Tsuda Motoyuki, Kawakami Isao, Shiraishi Suhei
Department of Life Science, Graduate School of Science, Himeji Institute of Technology, 3-2-1 Kouto, Kamigori, Ako-gun, Hyogo, Japan.
Zoolog Sci. 2003 Jan;20(1):13-22. doi: 10.2108/zsj.20.13.
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.
玻璃海鞘的幼体在发育过程中会改变它们的光行为。刚孵化出的幼体对任何强度的光刺激都没有反应。孵化后4小时，幼体在光照停止时开始游动，光照开始时停止游动。在较弱的光强度（5.0×10⁻³ J/m²·s）下，幼体对单次刺激或光的开始和停止的重复刺激表现出相似的反应，直到孵化后10小时。在较强的光强度（3.2×10⁻¹ J/m²·s）下，当刺激重复时，它们表现出游泳反应的敏感化和习惯化。孵化后3小时，幼体对任何光强度的初始刺激都没有反应，但在几次重复刺激（敏感化）后，它们在光强度高于4.0×10⁻² J/m²·s时表现出游泳反应。在5小时且光强度高于1.0×10⁻² J/m²·s时，幼体对第一次刺激表现出光反应，但经过几次重复后，幼体在光照开始时不再停止游动（习惯化）。一系列在较强光强度下的重复刺激导致更大程度的习惯化；这种习惯化持续约1分钟。由于玻璃海鞘的幼体中枢神经系统仅由约100个神经元组成，海鞘幼体的学习行为应为脊椎动物记忆的最小机制提供见解。
