title: Identification of oscillatory firing neurons associated with locomotion in the earthworm through synapse imaging.
abstract: We used FM imaging to identify neurons that receive sensory feedback from the body wall in a circuit for octopamine (OA)-evoked rhythmic locomotion in the earthworm, Eisenia fetida. We visualized synapses in which postsynaptic neurons receive the sensory feedback, by using FM1-43 dye to label the synapses of both motor and sensory pathways that are associated with locomotion, then clearing the motor pathway synapse labeling, and finally identifying the target synapses by distinguishing physiologically functional synapses through destaining using a high-K(+) solution. A pair of synaptic regions associated with the sensory feedback was found to be located two or three cell body-widths away from the midline, between the anterior parts of the roots of the second lateral nerves (LNs) at the segmental ganglia (SGs). Using conventional intracellular recording and dye loading of the cell bodies surrounding these synaptic regions, we identified a pair of bilateral neurons with cell bodies larger than those of other cells in these regions, and named them "Oscillatory firing neurons Projecting to Peripheral nerves" (OPPs). These had a bipolar shape and projected neurites to the ipsilateral first and third LNs, fired rhythmically, and had a burst timing synchronized with the motor pattern bursts from the ipsilateral first LNs. Current injection into an OPP caused firing in the ipsilateral first LNs, supporting the hypothesis that OPPs functionally project to the peripheral nerves. OPPs also sent neurites to the adjacent anterior and posterior SGs, suggesting connections with the adjacent segments. We conclude that FM imaging can be used to identify neurons involved in specific functions, and that OPPs are the first neurons to be associated with OA-induced locomotion in the earthworm.
authors.affiliation: Center for Biosciences and Informatics, Graduate School of Science and Technology, Keio University, Yokohama, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Shimoi
authors.affiliation: Department of Human and Information Science, Tokai University, Kanagawa, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Mizutani
authors.affiliation: Center for Biosciences and Informatics, Graduate School of Science and Technology, Keio University, Yokohama, Japan.
authors.forename: D
authors.initials: D
authors.lastname: Kojima
authors.affiliation: Department of Mathematical Sciences and Physics, College of Science and Engineering, Kanto Gakuin University, Yokohama, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Kitamura
authors.affiliation: Center for Biosciences and Informatics, Graduate School of Science and Technology, Keio University, Yokohama, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Hotta
authors.affiliation: Department of Biological Sciences, Faculty of Science, Hokkaido University, Sapporo, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Ogawa
authors.affiliation: Center for Biosciences and Informatics, Graduate School of Science and Technology, Keio University, Yokohama, Japan. Electronic address: oka@bio.keio.ac.jp.
authors.forename: K
authors.initials: K
authors.lastname: Oka
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000344:Afferent Pathways / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D000818:Animals; D004525:Efferent Pathways / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D004558:Electric Stimulation; D056228:Feedback, Sensory / Q000502:physiology; D005456:Fluorescent Dyes / Q000494:pharmacology; D008124:Locomotion / Q000187:drug effects / Q000502:physiology*; D008839:Microelectrodes; D016501:Neurites / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D009655:Octopamine / Q000494:pharmacology; D009835:Oligochaeta / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D010507:Periodicity; D011188:Potassium / Q000378:metabolism; D011726:Pyridinium Compounds / Q000494:pharmacology; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology; D013569:Synapses / Q000187:drug effects / Q000502:physiology*
chemical_list: D000316:Adrenergic alpha-Agonists; C073804:FM1 43; D005456:Fluorescent Dyes; D011726:Pyridinium Compounds; D000644:Quaternary Ammonium Compounds; D009655:Octopamine; D011188:Potassium
keywords: FM1-43; activity-dependent staining; octopamine; rhythmic behavior; screening for functional neurons; sensory feedback