Toshio Arakawa

Excitatory and inhibitory action of GABA on synaptic transmission in slices of guinea pig superior colliculus.

The laminar distribution of gamma-aminobutyric acid (GABA) in the superior colliculus of the guinea pig was analyzed. The superficial gray layer, especially the upper half, was found to contain the highest amount, 37.4 +/- 1.1 mmol/kg dry. To investigate the role of GABA in the superficial gray layer, the effect of GABA on neurotransmission in the superficial gray layer was studied in superior colliculus slices in a perfusion system. Bath-applied GABA, 100 microM-1 mM, enhanced the amplitude of the postsynaptic field potential (PSP) in the superficial gray layer dose dependently and at concentrations above 1 mM it depressed the PSP dose dependently. A similar response pattern was obtained with muscimol (0.1-10 microM, enhancement; greater than 10 microM, depression). However, (-)-baclofen only inhibited the PSP dose dependently (0.1-1 microM). The excitatory effect of GABA was enhanced at concentrations of nipecotic acid less than 0.5 mM. Bicuculline 1 microM shifted the dose-response curve of GABA to the right and the excitatory effect was also enhanced. These results indicate that GABA has a dual action on neurotransmission in the superficial gray layer: an excitatory effect, possibly mediated by GABAA receptors and an inhibitory effect mediated by both GABAA and GABAB receptors.

Effect of ketone body (d-3-hydroxybutyrate) on neural activity and energy metabolism in hippocampal slices of the adult guinea pig

The role of ketone body on neural activity and energy metabolism in the brain was investigated. Guinea pig hippocampal slices were prepared, and postsynaptic field potentials (PSPs) were recorded in the granular cell layer of the dentate gyrus. ATP and phosphocreatine (CrP) in the tissue slice were measured after 60 and 120 min incubation in standard medium (1) with 10 mM glucose, (2) with 10 mM glucose plus 20 mM D,L-3-hydroxybutyrate (3-OHBA), (3) without glucose, (4) with 20 mM 3-OHBA instead of 10 mM glucose. In (3), both ATP and CrP in the slice decreased to 40-45% of the original level after 120 min. On the other hand, the ATP level was well maintained even 120 min after incubation in (1), (2) and (4), whereas the CrP level decreased to 62% in (4). Further, slices were incubated in (3) and (4) for 30, 60, and 120 min, and the presence of PSP was tested. In (3), the number of slices from which PSPs could be recorded decreased, and after 120 min PSPs were hardly observed. In (4), that number decreased gradually, and only 45% of the slices showed PSPs after 120 min. These results indicate that 3-OHBA can be a substrate to produce high-energy phosphate but cannot maintain the neural activity as glucose does.

Effects of accumulation of phosphocreatine on utilization and restoration of high-energy phosphates during anoxia and recovery in thin hippocampal slices from the guinea pig

Effects of accumulation of phosphocreatine (P-creatine) on utilization and restoration of high-energy phosphates during anoxia and recovery were studied using thin hippocampal slices from the guinea pig. Incubation of slices with creatine (5 to 30 mM) increased the content of tissue P-creatine, in a linear fashion, and these increases depended on the concentration of creatine and the incubation period to as long as 3 h. Concentration of ATP in the slices was not altered. A high concentration of tissue P-creatine (40 to 100 mmol/kg protein) accumulated by incubation with creatine reduced the rate of ATP exhaustion during anoxia whereas P-creatine itself was rapidly decreased. During reoxygenation after anoxia, concentrations of ATP and P-creatine rapidly recovered in slices preincubated with creatine. Concentrations of P-creatine previously exhausted during anoxia increased to 100 mmol/kg protein after 25 min of reoxygenation whereas the concentration was 35 mmol/kg in the control slice. Elevation of the concentration of P-creatine may therefore prolong the survival time of brain tissue during anoxia and facilitate recovery during reoxygenation.

