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K Yunokuchi

Publications and source records attributed to K Yunokuchi.

5 recordsLinked to original sources
PubMed2000

Different distribution of nifedipine- and omega-conotoxin GVIA-sensitive Ca2+ channels in rat hippocampal neurons.

The distribution patterns of nifedipine- and omega-conotoxin GVIA-sensitive Ca2+ channels in rat primary cultured hippocampal neurons were investigated with a confocal laser-scanning microscope. Cells were loaded with the calcium indicator dye Oregon Green/AM, and the responses to high potassium (90 mM) solution with and without the existence of L- and N-type Ca2+ channel blockers were imaged. In general, extracellular application of high [K+] solution induced a [Ca2+]o-dependent increase of [Ca2+]i in both somata and dendritic processes. The increase was reduced by a N-type channel blocker, omega-conotoxin GVIA, and the reduction was greater in dendritic processes than in somata and proximal dendrites. In contrast, the reduction induced by the L-type calcium channel blocker, nifedipine, was observed evenly all over the neurons. The results demonstrated the heterogeneous distribution of nifedipine- and omega-conotoxin GVIA-sensitive calcium channels in cultured hippocampal neurons.

Animals↗
PubMed1991

Tests of EEG localization accuracy using implanted sources in the human brain.

The accuracy with which electrical sources in the brain can be localized by using electroencephalograms measured on the scalp is not well known. In this study, tests of localization accuracy were performed by using implanted dipolar sources in the human brain. These dipoles are created by passing a weak (subthreshold) current through intracerebral electrodes implanted in the brains of epileptic patients for seizure monitoring. The locations of these dipoles are accurately known from roentgenographs. First, 16 electroencephalograms produced by these dipoles were recorded, then inverse solutions were calculated for the apparent sources of these electroencephalograms. Finally, the locations of the apparent sources were compared with the known locations of the implanted dipoles to determine localization error. The average localization error for a total of 28 dipoles in 3 subjects was 1.1 cm. These results indicate that good localization accuracy for focal sources in the brain can be provided by scalp electroencephalograms.

Brain↗
PubMed1991

Developing a more focal magnetic stimulator. Part II: Fabricating coils and measuring induced current distributions.

First, our program for fabricating stimulator coils that are focal is reviewed. These are in the figure-eight shape, where the goal is to make them successively more focal, hence of successively smaller size. Although smaller coils require larger pulse currents, with resulting stress and heat problems, operating prototypes were readily fabricated with circle diameters down to 2.5 cm. However, for smaller diameters, the coil casings were fractured, and new casing techniques are being explored. Second, our program is reviewed for measuring the distribution of current induced in saline tanks by stimulator coils, to determine their focality. A coaxial probe measures the potential difference between two neighboring points in the tank, yielding the local current density. Measurements are presented due to several shapes of tanks and coil configurations. In a spherical tank, results confirm the theory that there can be neither radial current induced anywhere in the sphere nor any current at the sphere center. In tanks approximating a semi-infinite volume and the human limb, arrow-map distributions are shown, due to a commercial "pancake" coil and several figure-eight coils. In the semi-infinite tank, where the distribution can also be computed theoretically, the measured distribution agrees with the computations, thus validating the measurements. In the limb tank, the distribution is compressed and is somewhat more focal than in the semi-infinite tank, depending on the coil orientation.

Animals↗
PubMed1990

MEG versus EEG localization test using implanted sources in the human brain.

It is believed that the magnetoencephalogram (MEG) localizes an electrical source in the brain to within several millimeters and is therefore more accurate than electroencephalogram (EEG) localization, reported as 20 mm. To test this belief, the localization accuracy of the MEG and EEG were directly compared. The signal source was a dipole at a known location in the brain; this was made by passing a weak current pulse simulating a neural signal through depth electrodes already implanted in patients for seizure monitoring. First, MEGs and EEGs from this dipole were measured at 16 places on the head. Then, computations were performed on the MEG and EEG data separately to determine the apparent MEG and EEG source locations. Finally, these were compared with the actual source location to determine the MEG and EEG localization errors. Measurements were made of four dipoles in each of three patients. After MEGs with weak signals were discounted, the MEG average error of localization was found to be 8 mm, which was worse than expected. The average EEG error was 10 mm, which was better than expected. These results suggest that the MEG offers no significant advantage over the EEG in localizing a focal source. However, this does not diminish other uses of the MEG.

Adult↗