title: [125I]iodomelatonin binding sites in the chicken brain: diurnal variation and effect of melatonin injection or pinealectomy.
abstract: The diurnal variation of [125I]iodomelatonin binding sites in the brain and serum melatonin levels were studied at 4-hour intervals under a 12 h:12 h light:dark cycle in 5-week-old chicks. There was a diurnal rhythm of [125I]iodomelatonin binding capacities in brain membrane preparations with the peak in the light period and the trough in the dark period. However, a diurnal variation with high levels in the dark and low levels in the light was observed in serum melatonin concentrations. The binding capacity of [125I]iodomelatonin was inversely related to the serum melatonin level. Four-week-old chicks were injected with melatonin (1 mg melatonin/kg; i.p.) twice a day (shortly after the light onset and shortly before light offset) for 3 weeks. When chickens were killed at 7 weeks, there was no diurnal rhythm of melatonin in the circulation. In addition, melatonin injection also abolished the diurnal variation of [125I]iodomelatonin binding sites in brain membrane preparations in these animals. This was achieved by decreasing the binding capacity in the light period. Pinealectomy in 2-day-old chickens increased the density of [125I]iodomelatonin binding sites in the brain membrane preparations both at midlight and middark when the chicks were later sacrificed at 6 weeks of age, although the rhythm of binding sites persisted. It is suggested that the [125I]iodomelatonin binding capacity in the chicken brain is regulated by endogenous melatonin and influenced by exogenous melatonin. In addition, the rhythmicity of [125I]iodomelatonin binding sites in the chicken brain is affected by, but not dependent on, pineal melatonin.
authors.affiliation: Department of Neurendocrinology, Clarke Institute of Psychiatry, Toronto, Ontario, Canada.
authors.forename: H
authors.initials: H
authors.lastname: Yuan
authors.forename: S F
authors.initials: SF
authors.lastname: Pang
mesh_terms: D000818:Animals; D001665:Binding Sites; D001921:Brain / Q000378:metabolism* / Q000648:ultrastructure; D001923:Brain Chemistry; D002462:Cell Membrane / Q000737:chemistry / Q000648:ultrastructure; D002645:Chickens; D002940:Circadian Rhythm / Q000502:physiology*; D005260:Female; D007274:Injections, Intraperitoneal; D007457:Iodine Radioisotopes; D008027:Light; D008297:Male; D008550:Melatonin / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000097:blood / Q000378:metabolism / Q000494:pharmacology*; D010870:Pineal Gland / Q000601:surgery*; D011485:Protein Binding; D044094:Receptors, Melatonin; D017981:Receptors, Neurotransmitter / Q000032:analysis / Q000378:metabolism; D013997:Time Factors
chemical_list: D007457:Iodine Radioisotopes; D044094:Receptors, Melatonin; D017981:Receptors, Neurotransmitter; C044556:2-iodomelatonin; D008550:Melatonin