title: Axon cap morphology of the sea robin (Prionotus carolinus): Mauthner cell is correlated with the presence of "signature" field potentials and a C-type startle response.
abstract: Studies on the Mauthner cell (M-cell) of goldfish, Carassius auratus, have facilitated our understanding of how sensory information is integrated in the hindbrain to initiate C-type fast startle responses (C-starts). The goldfish M-cell initial segment/axon hillock is surrounded by a composite axon cap consisting of a central core and a peripheral zone covered by a glial cell layer. The high resistivity of the axon cap results in "signature" field potentials recorded on activation of the M-cell, allowing unequivocal physiological identification of the M-cell and of its feedback and reciprocal inhibitory networks that are crucial in ensuring that only one M-cell is active and that it fires only once. Phylogenetic mapping of axon cap morphology to muscle activity patterns and behavior predicts that teleost fishes that have a composite axon cap, like that of the goldfish, will perform C-start behavior with primarily unilateral muscle activity. We have chosen to study these predictions in the northern sea robin, Prionotus carolinus, a percomorph fish. Although sea robins have a very different phylogenetic position, body form, and habitat compared with the goldfish, they display the correlation of axon cap morphology to physiology and C-start behavior. Differences in response parameters suggest some evolutionary trade-offs in sea robin C-start behavior compared with that of the goldfish, but the correlations in morphology, physiology, and behavior are common features of both otophysan and nonotophysan teleosts. The M-cell will continue to provide an unprecedented opportunity to study the evolution of a neural circuit in the context of behavior.
authors: Department of Biology, Williams College, Williamstown, Massachusetts 01267, USA. steven.j.zottoli@williams.edu
authors: Steven J
authors: SJ
authors: Zottoli
authors: Tina W
authors: TW
authors: Wong
authors: Mark A
authors: MA
authors: Agostini
authors: Jason R
authors: JR
authors: Meyers
mesh_terms: D000818:Animals; D001369:Axons / Q000502:physiology* / Q000648:ultrastructure*; D001522:Behavior, Animal; D004576:Electromyography; D004594:Electrophysiology / Q000379:methods; D005399:Fishes / Q000033:anatomy & histology* / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology*; D036421:Nerve Fibers, Unmyelinated / Q000502:physiology; D009474:Neurons / Q000166:cytology / Q000502:physiology; D013216:Reflex, Startle / Q000502:physiology*; D012249:Rhombencephalon / Q000166:cytology; D013550:Swimming / Q000502:physiology