Cu-Ag alloy Bitter type magnet for repeating pulsed field

Cu-Ag alloy is used for the repeating pulsed field magnets. It is found that fields up to 22 T or more will be available for this purpose instead of 16 T which is obtained with normal copper magnet used at present. This result is a big advantage for neutron diffraction experiments.

High energy spin excitation of a high-Tc superconductor La1.85Sr0.15CuO4

High energy inelastic neutron scattering has been performed on a single crystal of La1.85Sr0.15CuO4 (Tc=37K) by using pulse neutron technique. The whole spectrum of the quantum magnetic excitation in the wide range of the energy-momentum space has been clearly observed for the first time. The shape of the spectrum is very broad and continuous and the excitation persists up to 280meV above the well known incommensurate magnetic excitation around (π, π, 0).

The effect of GABA on neurotransmission in frog tectal slices.

The regional distribution of gamma-aminobutyric acid (GABA) was determined in the central nervous system of the frog. The highest amount of GABA was found in the tectum (35.7 +/- 2.3 mmol/kg protein). A thin tectal slice (400-600 microns thick) preparation was developed in which the postsynaptic potential (PSP) could be elicited. The addition of GABA to the perfusion medium depressed the PSP in a dose-dependent manner in the concentration range 1-12.5 mM at 28 degrees C. Nipecotic acid, a GABA uptake inhibitor, at a concentration of 0.5 mM shifted the dose-response curve for GABA to the left. These results from the frog, a cold-blooded animal, were in good agreement with those for hippocampal slices from the guinea-pig.

Structural instability of high-Tc superconductor La1.85Sr0.15CuO4

Investigation on a high-Tc superconductor, La1.85Sr0.15CuO4, was performed in the wide range of Q-E space by means of neutron scattering and synchrotron radiation. The structure as well as the phonon dynamics showed a clear evolution at Tc. We found a spontaneous strain and phonon softening, which proves a strong coupling between lattice and superconductivity.

Anomalous structure and phonon dynamics in La1.85Sr0.15CuO4

We performed X-ray diffraction and neutron scattering experiments on high quality single crystals of La1.85Sr0.15CuO4. We found a forbidden (1,0,0) peak, which develops below the HTT-LTO structural transition temperature, and an anomalous behavior of acoustic phonon at (2,2,0). These results indicate that the structural anomaly has a strong relation with an superconductivity.

Structure and phonon anomaly in La1.85Sr0.15CuO4

We performed X-ray diffraction and neutron scattering on a single crystal La1.85Sr0.15CuO4. We found that the lattice anomaly is caused by the optical tilt phonon associated with the expansion of the c-lattice constant below Tc. We also found that the (100) peak starts to develop below the HTT-LTO structural phase transition temperature. These results suggest that there is a strong relation between the superconductivity and the structural instability.

Discrepant effects of vasoconstrictors on the growth of early passaged cultured rat mesangial cells

Summary: Mesangial cell growth stimulation by endothelin (ET) and arginine vasopressin (AVP) has been reported, but only in studies using late (3 times) pasaged cells. In the present study, we examined the effects of ET, AVP and platelet activating factor (PAF) on the proliferation of early (<3 times) passaged cultured rat mesangial cells which maintained their original characteristics. Cell growth was estimated by [3H]‐thymidine incorporation into DNA and by counting cell nuclei. After 48 h preincubation in minimal essential medium containing 0.5% fetal calf serum, ET‐1 (1‐100 nmol/L), AVP (100 pmol/L‐1 μmol/L) or PAF (1–100 nmol/L) was added to the incubation medium. In contrast to studies using late passaged cells, ET‐1 attenuated and AVP did not increase thymidine uptake (ET‐1: 18.4% inhibition at 10 nmol/L) or cell counts in early passaged cells, while the growth stimulatory effects of these agents were reproduced in late passaged cells. Platelet activating factor showed definite stimulation of cell growth in both early and late passaged cells in a dose‐dependent manner. These data strongly suggest that ET‐1 attenuates, and AVP does not stimulate, the cell growth of original mesangial cells. the PAF‐induced cell growth seems to be the constant feature of mesangial cells in vivo.