141 research outputs found
Pretectal neurons control hunting behaviour
For many species, hunting is an innate behaviour that is crucial for survival, yet the circuits that control predatory action sequences are poorly understood. We used larval zebrafish to identify a population of pretectal neurons that control hunting. By combining calcium imaging with a virtual hunting assay, we identified a discrete pretectal region that is selectively active when animals initiate hunting. Targeted genetic labelling allowed us to examine the function and morphology of individual cells and identify two classes of pretectal neuron that project to ipsilateral optic tectum or the contralateral tegmentum. Optogenetic stimulation of single neurons of either class was able to induce sustained hunting sequences, in the absence of prey. Furthermore, laser ablation of these neurons impaired prey-catching and prevented induction of hunting by optogenetic stimulation of the anterior-ventral tectum. We propose that this specific population of pretectal neurons functions as a command system to induce predatory behaviour
Enhanced antiproton production in Pb(160 AGeV)+Pb reactions: evidence for quark gluon matter?
The centrality dependence of the antiproton per participant ratio is studied
in Pb(160 AGeV)+Pb reactions. Antiproton production in collisions of heavy
nuclei at the CERN/SPS seems considerably enhanced as compared to conventional
hadronic physics, given by the antiproton production rates in and
antiproton annihilation in reactions. This enhancement is consistent
with the observation of strong in-medium effects in other hadronic observables
and may be an indication of partial restoration of chiral symmetry
Sparse Coding Predicts Optic Flow Specificities of Zebrafish Pretectal Neurons
Zebrafish pretectal neurons exhibit specificities for large-field optic flow
patterns associated with rotatory or translatory body motion. We investigate
the hypothesis that these specificities reflect the input statistics of natural
optic flow. Realistic motion sequences were generated using computer graphics
simulating self-motion in an underwater scene. Local retinal motion was
estimated with a motion detector and encoded in four populations of
directionally tuned retinal ganglion cells, represented as two signed input
variables. This activity was then used as input into one of two learning
networks: a sparse coding network (competitive learning) and backpropagation
network (supervised learning). Both simulations develop specificities for optic
flow which are comparable to those found in a neurophysiological study (Kubo et
al. 2014), and relative frequencies of the various neuronal responses are best
modeled by the sparse coding approach. We conclude that the optic flow neurons
in the zebrafish pretectum do reflect the optic flow statistics. The predicted
vectorial receptive fields show typical optic flow fields but also "Gabor" and
dipole-shaped patterns that likely reflect difference fields needed for
reconstruction by linear superposition.Comment: Published Conference Paper from ICANN 2018, Rhode
Expression and Roles of Teneurins in Zebrafish
The teneurins, also known as Ten-m/Odz, are highly conserved type II transmembrane
glycoproteins widely expressed throughout the nervous system. Functioning as
dimers, these large cell-surface adhesion proteins play a key role in regulating
neurodevelopmental processes such as axon targeting, synaptogenesis and neuronal
wiring. Synaptic specificity is driven by molecular interactions, which can occur either in
a trans-homophilic manner between teneurins or through a trans-heterophilic interaction
across the synaptic cleft between teneurins and other cell-adhesion molecules, such as
latrophilins. The significance of teneurins interactions during development is reflected in
the widespread expression pattern of the four existing paralogs across interconnected
regions of the nervous system, which we demonstrate here via in situ hybridization and
the generation of transgenic BAC reporter lines in zebrafish. Focusing on the visual
system, we will also highlight the recent developments that have been made in furthering
our understanding of teneurin interactions and their functionality, including the instructive
role of teneurin-3 in specifying the functional wiring of distinct amacrine and retinal
ganglion cells in the vertebrate visual system underlying a particular functionality. Based
on the distinct expression pattern of all teneurins in different retinal cells, it is conceivable
that the combination of different teneurins is crucial for the generation of discrete visual
circuits. Finally, mutations in all four human teneurin genes have been linked to several
types of neurodevelopmental disorders. The opportunity therefore arises that findings
about the roles of zebrafish teneurins or their orthologs in other species shed light on
the molecular mechanisms in the etiology of such human disorders
Micro-Canonical Hadron Production in pp collisions
We apply a microcanonical statistical model to investigate hadron production
in pp collisions. The parameters of the model are the energy E and the volume V
of the system, which we determine via fitting the average multiplicity of
charged pions, protons and antiprotons in pp collisions at different collision
energies. We then make predictions of mean multiplicities and mean transverse
momenta of all identified hadrons. Our predictions on nonstrange hadrons are in
good agreement with the data, the mean transverse momenta of strange hadron as
well. However, the mean multiplicities of strange hadrons are overpredicted.
