Primitive roles for inhibitory interneurons in developing frog spinal cord

Understanding the neuronal networks in the mammal spinal cord is hampered by the diversity of neurons and their connections. The simpler networks in developing lower vertebrates may offer insights into basic organization. To investigate the function of spinal inhibitory interneurons in Xenopus tadpoles, paired whole-cell recordings were used. We show directly that one class of interneuron, with distinctive anatomy, produces glycinergic, negative feedback inhibition that can limit firing in motoneurons and interneurons of the central pattern generator during swimming. These same neurons also produce inhibitory gating of sensory pathways during swimming. This discovery raises the possibility that some classes of interneuron, with distinct functions later in development, may differentiate from an earlier class in which these functions are shared. Preliminary evidence suggests that these inhibitory interneurons express the transcription factor engrailed, supporting a probable homology with interneurons in developing zebrafish that also express engrailed and have very similar anatomy and functions

Latent heat in the chiral phase transition

The chiral phase transition at finite temperature and density is discussed in the framework of the QCD-like gauge field theory. The thermodynamical potential is investigated using a variational approach. Latent heat generated in the first-order phase transition is calculated. It is found that the latent heat is enhanced near the tricritical point and is more than several hundred MeV per quark.Comment: 6 pages, 3 figure

Spinal V2b neurons reveal a role for ipsilateral inhibition in speed control

The spinal cord contains a diverse array of interneurons that govern motor output. Traditionally, models of spinal circuits have emphasized the role of inhibition in enforcing reciprocal alternation between left and right sides or flexors and extensors. However, recent work has shown that inhibition also increases coincident with excitation during contraction. Here, using larval zebrafish, we investigate the V2b (Gata3+) class of neurons, which contribute to flexor-extensor alternation but are otherwise poorly understood. Using newly generated transgenic lines we define two stable subclasses with distinct neurotransmitter and morphological properties. These V2b subclasses synapse directly onto motor neurons with differential targeting to speed-specific circuits. In vivo, optogenetic manipulation of V2b activity modulates locomotor frequency: suppressing V2b neurons elicits faster locomotion, whereas activating V2b neurons slows locomotion. We conclude that V2b neurons serve as a brake on axial motor circuits. Together, these results indicate a role for ipsilateral inhibition in speed control

Chiral phase transition at high temperature in the QCD-like gauge theory

The chiral phase transition at high temperature is investigated using the effect ive potential in the framework of the QCD-like gauge theory with a variational a pproach. We have a second order phase transition at $T_c=136$MeV. We also investigate numerically the temperature dependence of condensate, $f_\pi$ a nd $a_2(T)$(coefficient of the quadratic term in the effective potential) and es timate the critical exponents of these quantities.Comment: 12 pages,7 figure

Self-consistent nonperturbative anomalous dimensions

A self-consistent treatment of two and three point functions in models with trilinear interactions forces them to have opposite anomalous dimensions. We indicate how the anomalous dimension can be extracted nonperturbatively by solving and suitably truncating the topologies of the full set of Dyson-Schwinger equations. The first step requires a sensible ansatz for the full vertex part which conforms to first order perturbation theory at least. We model this vertex to obtain typical transcendental equations between anomalous dimension and coupling constant $g$ which coincide with know results to order $g^4$.Comment: 15 pages LaTeX, no figures. Requires iopart.cl

Non-Abelian Walls in Supersymmetric Gauge Theories

The Bogomol'nyi-Prasad-Sommerfield (BPS) multi-wall solutions are constructed in supersymmetric U(N_C) gauge theories in five dimensions with N_F(>N_C) hypermultiplets in the fundamental representation. Exact solutions are obtained with full generic moduli for infinite gauge coupling and with partial moduli for finite gauge coupling. The generic wall solutions require nontrivial configurations for either gauge fields or off-diagonal components of adjoint scalars depending on the gauge. Effective theories of moduli fields are constructed as world-volume gauge theories. Nambu-Goldstone and quasi-Nambu-Goldstone scalars are distinguished and worked out. Total moduli space of the BPS non-Abelian walls including all topological sectors is found to be the complex Grassmann manifold SU(N_F) / [SU(N_C) x SU(N_F-N_C) x U(1)] endowed with a deformed metric.Comment: 62 pages, 17 figures, the final version in PR

