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The purpose of the study was to explore parallel and divergent features of the daily rhythms of melatonin and plasma free fatty acids (FFA) in goats exposed to different lighting conditions. From these features, we attempted to analyze whether the endogenous melatonin rhythm plays any role in the maintenance of the FFA rhythm. Seven Finnish landrace goats were kept under artificial lighting that simulated the annual changes of photoperiod at 60 degrees N (longest photoperiod, 18 h; shortest, 6 h). The ambient temperature and feeding regimen were kept constant. Blood samples were collected 6 times a year at 2 h intervals for 2 d, first in the prevailing light-dark (LD) conditions and then after 3 d in constant darkness (DD). In LD conditions, the melatonin levels always increased immediately after lights-off and declined around lights-on, except in winter (18 h darkness), when the low daytime levels were restored clearly before lights-on. The FFA levels also displayed a consistent rhythmicity, with low levels at night and a transient peak around lights-on. In DD conditions, the melatonin profiles were very similar to those found in the habitual LD conditions, but the rhythm tended to advance. The FFA rhythm persisted also in DD, and the morning peak tended to advance. There was an overall parallelism between the two rhythms, with one significant exception. In winter in LD conditions, the morning rise in FFA levels coincided with lights-on and not with the declining phase of melatonin, whereas in DD conditions, the FFA peak advanced several hours and coincided with the declining phase of melatonin. From this finding and comparisons of the calculated rhythm characteristics, i.e., phase-shifts, phase differences, and correlations, we conclude that the daily rhythm of FFA levels is most probably generated by an endogenous oscillator, primarily adjusted by dawn, whereas the melatonin rhythm in this species is regulated by an oscillator primarily adjusted by dusk. The results did not exclude a modulatory effect of melatonin on the daily FFA profiles, but melatonin secretion, alone, does not explain the patterns sufficiently.

Objective: This study aimed to investigate how local pain relief is mediated by laser therapy and how dose affects the relationship. Methods: Inflammation was induced in the hind-paws of Wistar rats. Two groups of rats received 780-nm laser therapy (Spectra-Medics Pty Ltd.) at one of two doses (2.5 and 1 J/cm(2)). One group acted as a control. Scores of nociceptive threshold were recorded using paw pressure and paw thermal threshold measures. Results: A dose of 1 J/cm(2) had no statistically significant effect on antinociceptive responses. A dose of 2.5 J/cm(2) demonstrated a statistically significant effect on paw pressure threshold (p < 0.029) compared to controls. There was no difference in paw thermal threshold responses and paw volumes at either dose. Immunohistochemistry in control animals demonstrated normal beta-endorphin containing lymphocytes in control inflamed paws but no beta-endorphin containing lymphocytes in rats that received laser at 2.5 J/cm(2). Conclusion: The results confirm previous findings that the effect of laser therapy is dose-related. The mechanism of effect may occur via a differentiated pressure-sensitive neural pathway rather than a thermal-sensitive neural pathway. The significance of the immunohistochemistry findings remains unknown.

Melatonin is synthetized from serotonin in two steps driven by the enzymes N-acetyltransferase and hydroxyindole-O-methyltransferase. Constant light treatment reduces rat pineal hydroxyindole-O-methyltransferase activity while the activation of N-acetyltransferase becomes supersensitive to adrenergic stimulation. We studied the effect of this discrepancy on the production of melatonin. Male rats were kept under 12/ 12-h light/dark (LD) conditions or for 7 days under constant light (LL). They received subcutaneous injections of isoproterenol or methoxamine in the middle of the light period (LD-rats) or the estimated rest phase (LL-rats). A low dose of isoproterenol (0.1 mg/kg) increased pineal melatonin only marginally in LD-rats, while a maximum effect was found in LL-rats. A medium dose (0.2mg/kg) produced similar levels in both groups. A high dose (0.4 mg/kg) elevated pineal melatonin contents significantly more in normal than light-treated rats. Methoxamine (0.8 mg/kg) had no effects alone nor combined with isoproterenol. The results suggest supersensitivity with reduced capacity for melatonin formation in constant light-treated rats.

