Further Evidence for Shape Coexistence in

Isomers close to doubly magic _{28}^{78}Ni_{50} provide essential information on the shell evolution and shape coexistence near the Z=28 and N=50 double shell closure. We report the excitation energy measurement of the 1/2^{+} isomer in _{30}^{79}Zn_{49} through independent high-precision mass measurements with the JYFLTRAP double Penning trap and with the ISOLTRAP multi-reflection time-of-flight mass spectrometer. We unambiguously place the 1/2^{+} isomer at 942(10) keV, slightly below the 5/2^{+} state at 983(3) keV. With the use of state-of-the-art shell-model diagonalizations, complemented with discrete nonorthogonal shell-model calculations which are used here for the first time to interpret shape coexistence, we find low-lying deformed intruder states, similar to other N=49 isotones. The 1/2^{+} isomer is interpreted as the bandhead of a low-lying deformed structure akin to a predicted low-lying deformed band in ^{80}Zn, and points to shape coexistence in ^{79,80}Zn similar to the one observed in ^{78}Ni. The results make a strong case for confirming the claim of shape coexistence in this key region of the nuclear chart.

4D-imaging of drip-line radioactivity by detecting proton emission from 54mNi pictured with ACTAR TPC.

Proton radioactivity was discovered exactly 50 years ago. First, this nuclear decay mode sets the limit of existence on the nuclear landscape on the neutron-deficient side. Second, it comprises fundamental aspects of both quantum tunnelling as well as the coupling of (quasi)bound quantum states with the continuum in mesoscopic systems such as the atomic nucleus. Theoretical approaches can start either from bound-state nuclear shell-model theory or from resonance scattering. Thus, proton-radioactivity guides merging these types of theoretical approaches, which is of broader relevance for any few-body quantum system. Here, we report experimental measurements of proton-emission branches from an isomeric state in 54mNi, which were visualized in four dimensions in a newly developed detector. We show that these decays, which carry an unusually high angular momentum, ℓ = 5 and ℓ = 7, respectively, can be approximated theoretically with a potential model for the proton barrier penetration and a shell-model calculation for the overlap of the initial and final wave functions.

Two-Proton Radioactivity of

In an experiment with the BigRIPS separator at the RIKEN Nishina Center, we observed two-proton (2p) emission from ^{67}Kr. At the same time, no evidence for 2p emission of ^{59}Ge and ^{63}Se, two other potential candidates for this exotic radioactivity, could be observed. This observation is in line with Q value predictions which pointed to ^{67}Kr as being the best new candidate among the three for two-proton radioactivity. ^{67}Kr is only the fourth 2p ground-state emitter to be observed with a half-life of the order of a few milliseconds. The decay energy was determined to be 1690(17) keV, the 2p emission branching ratio is 37(14)%, and the half-life of ^{67}Kr is 7.4(30) ms.

Precision Mass Measurements of

Masses adjacent to the classical waiting-point nuclide ^{130}Cd have been measured by using the Penning-trap spectrometer ISOLTRAP at ISOLDE/CERN. We find a significant deviation of over 400 keV from earlier values evaluated by using nuclear beta-decay data. The new measurements show the reduction of the N=82 shell gap below the doubly magic ^{132}Sn. The nucleosynthesis associated with the ejected wind from type-II supernovae as well as from compact object binary mergers is studied, by using state-of-the-art hydrodynamic simulations. We find a consistent and direct impact of the newly measured masses on the calculated abundances in the A=128-132 region and a reduction of the uncertainties from the precision mass input data.

Probing the N=32 Shell Closure below the Magic Proton Number Z=20: Mass Measurements of the Exotic Isotopes

The recently confirmed neutron-shell closure at N=32 has been investigated for the first time below the magic proton number Z=20 with mass measurements of the exotic isotopes (52,53)K, the latter being the shortest-lived nuclide investigated at the online mass spectrometer ISOLTRAP. The resulting two-neutron separation energies reveal a 3 MeV shell gap at N=32, slightly lower than for 52Ca, highlighting the doubly magic nature of this nuclide. Skyrme-Hartree-Fock-Bogoliubov and ab initio Gorkov-Green function calculations are challenged by the new measurements but reproduce qualitatively the observed shell effect.

