Abstract
Recently, three novel flexor muscles (M1, M2 and M3) in the posterior tentacles of the snail have been described, which are responsible for the patterned movements of the tentacles of the snail, Helix pomatia. In this study, we have demonstrated that the muscles received a complex innervation pattern via the peritentacular and olfactory nerves originating from different clusters of motoneurons of the cerebral ganglia. The innervating axons displayed a number of varicosities and established neuromuscular contacts of different ultrastructural forms. Contractions evoked by nerve stimulation could be mimicked by external acetylcholine (ACh) and glutamate (Glu), suggesting that ACh and Glu are excitatory transmitters at the neuromuscular contacts. Choline acetyltransferase and vesicular glutamate transporter immunolabeled axons innervating flexor muscles were demonstrated by immunohistochemistry and in Western blot experiments. Nerve- and transmitter-evoked contractions were similarly attenuated by cholinergic and glutamatergic antagonists supporting the dual excitatory innervation. Dopamine (DA, 10−5 M) oppositely modulated thin (M1/M2) and thick (M3) muscle responses evoked by stimulation of the olfactory nerve, decreasing the contractions of the M1/M2 and increasing those of M3. In both cases, the modulation site was presynaptic. Serotonin (5-HT) at high concentration (10−5 M) increased the amplitude of both the nerve- and the ACh-evoked contractions in all muscles. The relaxation rate was facilitated suggesting pre- and postsynaptic site of action. Our data provided evidence for a DAergic and 5-HTergic modulation of cholinergic nerves innervating flexor muscles of the tentacles as well as the muscles itself. These effects of DA and 5-HT may contribute to the regulation of sophisticated movements of tentacle muscles lacking inhibitory innervation.
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Acknowledgments
Authors express their gratitude to H. Kimura providing the cChAT antisera and Jean-Pierre Bellier (Molecular Neuroscience Research Center, Shiga University of Medical Science, Seta Tsukinowa-cho, Otsu, Shiga 520-2192 Japan) for the mediation our request to H. Kimura. This work was supported by grants from the Hungarian Scientific Research Fund (OTKA) No. 782248 (KE).
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The authors declare that they have no conflict of interest.
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The authors declare that the experiments comply with the current ethical laws of Hungary.
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Krajcs, N., Hernádi, L., Elekes, K. et al. Excitatory neurotransmitters in the tentacle flexor muscles responsible for space positioning of the snail olfactory organ. Invert Neurosci 14, 59–69 (2014). https://doi.org/10.1007/s10158-013-0164-y
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DOI: https://doi.org/10.1007/s10158-013-0164-y