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PubMed2003

AMPA-evoked ion influx is strongest in tangential neurons of the rat neocortical intermediate zone close to the front of the migratory stream.

In addition to the classically described radially migrating neurons, embryonic cortical areas receive neurons originating from the basal ganglia. One of the migration routes is in the intermediate zone. The front of this migration moves toward the hippocampus synchronously with the edge of the dorsally extending cortical plate. We investigated whether cells close to the front have specific properties compared with those at less advanced positions. Activation of AMPA receptors in the presence of cobalt showed that a strong influx of divalent cations could be triggered in front cells by low agonist concentration, whereas the less advanced cells needed a higher concentration to incorporate detectable amounts of cobalt. As shown by in situ hybridization, this discrepancy was not due to differential expression of GluR-2 (known to reduce permeability for divalent cations). In vivo, release of an endogenous agonist presumably affects more, or differently, the tangential cells close to the front.

Animals↗
PubMedDate not supplied

The unfolding story of two lissencephaly genes and brain development.

Formation of our highly structured human brain involves a cascade of events, including differentiation, fate determination, and migration of neural precursors. In humans, unlike many other organisms, the cerebral cortex is the largest component of the brain. As in other mammals, the human cerebral cortex is located on the surface of the telencephalon and generally consists of six layers that are formed in an orderly fashion. During neuronal development, newly born neurons, moving in a radial direction, must migrate through previously formed layers to reach their proper cortical position. This is one of several neuronal migration routes that takes place in the developing brain; other modes of migration are tangential. Abnormal neuronal migration may in turn result in abnormal development of the cortical layers and deleterious consequences, such as Lissencephaly. Lissencephaly, a severe brain malformation, can be caused by mutations in one of two known genes: LIS1 and doublecortin (DCX). Recent in vitro and in vivo studies, report on possible functions for these gene products.

1-Alkyl-2-acetylglycerophosphocholine Esterase↗
PubMed1993

The effect of a cyclooxygenase inhibitor on the in vivo polymorphonuclear leukocyte migration to Pseudomonas aeruginosa peptide chemotactins.

Pseudomonas aeruginosa chemotactic peptides (PAPCs) induced migration of polymorphonuclear leukocytes (PMNL) into the lungs when administered by the aerosol route. Migration of PMNL into the lungs and total protein content of lung lavage fluids in response to PAPCs aerosol challenge, and mortality from lethal challenge with P. aeruginosa were decreased by piroxicam treatment.

Aerosols↗
PubMed1988

Topography of interhemispheric connections in neocortex of mice with congenital deficiencies of the callosal commissure.

Normally, axons within the corpus callosum are ordered according to the cortical regions from which they originate, and callosal cells and terminations form elaborate cortical patterns related to the underlying topographic representations of the sensory periphery. About 30% of mice of the BALB/c strain show congenital deficiencies of the callosal commissure which range from total absence of the corpus callosum to a moderate reduction in the size of this commissure. In the light of current theories about the origin of these callosal deficiencies, it seems likely that fibers crossing the midplane in mutant mice have to circumvent local disturbances along their migration path. Since these disturbances in fiber trajectory may, in turn, alter the overall pattern of callosal projections, we set out to investigate whether the distribution of callosal connections in mice with marked deficiencies of the corpus callosum is as ordered as in normal mice. In groups of normal and mutant mice, we used multiple injections of horseradish peroxidase to reveal the overall distribution of callosal connections and restricted injections of horseradish peroxidase conjugated with wheat germ agglutinin to reveal finer aspects of the organization of the callosal pathway in these animals. Our results show that the number of labeled cells is reduced in mice with a small corpus callosum and that no labeled cells are present in the neocortex of acallosal mice. Furthermore, the topographic distribution of fibers within the corpus callosum of mutant mice can be significantly less ordered than in normal mice. However, even in mice with extreme deficiencies of the corpus callosum, callosal fibers originate from and terminate in all major areas of the cortex, and, within these areas, callosal cells and terminations are distributed according to the normal plan. The laminar distribution of callosal cells also appears normal in these mice. These findings indicate that gross developmental anomalies of the corpus callosum do not prevent normal specification of the callosal pattern during development. Within the context of current theories about the origin of congenital callosal deficiencies, our findings suggest that callosal fibers are able to establish appropriate contralateral connections in spite of alterations of their migration route. They also suggest that fiber topography within the corpus callosum does not play an important role in guiding migrating axons to their correct contralateral targets. Finally, our failure to find labeled fibers within the anterior commissure indicates that this commissure does not serve as an alternative route for deviated callosal axons.

