title: Circadian rhythms of ocular melatonin in the wrasse Halichoeres tenuispinnis, a labrid teleost.
abstract: Using in vivo and in vitro methods we studied the regulation of ocular melatonin rhythms in the wrasse Halichoeres tenuispinnis, by either light or the circadian clock. Rhythmic changes in ocular melatonin levels under light-dark (LD) cycles were persistent under constant darkness (DD), and had a circadian periodicity of approximately 24h. However, ocular melatonin levels remained low under constant light conditions. When wrasse were exposed to a single 6-h light pulse at three different circadian phases under DD, phase-dependent phase shifts in the circadian rhythms of ocular melatonin were observed. When eyecups were prepared during mid-light periods or at the onset of darkness, and incubated in vitro in either light or dark periods, both time and light conditions affected melatonin release. These results indicate that the melatonin rhythms in the wrasse eye are driven by an ocular circadian clock that is entrained to LD cycles via local photoreceptors.
authors.affiliation: Department of Applied Biochemistry, Faculty of Agriculture, Utsunomiya University, 350 Mine-machi, Utsunomiya, Tochigi 321-8505, Japan. iigo@cc.utsunomiya-u.ac.jp
authors.forename: Masayuki
authors.initials: M
authors.lastname: Iigo
authors.forename: Emi
authors.initials: E
authors.lastname: Ikeda
authors.forename: Masaru
authors.initials: M
authors.lastname: Sato
authors.forename: Shigekatsu
authors.initials: S
authors.lastname: Kawasaki
authors.forename: Fumitaka
authors.initials: F
authors.lastname: Noguchi
authors.forename: Genjirou
authors.initials: G
authors.lastname: Nishi
mesh_terms: D000818:Animals; D002940:Circadian Rhythm; D003624:Darkness; D005123:Eye / Q000737:chemistry*; D008027:Light; D008550:Melatonin / Q000032:analysis*; D010473:Perciformes / Q000378:metabolism*; D017440:Photoperiod; D010786:Photoreceptor Cells / Q000502:physiology; D013997:Time Factors
chemical_list: D008550:Melatonin