• Journal of Photoscience
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• v.9 no.2
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• pp.13-16
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• 2002

A comparison of the functional components underlying photoperiodism and circadian rhythmicity in the same species is an interesting issue in the context of unravelling clock mechanisms. In the present study, covering or surgical removal of the compound eyes was performed to localize photoreceptors for photoperiodism to control reproductive diapause and for entrainment of circadian locomotor rhythms in the blow fly Protophormia terraenovae. Intact flies showed a long-day photoperiodic response. When the compound eyes were covered by silver paint, diapause incidence increased under diapause-averting conditions of a long-day photoperiod and constant light, as if flies were kept under constant darkness. Covering of a medial region of the head capsule or solvent painting of the compound eyes gave no significant effects. When the compound eyes were removed, flies did not distinguish the photoperiod, whereas removal of antennal lobes or ocelli did not affect the photoperiodism. Intact flies showed a freerunning rhythm under constant darkness. The rhythm entrained to light-dark (LD) cycles with light of high and low intensity. When the compound eyes and ocelli were surgically removed, the rhythm entrained to LD cycles with light of high intensity but freeran under LD cycles with light of low intensity. The results suggest the retinal pathways are involved in photoperiodism and that flies use both retinal and extraretinal pathways for rhythm entrainment. Under dim light-LD cycles, the retinal pathways mainly mediate rhythm entrainment. Retinal photoreceptors seem to be used both for photoperiodism and entrainment of the rhythm.

• Journal of Photoscience
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• v.9 no.2
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• pp.5-8
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• 2002

Photoperiodism is an important adaptive phenomenon in various physiological parameters including reproduction to cope with seasonal changes. Involvement of extraretinal photoreceptors in the photoperiodism in non-mammalian vertebrates has been well established. In addition, circadian clock system is known to be involved in the photoperiodic time measurement. The pathway consists of light-input system, time measurement system (circadian clock), gonadotropin releasing hormone (GnRH) production in the hypothalamus, luteinizing hormone (LH) and follicle stimulating hormone (FSH) production in the pituitary, and final gonadal development. Recently, several laboratories reported photopigments newly cloned in the pineal, eyes and deep brain in addition to already known visual pigments in the retina. These are pinopsin, parapinopsin, VA-opsin, melanopsin, etc. All these photopigments belong to the opsin family having retinal as the chromophore. However, the function of these photopigments remains unknown. I reviewed the studies on the location of the photopigments by immunocytochemistry. I also discussed the results on the action spectra for induction of gonadal development in relation with the location of the photoreceptors. Various physiologically active substances distribute in the vertebrate brain. Such substances are GnRH, GnIH, neuropeptide Y, vasoactive intestinal peptide, c-Fos, galanin, neurosteroids, etc. I summarized the immunhistochemical studies on the distribution and the photoperiodic changes of these substances and discussed the route from the deep brain photoreceptor to GnRH cells.