High-frequency effects in the FitzHugh-Nagumo neuron model

The effect of a high-frequency signal on the FitzHugh-Nagumo excitable model is analyzed. We show that the firing rate is diminished as the ratio of the high-frequency amplitude to its frequency is increased. Moreover, it is demonstrated that the excitable character of the system, and consequently the firing activity, is suppressed for ratios above a given threshold value. In addition, we show that the vibrational resonance phenomenon turns up for sufficiently large noise strength values.Comment: 4 pages, 4 figures (to appear in Physical Review E

Magnetic switching of spin-scattering centers in Dresselhaus [110] circuits

Spin carriers subject to Dresselhaus [110] (D110) spin-orbit coupling (SOC) gather null spin phases in closed circuits, contrary to usual Rashba and Dresselhaus [001] SOC. We show that D110 spin phases can be activated in square circuits by introducing an in-plane Zeeman field, where localized field inhomogeneities act as effective spin-scattering centers. Our simulations show rich interference patterns in the quantum conductance, which work as maps for a geometric classification of the propagating spin states. We also find that disorder facilitates low-field implementations.Comment: evised version, 6 pages + supplemental materia

Field evidence of dispersal of branchiopods, ostracods and bryozoans by teal (Anas crecca) in the Camargue (southern France).

Abstract Invertebrate propagules may survive internal and external transports by waterbirds, thus facilitating their dispersal between aquatic habitats. However, field data on such transport remain limited, especially for exozoochory. We quantified and compared the rates of internal and external invertebrate transports simultaneously in a wintering population of teal (Anas crecca) in the Camargue (southern France). We inspected lower gut (rectum) contents of birds that had been shot (N = 366) and washed birds that had been live-trapped (N = 68) during the winters 2006-2007 and 2007-2008. At least one propagule was recorded in 2.5% and 10.3% of internal and external samples, respectively. Cladoceran, ostracod, plumatellid bryozoan and anostracan propagules were all recorded in both internal and external samples. Hatching confirmed their viability, except for anostracan eggs. At least three cladoceran species and two ostracod species were recorded, none of which had previously been shown to be dispersed by birds. Amongst external samples, we recorded a significant seasonal trend in 1 year with most propagules recorded before December, keeping with a seasonal decline in the availability of propagules on the water surface. This study provides evidence that teal may be important vectors of invertebrate dispersal both within the Camargue and along migratory flyways

Regulation of Motor Function and Behavior by Atypical Chemokine Receptor 1

The final publication is available at Springer via http://dx.doi.org/10.1007/s10519-014-9665-7Atypical Chemokine Receptor 1 (ACKR1), previously known as the Duffy Antigen Receptor for Chemokines, stands out among chemokine receptors for its high selective expression on Purkinje cells of the cerebellum, consistent with the ability of ACKR1 ligands to activate Purkinje cells in vitro. Nevertheless, evidence for ACKR1 regulation of brain function in vivo has been lacking. Here we demonstrate that Ackr1−/− mice have markedly impaired balance and ataxia when placed on a rotating rod and increased tremor when injected with harmaline, a drug that induces whole-body tremor by activating Purkinje cells. Ackr1−/− mice also exhibited impaired exploratory behavior, increased anxiety-like behavior and frequent episodes of marked hypoactivity under low-stress conditions. The behavioral phenotype of Ackr1−/− mice was the opposite of the phenotype occurring in mice with cerebellar degeneration and the defects persisted when Ackr1 was deficient only on non-hematopoietic cells. We conclude that normal motor function and behavior depend in part on negative regulation of Purkinje cell activity by Ackr1