Organization of rat circadian rhythms during daily infusion of melatonin or S20098, a melatonin agonist

Abstract

Daily administration of melatonin or S20098, a melatonin agonist, is known to entrain the free-running circadian rhythms of rats. The effects of the duration of administration on entrainment were studied. The animals demonstrated free-running circadian rhythms (running-wheel activity, body temperature, general activity) in constant darkness. Daily infusions of melatonin or S20098 for 1, 8, or 16 h entrained the circadian rhythms to 24 h. Two daily infusions of 1 h (separated by 8 h) entrained the activity peak within the shorter time interval. The entraining properties of melatonin and S20098 were similar and were affected neither by pinealectomy nor by infusion of 1- or 8-h duration. However, with 16-h infusion, less than half of the animals became entrained. Once entrained, the phase angle between the onset of infusion and the rhythms (onset of activity or acrophase of body temperature) increased with the duration of infusion. Before entrainment, the free-running period increased with the duration of infusion, an effect that was not predictable from the phase response curve.

Morning melatonin ingestion and diurnal variation of short-term maximal performances in soccer players

“…Similarly, previous studies have shown that diurnal MEL ingestion affect essentially cognitive performances more than physical ones (6). For this reason, it should be noted that timing of MEL administration could influence specially the circadian rhythm of physiological parameters (17). In this way, morning MEL administration has been shown to phase delay circadian rhythms, while its administration in the late afternoon advanced it (19).…”

Reciprocal Relationships between General (Propofol) Anesthesia and Circadian Time in Rats

“…The distal end of the catheter was placed on a swivel fixed to a bar hung from the top of the cage. This method has been previously described, except that the catheter was implanted subcutaneously (Pitrosky et al, 1999). The swivel was connected to a syringe carried by a pump (Harvard Apparatus, Holliston, MA, USA) controlled by an electronic timer.…”

“…Nonphotic cues (eg transient behavioral arousal associated with motor activity) studied in nocturnal mammals are capable of inducing phase-advances especially when applied during the middle of the day (ie the resting period in nocturnal species), with little or no resetting effects during the night (for review, see Challet and Pevet, 2003). Propofol anesthesia produces phase advances in the late subjective day, similar to treatment with exogenous melatonin (Pitrosky et al, 1999). As far as we are currently aware, besides general anesthesia the only other synchronizing cues which share the ability to produce circadian phase-advances in the early subjective night are dark pulses applied in constant light (Dwyer and Rosenwasser, 2000;Mendoza et al, 2004).…”

Generation of the Melatonin Endocrine Message in Mammals: A Review of the Complex Regulation of Melatonin Synthesis by Norepinephrine, Peptides, and Other Pineal Transmitters

“…In rats and hamsters with free-running circadian rhythms, pharmacological doses of exogenous MEL are capable of synchronizing the circadian rhythms of locomotor activity and MEL synthesis (see Redman et al, 1983;Armstrong and Chessworth, 1987;Humlova and Illnerova, 1990;Kirsch et al, 1993;Drijfhout et al, 1996b;Grosse and Davis, 1998;Pitrosky et al, 1999;FIG. 2. Schematic representation of the different theoretical models explaining how the photoperiodic MEL endocrine message is decoded.…”