| Budget Amount *help |
¥1,900,000 (Direct Cost: ¥1,900,000)
Fiscal Year 1987: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1986: ¥1,400,000 (Direct Cost: ¥1,400,000)
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| Research Abstract |
To analyse the taste receptive mechanisms for amino acids on the taste receptors and processing of taste information in the central nervous system, electrophysiological and anatomical HRP (horseradish peroxidase) tracing methods were performed in fishes, carp and Japanese sea catfish.
Taste responses to amino acids in the carp facial taste system were highly stereospecific; the L-isomers of an amino acid was stimulatory, but the enantiomer was not. The gustatory receptors were responsive to 12 amino acids among 31 compounds. Experiments using analogs and derivatives of amino acids revealed that the <alpha>-amino group and the <alpha>-hydrogen were essential for maximal effectiveness, and that for some amino acids on ionically charged primary carboxyl group was generally unnecessary for a maximal receptor response. Cross-adaptation experiments showed that six receptive mechanisms of the receptor were identified. However, these results are not sufficient to describe detailed receptor site
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s on the taste membrane. It is critical to make another research project like using simple cell system for its resolution. In the sea catfish, only 7 amino acids were stimulatory for the taste system, and were classified 3 groups of receptive mechanisms by cross-adaptation experiments. These results indicated that taste receptive mechanisms of fishes may be highly species specific.
On single unit taste responses from the FL (facial lobe) of the medulla, the response spectrum for amino acids was similar to that from the peripheral nerve. However, the recordings in the niF (nucleus intermedius facialis) were so complexed; i.e. receptive fields of the units were varied, which might be concerned in gustatory short reflex. Taste recordings from the nGS (superior secondary gustatory nucleus) in the pons were only a few so far, showing strange features of the firing pattern differing from those of the lower levels.
Neural tracing studies with HRP revealed the followings: The FL projects bilaterally to the posterior thalamic nucleus and nGS. The FL has reciprocal connections with the nucleus lobobulbaris, medial reticular formation of the rostral medulla, and descending trigeminal nucleus. Also, the FL receives inputs from the raphe nuclei, pretectal nucleus and perilemniscal neurons located adjascent to the ascending gustatory lemniscal tract. The VL (vagal lobe) projects bilaterally to the nGS, lateral reticular formation and ipsilaterally to the n. ambiguus. The VL has reciprocal connection with the ipsilateral lobobulbar nucleus, the medullary reticular formation and perilemniscal neurons as well as the FL does. These anatomical findings are essential interpret the electrophysiological data obtained. Less
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