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.

Bimodal circadian secretion of melatonin from the pineal gland in a living CBA mouse

“…Together with melatonin secretion, we could simultaneously monitor circadian locomotor activity. The circadian rhythms of pineal melatonin concentrations and locomotor activity were closely coupled under both normal LD and continuous dark conditions over long periods of time, supporting the hypothesis that the two overt rhythms are regulated by a common or very similar timing mechanism under physiological conditions (32). In this study, we found that melatonin levels displayed a clear phase-advance from the next cycle, although the rhythm of the locomotor activity takes a few more days to exhibit an explicit phase advance.…”

Effects of the TAU Mutation on Circadian Organization

“…Depending on the phase of the light pulse, a may be transiently decreased (Fig. 7B-I Such independent shifts of evening and morning oscillators in response to light pulses were observed during experiments by Elliot and Tamarkin (1994) and Shimomura (1998) (Fig. 7C).…”

“…This two-oscillator model was explored theoretically by Daan and Berde (1978) Evening oscillator (E): Kawato and Suzuki (1980), Kawato (1985), and Mori et al (1994). The two-oscillator model explains the results of many experiments on hamsters (Pittendrigh and Daan 1976b;Elliot and Tamarkin, 1994;Gorman et al, 1998), and therefore we employ it here. The coupling of oscillators adds greatly to the difficulty of understanding the interdependence of x and PRC shapes because it is necessary to consider the intrinsic properties of the constituent oscillators, the nature of the coupling, and the emergent properties of the coupled system.…”

Seasonal variations in daily rhythms of activity in athletic horses

“…In temperate zones, the photoperiod markedly changes across seasons and affects mammalian physiology and behaviour (Sumova et al, 2004). For instance, in nocturnal rodents, the duration of locomotor activity reflects the photoperiod as being shorter on long summer than on -E-mail: giuseppe.piccione@unime.it short winter days (Puchalski and Lynch, 1991;Elliott and Tamarkin, 1994). The rhythmic production of the pineal hormone melatonin, which is a part of the timekeeping system, is also highly photoperiod-dependent, both in nocturnal and in diurnal animals; the high nocturnal melatonin production is shorter on long summer than on short winter days (Illnerová , 1991).…”