title: Serotonin differentially modulates Ca2+ transients and depolarization in a C. elegans nociceptor.
abstract: Monoamines and neuropeptides modulate neuronal excitability and synaptic strengths, shaping circuit activity to optimize behavioral output. In C. elegans, a pair of bipolar polymodal nociceptors, the ASHs, sense 1-octanol to initiate escape responses. In the present study, 1-octanol stimulated large increases in ASH Ca(2+), mediated by L-type voltage-gated Ca(2+) channels (VGCCs) in the cell soma and L-plus P/Q-type VGCCs in the axon, which were further amplified by Ca(2+) released from intracellular stores. Importantly, 1-octanol-dependent aversive responses were not inhibited by reducing ASH L-VGCC activity genetically or pharmacologically. Serotonin, an enhancer of 1-octanol avoidance, potentiated 1-octanol-dependent ASH depolarization measured electrophysiologically, but surprisingly, decreased the ASH somal Ca(2+) transients. These results suggest that ASH somal Ca(2+) transient amplitudes may not always be predictive of neuronal depolarization and synaptic output. Therefore, although increases in steady-state Ca(2+) can reliably indicate when neurons become active, quantitative relationships between Ca(2+) transient amplitudes and neuronal activity may not be as straightforward as previously anticipated.
authors.affiliation: Department of Biological Sciences, The University of Toledo, Toledo, Ohio.
authors.forename: Jeffrey A
authors.identifier: http://orcid.org/0000-0001-6735-5680
authors.initials: JA
authors.lastname: Zahratka
authors.affiliation: Department of Biological Sciences, The University of Toledo, Toledo, Ohio.
authors.forename: Paul D E
authors.initials: PD
authors.lastname: Williams
authors.affiliation: Department of Biological Sciences, The University of Toledo, Toledo, Ohio.
authors.forename: Philip J
authors.initials: PJ
authors.lastname: Summers
authors.affiliation: Department of Biological Sciences, The University of Toledo, Toledo, Ohio.
authors.forename: Richard W
authors.initials: RW
authors.lastname: Komuniecki
authors.affiliation: Department of Biological Sciences, The University of Toledo, Toledo, Ohio Bruce.bamber@utoledo.edu.
authors.forename: Bruce A
authors.initials: BA
authors.lastname: Bamber
mesh_terms: D020003:1-Octanol / Q000494:pharmacology; D000200:Action Potentials; D000818:Animals; D001369:Axons / Q000378:metabolism / Q000502:physiology; D017173:Caenorhabditis elegans / Q000378:metabolism* / Q000502:physiology; D015220:Calcium Channels / Q000378:metabolism; D020013:Calcium Signaling; D009619:Nociceptors / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D012701:Serotonin / Q000494:pharmacology*
chemical_list: D015220:Calcium Channels; D012701:Serotonin; D020003:1-Octanol
keywords: 1-octanol; 5-HT; ASH; C. elegans; Ca2+ dynamics; Ca2+ imaging; electrophysiology; neuromodulation; nociception