Journal of Comparative Physiology A

, Volume 159, Issue 2, pp 201–213 | Cite as

Neuronal mechanisms of a hydromedusan shadow reflex

I. Identified reflex components and sequence of events
  • S. A. Arkett
  • A. N. Spencer


  1. 1.

    Intracellular recordings from three neuronal systems (swimming motor neurons — SMNs, burster — ‘B’ system, oscillator — ‘O’ system) and two effector systems (swimming and tentacle myoepithelium) are used to demonstrate the mechanism of the Stereotypie shadow reflex of the hydromedusanPolyorchis penicillatus.

  2. 2.

    The two motor systems, SMNs and ‘B’ system which drive swimming muscle and tentacle muscle contractions respectively, spike spontaneously in lighted conditions. At light OFF, these systems depolarize and give a burst of action potentials (Figs. 2a, 3a, b). This response is lost if the ocelli are removed (Figs. 2b, 3c). Neither system showed any bursting activity in response to decreasing light intensity when chemical synapses are blocked by bathing the preparation in excess Mg++ (Figs. 2c, 3d, 4e).

  3. 3.

    The non-spiking ‘O’ system shows regular membrane potential oscillations in lighted conditions. At light OFF, the ‘O’ system rapidly hyperpolarizes and the oscillations cease (Fig. 4a, b). There is a similar response to shadows after the ocelli are removed (Fig. 4c). Even when chemical synapses are blocked by excess Mg++, the ‘O’ system shows a rapid hyperpolarization at light OFF and depolarization at light ON (Fig. 4e).

  4. 4.

    Typical ‘O’ system recordings can be made from deep within the ocellar cup (Fig. 5).

  5. 5.

    ‘B’ system action potentials show a 1∶1 correlation with large EPSPs which can be recorded from the tentacle myoepithelium and epithelium covering the outer nerve-ring (ONR) (Figs. 6–9). These 4–6 mV EPSPs are delayed by 8–10 ms from the peak of the ‘B’ system action potential and are correlated with tentacle contractions.

  6. 6.

    The behavioral sequence of the shadow reflex consists of an initial rapid swimming muscle contraction, followed by several rapid tentacle contractions and is completed by 2–4 additional swimming muscle contractions (Fig. 11).



Motor Neuron Muscle Contraction System Recording Motor System Neuronal System 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.



swimming motor neurons


outer nerve-ring


inner nerve ring


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  1. Anderson PAV (1979) Ionic basis of action potentials and bursting activity in the hydromedusan jellyfishPolyorchis penicillatus. J Exp Biol 78:299–302Google Scholar
  2. Anderson PAV, Mackie GO (1977) Electrically coupled photosensitive neurons control swimming in a jellyfishPolyorchis. Science 197:186–188Google Scholar
  3. Arkett SA (1985) The shadow response of a hydromedusan (Polyorchis penicillatus): behavioral mechanisms controlling diel and ontogenic vertical migration. Biol Bull 169:297–312Google Scholar
  4. Arkett SA, Spencer AN (1986) Neuronal mechanisms of a hydromedusan shadow reflex. II. Graded response of reflex components, possible mechanisms of photic integration, and functional significance. J Comp Physiol A 159:215–225Google Scholar
  5. Eakin RM, Westfall JA (1962) Fine structure of photoreceptors in the hydromedusaPolyorchis penicillatus. Proc Natl Acad Sci 48:826–833Google Scholar
  6. Hisada M (1956) A study on the photoreceptor of a medusaSpirocodon saltatrix. J Fac Sci Hokkaido Univ Ser VI, Zool 12:529–533Google Scholar
  7. Kikuchi K (1947) On the shadow reflex ofSpirocodon saltatrix and their vertical distribution in the sea. Zool Mag 57:144–146 (in Japanese)Google Scholar
  8. King MG, Spencer AN (1981) The involvement of nerves in the epithelial control of crumpling behavior in a hydrozoan jellyfish. J Exp Biol 94:203–218Google Scholar
  9. Mackie GO (1975) Neurobiology ofStomotoca. II. Pacemaker and conduction pathways. J Neurobiol 6:339–378Google Scholar
  10. Murbach L (1909) Some light reactions of the medusaGonionemus. Biol Bull 17:354–368Google Scholar
  11. Ohtsu K (1983) UV-visible antagonism in extraocular photosensitive neurons of the anthomedusaSpirocodon saltatrix. J Neurobiol 14:145–156Google Scholar
  12. Satterlie RA (1985) Putative extraocellar photoreceptors in the outer nerve-ring ofPolyorchis penicillatus. J Exp Zool 233:133–139Google Scholar
  13. Satterlie RA, Spencer AN (1983) Neuronal control of locomotion in hydrozoan medusae: a comparative study. J Comp Physiol 150:195–207Google Scholar
  14. Singla CL (1974) Ocelli of hydromedusae. Cell Tissue Res 149:413–429Google Scholar
  15. Singla CL (1978) Fine structure of the neuromuscular system ofPolyorchis penicillatus (Hydromedusae, Cnidaria). Cell Tissue Res 193:163–174Google Scholar
  16. Singla CL, Weber C (1982) Fine structure studies of the ocelli ofPolyorchis penicillatus and their connection with the nerve-ring. Zoomorphology 99:117–131Google Scholar
  17. Sokal RR, Rohlf FJ (1969) Biometry. Freeman, San FranciscoGoogle Scholar
  18. Spencer AN (1978) Neurobiology ofPolyorchis. I. Function of effector systems. J Neurobiol 9:143–157Google Scholar
  19. Spencer AN (1979) Neurobiology ofPolyorchis. II. Structure of effector systems. J Neurobiol 10:95–117Google Scholar
  20. Spencer AN (1981) The parameters and properties of a group of electrically coupled neurons in the central nervous system of a hydrozoan jellyfish. J Exp Biol 93:33–50Google Scholar
  21. Spencer AN (1982) The physiology of a coelenterate neuromuscular synapse. J Comp Physiol 148:353–363Google Scholar
  22. Spencer AN, Arkett SA (1984) Radial symmetry and the organization of central neurones in a hydrozoan jellyfish. J Exp Biol 110:69–90Google Scholar
  23. Spencer AN, Satterlie RA (1980) Electrical and dye-coupling in an identified group of neurons in a coelenterate (Polyorchis). J Neurobiol 2:13–19Google Scholar
  24. Tamasige M, Yamaguchi T (1967) Equilibrium orientation controlled by ocelli in an anthomedusan,Polyorchis karafutoensis. Zool Mag 76:35–36Google Scholar
  25. Toh Y, Yoshida M, Tatedo H (1979) Fine structure of the ocellus of the hydromedusa,Spirocodon saltatrix. J Ultrastruct Res 68:341–352Google Scholar
  26. Yamamoto M, Yoshida M (1980) Fine structure of ocelli of an anthomedusaNemopsis dofleini with special reference to synaptic organization. Zoomorphol 96:169–181Google Scholar

Copyright information

© Springer-Verlag 1986

Authors and Affiliations

  • S. A. Arkett
    • 1
  • A. N. Spencer
    • 1
  1. 1.Department of ZoologyUniversity of AlbertaEdmontonCanada

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