Abstract
(1) The effect of tannic acid (TA), a dominant component of plant allelochemicals, was investigated on the locomotion and feeding of the pond snail, Lymnaea stagnalis. The effect of TA on the neuronal background underlying feeding activity was also analysed. (2) TA affected the spontaneous locomotion and of juvenile snails in a concentration-dependent way. Low (10 μM) TA concentration resulted in an increased (sliding or swimming) activity compared to the control; meanwhile, high (100 μM) TA concentration inhibited the locomotion of the animals. (3) Low (10 μM) TA concentration increased the frequency of sucrose-evoked feeding of intact animals, whereas high (100 μM) TA concentration resulted in significantly longer feeding latency and decreased feeding rate. The feeding changes proved to be partially irreversible, since after 48 h maintained in clear water, the animals tested in 100 μM TA previously still showed lower feeding rate in sucrose. (4) Electrophysiological experiments on semi-intact preparations showed that application of 100 μM TA to the lip area inhibited the fictive feeding pattern of central neurons, the cellular response to sucrose. (5) On isolated CNS preparation, 100 μM TA applied in the bathing solution, however, failed to inhibit the activation of the central feeding (CPG) interneurons following application of extracellular dopamine. Our results suggest that TA affects both afferent and efferent peripheral functions in Lymnaea. TA reduces feeding activity by primarily blocking feeding sensory pathways, and its negative effect on locomotion may imply sensory pathways and/or ciliary activity.
Highlights
TanninsTannins, a heterogenous group of high molecular weight (500–3000 Da) water-soluble compounds, members of the even more complex family of polyphenolics, are among the most studied plant secondary metabolites from a chemical–ecological aspect (Salminen and Karonen 2011)
The feeding changes proved to be partially irreversible, since after 48 h maintained in clear water, the animals tested in 100 μM tannic acid (TA) previously still showed lower feeding rate in sucrose
Our results suggest that TA affects both afferent and efferent peripheral functions in Lymnaea
Summary
A heterogenous group of high molecular weight (500–3000 Da) water-soluble compounds, members of the even more complex family of polyphenolics, are among the most studied plant secondary metabolites from a chemical–ecological aspect (Salminen and Karonen 2011). The synthesis of these phenolic compounds is not restricted to plant species found in particular habitats, as it is . Myriophyllum) were shown to contain high amount of polyphenolics (3–150 mg/g dry weight), and release them in the environment (2–4 mg/g dry wt of tannic acid equivalent) in a 10-day period (Gross et al 1996; Choi et al 2002; Li et al 2004)
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