Conservation of photoperiod-responsive mechanisms in humans

Abstract

In animals, circadian pacemakers respond to seasonal changes in day length by making corresponding adjustments in the durations of diurnal and nocturnal periods of circadian rhythms; these adjustments mediate effects of photoperiod on breeding and other seasonally recurring phenomena. Little is known about photoperiod responses of human circadian pacemakers. To investigate this question, we recorded and compared circadian rhythm profiles of 15 individuals after chronic exposures to short (8 h) and long (14 h) nights. As occurs in animals, durations of nocturnal periods of active melatonin secretion (11.9 +/- 1.6 vs. 10.3 +/- 1.3 h, df = 14, t = 4.583, P < 0.0005, paired t test), high prolactin secretion (12.9 +/- 2.1 vs. 9.9 +/- 2.2 h, df = 11, t = 2.917, P < 0.01), and sleep (10.6 +/- 0.8 vs. 7.6 +/- 0.4 h, df = 14, t = 17.122, P < 0.0005) were longer after exposure to long nights than after short ones. Durations of nocturnal periods of low rectal temperature (11.6 +/- 2.3 vs. 9.5 +/- 1.6 h, df = 12, t = 3.912, P < 0.001) and rising cortisol secretion (10.8 +/- 1.6 vs. 9.3 +/- 1.9 h, df = 14, t = 3.130, P < 0.005) were also longer. Some of these differences persisted during 24-h periods of enforced wakefulness in constant dim light, indicating that prior exposure to the two regimes induced abiding changes in the timing of internal processes, such as circadian pacemaker oscillations, that control the durations of nocturnal and diurnal periods of the rhythms.

Light Therapy for Seasonal Affective Disorder with Blue Narrow-Band Light-Emitting Diodes (LEDs)

“…Further studies suggested a link between circadian regulation, melatonin and SAD, as it was determined that light not only acutely suppressed melatonin and entrained the circadian melatonin rhythm, but also elicited changes in the duration of elevated melatonin production relative to photoperiod length (Wehr et al 1993). Lengthened duration of elevated nocturnal melatonin secretion during the winter nights has been implicated as an underlying physiological seasonal change associated with the pathology of winter depression (Wehr et al 2001).…”

Evidence for a biological dawn and dusk in the human circadian timing system

“…Their compliance was monitored with sleep logs. Volunteers participated in five different studies, the details of which have been published elsewhere (Wehr et al 1993(Wehr et al , 1995aWehr, 1996;Aeschbach et al 1997Aeschbach et al , 1999. All research was consistent with the Declaration of Helsinki and was approved by the institutional review board of the Intramural Research Program of the National Institute of Mental Health (NIMH).…”

“…Healthy volunteers were admitted to an inpatient research unit where they lived for one or more weeks under controlled light-dark cycles. Circadian rhythms were measured on two occasions, once after the volunteers had been exposed to a conventional schedule of 16 h of light and 8 h of darkness each day for 1 week (LD 16:8), and once after they had been exposed to 10 h of light and 14 h of darkness each day for 4 weeks (LD 10:14) (for details see Wehr et al 1993).…”

“…For 24 h profiles of scores on the Stanford Sleepiness Scale in each individual, the times of onset and offset of a nocturnal period of increasing sleepiness were defined, respectively, as the last time, following the beginning of the measurement period, that the individual recorded their lowest rating on this scale and the first subsequent time that they recorded their highest rating on this scale, respectively (Wehr et al 1993). Data for 18 pairs of profiles from 10 men and one woman in Study 1 and from nine men in Study 3 were available for analysis.…”

Vieillissement et rythmes biologiques chez les primates

“…Ces effets du vieillissement ont surtout été démontrés sur les rythmes journaliers et peu de travaux concernent les rythmes saisonniers présents chez les primates et l'homme. Même si les facteurs socioculturels jouent un effet de masque, l'existence des rythmes saisonniers chez l'homme est attestée par divers paramètres parmi lesquels les rythmes de reproduction, les données épidémiologiques, les variations métaboliques et le statut hormonal sont les plus pertinents [6]. Ainsi, parmi toutes les théories actuelles sur le vieillissement [7], il a été suggéré que le déclin des performances physiologiques et comportementales observé lors du vieillissement, ainsi que l'apparition de pathologies, seraient en partie le résultat d'une désynchronisation des rythmes biologiques.…”