title: Circadian rhythm of iguana electroretinogram: the role of dopamine and melatonin.
abstract: The amplitude of the b-wave of the electroretinogram (ERG) varies with a circadian rhythm in the green iguana; the amplitude is high during the day(or subjective day) and low during the night (or subjective night). Dopamine and melatonin contents in the eye are robustly rhythmic under constant conditions; dopamine levels are high during the subjective day, and melatonin levels are high during the subjective night. Dopamine and melatonin affect the amplitude of the b-wave in an antagonistic and phase-dependent manner: dopamine D2-receptor agonists injected intraocularly during the subjective night produce high-amplitude b-waves characteristic of the subjective day, whereas melatonin injected intraocularly during the subjective day reduces b-wave amplitude. Sectioning the optic nerve abolishes the circadian rhythms of b-wave amplitude and of dopamine content. The results of this study suggest that in iguana, a negative feedback loop involving dopamine and melatonin regulates the circadian rhythm of the ERG b-wave amplitude that is at least in part generated in the brain.
authors.affiliation: Department of Biology and National Science Foundation Centerfor Biological Timing, University of Virginia, Charlottesville, VA 22904-4328, USA. mm7e@virginia.edu
authors.forename: Manuel
authors.initials: M
authors.lastname: Miranda-Anaya
authors.forename: Paul A
authors.initials: PA
authors.lastname: Bartell
authors.forename: Michael
authors.initials: M
authors.lastname: Menaker
mesh_terms: D000818:Animals; D002940:Circadian Rhythm / Q000502:physiology*; D003624:Darkness; D004298:Dopamine / Q000172:deficiency / Q000502:physiology*; D018491:Dopamine Agonists / Q000494:pharmacology; D018492:Dopamine Antagonists / Q000494:pharmacology; D004596:Electroretinography; D007076:Iguanas / Q000502:physiology*; D008550:Melatonin / Q000502:physiology*; D020221:Optic Nerve Injuries; D017440:Photoperiod; D012160:Retina / Q000502:physiology*
chemical_list: D018491:Dopamine Agonists; D018492:Dopamine Antagonists; D008550:Melatonin; D004298:Dopamine