This study was carried out to clarify the role of alpha2-adrenoceptors in the regulation of pineal melatonin synthesis. Medetomidine, a selective alpha2-adrenoceptor agonist, was previously found to be a potent suppressor of nocturnal melatonin levels in rats. Medetomidine and alpha2-adrenoceptor antagonists atipamezole and yohimbine were injected into rats in different conditions, and their pineal melatonin contents were measured by radioimmunoassay. Experiment 1: Blocking the alpha2-adrenoceptors and possible non-adrenergic binding sites with atipamezole did not counteract the light-induced suppression of nocturnal melatonin. These receptors are, thus, not essential for the suppression of melatonin by light. Experiment 2: Blocking the alpha2-adrenoceptors with atipamezole or yohimbine did not sensitize the pineal melatonin synthesis to daytime darkness in the light/dark-entrained rats. The binding sites are not involved in keeping the daytime melatonin levels low, even in darkness. Experiment 3: The rats were sensitized to daytime darkness by keeping them for seven days in constant light. The dark-elicited melatonin rise was suppressed by a lower dose of medetomidine than the normal nocturnal rise in light/dark-entrained rats, while atipamezole had no effect. The results showed that alpha2-adrenoceptor insufficiency is not involved in the constant light-induced pineal supersensitivity. In summary, the experiments indicated that the physiological regulation of melatonin synthesis by ambient lighting in rats does not depend on alpha2-adrenergic mechanisms.

We investigated whether alpha2-adrenergic mechanisms participate in the regulation of the daily melatonin rhythm. Female Wistar rats, living under 12:12 h light-dark conditions, received a subcutaneous injection of saline or medetomidine (alpha2-adrenoceptor agonist; 100 microg/kg) 1 h after lights off. Thereafter they were kept in continuous darkness. Pineal glands were collected for melatonin measurements at 2-h intervals during the first and second subjective nights. During both nights, a significant elevation of melatonin levels in medetomidine-injected rats was found 2 h later than in control rats. We interpret the first-night delay to be a sign of medetomidine's suppressive effect on melatonin synthesis, and the second-night delay a medetomidine-induced resetting of the circadian clock controlling the melatonin onset.

This study was done to clarify the role of alpha2-adrenoceptors in the regulation of pineal melatonin synthesis. A selective alpha2-adrenoceptor agonist, medetomidine, and antagonist, atipamezole, were injected subcutaneously into rats and their pineal melatonin contents were measured by radioimmunoassay. Medetomidine (120 microg/kg) suppressed melatonin at night to a similar extent during the rising and descending phase of melatonin synthesis, but it did not affect the daytime level. A dose of 12 microg/kg was ineffective; doses of 30-180 microg/kg suppressed nocturnal melatonin levels close to the daytime levels. Significant suppression was reached within 15 min and the effect started to fade 3 h after the injection (120 microg/kg). At midday, medetomidine did not inhibit isoproterenol-stimulated synthesis of melatonin. Atipamezole (0.4 or 1.2 mg/kg) had no effect alone, but it counteracted the medetomidine-induced suppression. The effects of alpha2-adrenoceptor ligands on melatonin synthesis depend on the time of day and/or on the activity of the pineal sympathetic nerves.

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 measured by radioimmunoassay. At 2 weeks of age high melatonin contents were found from lights-off to lights-on in both conditions suggesting dominance of the photic regulation. At 3 weeks of age the signs of the circadian regulation in the melatonin profiles were evident: a lag period after the light offset in control conditions and a significant decline before the light onset in both conditions. However, in 14: 14-hr LD conditions the melatonin content did not decrease to daytime levels until the lights were on. This could suggest incomplete maturation of the circadian system. The phase relationships between the melatonin peak and LD cycle were different in the two conditions. A statistically significant LD difference was first found at the age of 8–10 days in male pups and at 14 days in female pups under both lightings. The results suggest that the abnormally long LD cycle did not cause any major disorders in the development of photic or circadian regulation of the melatonin synthesis.

