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1 March 2007 Developmental Changes in Heart Photosensitivity of the Isopod Crustacean Ligia exotica
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During juvenile development, the cardiac pacemaker of the isopod crustacean Ligia exotica is transferred from the myocardium to the cardiac ganglion of the neurogenic heart. In adult, light stimulus decreases the beat frequency of the heart. To elucidate developmental changes in the photosensitivity of the juvenile Ligia heart, we examined the effect of a light stimulus on the semi-isolated heart of juveniles at various developmental stages by the recording membrane potential of the myocardium. We also examined the effect of hyperpolarizing current injection into the myocardium, because this causes different effects on the beat frequency between myogenic and neurogenic hearts. In newly hatched juveniles, beat frequency decreased upon current injection but exhibited no response to white light. In contrast, 10 days after hatching, beat frequency did not change upon current injection, but decreased in response to white light. The heart photoresponse of juveniles was reversibly eliminated by application of tetrodotoxin, which changes the heartbeat from neurogenic to myogenic by suppressing cardiac ganglion activity. The proportion of juveniles exhibiting a heart photoresponse increased gradually up to 100% during the period between 3 and 10 days after hatching. The results suggest that the heart photoresponse of L. exotica appears in association with transfer of the cardiac pacemaker from the myocardium to the cardiac ganglion during juvenile development.

Hiroshi Miyamoto, Hiroko Horiguchi, Takahiko Hariyama, and Hiroshi Yamagishi "Developmental Changes in Heart Photosensitivity of the Isopod Crustacean Ligia exotica," Zoological Science 24(3), 273-276, (1 March 2007).
Received: 3 August 2006; Accepted: 1 October 2006; Published: 1 March 2007

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