Agenesis of Corpus Callosum↗
PubMed1998

The navigational feats of green sea turtles migrating from Ascension Island investigated by satellite telemetry.

Previous tagging studies of the movements of green turtles (Chelonia mydas) nesting at Ascension Island have shown that they shuttle between this remote target in the Atlantic Ocean and their feeding grounds on the Brazilian coast, a distance of 2300 km or more. Since a knowledge of sea turtle migration routes might allow inferences on the still unknown navigational mechanisms of marine animals, we tracked the postnesting migration of six green turtle females from Ascension Island to Brazil. Five of them reached the proximity of the easternmost stretch of the Brazilian coast, covering 1777-2342 km in 33-47 days. Their courses were impressively similar for the first 1000 km, with three turtles tracked over different dates following indistinguishable paths for the first 300 km. Only the sixth turtle made some relatively short trips in different directions around Ascension. The tracks show that turtles (i) are able to maintain straight courses over long distances in the open sea; (ii) may perform exploratory movements in different directions; (iii) appropriately correct their course during the journey according to external information; and (iv) initially keep the same direction as the west-south-westerly flowing current, possibly guided by chemical cues.

Animals↗
PubMed1992

[Study on radionuclide migrating along the channel].

The study of impedance line along channel had been performed with the radionuclide tracing method in 15 healthy human being and 4 guinea pigs. These images of tracer migrating routes approximately corresponded with classical courses of channel. The study proved that these line-shaped tracer migration were not by the way of lymphatic and blood vessels as well as nerves. This image of radionuclide migrating along channel may used as the guide for the observation of micro-autoradiography. In this study, satisfactory migrating image along the channel was also obtained by 131I instead of 99mTC. So a new way was opened up for both macro- and micro-autoradiographic study.

Adult↗
PubMed1990

Embryonic development of four different subsets of cholinergic neurons in rat cervical spinal cord.

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 ChAT-positive cells 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.

Animals↗
PubMed2006

Leptin is synthesized in the liver and adipose tissue of the dunlin (Calidris alpina).

Fat is the main source of energy for birds during a long-distance flight. Migration routes are usually divided into several steps. In stopover sites migratory birds restore energy reserves needed for continuation of migration. During a long-distance flight and when foraging at a stopover site birds should be able to assess their actual reserves accumulated in the form of fat stores. The information about energy being stored in body reserves may be provided by circulating factors involved in body mass regulation, such as adipose-derived hormone leptin. To date, little is known about the expression and potential role of leptin in birds. The aim of the present study was to determine whether leptin is synthesized in the liver and adipose tissue of the dunlin (Calidris alpina), a long-distance migrant. Western blot analysis with leptin-specific antibody detected a protein with a molecular mass of approximately 15-16 kDa in dunlin liver and adipose tissue. To our knowledge, this is the first report demonstrating leptin expression in the liver and adipose tissue of a migratory bird. This finding raises the possibility that in birds leptin may signal the status of energy reserves during migratory flight.

Adipose Tissue↗
PubMed2004

The influence of climate on the timing and rate of spring bird migration.

Ecological processes are changing in response to climatic warming. Birds, in particular, have been documented to arrive and breed earlier in spring and this has been attributed to elevated spring temperatures. It is not clear, however, how long-distance migratory birds that overwinter thousands of kilometers to the south in the tropics cue into changes in temperature or plant phenology on northern breeding areas. We explored the relationships between the timing and rate of spring migration of long-distance migratory birds, and variables such as temperature, the North Atlantic Oscillation (NAO) and plant phenology, using mist net capture data from three ringing stations in North America over a 40-year period. Mean April/May temperatures in eastern North America varied over a 5 degrees C range, but with no significant trend during this period. Similarly, we found few significant trends toward earlier median capture dates of birds. Median capture dates were not related to the NAO, but were inversely correlated to spring temperatures for almost all species. For every 1 degrees C increase in spring temperature, median capture dates of migratory birds averaged, across species, one day earlier. Lilac (Syringa vulgaris) budburst, however, averaged 3 days earlier for every 1 degrees C increase in spring temperature, suggesting that the impact of temperature on plant phenology is three times greater than on bird phenology. To address whether migratory birds adjust their rate of northward migration to changes in temperature, we compared median capture dates for 15 species between a ringing station on the Gulf Coast of Louisiana in the southern USA with two stations approximately 2,500 km to the north. The interval between median capture dates in Louisiana and at the other two ringing stations was inversely correlated with temperature, with an average interval of 22 days, that decreased by 0.8 days per 1 degrees C increase in temperature. Our results suggest that, although the onset of migration may be determined endogenously, the timing of migration is flexible and can be adjusted in response to variation in weather and/or phenology along migration routes.