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 < 10 lux from 18.00 to 11.00 h. In the light-exposure sessions, placebo or 0.5 mg melatonin was administered orally 60 min prior to the light pulse, timed at the rising phase of the melatonin synthesis. The after-light sessions, one day after the light exposure, were like the control sessions. The average delays of the melatonin half-rise and half-decline times were equal (about 0.7 h) in the placebo and melatonin replacement experiments. The maintenance of high melatonin levels during the light exposure did not counteract the influence of bright light on the melatonin rhythm. Thus, in the adjustment of the melatonin rhythm, light is a stronger regulator than melatonin itself.

Photic regulation of the pineal melatonin synthesis was studied in 3- to 21-day-old rat pups by exposing the animals to light at night (30-40 min) or to darkness during the day (30-240 min). The pineal melatonin contents were measured by radioimmunoassay. A significant day/night difference in the melatonin content and the nocturnal light-induced decrease were not found until second postnatal week. A novel finding was that at the age of 13-17 days a daytime dark exposure elevated the pineal melatonin content; it was twofold as compared with the normal daytime level and about half of the nocturnal peak level. In 21-day-old rats the response had disappeared, while the nocturnal suppression by light persisted. The dark-induced increase of the melatonin synthesis was independent of the opening of the eyelids which occurs in pups at the age of two weeks, but it was greater in maternally isolated than non-isolated pups. The results suggest that one component of the circadian regulatory system matures at the end of the third postnatal week. This mechanism inhibits the elevation of the melatonin synthesis by darkness during the daytime.

Sleep disorders are common in NCL patients. The patients have problems such as frequent awakenings, difficulties with sleep onset, nightmares, and night terrors. The aim of the study was to examine whether the sleep disturbance in NCL can be explained on the basis of desynchronised circadian rhythms. Therefore we studied diurnal patterns of melatonin, cortisol, body temperature, and motor activity of 14 patients. The group consisted of 8 JNCL patients, 5 INCL children, and one boy with Jansky-Bielschowsky disease of the variant type. There were healthy age- and sex-matched control subjects. The blood samples for serum melatonin and cortisol were collected every 2 hours during 24-hour periods. Body temperature was recorded continuously for a 24-hour period by a polygraph. Diurnal motor activity was measured by wrist actigraphy for 5 days. In most of our patients sleep was fragmented and the sleep phase was irregular. Disturbances in the daily hormonal rhythms occurred only in the minority of the patients and only at an advanced stage of the disease. Although disturbances in the body temperature rhythm were found in about half of the patients, a general failure in the circadian regulatory system does not explain the frequent disturbances of the sleep-wake cycle of the NCL patients.

The daily rhythms of salivary melatonin, salivary cortisol, and axillary body temperature were measured in nine healthy volunteers in midsummer, around the autumn equinox, and in midwinter, at a latitude of 60°N. The aim was to find out whether these rhythms were dependent on variations of the natural daylength. The samples were collected every 2 hr during 24-hr periods in everyday conditions. The individual rhythms were characterized with the acrophase estimates of the best-fitting cosine curve models and with the half-rise and half-decline times calculated from the raw data. The melatonin and cortisol rhythms were delayed significantly (about 1 hr) in midwinter as compared with summer and autumn. The most advanced rhythms were found in autumn. The shifts of the melatonin and cortisol rhythms could be explained as a result of the changes of natural illumination. The overt temperature rhythms did not differ significantly among the sampling months. The lack of seasonal patterns in temperature rhythms probably primarily reflected the socially determined rest-activity cycles of the subjects.