Observation of the ß-delayed γ-proton decay of (56)Zn and its impact on the Gamow-Teller strength evaluation.

We report the observation of a very exotic decay mode at the proton drip line, the ß-delayed γ-proton decay, clearly seen in the ß decay of the T_{z}=-2 nucleus ^{56}Zn. Three γ-proton sequences have been observed after the ß decay. Here this decay mode, already observed in the sd shell, is seen for the first time in the fp shell. Both γ and proton decays have been taken into account in the estimation of the Fermi and Gamow-Teller strengths. Evidence for fragmentation of the Fermi strength due to strong isospin mixing is found.

Direct observation of two protons in the decay of 54Zn.

The two protons emitted in the decay of 54Zn have been individually observed for the first time in a time projection chamber. The total decay energy and the half-life measured in this work agree with the results obtained in a previous experiment. Angular and energy correlations between the two protons are determined and compared to theoretical distributions of a three-body model. Within the shell model framework, the relative decay probabilities show a strong contribution of the p2 configuration for the two-proton emission. After 45Fe, the present result on 54Zn constitutes only the second case of a direct observation of the ground state two-proton decay of a long-lived isotope.

Presynaptic N-methyl-D-aspartate receptors at the parallel fiber-Purkinje cell synapse.

At the cerebellar synapse between the parallel fibers (PFs) and the Purkinje cells in the cerebellum, we have found that application of N-methyl-d-aspartate (NMDA) reversibly depresses the postsynaptic current. We present evidence that this depression involves NMDA receptors located on the presynaptic axons and requires that the NMDA application be combined with action potentials in the PFs. Unexpectedly, unlike other modulations mediated by presynaptic receptors, the NMDA-induced inhibition does not involve a depression of transmitter release. Because it is blocked by both nitric oxide synthase and soluble guanylate cyclase inhibitors, we propose that it involves a trans-synaptic mechanism in which NO released by the PFs decreases the glutamate sensitivity of the Purkinje cell.

[Diagnosis and management of an intraoperative vertebral artery injury]. / Diagnose und Notfallmanagement einer intraoperativen Verletzung der Arteria vertebralis.

A patient with cervical myelopathy caused by marked degenerative alterations of the cervical spinal column at the level of cervical vertebrae 3/4 and relative spinal canal stenosis in the area of cervical vertebrae 5-7 was treated in the department of neurosurgery because of progressive myatrophy and paresis of muscles innervated from cervical nerves 5-7. The operation was performed with vertebrectomy of cervical vertebra 6, implantation of a Harms titanium cage with autograft and a plate and spongy bone screw fixation system. There exists an unusual--and not often publicized--complication during this surgical procedure in the area of the cervical spine, namely penetrating injury of the vertebral artery caused by the treatment with a plate and spongy bone screw fixation system. We describe such an injury of the left vertebral artery. The vertebral artery was intraoperatively embolized using mechanical embolization coils.

Glycine uptake governs glycine site occupancy at NMDA receptors of excitatory synapses.

Glycine uptake governs glycine site occupancy at NMDA receptors of excitatory synapses. J. Neurophysiol. 80: 3336-3340, 1998. At central synapses occupation of glycine binding sites of N-methyl--aspartate receptors (NMDA-Rs) is a necessary prerequisite for the excitatory neurotransmitter glutamate to activate these receptors. There is conflicting evidence as to whether glycine binding sites normally are saturated. If they are not, then alterations in local glycine concentration could modulate excitatory synaptic transmission. By using an in vitro brain stem slice preparation we investigated whether the glycine site is saturated for synaptically activated NMDA-Rs in neonatal rat hypoglossal motoneurons. We found that the NMDA-R-mediated component of spontaneous miniature excitatory postsynaptic currents could be potentiated by exogenously applied glycine as well as by -serine. The effects of glycine were observed only at concentrations (100 microM or more) two orders of magnitude above the apparent dissociation constant of glycine from NMDA receptors. In contrast, -serine, a nontransported NMDA-R glycine site agonist, was effective in the low micromolar range, i.e., at concentrations similar to those found to be effective on isolated cells or on outside-out patches. We conclude that at these synapses the glycine concentration around synaptic NMDA-Rs is set below the concentration required to saturate their glycine site and is likely to be stabilized by a powerful glycine transport mechanism.

