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

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Abstract
Ionizing radiation was used to selectively separate the circadian oscillator function of the eye of Aplysia from some of its other functions.sbd.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 4 other functions of this eye (1 rad = 0.01 J/kg = 0.01/Gy). A 50% survival of the oscillator function was estimated for 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 circadian oscillators in the eye.sbd.most in the posterior portion near the optic nerve. An appropriate target size was obtained from target theory, .apprxeq. 108.ANG.3, which is larger than the target size for viral infectivity function, as an example. There are reservations about estimating target size in a complex organ such as the eye. This approximate target size and the fact that recovery or repair can occur in vivo suggest that the oscillatory may involve nucleic acid molecules.