Biomedical subjects

R Yanagihashi

Publications and source records attributed to R Yanagihashi.

3 recordsLinked to original sources

PubMed1992

Studies on long-term potentiation of the population spike component of hippocampal field potential by the tetanic stimulation of the perforant path rats: effects of a dopamine agonist, SKF-38393.

Long-term potentiation of the field potentials recorded in the dentate gyrus of the hippocampus was observed in freely-moving rats by delivering a brief tetanic stimulation to the perforant path, and the effects of the D1 agonist, SKF-38393, on it was investigated. The field potential was divided into two components; excitatory postsynaptic potential (EPSP) and population spike. In Expt. I, synaptic stimulus-response (S-R) relationship, spike S-R relationship, and EPSP-spike (E-S) relationship were plotted. The estimated slope of the regression line in the spike S-R relationship was enhanced after delivery of the tetanic stimulation (10 pulse at 400 Hz), where that in synaptic S-R relationship was not enhanced. The estimated slope of the regression line in the E-S relationship was also enhanced by the tetanic stimulation. In Expt. II, time-dependent change of the field potential after tetanic stimulation was investigated. The population spike was enhanced significantly for about 2 h following tetanic stimulation, while pEPSP did not change significantly. These changes following tetanic stimulation in Expt. I and II were significantly inhibited by previous administration of SKF-38393 (10 mg/kg, i.p.), and the effect of this drug was dose-dependently antagonized by the D1 antagonist, SCH-23390 (0.1, 0.2 and 0.5 mg/kg, i.p.). These results suggest that a brief tetanic stimulation of the perforant path induces long-term potentiation of the population spike without potentiating the synaptic input in the perforant path-dentate synapses, and that potentiation of the population spike is inhibited by the dopaminergic D1 mechanism.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗

PubMed1991

The effects of apomorphine on the hippocampal field potential in freely moving rats: pharmacological evidence of the involvement of D2 receptors.

The effects of apomorphine on the hippocampal field potential of dentate granule cells were investigated in freely-moving male Sprague-Dawley rats. Five sequential field potentials were recorded from the dentate gyrus of the dorsal hippocampus, by stimulating the perforant path in the entorhinal cortex at 30 sec intervals. The slope of the population excitatory postsynaptic potential (EPSP) slope and the amplitude of the population spike of these field potentials were analyzed and averaged with a computer. The effects of apomorphine were observed at intervals of 15 min over 2 hr. Although the slope of the population EPSP showed no significant change after the administration of apomorphine (1.0 mg/kg, i.p.), the amplitude of the population spike was enhanced by about 30%. This enhancement continued for about 90 min. These results suggest that the apomorphine does not change the synaptic input from the perforant path to the granule cells but enhances the excitability of the hippocampal dentate granule cells. This effect of apomorphine on the amplitude of the population spike was decreased by sulpiride (20 mg/kg, i.p.) but was not affected by SCH-23390 (0.1 mg/kg, i.p.). These results lead to the conclusion that the enhancement of the excitability of the dentate granule cells by apomorphine is caused by the activation of the postsynaptic D2 receptors.

Animals↗

PubMed1986

Nigral-induced decrease in striatal blood flow and the influence on this decrease of several drugs in reserpinized and non-reserpinized cats.

The effect of nigral electrical stimulation on regional blood flow in the caudate nucleus and the cerebral cortex, and the influence of several drugs on these effects were examined in reserpinized or non-reserpinized cats. A double-thermistor element was inserted into the left caudate nucleus, and a plate-type thermocouple element was put on the left cerebral cortex. The left substantia nigra was electrically stimulated for 10 sec through a concentric bipolar electrode with a diameter of 0.3 mm (30 Hz, 1 msec, 10-30 V). In non-reserpinized cats, the nigral stimulation caused a decrease in striatal blood flow, increase in cortical blood flow and rise in mean blood pressure. Hexamethonium (3 mg/kg, i.v.) blocked completely the rise in mean blood pressure following nigral stimulation, but did not affect a decrease in striatal blood flow, indicating that a decrease in striatal blood flow following nigral stimulation was not due to the activation of the peripheral sympathetic nervous system. Nigral-induced decrease in striatal blood flow in non-reserpinized cats was blocked by haloperidol (0.1 mg/kg, i.v.), methysergide (1 mg/kg, i.v.) and reserpine (2 mg/kg, i.v.), but not by phentolamine (7 mg/kg, i.v.). In reserpinized cats, nigral stimulation caused an increase in striatal blood flow in contrast to a decrease in non-reserpinized cats. After administration of 5-HTP (50 mg/kg, i.v.) in reserpinized cats, nigral stimulation decreased the striatal blood flow. On the other hand, after administration of L-DOPA (30 mg/kg, i.v.) in reserpinized cats, nigral stimulation increased striatal blood flow.(ABSTRACT TRUNCATED AT 250 WORDS)

5-Hydroxytryptophan↗