BACKGROUND: The suppression of melatonin by light at 00.30 hours has been shown to be greater in winter than in summer on patients with seasonal affective disorder (SAD) but not in matched normal controls. METHOD: In this study 12 patients with SAD and 12 matched normal controls were exposed to ...

There is a light-dependent diurnal rhythm in scleral precursor synthesis (SPS). In form-deprivation myopia (FDM) there is an increase in SPS. Daily periods of normal vision prevent FDM, but light intensities that maintain the retinal dark-light switch in its dark state do not, implicating melatonin, dopamine, enkephalin, neurotensin and somatostatin ...

BACKGROUND: The AcuVision 1000 Trainer is an instrument designed to assess and train eye-hand coordination in athletes. Variable environmental conditions are encountered when sports-vision screenings are performed. The effect of these factors on scores attained on sports-vision testing equipment is an important consideration when results for different populations are compared. ...

Ocular melatonin rhythms in the goldfish were studied and compared to those in the pineal organ and plasma. Under light:dark (LD) of 12 h light:12 h dark, melatonin contents in the eye as well as the pineal organ and plasma exhibited clear day-night changes with higher levels at mid-dark than ...

Nocturnal patterns of pineal melatonin concentrations were measured at hourly intervals in the European hamster, Cricetus cricetus, maintained under different natural or experimental environmental conditions. There were pronounced variations in the night peak of pineal melatonin both in the duration and the amplitude of the melatonin peak and in the ...

The next day after an early morning awakening of human subjects coupled with a single exposure to bright light from 0600 to 0900 h, the salivary melatonin rhythm was phase advanced by about 1 h as compared with the pre-treatment profile. The phase advance was maintained for 4 days when ...

Dopamine plays an important role in regulation of melatonin biosynthesis in retinas of several vertebrate species. In the avian retina, the dopamine receptor that controls melatonin production represents a D4-like subtype. Stimulation of this receptor by quinpirole (QNP) results in a dose-dependent decline of the nighttime activity of serotonin N-acetyltransferase ...

Melatonin was measured in a species of aerobic photosynthetic bacteria, Erythrobacter longus, grown in either constant light or constant dark. A radioimmunoassay was used to quantify melatonin levels and thin-layer chromatography to confirm the identity of melatonin immunoactivity. Melatonin levels were significantly higher (nearly 2.3-fold) in the dark-grown than in ...

The morphological diversity and dynamic aspects of presynaptic bodies are summarised. Molecular characteristics of the presynaptic machinery are discussed and the signals that control the plasticity of the presynaptic bodies are examined. A review is presented of recent findings regarding the physiology of tonically active synapses. The significance of the ...

Administration of melatonin is useful in the treatment of desynchronized conditions. The mechanisms through which melatonin exerts its effect are not completely clear. Melatonin exerts direct effects on several biological functions, such as the regulation of body temperature, but there is no proof that these actions are important in the ...

Ovarian follicular kinetics and gravimetric changes in the ovary and oviducts were studied in the skipper frog, Rana cyanophlyctis, following exposure to continuous light and melatonin treatment during the breeding season. Daily late-afternoon injections of melatonin (15 micrograms subcutaneous) for 30 days decreased the gonadosomatic index (GSI), whereas continuously available ...

This study examined the combined effect of thermocycles with either variable or constant photic conditions on melatonin production by pineal organs in vitro in the gecko, Christinus marmoratus. A 30 degrees C:15 degrees C thermocycle elicited a rhythm of melatonin production under conditions of 12L:12D, constant light or constant darkness ...

We investigated whether the contemporaneous administration of melatonin can modify circadian phase shifts induced by bright light stimuli. After a baseline evaluation, 10 women were exposed for three consecutive nights to a 4-h bright light stimulus (>3,000 lx) initiated at the time of the estimated core body temperature (BT(c)) nadir. ...

The aim of this study was to replicate and extend previous work in which the authors observed lower, shorter, and advanced nocturnal melatonin secretion patterns in premenstrually depressed patients compared to those in healthy control women. The authors also sought to test the hypothesis that the therapeutic effect of bright ...

The effects of caffeine ingestion and exposure to bright light, both separately and in combination, on salivary melatonin and tympanic temperature were assessed in humans. Four treatments during a 45.5 h sleep deprivation period were compared: Dim Light-Placebo, Dim Light-Caffeine, Bright Light-Placebo and Bright-Light Caffeine. The Dim Light-Caffeine condition (200 ...

Effects of bright light exposure at midday were examined on plasma melatonin rhythm in humans under controlled living conditions. Bright light of 5000 1x was provided from the ceiling at midday (1100-1700 h) for 3 consecutive days and the circadian rhythm in plasma melatonin was determined from the fourth to ...

The pineal organ and its hormone melatonin are significant components of avian circadian pacemaking systems. In songbirds, pinealectomy results in the abolition or destabilization of overt circadian rhythms such as the rhythm of locomotor activity, feeding, or body temperature. A stable rhythmicity can be restored either by reimplanting a pineal ...