Animal Migration↗
PubMed1996

Migration of neurons containing gonadotropin releasing hormone (GnRH) in slices from embryonic nasal compartment and forebrain.

During development, neurons containing gonadotropin-releasing hormone traverse fiber bundles in the nose, cross into the brain, and move through a maze of glial and axonal fibers. To test whether GnRH neurons utilize cues intrinsic to their migration route to traverse the nasal/brain boundary, tissue slices that maintain connections between the forebrain and nasal compartment were prepared from mouse embryos. Cell migration between the nasal and brain compartments was evident based on changes in cell positions after successive days in vitro.

Animals↗
PubMed1994

Removal of olfactory placode prevents the development of LHRH neurons in the forebrain of the chick embryo: possible interaction between migrating LHRH neurons and highly polysialylated form of neural cell adhesion molecule (NCAM-H).

A unilateral olfactory placodectomy prevented the development of LHRH- and NCAM-H-expressing neurons as well as NCAM-H expressing olfactory nerve on the operated side, whereas the development of LHRH- and NCAM-H-expressing neurons and olfactory nerve was not disturbed. In the embryos with an incomplete olfactory placodectomy, a small number of LHRH-immunoreactive (ir) cells expressing NCAM-H were detected in the olfactory epithelial fragments and in the NCAM-H-positive olfactory nerve remants which ceased to extend their axons to the forebrain. The lack of the central projection of the olfactory nerve caused stagnation of LHRH-ir cells, no LHRH-ir cells being found in the forebrain. These results clearly suggest the importance of the structural support for the migration of LHRH-ir cells. Furthermore, the migrating LHRH-ir cells deviated from the poorly developed olfactory nerve and migrated not only to the central direction but also to the peripheral direction of the NCAM-H-positive medial nasal branch of the ophthalmic nerve of the trigeminal nerve. This suggests that the migration route of the LHRH neurons is not programmed in detail in the precursor cells of LHRH neurons in the olfactory placode. Since the migrating LHRH-ir cells were never independent of NCAM-H-positive neural elements in the operated embryos, it is suggested that not only the structural support for the migration but also the possible interaction between the migration of LHRH-ir cells and NCAM-H and/or other unknown factors may be needed for successful LHRH neuronal migration.

Animals↗
PubMed1980

Invited review: guidance cue patterns and cell migration in multicellular organisms.

In multicellular organisms, guidance cues are either diffusible molecules or cellular or extracellular surfaces that are found in reproducible locations and that orient migrating cells and cell processes. The pattern of the guidance cues usually determines the complex in vivo migration routes of motile cells and cell processes. Within organisms, guidance cues are found to be organized in two general patterns: a) broad gradients--such as diffuse chemotactic gradients; b) discrete routes (substrate pathways)--such as chemotactic gradients confined to long channels, and such as the axon surface which represents a long specific highway for migrating Schwann cells.

Amphibians↗
PubMed2005

Global circumnavigations: tracking year-round ranges of nonbreeding albatrosses.

Although albatrosses are paradigms of oceanic specialization, their foraging areas and migration routes when not breeding remain essentially unknown. Our continuous remote tracking of 22 adult gray-headed albatrosses for over 30 bird-years reveals three distinct strategies: (i) Stay in breeding home range; (ii) make return migrations to a specific area of the southwest Indian Ocean; and (iii) make one or more global circumnavigations (the fastest in just 46 days). The consistencies in patterns, routes, and timings offer the first hope of identifying areas of critical habitat for nonbreeding albatrosses, wherein appropriate management of longline fisheries might alleviate the plight of the world's most threatened family of birds.

Animal Migration↗
PubMed2000

Mitochondrial DNA phylogeography of Acrossocheilus paradoxus (Cyprinidae) in Taiwan.

