Abstract
Stimulation of the tail nerve (pedal nerve 9, p9) of the mollusk, Aplysia californica, causes release of serotonin (5-HT), which mediates sensitization of withdrawal responses. There are about 35 serotonin-immunoreactive (5-HT-ir) axons in p9, yet the cell bodies of these axons have not been located. Backfills of p9 were combined with 5-HT immunohistochemistry to locate the cell bodies of 5-HT-ir neurons with axons in p9. About 100 neurons had axons in p9. Only about ten neurons, however, were both backfilled and 5-HT-ir. These double-labeled neurons were all located in the pedal ganglion associated with p9, which had a total of approximately 42 5-HT-ir somata. The discrepancy between the number of 5-HT-ir axons and double-labeled cell bodies is not likely due to neurons having multiple axons in the nerve; intracellular fills suggest that these neurons do not branch before entering p9. Additionally, no evidence was found for peripheral 5-HT-ir cell bodies that project axons centrally through p9. Thus, approximately 70% of the neurons that give rise to the 5-HT-ir axons in tail nerve are unaccounted for, but likely to reside in the pedal ganglion.
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Acknowledgments
We are grateful to Manfred Schmidt and Vivian Vu-Ngo for their help in teaching SJ vibratome sectioning. We thank Claudia Sanabria and Birgit Neuhaus for assistance with confocal microscopy. We thank Joshua Lillvis and Akira Sakurai for their comments on this manuscript and their help throughout this study. This project was funded in part by a grant from NSF.
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Jhala, S., Tamvacakis, A.N. & Katz, P.S. Toward locating the source of serotonergic axons in the tail nerve of Aplysia . Invert Neurosci 11, 91–96 (2011). https://doi.org/10.1007/s10158-011-0121-6
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DOI: https://doi.org/10.1007/s10158-011-0121-6