Annual variations in day length are responsible for seasonal changes in reproductive activity in sheep. However, in constant photoperiodic conditions, ewes express an endogenous rhythm characterized by alternations of reproductive activity and quiescence that are not synchronized among animals. Thus, the main role of photoperiod in the natural environment appears ...

The present study investigated the effect of dim white light on nocturnal plasma melatonin in males and females. Subjects were exposed to light between 2400 hr and 0100 hr. No significant gender differences were found with both 200 lux (p > 0.1) and 500 lux (p > 0.1) of light. ...

The effects of bright artificial light on the subjective mental state of 10 female nurses working shifts at a university hospital were assessed. We investigated two series of five consecutive workshifts rotations comprising one normal, two night and two evening shifts, using two self-administered rating scales. The subjects were exposed ...

The chick pineal gland contains histamine and tele-methylhistamine. The levels of both substances are elevated after treatment of chicks with the amino acid precursor of histamine, L-histidine (1 g/kg, ip). In control and L-histidine-loaded animals the pineal levels of histamine and tele-methylhistamine are higher in light-exposed than in dark-adapted animals ...

Rhythms of daily activity are found in all vertebrate species, some of them being diurnal (like humans, dogs, pigeons), others--nocturnal (like mice, rats and bats). Some species undergo very pronounced seasonal changes, as they hibernate in the winter or mate only at the specific seasons. The main regulator (a clock ...

Eight young males were subjected to a single blind cross-over test to see the effects of vitamin B12 (methylcobalamin; VB12) on the phase-response of the circadian melatonin rhythm to a single bright light exposure. VB12 (0.5 mg/day) or vehicle was injected intravenously at 1230 h for 11 days, which was ...

Seasonal rhythms of reproduction in the Syrian hamster are triggered by the pineal hormone melatonin. By varying the parameters of systemic infusions of exogenous melatonin delivered to pinealectomized hamsters, it has been shown that the hypothalamus is sensitive to the duration of individual signals, which serve as an inverse coding ...

The role exerted by melatonin in human physiology has not been completely ascertained. Melatonin levels have been measured in different physiopathological conditions, but the effects induced by melatonin administration or withdrawal have been tested only recently. Some effects have been clearly documented. Melatonin has hypothermic properties, and its nocturnal secretion ...

Previous data have demonstrated that a single 1-hr light pulse at night affects the secretion of melatonin in the ram if it was given at the appropriate time. This paper reports the effect on melatonin secretion of a 1-hr light pulse given at two different times at night to two ...

6-Sulphatoxymelatonin (aMT6S) excretion was examined in the urine of rhythmic and arrhythmic blind subterranean mole rats (Spalax ehrenbergi) to test the correlation between melatonin secretion (as represented by aMT6S) and variability in circadian locomotor activity. Activity pattern was tested in four males, first for a week under short photoperiod [light:dark ...

The aim of the study was to determine whether a discrepancy between the genetically determined endogenous circadian period and an abnormally long Zeitgeber period disturbs the development of melatonin synthesis. Breeding pairs of rats were kept under 12:12- or 14:14-hr light:dark (LD) conditions. Pineal melatonin contents in the offspring were ...

Light can induce an acute suppression and/or circadian phase shift of plasma melatonin levels in subjects with normal color vision. It is not known whether this photic suppression requires an integrated response from all photoreceptors or from a specialized subset of photoreceptors. To determine whether normal cone photoreceptor systems are ...

We examined whether continuous melatonin administration through subcutaneously implanted silastic tubing accelerates reentrainment of circadian rhythms of locomotor activity to shifted illumination cycles. We found that rats required less time to reentrain to an advanced or delayed phase shift of a light-dark cycle while carrying a silastic implant filled with ...

1. The synthesis of the pineal hormone, melatonin, is under adrenergic control. The brain's rhythm generating system (suprachiasmatic nucleus and associated systems) which is synchronised by the light-dark cycle controls norepinephrine release from the sympathetic nerve terminal resulting in cAMP accumulation. Increased cAMP leads to induction of the rate-limiting enzyme, ...

Melatonin is a hormone released during darkness under the control of the hypothalamic circadian pacemaker. It has been shown that melatonin is suppressed by light as a function of intensity, with low levels of illumination producing small effects and more intense light greater, but not complete inhibition. The studies which ...

Eight healthy subjects were studied during 39-h spans (from 07:00 on one day until 22:00 the second) in which they remained awake. During one experiment, subjects were exposed to 100 lux of light between 18:00 and 8:00, and during a second experiment, they were exposed to 1000 lux during the ...

Adult Djungarian hamsters in long (16 h of light) or short (10 h of light) days for 6 wk were acutely exposed to a 1-G 60-Hz magnetic field (MF) for 15 min 2 h before dark. The nighttime rise in melatonin was delayed and duration reduced in MF-exposed hamsters in ...