Nucleotide sequences of 3' end of the cytochrome b gene, tRNA genes, D-loop control region, and the 5' end of the 12S rRNA of mitochondrial DNA (mtDNA) were used to assess the genetic and phylogeographic structure of Acrossocheilus paradoxus populations, a Cyprinidae fish of Taiwan. A hierarchical examination of populations in 12 major streams from three geographical regions using an analysis of molecular variance (AMOVA) indicates high genetic differentiation both among populations (PhiST = 0.511, P < 0.001) and among regions (PhiCT = 0.368, P < 0.001). Limited migration largely contributed to the genetic differentiation. High nucleotide diversity (1.13%) and haplotype diversity (0.80%) were detected among populations. The degree of genetic differentiation was correlated with geographical distance between populations, a result consistent with the one-dimensional stepping stone models. A neighbour-joining tree recovered by (DAMBE) supports the pattern of isolation by distance and reveals a closer relationship between populations of the central and southern regions. A minimum spanning network based on nucleotide substitutions reflected migration routes from populations of the central region to the northern and southern regions, respectively. Postglacial colonization and expansion can explain the phylogeographical pattern. Single and ancient migration events may have allowed the northern region to attain the monophyly of mtDNA alleles. In contrast, most populations within geographical regions are either paraphyletic or polyphyletic due to the relatively shorter time period for coalescence. Both low haplotype number and genetic variability suggest a bottleneck event in the Chingmei population of northern Taiwan. Based on coalescence theory, the monophyly of the Tungkang population of the southern region may be associated with a founder event.

Animals↗
PubMed1981

Transfer of lymphocytes of Peyer's patches between immunoglobulin allotype congenic mice: repopulation of the IgA plasma cells in the gut lamina propria.

Repopulation of the IgA plasma cells in the gut lamina propria was studied by lymphocyte transfers between histocompatible, immunoglobulin allotype congenic mice (CB-20 and BALB/cJ). Among the lymphocytes transferred, Peyer's patch lymphocytes showed the highest efficiency in the repopulation. The donor IgA plasma cells appeared suddenly in the gut lamina propria in substantial numbers at day 8, increased exponentially, and repopulated essentially tne entire gut lamina propria at days 12 to 14. By sequential transfer of lymphoid cells, lymphoid cell culture, splenectomy, and jejunum-shielded total body irradiation of the recipient mice, the majority of the patch IgA precursors were found migrating directly to the spleen rather than to the gut lamina propria. The patch IgA precursors resided in the spleen for at least 5 days and then migrated to the gut lamina propria, where they further divided and matured into IgA plasma cells. However, the spleen is not a completely obligatory tissue in the migration route because the repopulation was only partially reduced when patch cells were transferred into splenectomized recipients. In the splenectomized recipients, the patch IgA precursors did not migrate directly to the gut lamina propria either, which suggests that indirect homing to the gut lamina propria is a characteristic of the patch IgA precursor cells.

Animals↗
PubMed1990

Migration of neuroblasts by perikaryal translocation: role of cellular elongation and axonal outgrowth in the acoustic nuclei of the chick embryo medulla.

The neuroblasts forming nucleus magnocellularis, the avian homologue of the mammalian ventral cochlear nucleus, migrate by growth and elongation of their leading processes and by perikaryal translocation through these processes from the matrix zone of the rhombic lip to the acoustico-vestibular anlage. Golgi methods were used on staged chick embryos to reconstruct the morphogenetic phases of migration and early differentiation in situ. Fluorescence labeling of the living cells in vitro elucidated the role of axonal growth in the migratory process. In situ, branching cochlear nerve fibers, tipped with growth cones, enter the acoustico-vestibular anlage at E4.5-5.5 before migration of the magnocellularis neuroblasts at E.5.5-6.5. The premigratory neuroblasts in the matrix zone of the rhombic lip resemble primitive epithelial cells, which extend branched, curving processes into a characteristic formation, the rhombic whorl. The leading process of the migrating magnocellularis neuroblasts gives rise to a bifurcating axon at the interface between the matrix and mantle zones. The lateral branch becomes the recurrent ipsilateral collateral; the medial branch crosses the midline, heading toward the contralateral target site in the region of the presumptive nucleus laminaris. The cell bodies of the migratory neuroblasts appear in intermediate locations along the migration route as they translocate radially through their leading processes past the axonal bifurcation and then tangentially and obliquely into the mantle zone. Neuroblasts destined for nucleus laminaris migrate coincidentally with magnocellularis neuroblasts. Nucleus angularis neuroblasts migrate later in development, after E6.5. In vitro, injections of a nontoxic fluorescent dye (diI) were made into explants of the medulla in the region of the contralateral target area at the time of neuroblast migration. DiI retrogradely labeled the cell bodies of premigratory magnocellularis neuroblasts in the matrix zone and of migratory neuroblasts in the mantle zone through their medial, crossing axonal branches. The morphology of the living neuroblasts in the explants resembled that in the Golgi impregnations at the corresponding stages of migration. Anterograde axonal transport also occurred. These results demonstrate migration by perikaryal translocation and early axon extension of a specific group of neuroblasts in the central nervous system. The morphology of the migrating neuroblasts is such that a simple radial arrangement of cellular guides, glial or otherwise, would not account for their configurations. The available evidence supports the proposition that cellular elongation and perikaryal translocation constitute the general mode of neuronal migration in the central nervous system. The early extension of axons into their target sites may play a critical role in migration and early development of specific types of neurons.

