Search

Although light is considered the primary entrainer of circadian rhythms in humans, nonphotic stimuli, including exercise and melatonin also phase shift the biological clock. Furthermore, in birds and nonhuman mammals, auditory stimuli are effective zeitgebers. This study investigated whether a nonphotic auditory stimulus phase shifts human circadian rhythms. Ten subjects (5 men and 5 women, ages 18–72, mean age ± SD, 44.7 ± 21.4 yr) completed two 4-day laboratory sessions in constant dim light (<20 lux). They received two consecutive presentations of either a 2-h auditory or control stimulus from 0100 to 0300 on the second and third nights (presentation order of the stimulus and control was counterbalanced). Core body temperature (CBT) was collected and stored in 2-rain bins throughout the study and salivary melatonin was obtained every 30 min from 1900 to 2330 on the baseline and poststimulus/postcontrol nights. Circadian phase of dim light melatonin onset (DLMO) and of CBT minimum, before and after auditory or control presentation was assessed. The auditory stimulus produced significantly larger phase delays of the circadian melatonin (mean ± SD, -0.89 ± 0.40 h vs. -0.27 ± 0.16 h) and CBT (-1.16 ± 0.69 h vs. -0.44 ± 0.27 h) rhythms than the control. Phase changes for the two circadian rhythms also positively correlated, indicating direct effects on the biological clock. In addition, the auditory stimulus significantly decreased fatigue compared with the control. This study is the first demonstration of an auditory stimulus phase-shifting circadian rhythms in humans, with shifts similar in size and direction to those of other nonphotic stimuli presented during the early subjective night. This novel stimulus may be a useful countermeasure to facilitate circadian adaptation after transmeridian travel or shift work. [ABSTRACT FROM AUTHOR]

Determines if augmenting the amplitude of the rhythm of the endogenous molecule melatonin would augment the response of the circadian timing system of the hamster to a nonphotic phase-shifting agent, triazolam. Composition of the circadian timing system; Determination if the feeding regimen delivered a physiological or pharmacological dose of melatonin; Influence of melatonin on the activity of suprachiasmatic nuclei neurons.

Tests whether melatonin can facilitate phase shifts in a simulated night-work protocol. Information on the use of the pineal hormone melatonin to produce phase shifts in circadian rhythms; Comparison of phase advances produced by melatonin and by placebo pills; Role of melatonin in promoting adaptation to night work and jet travel.

Presents information on a study which examined the effects of melatonin agonist on age-related changes in circadian response to environmental stimulus. Methodology; Results of the study; Discussion.

Deals with a study which examined the relationship of circadian rhythms and pineal melatonin in the rest-activity cycle of nocturnally active rodents. Methodology of the study; Discussion on the results of the study; Perspectives.

Presents information on a study which explored the human circadian rhythms in sleep, activity, plasma melatonin and rectal temperature under time cues in Antartica. Materials and methods; Results; Perspectives.

Focuses on a study on the effects of periodic infusions of melatonin or the melatonin agonist S20098 of variable duration or pattern on the circadian rhythms of rats. Methodology of the study; Results and discussion; Conclusion.

Presents information on a study which investigated the possibility that interstrain differences in the diurinal pattern of wheel running activity rhythms are reflected in the melatonin profiles of rats. Urine collection; Collection of plasma and pineal glands; Discussion of results.

Examines the capability of daily melatonin injections to entrain circadian rhythms in different seasons. Information on the locomotor rhythms of lizards; Role of suprachiasmatic nuclei (SCN) in the mediation of summer locomotor rhythms to melatonin; Significance of the results of the study.