This study investigated the role of the circadian timing system (CTS) in photoperiodic time measurement by examining the response of the tau mutant hamster to programmed infusions of melatonin. The mutation is a single Mendelian gene defect which accelerates circadian period from 24 h in the wild-type (WT) to 20 ...

Effects of a single light exposure on the circadian rhythm in plasma melatonin were, examined in young males to obtain the threshold of light intensity for suppressing the nocturnal melatonin level on the one hand and to understand the relationship between the light-induced phase shift of melatonin rhythm and the ...

Patients with seasonal affective disorder (SAD) were treated for 1 week either with a daily 1-h morning walk outdoors (natural light) or low-dose artificial light (0.5 h@2800 lux). The latter treatment (given under double-blind conditions) can be considered mainly placebo and did not improve any of the depression self-ratings, whereas ...

In the vertebrate retina and pineal gland, melatonin production displays diurnal variations with high levels at night. Hydroxyindole-O-methyltransferase (HIOMT, EC 2.1.1.4) catalyses the last step of melatonin biosynthesis. In the present study, a cDNA encoding chicken HIOMT was used to examine the effects of environmental lighting on HIOMT mRNA expression ...

The pineal organ of teleost fish receives photic information directly through specialized photoreceptor cells that transmit their light response to second-order neurons and respond also with an endocrine light-dependent melatonin signal. In the present study we have analyzed the action of diazepam, a full agonist of the benzodiazepine receptor, on ...

In order to investigate the influence of various environmental parameters on melatonin excretion, the night-time urinary melatonin excretion of 16 healthy volunteers was measured in samples collected monthly over a period of one year. No significant interindividual differences were detected in the monthly rate of change of melatonin excretion. A ...

The present study tested the hypothesis that daily melatonin treatments influence the biological clock mechanism controlling the circadian melatonin rhythm. Adult male and female Djungarian hamsters in light:dark = 16L:8D (lights on 0300-1900 h) were administered melatonin subcutaneously (s.c.) each day (5 micrograms/0.2 ml saline) in the morning at 1000 ...

Salivary melatonin levels were measured in 6 healthy volunteers in order to determine whether the phase shift caused by a single 60-min light pulse of 2000 lux might be inhibited by maintaining high melatonin concentration. In the control sessions, the samples were collected at 60-min intervals under lighting of < ...

Melatonin release was measured from zebrafish pineal organs and retinas maintained in flow-through culture. Pineal organs released melatonin in a strong circadian rhythm through 5 days in constant darkness, and the phase of this rhythm was reset by in vitro exposure to phase-shifted light cycles. In contrast, the retinal melatonin ...

The teleost pineal organ is a photoreceptive endocrine organ that synthesizes the hormone melatonin through specialized intrapineal photoreceptor cells in a light-dependent manner. The present study investigated whether the methoxyindoles 5-methoxytryptophol (5-MTOL), 5-methoxyindoleacetic acid (5-MIAA), and 5 methoxytryptamine (5-MT) correspond to melatonin secretion synthesized and released from explanted, superfused pineal ...

The SCN of the hypothalamus, the site of the circadian pacemaker in mammals, is endowed with melatonin receptors of the ML-1 subtype. Here, we present evidence suggesting that activation of melatonin receptors in the SCN regulates circadian rhythms of behavior in the mouse. In a paradigm simulating a eastbound transmeridian ...

The melatonin secretory pattern of the perifused rat and chicken pineal was compared in response to different lighting conditions and norepinephrine administration. The following main differences were observed. 1. Explanted (perifused) rat pineal showed, after a rapid initial surge, a steady continuous basal secretion of melatonin. This was independent from ...

The rhythmic production of melatonin is governed by intrapineal oscillators in all fish species so far investigated except the rainbow trout. To determine whether the latter represents an exception among fish, we measured in vitro melatonin secretion in pineal organs of nine wild freshwater and six marine teleost species cultured ...

Melatonin (N-acetyl-5-methoxytryptamine) is an evolutionary highly conserved molecule that plays an important role in conveying the clock and calendar information to all living organisms, including man. Melatonin is synthesized in the rhythmic fashion, primarily by the pineal gland, and, to a lesser degree, by extrapineal tissues-namely the retina, the Harderian ...

The levels of histamine (HA) and tele-methylhistamine (t-MeHA) in chick pineal gland were measured by RIA at two time points, i.e. at the end of the light (L) phase and in the middle of the dark (D) phase of 12 h: 12 h L:D cycle. The chick pineal gland showed ...

Melatonin is produced only during nighttime darkness. Its onset during the evening is a useful marker for circadian phase position, when melatonin levels are sampled frequently and under conditions of dim light or darkness. This marker is termed the dim light melatonin onset (DLMO). Recently, we have described a phase ...