In several animal species the response of the pineal melatonin synthesis to light alters during the night, but the possible changes in humans are not exactly known. Nine volunteers were exposed to 500‐lx light for one hour at different times over the course of the rising phase of the melatonin synthesis. The exposure times were related to the individual circadian phases by using the time point of the half‐maximal melatonin level as a reference. Melatonin was measured by radioimmunoassay in salivary samples collected at 15–120‐min intervals. Only when the melatonin levels were related to the prelight levels, the light‐induced suppression was smaller and the postlight recovery was greater in the early than in the late rising phase. No differences were found, if the levels were related to the corresponding control values. Thus, the sensitivity of the human melatonin synthesis to light did not change during the rising phase. It cannot explain the increase of the light‐induced phase delays of circadia...

The pineal melatonin patterns were measured in rats kept 1, 2, 3, 4, 6, 8, 16, or 28 days under the lighting conditions with a dark period of 90 min only (from 18:00 to 19:30 h). The samples were collected at 30-min intervals, and melatonin was measured by radioimmunoassay. During the first and second dark pulse the melatonin levels were low, but thereafter they were significantly higher than the usual daytime levels. The increase of the synthesis started within 15 min after the light offset. The results suggest a stable adjustment of the melatonin rhythm by the dark pulses.

Salivary melatonin levels were measured in 12 healthy volunteers in order to determine whether a moderate light intensity, which suppresses the nocturnal rise of melatonin, was able to shift the melatonin rhythm. The samples were collected at 1-hr intervals under lighting of < 100 lux (experiment 1) or < 10 lux (experiment 2). The control melatonin profiles were determined during the first night. In the second night the subjects were exposed to light of 500 lux for 60 min during the rising phase of melatonin synthesis. The third series of samples was collected during the third night. The mean decrease of melatonin levels by the exposure to light was 56% of the prelight concentrations. The melatonin onset times were delayed significantly (about 30 min) the night after the exposure to light. The melatonin offset times tended to be delayed in experiment 2. The shifts of the melatonin offset correlated positively with the amount of the melatonin suppression. The results suggest that a relatively small and short lasting light-induced interruption of melatonin synthesis may affect the melatonin rhythm in humans.

The ability of a short dark pulse to entrain the circadian rhythms in rats was investigated. Pineal melatonin contents and serum levels of corticosterone and thyrotropin, a thyroid-stimulating hormone (TSH), were measured and locomotor activity was recorded under 12:12-h light-dark cycles (LD; darkness from 1800 to 0600 h) and under a 22.5:1.5 h LD lighting schedule (darkness from 1800 to 1930 h). The 90-min dark pulse was enough to trigger the rise of melatonin synthesis, but a free-running component was detected in the locomotor activity. Corticosterone levels showed diurnal variations under both conditions. The decrease of corticosterone and the increase of melatonin were phase locked, but the corticosterone pattern was distorted under the dark-pulse conditions. The 24-h rhythm of TSH was detectable in the control but not in the dark-pulse schedule. The results suggest that the circadian rhythm of pineal melatonin and the decrease of serum corticosterone levels were entrainable by the dark pulses, whereas the increase of corticosterone, the variations of TSH, and the rhythm of locomotor activity were not.

The daily rhythms of melatonin, cortisol and body temperature were studied in 16 institutionalized subjects with the Lennox-Gastaut syndrome. The results of 9 subjects with normal daily rhythms of sleep and wakefulness (group 1) were compared with those of 7 subjects with disordered sleep (group 2). Salivary samples were collected and axillary temperature was measured every 2 h during two or three separate 26-h periods. The hormones were measured by radioimmunoassays. The rhythms were characterized with single cosinor analysis. Two subjects in group 1 and six subjects in group 2 had abnormalities in their rhythms of temperature, cortisol or melatonin. All three rhythms were disrupted in two subjects of group 2. These two subjects were the only ones with disrupted cortisol rhythm. The diversity of rhythm pathologies suggested partly separate regulatory mechanisms for each rhythm. The co-occurrence of circadian rhythm sleep disorders with the deteriorated melatonin rhythm raised the question as to whether the sleep disorders of these subjects, like those of subjects with healthy brains, could be relieved by the induction of normal melatonin rhythm.

