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Biomedical subjects

C Yamamoto

Publications and source records attributed to C Yamamoto.

At least 253 records · Page 14Linked to original sources
PubMed1983

Membrane potential fluctuations associated with glutamate- and homocysteate-induced depolarizations in hippocampal neurons.

Depolarizations induced by L-glutamate (Glu) or D-homocysteate (DH) in CA3 neurons were accompanied by increases in membrane potential fluctuation in thin hippocampal sections of the guinea pig. The properties of the Glu- and DH-induced noises suggest that they were induced by gating actions of amino acids on the ionic channels, and that an average open-gate time for DH is shorter than that for Glu.

Animals↗
PubMed1983

Selective activation of synapses near the tip of drug-ejecting microelectrode, and effects of antagonists of excitatory amino acids in the hippocampus.

A technique was developed to selectively facilitate transmission through synapses near the tip of a drug-ejecting micropipette by increasing Ca2+ concentration in a small space surrounding the tip. By means of this technique, we found that antagonists of excitatory amino acids, cis-2,3-piperidine dicarboxylic acid, gamma-D-glutamylglycine and glutamic acid diethylester, blocked excitation induced in CA3 neurons by glutamate and by mossy fiber stimulation in thin hippocampal sections of the guinea pig.

Amino Acids↗
PubMed1983

Suppressing action of 2-amino-4-phosphonobutyric acid on mossy fiber-induced excitation in the guinea pig hippocampus.

The action of 2-amino-4-phosphonobutyric acid (APB) on mossy fiber-induced excitation in CA3 neurons was studied in vitro with thin sections of guinea pig hippocampus. D- and DL-APB suppressed field potentials induced in regio CA3 by granular layer stimulation. Threshold concentration of DL-APB to induce the suppression was 2--5 microM. D-APB was about 10-fold less potent than DL-APB. Field potentials induced by fimbrial stimulation were much less affected. DL-APB was without effect on antidromic activation of granule cells. 2-Amino-phosphonovaleric acid had a similar but less potent action. Gamma-D-glutamylglycine and cis-2,3-piperidine dicarboxylic acid were almost ineffective. DL-APB suppressed excitatory postsynaptic potentials recorded intracellularly from CA3 neurons in response to granular layer stimulation but caused no marked changes in resting potentials, action potentials and membrane conductance. Single cell discharges induced by iontophoretic administration of glutamate (Glu) or aspartate (Asp) were unaffected when mossy fiber-induced excitation was suppressed by D- or DL-APB. DL-APB had no suppressing action on Glu- or Asp-induced depolarizing potentials. These results indicate that APB is relatively specific blocker of synaptic transmission between mossy fibers and CA3 neurons, and that this action does not result from blockade of receptors for Glu or Asp.

Aminobutyrates↗
PubMed1982

Black widow spider venom: excitatory action on hippocampal neurons.

Electrical activities of thin hippocampal sections of the guinea pig were studied in vitro during and after administration of black widow spider venom (BSV). In CA3 neurons, BSV induced spontaneous discharges which were suppressed by Co2+ or Mn2+. During BSV administration, trains of potential changes resembling excitatory postsynaptic potentials (EPSPs) were recorded intracellularly. The EPSP-like potentials were blocked by TTX. BSV seems to induce impulses in presynaptic fibers or terminals and thereby facilitates release of neurotransmitters.

Animals↗
PubMed1982

Excitatory actions of homocysteic acid on hippocampal neurons.

The actions of D- and D,L-homocysteate (DH and DLH) on CA3 neurons were studied in thin sections of the guinea pig hippocampus. DH and DLH administered to the stratum radiatum induced large depolarizations in CA3 neurons. The responses to DH and DLH were accompanied by increases in membrane conductance. The amplitudes of the responses increased and decreased, respectively, during tonic hyperpolarizing and depolarizing currents. In neurons injected with Cs+, these responses were reversed in polarity at membrane potentials of -13 to -19 mV. These results indicate that receptors for homocysteate in the hippocampus have different properties from those found in the spinal cord and are quite similar to glutamate receptors.

Animals↗
PubMed1982

Sensitivity of hippocampal neurons to glutamic acid and its analogues.

In thin slices of the guinea-pig hippocampus, depolarizations induced by glutamate (Glu) and its analogues were studied by intracellular recording. It was found that Glu induced stereospecific responses, that L-Glu was more potent than homocysteate and N-methyl-D-aspartate. It is probable that the high-affinity uptake mechanism played a decisive role in termination of L-Glu excitation.

Animals↗
PubMed1982

Quantal analysis of excitatory postsynaptic potentials induced in hippocampal neurons by activation of granule cells.

