2,138 research outputs found
Releasing dentate nucleus cells from Purkinje cell inhibition generates output from the cerebrocerebellum
The cerebellum generates its vast amount of output to the cerebral cortex through the dentate nucleus (DN) that is essential for precise limb movements in primates. Nuclear cells in DN generate burst activity prior to limb movement, and inactivation of DN results in cerebellar ataxia. The question is how DN cells become active under intensive inhibitory drive from Purkinje cells (PCs). There are two excitatory inputs to DN, mossy fiber and climbing fiber collaterals, but neither of them appears to have sufficient strength for generation of burst activity in DN. Therefore, we can assume two possible mechanisms: post-inhibitory rebound excitation and disinhibition. If rebound excitation works, phasic excitation of PCs and a concomitant inhibition of DN cells should precede the excitation of DN cells. On the other hand, if disinhibition plays a primary role, phasic suppression of PCs and activation of DN cells should be observed at the same timing. To examine these two hypotheses, we compared the activity patterns of PCs in the cerebrocerebellum and DN cells during step-tracking wrist movements in three Japanese monkeys. As a result, we found that the majority of wrist-movement-related PCs were suppressed prior to movement onset and the majority of wrist-movement-related DN cells showed concurrent burst activity without prior suppression. In a minority of PCs and DN cells, movement-related increases and decreases in activity, respectively, developed later. These activity patterns suggest that the initial burst activity in DN cells is generated by reduced inhibition from PCs, i.e., by disinhibition. Our results indicate that suppression of PCs, which has been considered secondary to facilitation, plays the primary role in generating outputs from DN. Our findings provide a new perspective on the mechanisms used by PCs to influence limb motor control and on the plastic changes that underlie motor learning in the cerebrocerebellum
Frustrated minority spins in GeNi2O4
Recently, two consecutive phase transitions were observed, upon cooling, in
an antiferromagnetic spinel GeNiO at K and
K, respectively \cite{matsuno, crawford}. Using unpolarized and polarized
elastic neutron scattering we show that the two transitions are due to the
existence of frustrated minority spins in this compound. Upon cooling, at
the spins on the \kagome planes order ferromagnetically in the
plane and antiferromagnetically between the planes (phase I), leaving the spins
on the triangular planes that separate the \kagome planes frustrated
and disordered. At the lower , the triangular spins also order in the
plane (phase II). We also present a scenario involving exchange
interactions that qualitatively explains the origin of the two purely magnetic
phase transitions
Cu-NMR study on the disordered quantum spin magnet with the Bose-glass ground state
Cu-NMR study has been performed on the disordered spin-gap system
Tl1-xKxCuCl3 In the high-field H > HC=\Delta/\mu_B, where \Delta is the
spin-gap, the hyperfine field becomes extremely inhomogeneous at low
temperatures due to the field-induced magnetic order, indicating that the
ordered spin state must be different from the pure TlCuCl3. In the low field H
< HC, a saturating behavior in the longitudinal nuclear spin relaxation rate
1/T1 was observed at low temperatures, indicating existence of the magnetic
ground state proposed to be Bose-glass phase by Fisher.Comment: RHMF200
First Measurement of Collectivity of Coexisting Shapes based on Type II Shell Evolution: The Case of Zr
Background: Type II shell evolution has recently been identified as a
microscopic cause for nuclear shape coexistence. Purpose: Establish a low-lying
rotational band in 96-Zr. Methods: High-resolution inelastic electron
scattering and a relative analysis of transition strengths are used. Results:
The B(E2; 0_1^+ -> 2_2^+) value is measured and electromagnetic decay strengths
of the secdond 2^+ state are deduced. Conclusions: Shape coexistence is
established for 96-Zr. Type II shell evolution provides a systematic and
quantitative mechanism to understand deformation at low excitation energies.Comment: 5 pages, 4 figure
Universal trapping scaling on the unstable manifold for a collisionless electrostatic mode
An amplitude equation for an unstable mode in a collisionless plasma is
derived from the dynamics on the two-dimensional unstable manifold of the
equilibrium. The mode amplitude decouples from the phase due to the
spatial homogeneity of the equilibrium, and the resulting one-dimensional
dynamics is analyzed using an expansion in . As the linear growth rate
vanishes, the expansion coefficients diverge; a rescaling
of the mode amplitude absorbs these
singularities and reveals that the mode electric field exhibits trapping
scaling as . The dynamics for
depends only on the phase where is the derivative of the dielectric as
.Comment: 11 pages (Latex/RevTex), 2 figures available in hard copy from the
Author ([email protected]); paper accepted by Physical Review
Letter
Cell Death Dis.
The Gram-negative bacterium Shigella flexneri invades the colonic epithelium and causes bacillary dysentery. S. flexneri requires the virulence factor invasion plasmid antigen B (IpaB) to invade host cells, escape from the phagosome and induce macrophage cell death. The mechanism by which IpaB functions remains unclear. Here, we show that purified IpaB spontaneously oligomerizes and inserts into the plasma membrane of target cells forming cation selective ion channels. After internalization, IpaB channels permit potassium influx within endolysosomal compartments inducing vacuolar destabilization. Endolysosomal leakage is followed by an ICE protease-activating factor-dependent activation of Caspase-1 in macrophages and cell death. Our results provide a mechanism for how the effector protein IpaB with its ion channel activity causes phagosomal destabilization and induces macrophage death. These data may explain how S. flexneri uses secreted IpaB to escape phagosome and kill the host cells during infection and, may be extended to homologs from other medically important enteropathogenic bacteria
Characteristics of Japanese wrestlers with respect to function and structure of limbs
It is well known that hypertrophy and strength gain of the human skeletal muscle are induced by muscle training. It has also been shown that the training effect on size and strength of the skeletal muscle are altered the different athletic training protocols (1, 4). From these findings, it seems possible that wrestlers possess the hypertrophied muscle and stronger muscle strength by specific training.
In the present study, we assess the functional and structural characteristics of the skeletal muscle in Japanese wrestlers
Wave effect in gravitational lensing by a cosmic string
The wave effect in the gravitational lensing phenomenon by a straight cosmic
string is investigated. The interference pattern is expressed in terms of a
simple formula. We demonstrate that modulations of the interfered wave
amplitude can be a unique signature of the wave effect. We briefly mention a
possible chance of detecting the wave effect in future gravitational wave
observatories.Comment: 4 pages, 1 figur
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