The locomotor activity and pineal melatonin patterns of adult male rats were compared under two different lighting regimes. The animals were kept 8 days under 12/12 h light/dark cycles with abrupt or slowly decreasing and increasing transitions (twilight periods about 2 h). The onsets of high activity and melatonin rise were phase-locked in the two conditions and related to about half-maximal illuminance level of the gradual dusk. The high activity of the control rats stopped 30–60 min before the abrupt light onset and the rats under the gradual lighting transitions ceased the locomotor activity at about 1 hour before the half-maximal illuminance. The melatonin peak levels were found 4 h before the abrupt lights-on time. Under the slow illuminance transitions the average melatonin peak was related to the illuminance level between maximum and minimum in the morning. Thus, both the melatonin rhythm and the rest-activity rhythm under the gradual dawn and dusk were adjusted according to about half-maximal illuminances in the present conditions.

In this experiment we investigated whether the lack of the nocturnal melatonin peak under constant light would cause an increase in testosterone sensitivity. Castrated rats were kept under periodic or constant light for one week. They received a daily injection of vehicle, testosterone propionate (125 micrograms), melatonin (50 micrograms) or testosterone plus melatonin (125 micrograms + 50 micrograms). Serum and pituitary gonadotrophins and pineal melatonin were measured at the end of the experiment. Under constant light, testosterone injections reduced the serum luteinizing hormone concentration in castrated rats to that in intact rats, but, under periodic light, the decrease was smaller. Melatonin did not reverse the stronger effect of testosterone under constant light. The serum melatonin peak produced by the exogenous melatonin injection had a higher amplitude, shorter duration and earlier appearance than the physiological melatonin peak. Exogenous melatonin did not modify the physiological melatonin secretion, measured either as serum melatonin concentration or pineal melatonin content on the consecutive day. We conclude that the increase in testosterone negative feedback sensitivity of castrated rats under constant light was not due to the absence of the nocturnal melatonin pulse.

Intact and castrated male rats were kept for 1 week under constant or periodic light, during which time they received daily injections of either vehicle or testosterone propionate (125 or 250 micrograms day-1). Immediately after the experiment the rats were decapitated and serum and pituitary prolactin were measured radioimmunologically. The pituitary prolactin content was decreased after castration in both lighting conditions. Daily testosterone injections elevated the pituitary prolactin content of the castrated rats to the level of the intact rats in constant-light conditions but were ineffective under periodic light. Serum prolactin concentrations were not affected by constant light. We have previously shown that testosterone decreases the serum luteinizing hormone concentration of castrated rats more effectively under constant than under periodic light. In the present study we showed that serum prolactin was not elevated in constant light and thus could not be the cause of increased testosterone sensitivity. We also showed that testosterone elevates the pituitary prolactin content of castrated rats under constant but not under periodic light. This finding gives further support to the hypothesis that constant light sensitizes the hypothalamo-pituitary axis of castrated male rats to the effects of testosterone.

It has been reported that periodicity of lighting plays a role in the regulation of the function of the hypothalamus-anterior pituitary-thyroid axis in the rat. We studied whether other properties of lighting influence the levels of pituitary and serum thyrotropin (TSH) in adult male rats. The animals were reared 7 days under various lighting conditions, then trunk blood and adenohypophyses were collected at different times of the day, and TSH was measured radioimmunologically. In natural lighting conditions the diurnal variation of plasma and pituitary TSH levels was abolished, and the overall levels of plasma TSH were higher and those of pituitary TSH lower than in ordinary laboratory lighting conditions. The intensity of lighting affected the serum TSH levels; daytime serum TSH decreased in the rats under low daytime illuminances and in those under nighttime twilight instead of darkness. Changing the rate of the lighting transition at dawn and dusk had no influence on the TSH patterns. We conclude that, in addition to periodicity, other features of lighting affect the daily secretion patterns of TSH.

