抄録
Responses of brain regions lining the third ventricle to extracellular Na+ changes observed in the mouseYoshida, S.1, Mohri, T.2, Sutani, K.31Dept. Life Sci., Kinki Univ., Higashi-Osaka; 2Natl. Inst. Physiol. Sci., Okazaki; 3Natl. Inst. Adv. Ind. Sci. & Tech., Ikeda, JapanIntroduction: Neurons in the brain are particularly susceptible to high Na+ level, and they may possess some mechanism for sensing the extracellular Na+ concentration ([Na+]o). The aim of the present work is to search for such a mechanism. Methods: Coronally-sectioned brain slices (200 μm thickness) were obtained from adult mice (C57BL/6J) at the level of the median eminence (ME). Slices were loaded with SBFI (Na+-sensitive fluorescent dye) and Na+ images were monitored using an image analyzer ARGUS-50. Results: 1) In all regions lining the third ventricle (3V) and ME, [Na+]i was greatly increased by ouabain and decreased by amiloride, 2) when [Na+]o was raised from a control of 140 mM to 160-200 mM, a sustained elevation in [Na+]i was observed in ME but only a transient or little response was observed in the other regions, and 3) the transitional area between ME and the lateral wall of 3V responded inversely. Discussion: The data indicate that the basal level of [Na+]i in the brain regions lining 3V and ME is maintained by Na+ pumps and epithelial channels (ENaCs). The ME, which is devoid of a blood-brain barrier, seems to work as a sensor of [Na+]o. [Jpn J Physiol 54 Suppl:S154 (2004)]
