly thick and the first-order giant fibers do not fuse with each other at the chiasma. Three-dimensional images by whole-mount immunostaining clarified the innervation pattern in the peripheral nervous system in detail. Two commissural fibers link the left and right posterior funnel nerves ventrally and dorsally. The stellate commissure, which is absent in Sepia and Sepiola, connects the stellate ganglia with each other. A branch of the visceral nerve innervating the median pallial adductor muscle is characteristically thick. Tubulinergic reactivity of the cilia and axons reveals the presence of many ciliated cells giving off an axon toward brain nerves in the surface of the funnel, head integument, arm tips, and epidermal lines. Some of these features seem to reflect the inactive nekto-benthic life of the idiosepiid cuttlefish in the eelgrass bed.

Animals↗

Carpal tunnel syndrome: staging of median nerve compression by MR imaging.

The purpose of this prospective study was to determine the potential of MR imaging to depict morphologic alterations of the median nerve correlating with the stage of carpal tunnel syndrome (CTS). Eighteen wrists of normal subjects and 81 wrists of patients with CTS were examined. MR imaging was performed with proton-density- and T2-weighted spin-echo sequences. Staging of CTS was done on the basis of clinical and electrophysiological testing, including evaluation of the number of previous steroid infiltrations in conservative treatment. Median nerve flattening, cross-sectional area, and signal intensity were measured from the distal radius to the end of the carpal tunnel. Delineation and structure of the median nerve were recorded qualitatively by two experienced radiologists in consensus. Three major MR imaging criteria of early CTS were (a) isolated prestenotic and intracarpal swelling of the median nerve (P < .01), (b) the absence of significant flattening, and (c) a generalized increase in signal intensity retrograde to the distal radius (P < .01). The nerve showed sharply delineated contours and a homogeneous signal pattern. Advanced CTS was characterized by retrograde swelling of the median nerve to the distal radius (P < .01) and decreased signal intensity (P < .05). Demarcation of the nerve became poorer, and its signal pattern appeared fasciculated. After steroid infiltration, the median nerve was difficult to delineate, showed an inhomogeneous structure, and swelling was less pronounced than without steroid infiltration (P < .05). MR imaging yields typical morphologic findings that correlate with the duration and severity of median nerve compression. Hence, MR imaging allows staging of median nerve compression in CTS and thus may contribute to therapeutic decision-making.

Carpal Tunnel Syndrome↗

Cytoplasmic domain of NCAM 180 reduces NCAM-mediated neurite outgrowth.

The neural cell adhesion molecule (NCAM) is one of the best-characterized cell adhesion molecules of the immunoglobulin superfamily. In the nervous system, NCAM is involved in cell migration, axon fasciculation and in neurite outgrowth. Neurite outgrowth is mediated by homophilic NCAM-NCAM interactions. Alternative splicing generates three major isoforms of NCAM differing in their intracellular portion. Two of them, NCAM 180 and NCAM 140, are transmembrane proteins with large intracellular domains. The present study is concerned with novel details of the intracellular domains of NCAM 140 and NCAM 180. We expressed these NCAM isoforms consisting only of the transmembrane and intracellular domains (without extracellular domains) in PC12 cells and elaborated their function in neurite outgrowth assays. Our data demonstrate that membrane-associated NCAM 180 interferes with neurite outgrowth, whereas membrane-associated NCAM 140 promotes neurite outgrowth.

Animals↗

Changes in the amounts of chondroitin sulfate proteoglycans in rat brain after neonatal hypoxia-ischemia.

Chondroitin sulfate proteoglycans have been shown to participate in the pathogenesis of neuronal damages in the injured adult central nervous system (CNS). Upregulated expression of chondroitin sulfate proteoglycans has been reported around the injured sites and depletion of these chondroitin sulfate proteoglycans brings about increased axonal regeneration in the injured adult CNS. To examine if chondroitin sulfate proteoglycans are also involved in the pathologic process of hypoxia-ischemia in the neonatal brain, expressions of three chondroitin sulfate proteoglycans, neurocan, phosphacan, and neuroglycan C, were examined in rat brains after neonatal hypoxia-ischemia. Hypoxic-ischemic rats were produced by ligating the right carotid artery of 7-day-old rats, followed by 8% oxygen exposure. Western blot analysis revealed that in contrast to injured adult CNS, the amount of neurocan was reduced 24 hr after hypoxia in the neonatal hypoxic-ischemic cerebral hemisphere. The amounts of phosphacan and neuroglycan C were also reduced significantly 24 hr after hypoxia at the right injured cortex compared to those at the left cortex. Surprisingly, the immunohistologic staining for phosphacan was conversely intensified both at 24 hr and 8 days after hypoxia at the infarcted area. In addition, the habenula and fascicules retroflexus in the right cerebral hemisphere degenerated and became intensely immunostained with the anti-phosphacan antibody shortly after hypoxia. Hypoxic-ischemic insult may unmask phosphacan epitopes at the injured sites, resulting in intensified immunostaining. Because intensified immunostaining for neurocan and neuroglycan C was not observed, unmasking seems to be specific to phosphacan among these three chondroitin sulfate proteoglycans.

Animals↗

Growth cones and the formation of central and peripheral neurites by sensory neurones in amphibian embryos.

We have examined the primary growth of neurites by Rohon-Beard sensory neurones in embryos of Xenopus, Rana, and Ambystoma. Using transmission electron microscopy we have confirmed that some central longitudinal neurites first grow directly under the basal lamina which surrounds the spinal cord in Xenopus embryos. Using scanning electron microscopy of dissected embryos we have followed the growth of neurites from the spinal cord to their target tissue, the skin. Comparisons between the three genera are made and detailed observations on growth cones during fasciculation, on the somites and on the basal lamina of the skin are presented. The observations are discussed in relation to possible influences on the course of growth of the developing neurites.

Ambystoma mexicanum↗

Influences of the neural cell adhesion molecule on axon growth and guidance.

The neural cell adhesion molecule (NCAM) has been shown to be a ligand in the formation of cell-cell bonds. This molecule is present on essentially the entire surface of differentiated nerve cells, including the cell body, neurite shaft, and growth cone. In mediating membrane-membrane adhesion, NCAM appears to ligate with itself, and one of its most obvious functions is in the self-association of nerve fibers to form fascicles. In most cases fasciculation occurs by the successive elongation of axons along other axons and, therefore, is likely to represent a growth cone-neurite shaft interaction as well as a shaft-to-shaft adhesion. Competition between neurite shafts and the surrounding substrate for growth cone adhesion probably represents a major factor in the branching of nerve bundles. In addition to neurons, NCAM appears on some glial and muscle cells. Recent experiments suggest that this molecule is involved in growth cone guidance along adhesive pathways on glial precursors in the vertebrate central nervous system, and in the initial interaction of axons with muscle prior to synaptogenesis.

Animals↗