Saliva and serum samples were collected from eight healthy volunteers every two hours during a 26-hour period. Melatonin concentrations were measured by radioimmunoassay after chloroform extraction using radioiodinated melatonin as a tracer. Five of the subjects had high serum melatonin levels at night (peak levels higher than 75 pg/ml); in three subjects the highest serum melatonin concentration was 20-40 pg/ml. All subjects had low levels (less than 10 pg/ml) during the day. The correlations between salivary and serum levels were calculated. The regression line y = 0.33x + 3.7 pg/ml, r = 0.95, P less than 0.001, was obtained for all detectable value pairs (n = 73). The regression and correlation coefficients were almost equal for the peak values of melatonin and during the rising and descending phases of the secretion patterns. However, no significant correlation was found between low daytime salivary and serum concentrations when calculated separately. In the five high-secretors the melatonin levels in saliva reflected reliably the changes in serum, but in the three low-secretors the correlation between salivary and serum melatonin was not significant. The proportion of melatonin found in saliva decreased with increasing serum melatonin levels. Circadian rhythm parameters were estimated by single cosinor analysis. The acrophases did not differ significantly within a subject in the concomitant measurements of serum and salivary melatonin. The measurements of salivary melatonin levels seem valid for studies on melatonin rhythms, but the melatonin concentrations measured in saliva do not always consistently reflect the absolute concentrations in blood.

Objective: We studied whether the endogenous melatonin patterns in adult patients with developmental brain disorders have any role in response to exogenous melatonin given as a sleep-promoting medicine. Methods: Participants included 15 adults (18–60 years, five females) with developmental brain disorders of varying etiologies, motor handicaps, and long-term history of sleep problems. According to the 24-h patterns of serum melatonin, patients were divided into two subgroups: lower and higher secretors. The pretreatment sleep disorder was characterized by a structured interview, 24-h ambulatory polysomnography and 7-day wrist actigraphy. Patients received 1, 3, or 6 mg fast-release melatonin tablets, each for 4 weeks in increasing order, at a constant time of 30 min before the desired sleep onset. Similarly, placebos with different codes were given during 3 × 4 weeks. The 7-day actigraphy was repeated at the end of each drug period. Outcome measures were six different parameters of non-parametric circadian rhythm analysis. Drug effects and 40 confounding/modulating factors were evaluated by applying two-level regression analyses with co-variables. Results: Exogenous melatonin decreased the fragmentation of the rest–activity rhythm, increased the day/night ratio of activity and advanced the onset of rest period. The effects on fragmentation and day/night ratio were more pronounced in the lower than higher secretors of melatonin. Other contributing factors in the drug effects were blindness and some features of the original sleep disorder (disrupted cyclicity of the sleep architecture in polysomnography or reported daytime somnolence). Conclusions: Exogenous melatonin consolidated the fragmented rest–activity in about half of the patients. Low endogenous serum melatonin levels at night predicted improvement by the drug. Higher doses were not more effective than the lowest dose.

The aim of the study was to differentiate the impact of lighting conditions and feeding times on the regulation of lipid metabolism of goats under different photoperiods throughout the year. Seven Finnish landrace goats were kept under artificial lighting that simulated the annual changes of photoperiod at 60 degrees N (the longest light period 18 h, the shortest 6 h). Ambient temperature and feeding regime were kept constant. Blood samples were collected six times a year at 2-h intervals for 2 days, first in light/dark (LD) conditions and then after 3 days in constant darkness (DD). Significant daily variations were detected in the concentrations of plasma free fatty acids (FFA) and glycerol throughout the year. The nocturnal decrease and morning rise of FFA levels were related to the photoperiod, while the trough levels of glycerol were associated with the concentrate meal times. In DD conditions, FFA and glycerol rhythms were unstable. A significant seasonal variation was detected in the overall FFA and glycerol levels suggesting decreased lipogenesis in winter, increased lipolysis in spring and high lipogenesis in summer and fall. There was no significant daily rhythm in serum leptin levels, nor did the profiles in LD and DD conditions differ. The leptin level was slightly lower in early fall than in the other seasons, paralleling a small decrease of body mass in the goats after the grazing season. The daily or annual variations of FFA and glycerol levels were not clearly related to leptin concentrations. The results suggest that lipid metabolism of goats is regulated by light even in constant temperature and feeding conditions; however, no significant contribution of leptin levels could be shown.

