title: Complex circadian regulation of pineal melatonin and wheel-running in Syrian hamsters.
abstract: Circadian regulation of pineal melatonin content was studied in Syrian hamsters (Mesocricetus auratus), especially melatonin peak width and the temporal correlation to wheel-running activity. Melatonin was measured by radioimmunoassay in glands removed at different circadian times with respect to activity onset (= CT 12). Pineal melatonin peak width (h; for mean > or = 125 pg/gland) and activity duration (alpha) were both 4-5 h longer after 12 or 27 weeks than after 5 or 6 days in continuous darkness (DD). Increased peak width was associated with a delay in the morning decline (M) of melatonin to baseline, correlated with a similar delay in wheel-running offset. In contrast, the evening rise (E) in melatonin occurred at approximately the same circadian phase regardless of the length of DD. Fifteen min light pulses produced similar phase-shifts in melatonin and activity. In a phase advance shift, M advanced at once, while E advanced only after several days of adjustment. Independent timing of shifts in the E and M components of the melatonin rhythm suggest that these events are controlled separately by at least two circadian oscillators whose mutual phase relationship determines melatonin peak width. This two-oscillator control of melatonin peak width is integral to the circadian mechanism of hamster photoperiodic time measurement.
authors.affiliation: Hopkins Marine Station, Stanford University, Pacific Grove, CA 93950.
authors.forename: J A
authors.initials: JA
authors.lastname: Elliott
authors.forename: L
authors.initials: L
authors.lastname: Tamarkin
mesh_terms: D000818:Animals; D002940:Circadian Rhythm / Q000187:drug effects / Q000502:physiology*; D006224:Cricetinae; D003624:Darkness; D008297:Male; D008550:Melatonin / Q000378:metabolism*; D008647:Mesocricetus; D009043:Motor Activity / Q000187:drug effects / Q000502:physiology*; D017440:Photoperiod; D010870:Pineal Gland / Q000187:drug effects / Q000378:metabolism*; D011433:Propranolol / Q000494:pharmacology; D011863:Radioimmunoassay; D012044:Regression Analysis
chemical_list: D011433:Propranolol; D008550:Melatonin