Opposite modulation of NMDA receptors by lysophospholipids and arachidonic acid: common features with mechanosensitivity.

1. Two classes of amphiphilic compounds, lysophospholipids and arachidonic acid, have been suggested to produce opposite deformations of the lipid bilayer. We have found that their effects on N-methyl-D-aspartate (NMDA) responses are opposite, and resemble those of mechanical deformations of the plasma membrane. 2. Lysophospholipids inhibited NMDA responses both in nucleated patches taken from cultured neurons and in cells expressing recombinant NMDA receptors. This inhibition was reversible, voltage independent and stronger at non-saturating doses of agonist. It was not linked to the charge of the polar head, and was not mimicked by lysophosphatidic acid or phosphatidylcholine. In outside-out patches, lysophospholipids reduced the open probability of NMDA-activated channels without changing their single-channel conductance. 3. The inhibition produced by lysophospholipids occluded that produced by a mechanical compression induced by changes in osmotic or hydrostatic pressure. 4. The potentiation of NMDA responses by arachidonic acid was observed both in native and recombinant receptors, including those in which the putative 'fatty acid binding domain' had been deleted. This suggests that, like lysophospholipids, arachidonic acid alters the NMDA receptor by insertion into the lipid bilayer. 5. Recombinant receptors in which the cytoplasmic tails had been modified or deleted were still sensitive to mechanical deformation. A linkage to the cytoskeleton is therefore not required for NMDA receptor mechanosensitivity. 6. The fact that the NMDA responses are depressed similarly by compression and lysophospholipids, and potentiated similarly by stretch and arachidonic acid supports the notion that the modulation of NMDA receptor activity by asymmetrical amphiphilic compounds involves pressure changes transmitted through the lipid bilayer. Compounds with a large hydrophilic head mimic the effects of a compression, and compounds with a small hydrophilic head mimic the effects of stretch.

Internal Mg2+ block of recombinant NMDA channels mutated within the selectivity filter and expressed in Xenopus oocytes.

1. The NMDA receptor channel is blocked by both external and internal Mg2+ ions, which are assumed to bind inside the channel on each side of a central barrier. We have analysed the internal Mg2+ block in recombinant NR1-NR2A NMDA receptors expressed in Xenopus oocytes. We have determined the effects of mutations of two asparagines that line the selectivity filter of the channel, one located within the NR1 subunit (N598) and the other within the NR2A subunit (N596). 2. The whole-cell current-voltage relation of wild-type NMDA channels shows inward rectification that reflects the voltage-dependent block produced by the internal Mg2+ of the oocyte. This inward rectification is slightly reduced in the NR2 mutant (N596S) but is abolished in the NR1 mutants (N598Q and N598S). This suggests that the NR1 asparagine plays a larger role than the NR2 asparagine in controlling the internal Mg2+ block. 3. Single-channel current-voltage relations confirm that the internal Mg2+ block is reduced in both the NR1 and NR2 mutants. However, the reduction is small and is similar for the two families of mutants. 4. The discrepancy between whole-cell and single-channel data is partly due to differential effects of internal Mg2+ on the open probabilities of the two conductance states present in NR1 mutant channels. 5. The results suggest that mutations of NR1 and NR2 asparagines lower the central barrier to Mg2+. An additional contribution of the NR2 asparagine to the external Mg2+ binding site (and possibly to the external barrier that controls access to this site) may account for the marked relief of external Mg2+ block produced by the NR2 mutation.

Temperature monitoring of interstitial thermal tissue coagulation using MR phase images.

The temperature-dependent water proton frequency shift was investigated for temperature monitoring of interstitial thermal coagulation. A procedure for on-line temperature calculation was developed, and errors due to temperature-dependent susceptibility were investigated by finite element analysis and reference measurements. The temperature coefficient of magnetic susceptibility and proton chemical shift were determined for brain tissue and other substances. With the proposed procedure, the location of isotherms could be well visualized during laser-induced interstitial coagulation in vitro and in vivo. Systematic errors caused by magnetic susceptibility changes with temperature depend strongly on the characteristics of the heat source and can exceed susceptibility effects caused by physiologic tissue changes. For the laser applicators discussed here, however, a first order compensation for this effect was found to be satisfactory, because it reduces the absolute error to the range of +/- 1 degrees C. The proposed method represents a very promising approach for monitoring of the interstitial thermal coagulation.