Animals↗
PubMed2002

Recent findings of Phlebotomus neglectus Tonnoir, 1921 in Italy and its western limit of distribution.

During the sand fly season of 2001, sand flies were collected in two different regions of Italy to investigate the northern distribution of Phlebotomus neglectus. The study areas were two provinces of northern Italy, Ivrea and Verona, in Piedmont and Veneto regions respectively. Sticky traps and CDC miniature light traps were used both inside and outside domestic and peri-domestic environments. Sand flies were also collected in domestic resting sites with mouth and electric aspirators. Of 1,295 sand fly specimens collected, 855 were from the Veneto region and 440 were from the Piedmont region. Five species of the genera Phlebotomus and Sergentomyia were identified. S. minuta (66.3%) was the most abundant sand fly followed by P. perniciosus (22.2%), P. neglectus (10.3%) and P. papatasi (1.2%). Only one specimen of P. mascittii was caught in Piedmont region. P. neglectus was found in 9 out of 15 (60%) of the sites where sand flies were found with a prevalence of 1.5% to 45.8%; the highest value was recorded in Piedmont region. P. neglectus was mostly associated with peridomestic and domestic sites. The results confirm previous observations on the presence of P. neglectus in northern Italy and suggest that this species is probably widespread in the area. From a review of all previous published and unpublished records of P. neglectus, it appears that this species is present in only two areas of the country, namely in the regions of Friuli Venezia Giulia, Veneto and Piedmont in northern Italy and the regions of Calabria, Apulia and Sicily in southern Italy. The apparent absence of P. neglectus in Central Italy is discussed and the resulting settlement through two probable migration routes from the East is analysed.

Altitude↗
PubMed2000

In ovo time-lapse analysis of chick hindbrain neural crest cell migration shows cell interactions during migration to the branchial arches.

Hindbrain neural crest cells were labeled with DiI and followed in ovo using a new approach for long-term time-lapse confocal microscopy. In ovo imaging allowed us to visualize neural crest cell migration 2-3 times longer than in whole embryo explant cultures, providing a more complete picture of the dynamics of cell migration from emergence at the dorsal midline to entry into the branchial arches. There were aspects of the in ovo neural crest cell migration patterning which were new and different. Surprisingly, there was contact between neural crest cell migration streams bound for different branchial arches. This cell-cell contact occurred in the region lateral to the otic vesicle, where neural crest cells within the distinct streams diverted from their migration pathways into the branchial arches and instead migrated around the otic vesicle to establish a contact between streams. Some individual neural crest cells did appear to cross between the streams, but there was no widespread mixing. Analysis of individual cell trajectories showed that neural crest cells emerge from all rhombomeres (r) and sort into distinct exiting streams adjacent to the even-numbered rhombomeres. Neural crest cell migration behaviors resembled the wide diversity seen in whole embryo chick explants, including chain-like cell arrangements; however, average in ovo cell speeds are as much as 70% faster. To test to what extent neural crest cells from adjoining rhombomeres mix along migration routes and within the branchial arches, separate groups of premigratory neural crest cells were labeled with DiI or DiD. Results showed that r6 and r7 neural crest cells migrated to the same spatial location within the fourth branchial arch. The diversity of migration behaviors suggests that no single mechanism guides in ovo hindbrain neural crest cell migration into the branchial arches. The cell-cell contact between migration streams and the co-localization of neural crest cells from adjoining rhombomeres within a single branchial arch support the notion that the pattern of hindbrain neural crest cell migration emerges dynamically with cell-cell communication playing an important guidance role.

Animals↗