Light-induced photoreceptor shedding in teleost retina blocked by dibutyryl cyclic AMP

In retinas of lower vertebrates, at least two retinal phenomena appear to be closely tied to the diurnal light-dark cycle: photoreceptor renewal and retinomotor movements. The authors have previously reported that treatments that elevate retinal cyclic AMP levels induce dark-adaptive retinomotor movements. In the present study, the authors have tested whether cyclic nucleotides might also inhibit the burst of rod outer segment shedding expected to occur shortly following light onset. Green sunfish (Lepomis cyanellus) entrained to a 12hL:12hD schedule were given intraocular injections 1 hr before the time of light onset and killed 1 hr after light onset. Epon sections of retinas were used for RPE phagosome counts and for measurements of photoreceptor and RPE retinomotor positions. It is reported that injection of the cyclic AMP analog dibutyryl cyclic AMP before light onset (1) completely blocked the light-induced burst of photoreceptor shedding seen at dawn in these fish; and (2) inhibited light-adaptive retinomotor movements in the pigment epithelium but not in photoreceptors.