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Published September 1, 1980 | public
Journal Article Open

The differential effects of ionizing radiation on the circadian oscillator and other functions in the eye of Aplysia


Ionizing radiation has been used to selectively separate the circadian oscillator function of the eye of Aplysia from some of its other functions--synchronous compound action potential (CAP) generation, the light response, synaptic transmission between photoreceptors and output neurons, and the bursting pacemaker mechanism. Doses of 4-krad (50 kV peak) x-rays have a minimal effect on the circadian rhythm of CAP frequency, measured from the optic nerve, whereas irradiation with a 40-krad dose abolishes the rhythm without affecting any of the four other functions of this eye (1 rad = 0.01 J/kg = 0.01/Gy). We estimate a 50% survival of the oscillator function at doses of about 6 krad. The oscillators of irradiated eyes are not merely desynchronized when the rhythm is abolished, because in vitro light-dark entrainment does not restore free-running rhythmicity. The results, including those from selective irradiation of the anterior or posterior poles of the eye, suggest that there are a number of circadian oscillators in the eye -- most of them in the posterior portion near the optic nerve. An approximate target size has been obtained from target theory, ~10^8 angstrom ^3, which is somewhat larger than the target size for viral infectivity function, as one example. There are reservations about estimating target size in a complex organ such as the eye. However, this approximate target size and the fact that recovery or repair can occur in vivo suggest that the oscillator may involve nucleic acid molecules.

Additional Information

© 1980 by the National Academy of Sciences. Communicated by James F. Bonner, June 9, 1980. We thank Profs. Bonner, Delbrück, and Maniatis for their comments on the manuscript. Mr. Floyd Schlechte produced the average curves (shown in Fig. 4) by computer for which we are grateful. We thank Prof. E.B. Lewis for use of the x-ray facility. The research was supported by grants from the National Institutes of Health (NS 07071, NS 13896) to F.S. and by a short-term grant from the National Aeronautics and Space Administration (NSG 7387). The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.


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