| Summary: | 碩士 === 國立東華大學 === 生物技術研究所 === 93 === When Oreochromis mossambicus (tilapia) goes from a hypoosmotic (freshwater; FW) to a hyperosmotic (seawater, SW) environment, the osmolarity and the ionic concentrations of sodium and chloride ion in the Cerebral Spinal Fluid are raised. However, the regulating mechanism in fish brain responding to salinity changes remains unclear. This study attempted to test whether chloride channel, ion transporter and gap junctions in the astrocytes of tilapia brain were activated to alter the physiological response during hyperosmotic stress. Using semi-quantitative RT-PCR, the mRNA expressions of two chloride channels (ClC3 and ClC5), ion transporters (NKA?, NKCC1-?and NKCC1-β) and gap junctions (Cx43 and Cx35) in tilapia brain and astrocyte were investigated. After 25 ppt SW transfer, ClC3 expression in tilapia brain was significantly increased within 1 h (P<0.01) and then decreased in 2 h (P<0.05), the expression was increased during transfer (16 and 24 h, P<0.001). ClC5 expression was increased from 4 h to 16 h (4 h, P<0.01; 8 h, P<0.01 and 16 h, P<0.05). NKCC 1-?expression was increased until 8 h (P<0.05) and NKCC 1-βexpression was not changed during SW transfer. NKA-? expression after SW transfer was increased within 1 h (P<0.05) then decreased at 2 h (P<0.05), the expression was increased after SW transfer (16 h, P<0.001 and 24 h, P<0.01). Cx35 expression in tilapia brain was altered (but not significantly) and Cx43 was significantly changed within 2-8 h. In the hyperosmotic (NaCl and mannitol induced) experiment, the mRNA expression of ClC3 was up regulated in NaCl-induced hyperosmotic treatment within 1, 2, 8 and 16 h (P<0.001) but not in mannitol-induced treatment. Compared to ClC3, ClC5 mRNA expression in both treatments were not elevated until 8 h in mannitol treatment (P<0.001) and 16 h in NaCl treatment. The expression of NKCC 1-?and NKA?3 was increased within 1 h in both treatments. The expressions of Cx35 mRNA at 1 and 2 h after NaCl treatment was significantly increased but not in mannitol treatment. Inductions of Cx43 mRNA at 1 and 2 h after NaCl treatment were very significant (p< 0.001), and were significant (p<0.05) in mannitol treatment. The results suggest that the alternations of ion channel (ClC3 and ClC5), ion transporter (NKA and NKCC) and gap junction (Cx43 and Cx45) in tilapia brain and astrocyte might contribute to the adaptation when fish facing hyperosmotic challenge.
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