Scalar-Quark Systems and Chimera Hadrons in SU(3)_c Lattice QCD

Light scalar-quarks \phi (colored scalar particles or idealized diquarks) and their color-singlet hadronic states are studied with quenched SU(3)_c lattice QCD in terms of mass generation in strong interaction without chiral symmetry breaking. We investigate ``scalar-quark mesons'' \phi^\dagger \phi and ``scalar-quark baryons'' \phi\phi\phi which are the bound states of scalar-quarks \phi. We also investigate the bound states of scalar-quarks \phi and quarks \psi, i.e., \phi^\dagger \psi, \psi\psi\phi and \phi\phi\psi, which we name ``chimera hadrons''. All the new-type hadrons including \phi are found to have a large mass even for zero bare scalar-quark mass m_\phi=0 at a^{-1}\simeq 1GeV. We find that the constituent scalar-quark and quark picture is satisfied for all the new-type hadrons. Namely, the mass of the new-type hadron composed of m \phi's and n \psi's, M_{{m}\phi+{n}\psi}, satisfies M_{{m}\phi+{n}\psi}\simeq {m} M_\phi +{n} M_\psi, where M_\phi and M_\psi are the constituent scalar-quark and quark mass, respectively. M_\phi at m_\phi=0 estimated from these new-type hadrons is 1.5-1.6GeV, which is larger than that of light quarks, M_\psi\simeq 400{\rm MeV}. Therefore, in the systems of scalar-quark hadrons and chimera hadrons, scalar-quarks acquire large mass due to large quantum corrections by gluons. Together with other evidences of mass generations of glueballs and charmonia, we conjecture that all colored particles generally acquire a large effective mass due to dressed gluon effects.Comment: 9 pages, 9 figure

Universality, the QCD critical/tricritical point and the quark number susceptibility

The quark number susceptibility near the QCD critical end-point (CEP), the tricritical point (TCP) and the O(4) critical line at finite temperature and quark chemical potential is investigated. Based on the universality argument and numerical model calculations we propose a possibility that the hidden tricritical point strongly affects the critical phenomena around the critical end-point. We made a semi-quantitative study of the quark number susceptibility near CEP/TCP for several quark masses on the basis of the Cornwall-Jackiw-Tomboulis (CJT) potential for QCD in the improved-ladder approximation. The results show that the susceptibility is enhanced in a wide region around CEP inside which the critical exponent gradually changes from that of CEP to that of TCP, indicating a crossover of different universality classes.Comment: 18 pages, 10 figure

Vsx2 in the zebrafish retina: restricted lineages through derepression

<p>Abstract</p> <p>Background</p> <p>The neurons in the vertebrate retina arise from multipotent retinal progenitor cells (RPCs). It is not clear, however, which progenitors are multipotent or why they are multipotent.</p> <p>Results</p> <p>In this study we show that the homeodomain transcription factor Vsx2 is initially expressed throughout the retinal epithelium, but later it is downregulated in all but a minor population of bipolar cells and all Müller glia. The Vsx2-negative daughters of Vsx2-positive RPCs divide and give rise to all other cell types in the retina. Vsx2 is a repressor whose targets include transcription factors such as Vsx1, which is expressed in the progenitors of distinct non-Vsx2 bipolars, and the basic helix-loop-helix transcription factor Ath5, which restricts the fate of progenitors to retinal ganglion cells, horizontal cells, amacrine cells and photoreceptors fates. Foxn4, expressed in the progenitors of amacrine and horizontal cells, is also negatively regulated by Vsx2.</p> <p>Conclusion</p> <p>Our data thus suggest Vsx2-positive RPCs are fully multipotent retinal progenitors and that when Vsx2 is downregulated, Vsx2-negative progenitors escape Vsx2 repression and so are able to express factors that restrict lineage potential.</p

Ion acceleration during internal magnetic reconnection events in TST-2

Characteristics of ion acceleration in the internal magnetic reconnection events (IRE) have been studied by means of a neutral particle energy analyzer (NPA) in Tokyo Spherical Tokamak (TST-2). The major and minor radii are 0.38 m and 0.25m, respectively. The magnetic field strength is 0.3T and the maximum plasma current is up to 140 kA. The electron and ion temperatures are 0.4-0.5 keV and 0.1 keV, respectively and the electron density is ~1x1019 m-3. The NPA can be scanned toroidally from q = 74&deg; (cw) to q = 114&deg; (ccw), where q = 90&deg; corresponds to the perpendicular sightline. The direction of the plasma current is cw. The NPA signals are digitized at every 50 ms. The NPA is calibrated in the energy range of 0.1 keV < E < 8.4 keV. When the IRE occurs, it is observed that the plasma current increases by ~ 20% and the loop voltage drops from 0.6 V to-5 V for ~ 0.1 ms. The enhanced charge exchange flux is observed by more than one order of magnitude at ~ 1 keV for this reconnection phase. The ion temperature increases by 80 eV at IREs. The angle q dependence of increment of Ti shows that DTi (q = 74&deg;) is higher than that for q = 114&deg;. This observation suggests that an ion is accelerated initially in the direction of magnetic field lines. The time evolution of the ion distribution function is simulated with a Fokker-Planck code taking into account the electric field effects.Comment: 12th International Congress on Plasma Physics, 25-29 October 2004, Nice (France