High-affinity zinc inhibition of NMDA NR1-NR2A receptors.

Micromolar concentrations of extracellular Zn2+ are known to antagonize native NMDA receptors via a dual mechanism involving both a voltage-independent and a voltage-dependent inhibition. We have tried to evaluate the relative importance of these two effects and their subunit specificity on recombinant NMDA receptors expressed in HEK 293 cells and Xenopus oocytes. The comparison of NR1a-NR2A and NR1a-NR2B receptors shows that the voltage-dependent inhibition is similar in both types of receptors but that the voltage-independent inhibition occurs at much lower Zn2+ concentrations in NR1a-NR2A receptors (IC50 in the nanomolar range) than in NR1a-NR2B receptors (IC50 in the micromolar range). The high affinity of the effect observed with NR1a-NR2A receptors was found to be attributable mostly to the slow dissociation of Zn2+ from its binding site. By analyzing the effects of Zn2+ on varied combinations of NR1 (NR1a or NR1b) and NR2 (NR2A, NR2B, NR2C), we show that both the NR1 and the NR2 subunits contribute to the voltage-independent Zn2+ inhibition. We have observed further that under control conditions, i.e., in zero nominal Zn2+ solutions, the addition of low concentrations of heavy metal chelators markedly potentiates the responses of NR1a-NR2A receptors, but not of NR1a-NR2B receptors. This result suggests that traces of a heavy metal (probably Zn2+) contaminate standard solutions and tonically inhibit NR1a-NR2A receptors. Chelation of a contaminant metal also could account for the rapid NR2A subunit-specific potentiations produced by reducing compounds like DTT or glutathione.

[Laser Doppler data analysis during interstitial laser thermotherapy with magnetic resonance control within the scope of an animal experiment study]. / Laser-Doppler-Datenanalyse während interstitieller Laserthermotherapie unter Magnetresonanz-Kontrolle im Rahmen einer tierexperimentellen Studie.

The aim of the present study was to investigate, using laser Doppler (LD) flowmetry, the phases immediately prior to and following experimental, neurosurgical laser therapy in animals. Two statistical models obtained on the basis of discriminant analysis are described. These models should enable the user to classify the sets of parameters calculated from the LD signals. With both models which contain 3 and 5 parameters, respectively. 100% discrimination of the two phases was attained. The usefulness of the models could be validated by results obtained with other models.

Coupling of permeation and gating in an NMDA-channel pore mutant.

We report a strong coupling between permeation and gating in a mutant NMDA channel (NR1 N598Q-NR2A). The channel opens to two states that differ by their conductance and, surprisingly, by their selectivity for two permeant monovalent cations, Na+ and Cs+. The two open states are linked to the closed state via a cyclic gating reaction that proceeds preferentially in one direction under biionic conditions, indicating that the gating mechanism is not at equilibrium. The direction and the magnitude of this gating asymmetry can be accounted for by assuming that ions bound to a site in the permeation pathway influence the gating of this mutant channel, and that in the closed state, the channel site is accessible to internal cations.

Probing the pore region of recombinant N-methyl-D-aspartate channels using external and internal magnesium block.

Mg2+ ions block N-methyl-D-aspartate (NMDA) channels by entering the pore from either the extracellular or the cytoplasmic side of the membrane in a voltage-dependent manner. We have used these two different block phenomena to probe the structure of the subunits forming NMDA channels. We have made several amino acid substitutions downstream of the Q/R/N site in the TMII region of both NR1 and NR2A subunits. Mutant NR1 subunits were coexpressed with wild-type NR2A subunits and vice versa in Xenopus oocytes. We found that individually mutating the first two amino acid residues downstream to the Q/R/N site affects mostly the block by external Mg2+. Mutations of residues five to seven positions downstream of the Q/R/N site do not influence the external Mg2+ block, but clearly influence the block by internal Mg2+. These data add support to the hypothesis that there are two separate binding sites for external and internal Mg2+ block. They also indicate that the C-terminal end of TMII contributes to the inner vestibule of the pore of NMDA channels and thus provide additional evidence that TMII forms a loop that reemerges toward the cytoplasmic side of the membrane.