| Co-Investigator(Kenkyū-buntansha) |
ISHIDA Yoshiyuki Yamaguchi university, School of Medicine, Assistant, 医学部, 助手 (20325210)
FUJIOKA Takashi Yamaguchi university, School of Medicine, Assistant, 医学部, 助手 (50304473)
SAKATA Yoshiyuki Yamaguchi university, School of Medicine, Assistant Professor, 医学部, 講師 (10034927)
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| Research Abstract |
In the superior colliculus (SC) of the fetal rat brain, changes in intracellular Cl^- following focal stimulation of the SC were examined by in vivo optical recordings with Cl^- sensitive fluorescent dye. In addition, the effect of hypoxia on changes in intracellular Cl^- induced by focal SC stimulation was also examined in fetal rats which were connected with the dams by the umbilical cord. Pregnant rats were anesthetized with urethane (1.3g/kg, i.p.), the uterus was exposed by cesarean section, and partially cut to exposure of the fetus. The fetal head was attached to a stereotaxic apparatus with dental cement, and the surface of the SC was exposed. Stimulating electrodes were implanted in the rostral part of the SC.Cl^- sensitive dye was applied to the surface of the SC for optical recording of intracellular Cl^-. Fetal asphyxia was brought about by occluding the umbilical cord with a fine clip, while the recovery of the umbilical blood flow was attained by local application of papa
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verine, a relaxant of blood vessels, to the occlusion site.
Focal SC stimulation increased intracellular Cl^-. This response was found to extend caudally to the entire SC from the stimulating site. In a total of 25 fetuses examined, 16 revealed Cl^- influx, 1 Cl^- efflux, and 2 both Cl^- influx and efflux following focal SC stimulation. The remaining 6 showed no change in intracellular Cl^-. Furthermore, a total of 12 fetuses were examined to assess the effect on the SC stimulation induced changes in intracellular Cl^- of hypoxia induced by umbilical cord occlusion. Before umbilical cord occlusion, 8 fetuses showed Cl^- influx following focal SC stimulation. However, 3 hours after the occlusion, the number of fetuses showing Cl^- influx was only one, and 10 fetuses revealed both Cl^- influx and efflux. The changes in intracellular Cl^- were attenuated by application of the GABA antagonist bicuculline in all cases (n=5) before umbilical cord occlusion and in 2 of 8 cases after the occlusion. These results suggest that following hypoxia Cl^- influx induced by focal SC stimulation is converted to Cl^- efflux. In addition, the changes in intracellular Cl^- are thought to occur via GABA receptors. Less
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