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N Uchimura

Publications and source records attributed to N Uchimura.

48 records · Page 3Linked to original sources
PubMed1989

Membrane properties and synaptic responses of the guinea pig nucleus accumbens neurons in vitro.

1. The membrane properties and synaptic responses of guinea pig nucleus accumbens neurons in vitro were studied with intracellular recording methods. 2. The population of neurons could be divided into groups of low (20-60 M omega, average 46.5 M omega) and high (60-180 M omega, average 96.5 M omega) input resistance. The resting membrane potential in both groups was approximately -70 mV. 3. Other membrane properties were quite similar in both groups. Inward rectification occurred at potentials more negative than -80 mV; this was blocked by Cs+ (2 mM). Membrane potential oscillations were observed at potentials between -65 and -55 mV; these were blocked by tetrodotoxin (TTX, 0.5 microM). Outward rectification occurred at potentials less negative than -45 mV; this was depressed by tetraethylammonium (TEA, 10 mM). 4. Action potentials elicited by small depolarizing current pulses (2-5 ms, 0.3-0.5 nA) were approximately 95 mV in amplitude and 1.0 ms in duration. The afterhyperpolarization following each action potential was less than 30 ms in duration, and no accommodation of action-potential discharge was seen at frequencies up to 40 Hz. The action potentials were reversibly blocked by TTX (0.3 microM). In addition, TTX-insensitive, Ca2+-dependent spikes were evoked by passing larger and more prolonged current pulses (greater than 40 ms, greater than 0.5 nA) across the membrane. 5. Focal electrical stimulation of the slice surface with low intensity (1 ms, less than 10 V) elicited excitatory postsynaptic potentials (EPSPs) in neurons of both high- and low-resistance groups. The reversal potential (+10.2 mV) for the EPSPs was close to the reversal potential (+7.7 mV) of the responses to glutamate applied in the superfusing solution. The N-methyl-D-aspartic acid (NMDA) receptor antagonists, D-alpha-aminoadipic acid (1 mM) and DL-2-amino-5-phosphonovaleric acid (DL-APV, 250 microM), reversibly depressed the EPSP; the glutamate uptake inhibitor, L-aspartic acid-beta-hydroxamate (50 microM), or removal of Mg2+ from the superfusate, augmented the EPSP. 6. When the intensity of the focal stimulus was increased (1 ms, greater than or equal to 10 V), a second larger depolarizing response (duration, 800 ms to 2 s) could be evoked in addition to the smoothly graded EPSP. This was seen only in cells of the high-resistance group (90-130 M omega).(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1989

Inward rectification in rat nucleus accumbens neurons.

1. Intracellular recordings were made from neurons in slices cut from the rat nucleus accumbens septi. Membrane currents were measured with a single-electrode voltage-clamp amplifier in the potential range -50 to -140 mV. 2. In control conditions (2.5 mM potassium), the resting membrane potential of the neurons was -83.4 +/- 1.1 (SE) mV (n = 157). Steady state membrane conductance was voltage dependent, being 34.8 +/- 1.7 nS (n = 25) at -100 mV and 8.0 +/- 0.7 nS (n = 25) at -60 mV. 3. Barium (1 microM) markedly reduced the inward rectification and caused a small inward current (40.6 +/- 8.7 pA, n = 8) at the resting potential. These effects became larger with higher barium concentrations, and, in 100 microM barium, the current-voltage relation was straight. 4. The block of the inward current by barium (at -130 mV) occurred with an exponential time course; the time constant was approximately 1 s at 1 microM barium and less than 90 ms with 100 microM. Strontium had effects similar to those of barium, but 1000-fold higher concentrations were required. Cesium chloride (2 mM) and rubidium chloride (2 mM) also blocked the inward rectification; their action reached steady state within 50 ms. 5. It is concluded that the nucleus accumbens neurons have a potassium conductance with many features of a typical inward rectifier and that this contributes to the potassium conductance at the resting potential.

Animals↗
PubMed1988

Abnormal molecules of mitochondrial aspartate aminotransferase in the liver of vitamin B-6--deficient rats may be produced in the mitochondrial matrix.

The distribution of mitochondrial aspartate aminotransferase (AspATm) in liver cells was studied in rats fed pyridoxine-deficient and control diets. Mitochondrial aminotransferase activity was found mainly in the matrix fraction, with smaller amounts in the outer membranes, intermembrane space and cytosol. The precursor of the enzyme was detected in the liver cytosol of both vitamin B-6--deficient and control rats, and its amount was similar in the two groups. When pyridoxal phosphate was added to the assay system, the ratio of enzyme activity to antigenic activity (E/A) of mitochondrial aspartate aminotransferase in the cytosol of both vitamin B-6--deficient and control rats was about 70% of that in the matrix of control rats. On the other hand, the E/A of the matrix enzyme in deficient rats was 53% of that of controls. From these results we concluded that pyridoxal phosphate is not necessary for translocation of mitochondrial aspartate aminotransferase into mitochondrial matrix and that abnormal molecules of the enzyme may be formed in the matrix of vitamin B-6--deficient rat liver.

Animals↗
PubMed1986

Hyperpolarizing and depolarizing actions of dopamine via D-1 and D-2 receptors on nucleus accumbens neurons.

The effect of dopamine (DA) on the nucleus accumbens neurons in guinea-pig brain slices was studied by intracellular recordings. DA caused a hyperpolarization in 28% of the neurons tested, a depolarization in 11%, and a hyperpolarization followed by a depolarization in 53%. The remaining neurons were unaffected. Analyses of the responses revealed that the DA hyperpolarization was produced by activation of the D-1 receptor and associated with an increase in potassium conductance, whereas the DA depolarization was generated by activation of the D-2 receptor and accompanied by a decrease in potassium conductance. DA uptake inhibitors augmented both the hyperpolarizing and depolarizing responses, while cyclic adenosine monophosphate selectively enhanced the former.

Animals↗
PubMed1980

Hypoglycemia in a child with hepatoblastoma.

A five-year-old boy with hepatoblastoma, who showed a severe hypoglycemia as an initial symptom, was studied. After resection of tumors, hypoglycemia disappeared and did not recur despite recurrence of tumor. A high concentration of insulin-like activity (ILA) was found in preoperative serum and in the tumor extract. Hypoglycemia in this patient seemed to depend mainly on ILA and in part on liver enzyme activities related to carbohydrate metabolism.

Carcinoma, Hepatocellular↗