This agrees with canonical and grandcanonical studies, where a strange
suppression factor is needed. We also investigate the influence of
event-by-event fluctuations of the E parameter.Comment: 15 pages 11 figure
Comparison of Strangeness Production between A+A and p+p Reactions from 2 to 160 AGeV
The measured K ratios from heavy-ion reactions are compared with
the K ratios from p+p reactions over the energy range 2-160 AGeV. The
K/ enhancement in heavy-ion reactions is largest at the lower energies,
consistent with strangeness production in secondary scattering becoming
relatively more important than initial collisions near the kaon production
threshold. The enhancement decreases steadily from 4 to 160 AGeV, suggesting
that the same enhancement mechanism of hadronic rescattering and decay of
strings may be applicable over this full energy range. Based on existing data,
the mid-rapidity K ratio is predicted to be for the
forthcoming Pb+Pb reactions at 40 AGeV/c.Comment: 14 pages, 4 figures, submitted to Phys. Rev.
Association between polymorphisms of TAS2R16 and susceptibility to colorectal cancer
Background: Genetics plays an important role in the susceptibility to sporadic colorectal cancer (CRC). In the last 10 years genome-wide association studies (GWAS) have identified over 40 independent low penetrance polymorphic variants. However, these loci only explain around 1‑4% of CRC heritability, highlighting the dire need of identifying novel risk loci. In this study, we focused our attention on the genetic variability of the TAS2R16 gene, encoding for one of the bitter taste receptors that selectively binds to salicin, a natural antipyretic that resembles aspirin. Given the importance of inflammation in CRC, we tested whether polymorphic variants in this gene could affect the risk of developing this neoplasia hypothesizing a role of TAS2R16 in modulating chronic inflammation within the gut. Methods: We performed an association study using 6 tagging SNPs, (rs860170, rs978739, rs1357949, rs1525489, rs6466849, rs10268496) that cover all TAS2R16 genetic variability. The study was carried out on 1902 CRC cases and 1532 control individuals from four European countries. Results: We did not find any statistically significant association between risk of developing CRC and selected SNPs. However, after stratification by histology (colon vs. rectum) we found that rs1525489 was associated with increased risk of rectal cancer with a (Ptrend of = 0.0071). Conclusions: Our data suggest that polymorphisms within TAS2R16 gene do not have a strong influence on colon cancer susceptibility, but a possible role in rectal cancer should be further evaluated in larger cohorts
A simple and effective F0 knockout method for rapid screening of behaviour and other complex phenotypes.
Hundreds of human genes are associated with neurological diseases, but translation into tractable biological mechanisms is lagging. Larval zebrafish are an attractive model to investigate genetic contributions to neurological diseases. However, current CRISPR-Cas9 methods are difficult to apply to large genetic screens studying behavioural phenotypes. To facilitate rapid genetic screening, we developed a simple sequencing-free tool to validate gRNAs and a highly effective CRISPR-Cas9 method capable of converting >90% of injected embryos directly into F0 biallelic knockouts. We demonstrate that F0 knockouts reliably recapitulate complex mutant phenotypes, such as altered molecular rhythms of the circadian clock, escape responses to irritants, and multi-parameter day-night locomotor behaviours. The technique is sufficiently robust to knockout multiple genes in the same animal, for example to create the transparent triple knockout crystal fish for imaging. Our F0 knockout method cuts the experimental time from gene to behavioural phenotype in zebrafish from months to one week
Hadronic observables from SIS to SPS energies - anything strange with strangeness ?
We calculate and (+) rapidity
distributions and compare to experimental data from SIS to SPS energies within
the UrQMD and HSD transport approaches that are both based on string, quark,
diquark () and hadronic degrees of freedom. The
two transport models do not include any explicit phase transition to a
quark-gluon plasma (QGP). It is found that both approaches agree rather well
with each other and with the experimental rapidity distributions for protons,
's, and . Inspite of this apparent agreement both
transport models fail to reproduce the maximum in the excitation function for
the ratio found experimentally between 11 and 40 AGeV. A
comparison to the various experimental data shows that this 'failure' is
dominantly due to an insufficient description of pion rapidity distributions
rather than missing 'strangeness'. The modest differences in the transport
model results -- on the other hand -- can be attributed to different
implementations of string formation and fragmentation, that are not
sufficiently controlled by experimental data for the 'elementary' reactions in
vacuum.Comment: 46 pages, including 15 eps figures, to be published in Phys. Rev.
Baryon Stopping and Charged Particle Distributions in Central Pb+Pb Collisions at 158 GeV per Nucleon
Net proton and negative hadron spectra for central \PbPb collisions at 158
GeV per nucleon at the CERN SPS were measured and compared to spectra from
lighter systems. Net baryon distributions were derived from those of net
protons, utilizing model calculations of isospin contributions as well as data
and model calculations of strange baryon distributions. Stopping (rapidity
shift with respect to the beam) and mean transverse momentum \meanpt of net
baryons increase with system size. The rapidity density of negative hadrons
scales with the number of participant nucleons for nuclear collisions, whereas
their \meanpt is independent of system size. The \meanpt dependence upon
particle mass and system size is consistent with larger transverse flow
velocity at midrapidity for \PbPb compared to \SS central collisions.Comment: This version accepted for publication in PRL. 4 pages, 3 figures.
Typos corrected, some paragraphs expanded in response to referee comments, to
better explain details of analysi
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