The aim of the study was to find out whether there is a daily rhythm in goat serum cortisol concentrations, whether the concentration profiles differ between normal light:dark and constant dark conditions, and whether any seasonal variations might be detected in daily cortisol secretion patterns. Seven Finnish landrace goats were kept at indoor temperature (18-23 degrees C) under artficial lighting that approximately simulated the annual changes of daylength at 60 degrees N. Blood samples were collected for cortisol measurements by radioimmunoassay at 2h intervals during six times of the year: winter (light:dark 6:18h), early spring (10:14h), late spring (14:10h), summer (18:6h), early fall (14:10h), and late fall (10:14h). Cortisol profiles were determined for two consecutive days, first in light:dark (LD) conditions and then in continuous darkness (DD). There was no significant daily rhythm in serum cortisol levels in any time of the year, nor did the profiles in LD and DD conditions show any differences. A significant seasonal variation was, however, detected among the overall cortisol levels. In winter, the concentrations were higher than in any other season, and from early spring to summer they were at their lowest. Under equal photoperiods, the cortisol levels were higher in fall than spring. The difference between winter and summer was confirmed the following year in LD conditions. There was on correlation between serum cortisol and progesterone levels. The results suggest that the possible circadian variation of cortisol secretion in goats is completely masked by external factors, and lighting conditions do not have immediate effects on the daily secretion patterns. The seasonal variation in the overall cortisol levels is most probably related to the changes in photoperiod, because other conditions were relatively constant during the experiment.

Binding of 2-[125I]melatonin to the anteroventral and anterodorsal nuclei of the rat limbic thalamus was analyzed with in vitro autoradiography. In both nuclei the binding was of high affinity (Kd values 24–41 pM) and was completed with by nanomolar concentrations of 6-hydroxymelatonin. Kd values were in the same range as those reported for other high-affinity binding sites in the brain. Bmax values were 0.68–2.99 fmol/mg protein. The results suggest that some effects of melatonin are mediated via the limbic thalamus.

The pineal hormone melatonin serves as a signal of day length in the regulation of annual rhythms of physiological functions and behavior. The duration of high melatonin levels in body fluids is proportional to the duration of the dark period of the day. Due to the direct suppression of melatonin by light, the overt melatonin rhythm may differ from the endogenous rhythm driven by the hypothalamic circadian clock. The aim of this study was to find out possible differences between the overt and endogenous melatonin rhythms in goats during the course of a year. Seven Finnish landrace goats (nonlactating females) were kept under artificial lighting that approximately simulated the annual changes of day length at 60°N. Blood samples for melatonin measurements by radioimmunoassay were collected at 2-h intervals during six seasons: winter (light:dark 6:18 h), early spring (10:14), late spring (14:10), summer (18:6), early fall (14:10), and late fall (10:14). Melatonin profiles were determined for 2 consecutive days, first in light-dark (LD) conditions and then in continuous darkness (DD). In LD conditions, the profiles matched the dark period with one exception: in winter, the mean peak duration was significantly shorter than the scotoperiod. In DD conditions, two types of endogenous melatonin patterns were found: a “winter pattern” (peak duration 13–15 h) in winter, early spring, early fall, and late fall, and a “summer pattern” (duration about 11 h) in late spring and summer. Thus, in equal habitual LD conditions in late spring and early fall (LD 14:10), the endogenous melatonin rhythms were not quite similar: the pattern in late spring resembled that in summer, and the pattern in early fall that in winter. These results suggest that, in addition to the light-adjusted overt melatonin rhythm, the endogenous rhythm of melatonin secretion varies during the course of a year.

