98 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
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
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
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
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.
Comparison of Atmospheric Neutrino Flux Calculations at Low Energies
We compare several different calculations of the atmospheric neutrino flux in
the energy range relevant for contained neutrino interactions, and we identify
the major sources of difference among the calculations. We find nothing that
would affect the predicted ratio of , which is nearly the same
in all calculations. Significant differences in normalization arise primarily
from different treatment of pion production by interactions of protons in the
atmosphere. Different assumptions about the primary spectrum and treatment of
the geomagnetic field are also of some importance.Comment: 15 pages, RevTeX , 5 postscript figures, submitted to Phys. Rev.
Understanding the retinal basis of vision across species
The vertebrate retina first evolved some 500 million years ago in ancestral marine chordates. Since then, the eyes of different species have been tuned to best support their unique visuoecological lifestyles. Visual specializations in eye designs, large-scale inhomogeneities across the retinal surface and local circuit motifs mean that all species' retinas are unique. Computational theories, such as the efficient coding hypothesis, have come a long way towards an explanation of the basic features of retinal organization and function; however, they cannot explain the full extent of retinal diversity within and across species. To build a truly general understanding of vertebrate vision and the retina's computational purpose, it is therefore important to more quantitatively relate different species' retinal functions to their specific natural environments and behavioural requirements. Ultimately, the goal of such efforts should be to build up to a more general theory of vision
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