The values of quantal content (m) and quantal amplitude (q) of excitatory postsynaptic potentials (EPSPs) elicited in CA3 neurons by activation of granule cells were estimated in thin hippocampal sections maintained in vitro. For this purpose, DL-homocysteate was administered to granule cells, and trains of EPSPs that were typical for single granule cell activation were recorded from individual CA3 neurons. The amplitudes of the first and second EPSPs in each train were measured. Fron the mean and variance of the amplitude of the EPSPs, the values of q and m were calculated. The values of m and q for the first EPSPs were estimated at 8.3 and 0.28 mV, respectively, on the average. Potentiation of the second EPSPs was accompanied by a two-fold increase in the values of m without changes in the values of q. Therefore, frequency potentiation in synapses between mossy fibers and CA3 neurons may be explained by an increase in number of released quanta. Amplitudes of EPSPs were found to fluctuate in a manner described by Poisson's law.

Animals↗
PubMed1982

Purification and properties of bovine brain dopamine beta-hydroxylase.

Dopamine beta-hydroxylase (DBH) was purified from bovine brain by a series of steps including extraction with 0.5% Triton X-100, ammonium sulfate fractionation, and serial chromatographies with Concanavalin A (Con A)-Sepharose, Biogel A-1.5 m, DEAE-Sephadex, and phenyl-Sepharose. The overall purification was approximately 4200-fold and the final specific activity was 147 nmol/min/mg protein. Bovine brain DBH was apparently a glycoprotein and interacted with immobilized Con A. Furthermore, the enzyme bound to phenyl-substituted agarose by hydrophobic interaction. An approximate molecular weight was estimated to be 400,000 by gel filtration; the protein eluted earlier than bovine adrenal DBH with a molecular weight estimated to be 290,000. The Km values toward tyramine and ascorbate were 1.53 and 1.42 mM, respectively, the optimal pH was 5.0 in the presence of 20 mM tyramine as substrate. Immunological titration studies indicated that bovine brain and adrenal DBH had common antigenic sites. Our data showed a close similarity between the bovine brain and adrenal enzymes.

Animals↗
PubMed1981

Postsynaptic inhibitory actions of catecholamines and opioid peptides in the bed nucleus of the stria terminalis.

Effects of catecholamines, enkephalins and related compounds on electrical activity of the bed nucleus of stria terminalis (BST) were studied in vitro on thin BST sections prepared from guinea pig brains. Norepinephrine (NE) and epinephrine (E) suppressed field potentials elicited by a single shock to the stria terminalis (ST). The effects of NE and E were mimicked by phenylephrine and blocked by phenoxybenzamine. Isoproterenol and dichloroisoproterenol were without effect. NE and E suppressed the spontaneous firing of BST neurons and discharges elicited by ST stimulation. Dopamine was a less potent depressant. [D-Ala2]-Met-enkephalinamide (EKA) suppressed the field potentials and spike discharges elicited by ST stimulation. Spikes occurring spontaneously or during administration of glutamate were also suppressed by EKA. The action of EKA was blocked by naloxone. Late inhibition induced by stimulation of the lateral division of the ST was blocked by naloxone in about a third of the neurons examined. These results indicate that norepinephrine suppresses the activity of BST neurons by activating postsynaptic alpha-receptors. It is also suggested that opioid peptides mediate inhibitory control of the amygdala over the BST.

Amygdala↗
PubMed1981

Highly sensitive assay for dopamine-beta-hydroxylase activity in human cerebrospinal fluid by high performance liquid chromatography-electrochemical detection: properties of the enzyme.

This paper describes a new, sensitive assay for dopamine-beta-hydroxylase (DBH) activity in human cerebrospinal fluid (CSF), serum and brain tissues by high performance liquid chromatography (HPLC) with electrochemical detection (ED). Dopamine (DA) was used as a substrate and was incubated under optimal conditions. Norepinephrine (NE) formed enzymatically from DA was isolated by a double-column procedure, the first column of Dowex-50-H+ and the second column of aluminum oxide. NE was adsorbed on the second aluminum oxide column and then eluted with 0.5 M-hydrochloric acid and assayed by HPLC-ED. Epinephrine (EN) was added to each incubation mixture as an internal standard, and this assay was therefore highly reproducible. The peak height in HPLC was linear from 500 fmol to 100 pmol of NE and EN. The lower limit of detection for NE formed enzymatically was about 30 pmol, which indicated that the sensitivity of this procedure was comparable to that of radioassay procedures. We applied the method to measurement of the activity of and examination of some of the characteristics of DBH in human CSF. DBH activity in CSF of Parkinsonian patients was lower than that of control patients. The properties of DBH in human CSF were similar to those in serum and adrenal medulla.

Adrenal Medulla↗