| Budget Amount *help |
¥3,500,000 (Direct Cost: ¥3,500,000)
Fiscal Year 2006: ¥2,000,000 (Direct Cost: ¥2,000,000)
Fiscal Year 2005: ¥1,500,000 (Direct Cost: ¥1,500,000)
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| Research Abstract |
Pairs of adult male crickets fight and immediately determine their dominant and subordinate statuses. The dominant male repeatedly produces aggressive (rival) song by rubbing his forewings together. Previous studies have suggested that aggressive song emitted by a dominant male prevents reduction of serotonin (5-hydroxytryptamine ; 5-HT) levels in his own brain. To test this hypothesis, we removed the plectrum (a sound-producing structure in the forewing) from male crickets and measured their brain 5-HT levels immediately after a 10-min aggressive interaction, using high-performance liquid chromatography and immunohistochemistry. Pairs of plectrum-removed males fought and established clear dominant-subordinate relationships, like the case of intact males. The plectrum-removed dominant males frequently rubbed their forewings together, but were unable to produce song. Brain 5-HT levels in the plectrum-removed males were significantly reduced immediately after the aggressive interaction, regardless of their dominance status. The decrease in 5-HT primarily occurred in the central body of the brain. In contrast, in pairs of intact males, aggressive interaction reduced brain 5-HT levels in the subordinate males, but not in the dominant males. Plectrum removal alone did not affect the brain 5-HT levels. These findings demonstrate that aggressive song emitted by a dominant male cricket, but not rotation opening/closing movements of his forewings, prevents reduction of 5-HT levels in his own brain (especially in the central body). It is strongly suggested that in aggressive male crickets, self-generated song affects brain functions such as synthesis and/or degradation of 5-HT in neurons of the central body, resulting in alteration of synaptic transmission.
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