title: Sensitization and habituation of the swimming behavior in ascidian larvae to light.
abstract: Ascidian larvae of Ciona intestinalis change their photic behavior during the course of development. Newly hatched larvae show no response to a light stimulus at any intensity. At 4 hr after hatching, larvae were induced to start to swimming upon the cessation of illumination, and to stop swimming upon the onset of illumination. At a weaker light intensity (5.0 x 10(-3) J/m (2).s), the larvae showed similar responses to either a single stimulus or repeated stimuli of onset and cessation of light until 10 hr after hatching. At a stronger light intensity (3.2 x 10(-1) J/m(2).s), when the stimulus was repeated, they showed sensitization and habituation of the swimming response. At 3 hr after hatching the larvae failed to show any response to an initial stimulus at any intensity of light, but after several repeated stimuli (sensitization) they showed a swimming response at light intensities above 4.0 x 10(-2) J/m (2).s. At 5 hr and with intensity above 1.0 x 10 (-2) J/m(2).s, the larvae showed photoresponses to the first stimulus, but after several repetitions the larvae failed to stop swimming upon the onset of light (habituation). A repeated series of stimuli at stronger intensities of light caused greater habituation; this habituation was retained for about 1 min. Since the larval central nervous system in Ciona is comprised of only about 100 neurons, learning behavior in ascidian larvae should provide insights for a minimal mechanism of memory in vertebrates.
authors.affiliation: Department of Life Science, Graduate School of Science, Himeji Institute of Technology, 3-2-1 Kouto, Kamigori, Ako-gun, Hyogo, Japan. mtsuda@sci.himeji-tech.ac.jp
authors.forename: Motoyuki
authors.initials: M
authors.lastname: Tsuda
authors.forename: Isao
authors.initials: I
authors.lastname: Kawakami
authors.forename: Suhei
authors.initials: S
authors.lastname: Shiraishi
mesh_terms: D000222:Adaptation, Physiological / Q000528:radiation effects; D000818:Animals; D002938:Ciona intestinalis / Q000502:physiology* / Q000528:radiation effects*; D007814:Larva / Q000502:physiology* / Q000528:radiation effects*; D008027:Light; D008568:Memory / Q000502:physiology; D010775:Photic Stimulation; D013550:Swimming / Q000502:physiology*; D013997:Time Factors