title: Dissociation of circadian and light inhibition of melatonin release through forced desynchronization in the rat.
abstract: Pineal melatonin release exhibits a circadian rhythm with a tight nocturnal pattern. Melatonin synthesis is regulated by the master circadian clock within the hypothalamic suprachiasmatic nucleus (SCN) and is also directly inhibited by light. The SCN is necessary for both circadian regulation and light inhibition of melatonin synthesis and thus it has been difficult to isolate these two regulatory limbs to define the output pathways by which the SCN conveys circadian and light phase information to the pineal. A 22-h light-dark (LD) cycle forced desynchrony protocol leads to the stable dissociation of rhythmic clock gene expression within the ventrolateral SCN (vlSCN) and the dorsomedial SCN (dmSCN). In the present study, we have used this protocol to assess the pattern of melatonin release under forced desynchronization of these SCN subregions. In light of our reported patterns of clock gene expression in the forced desynchronized rat, we propose that the vlSCN oscillator entrains to the 22-h LD cycle whereas the dmSCN shows relative coordination to the light-entrained vlSCN, and that this dual-oscillator configuration accounts for the pattern of melatonin release. We present a simple mathematical model in which the relative coordination of a single oscillator within the dmSCN to a single light-entrained oscillator within the vlSCN faithfully portrays the circadian phase, duration and amplitude of melatonin release under forced desynchronization. Our results underscore the importance of the SCN's subregional organization to both photic input processing and rhythmic output control.
authors.affiliation: Department of Biology and Program of Neurobiology and Behavior, Box 351800, University of Washington, Seattle, WA 98195, USA.
authors.forename: Michael D
authors.initials: MD
authors.lastname: Schwartz
authors.forename: Cheryl
authors.initials: C
authors.lastname: Wotus
authors.forename: Tiecheng
authors.initials: T
authors.lastname: Liu
authors.forename: W Otto
authors.initials: WO
authors.lastname: Friesen
authors.forename: Jimo
authors.initials: J
authors.lastname: Borjigin
authors.forename: Gisele A
authors.initials: GA
authors.lastname: Oda
authors.forename: Horacio O
authors.initials: HO
authors.lastname: de la Iglesia
mesh_terms: D000818:Animals; D001683:Biological Clocks / Q000502:physiology / Q000528:radiation effects; D002940:Circadian Rhythm / Q000502:physiology* / Q000528:radiation effects; D003344:Cortical Synchronization / Q000528:radiation effects*; D003624:Darkness; D008027:Light; D008297:Male; D008550:Melatonin / Q000378:metabolism* / Q000528:radiation effects; D009991:Oscillometry; D010507:Periodicity; D051381:Rats; D017208:Rats, Wistar; D013493:Suprachiasmatic Nucleus / Q000502:physiology / Q000528:radiation effects
chemical_list: D008550:Melatonin