日時：2011年7月9日(土)　 13: 00 ～ 15: 25

会場：鹿児島大学理学部220講義室


演題と演者
1）Primary Facial Taste Neurons of Japanese Sea Catfish, Plotosus japonicus: Morphology and Organization in the Ganglia. 　　　　　　　　
　　　　　　　　　　　　　　
　Nurdiyana Ahmad Denil (Graduate School of Science and Engineering, Kagoshima University)　

　The present study is initiated to reveal morphology of primary facial taste neurons and their organization in the peripheral ganglia of the Japanese sea catfish, Plotosus japonicus. Labeling techniques of taste neurons with different colors of fluorescent tracers were used in the alive or fixed specimens. Taste neurons are located in both the trigeminofacial complex and recurrent ganglia. The neurons of the complex ganglion send fibers to taste buds located in the anterior mouth cavity and head while those of recurrent ganglion send fibers to buds distributed in the trunk and fins. The ganglion cells are bipolar with round cell bodies with diameter ranging from 17.4±2.4μm (short diameter) to 25.9±1.9μm (long diameter). The central fibers are thinner in diameter (1-2μm) than the peripheral fibers (4-5μm). Application of tracers to the whole recurrent ramus labeled cell bodies only in the recurrent ganglion, showing somatotopic organization between the two ganglia. However, simultaneous labeling of the two rami, pectoral fin and trunk branches with different dyes showed no distinct somatotopic organization in the recurrent ganglion. We also confirmed distinct somatotopic projections of the pectoral and trunk ramus to the trunk-tail lobule in the facial lobe of the medulla.


2）The Neural Basis for Locating Food by the Marine Catfish, Plotosus japonicus　　　　　　　　　　　　　　
John Caprio (Louisiana State University, Baton Rouge, LA, United States)

　The Indo-Pacific catfish, Plotosus japonicus (“Gonzui”), is exceptionally sensitive to both specific amino acids and the minute lowering of the pH in its ambient environment. Both types of fibers, those that transmit amino acid information and those that respond to falling pH, are important in locating food for this species. The two major fiber types that process amino acid information include those that are most responsive to L-proline and betaine (Pro/Bet) and to L-alanine and glycine (Ala/gly), respectively. For the pH sensitive fibers, a transient drop of ~0.05-0.1 pH unit in the seawater (SW) (pH 8.2) bathing the receptive field (e.g. maxillary barbel) dramatically activates the innervating nerve to evoke a phasic burst of action potentials. Increases in pH have no effect; however, bathing the barbel with SW ? pH 7.8 can often inactivate the sensor. Upon replacing the barbel flow with pH 8.2 SW, the sensor quickly recovers its sensitivity. The sensitivity of this system to increasing acidity is unparalleled by any known pH biosensor and rivals that of a commercial pH meter. Thus, the normal functioning of the pH sensing system in Gonzui is likely to be compromised due to the continuing rise in atmospheric CO2 leading to marine acidification. Whether the afferent neural pathway for the pH fibers is trigeminal or facial is currently unknown. The facial nerve contains taste fibers that are unresponsive to declining pH, but evoke spikes of relatively small magnitude in response to amino acids. The fibers responsible for the pH effect are insensitive to amino acids and evoke spikes of large magnitude. The molecular nature of the sensor is also currently unknown; however, a novel type of acid-sensing (ASIC) channel is hypothesized as distilled water dramatically activates the sensor (i.e. ASIC channels are activated by simply reducing extracellular [Ca2+]). The biological significance of this exquisite sensitivity to slight drops in ambient pH is likely an adaptation for detecting polychaete worms, natural prey items. As the polychaete respires, transient drops in SW pH occur at the opening of the worm tube. These pH alterations along with amino acids leaching from the worm enable efficient detection of the prey by the sea catfish.


3）有明海奥部と瀬戸内海周防灘に残されている内湾生態系の原風景 -諫早湾の干潟復元の意義-　

　佐藤正典 (鹿児島大学大学院　理工学研究科　地球環境科学専攻)

　東京湾、伊勢湾、瀬戸内海など、日本の内湾は、古来、豊富な水産資源を生み出してくれる源だった。しかし、その豊かさは、今や瀕死の状態である。沿岸開発は、内湾生態系の要である干潟をつぶし、多くの生物種を絶滅の危機に追い込んでいる。食料の海外依存に慣れた人々はその重大性にまだ気づいていない。内湾生態系における魚介類や渡り鳥の本来の豊富さは、干潟（河口周辺に発達する遠浅の砂泥質の潮間帯における底生生物の高い生産力に支えられてきた。本講演では干潟に生息する主要な底生生物であるゴカイ類（環形動物　多毛綱）に焦点を当て、多くの種が、社会的にほとんど注目されないまま日本各地から姿を消している現状を紹介する。有明海と瀬戸内海周防灘には、日本の内湾の豊かさ（生物多様性と伝統漁業のセット）が、まだかろうじて残っている。日本各地で姿を消した様々な生物種が、まだここに生き残っていることのかけがえのなさを強調したい。

【問合せ先】清原貞夫
鹿児島大学大学院　理工学研究科　生命化学専攻
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