This study was performed to distinguish central and peripheral alpha(2)-adrenoceptors in the inhibition of rat pineal melatonin synthesis. The rats received lipo- or hydrophilic alpha(2)-adrenoceptor ligand injections at middark; after 1 or 2 h the pineal melatonin contents were measured. The lipophilic agonist medetomidine (100 microg/kg s.c.) suppressed the melatonin contents significantly, while the hydrophilic agonists ST-91 and p-aminoclonidine (10 or 100 microg/kg i.v.) did not. The suppression by medetomidine was counteracted by the lipophilic antagonist yohimbine (0.3-3.0 mg/kg i.p.) but not by the hydrophilic antagonist L-659,066 (1-10 mg/kg i.v.). In conclusion, the suppression of nocturnal melatonin synthesis by alpha(2)-adrenoceptor agonists is mainly of central origin.

Testosterone feedback sensitivity was measured as the ability of testosterone propionate to decrease serum LH and FSH of long-term castrated (4 wk) rats under four different lighting conditions: periodic light (12L:12D), constant light (LL), constant darkness (DD), and dim night illumination (1 lx) with a 12L:12D photoperiod. Rats were exposed to the different lighting conditions for 1 wk, during which they received daily testosterone propionate (125 micrograms or 250 micrograms s.c.). At the end of the experiment the rats were decapitated at 1100 h, and serum gonadotropin levels were measured by RIA. Serum LH of the rats kept under LL was reduced to the level of the intact rats with the smaller testosterone dose (125 micrograms/day). Under all other lighting conditions only the large dose (250 micrograms/day) was able to restore the serum LH concentration to the level of the intact rats. Serum FSH was restored only partially, and the effect was the same with both doses and similar under all lighting conditions. We conclude that the increase in testosterone negative feedback sensitivity was not caused by the lack of periodicity of illumination alone, but that sufficient intensity of lighting throughout the 24 h was needed as well.

Background: Light treatment through the eyes is effective in alleviating the symptoms of some psychiatric disorders. A recent report suggested that skin light exposure can affect human circadian rhythms. Bilirubin can serve as a hypothetical blood-borne mediator of skin illumination into the brain. We studied whether bright light directed to a large body area could suppress the pineal melatonin secretion or decrease serum total bilirubin in conditions that could be used for therapeutic purposes. Methods: Seven healthy volunteers participated in two consecutive overnight sessions that were identical except for a light exposure on the chest and abdomen in the second night from 12:00 am to 6:00 am (10,000-lux, 32 W/m2 cool white for six subjects and 3000-lux, 15 W/m2 blue light for one subject). Hourly blood samples were collected from 7:00 pm to 7:00 am for melatonin radioimmunoassays. Bilirubin was measured by a modified diazo method in blood samples taken at 12:00 am and 6:00 am and in urine samples collected from 7:00 pm to 11:00 pm and from 11:00 pm to 7:00 am . Results: The skin light exposure did not cause any significant changes in serum melatonin or bilirubin levels. The excretion of bilirubin in urine was also the same in both sessions. Conclusions: Significant melatonin suppression by extraocular light does not occur in humans. Robust concentration changes of serum total bilirubin do not have a role in mediating light information from the skin to the central nervous system.

The view that light affects the mammalian circadian clock only through the eyes was recently challenged by a study in which the phases of human circadian rhythms were shifted by extraocular light exposure. This finding has not been confirmed, however. We studied the effects of light exposure (3 h, broad spectrum fluorescent white light, 13000 lux) on abdomen and chest on the circadian rhythms of serum melatonin, cortisol and thyrotropin in six subjects. The protocol consisted of two 3-day sessions in a dimly lit (< 10 lux) experimental unit. In both sessions hourly serum samples were collected for hormone analysis on days 1 and 3. The skin light exposure was delivered on day 2 from 22.00 to 01.00h in one of the two sessions in a randomized order. In both sessions all three rhythms tended to delay, presumably due to the endogenous circadian cycle length being slightly longer than 24 h. However, the phase shifts did not differ significantly between the sessions. Thus, the present study does not support the existence of extraocular photic regulation of the circadian rhythms in humans.

In order to clarify the role of light in regulating body functions in sleeping humans, we studied whether the light-sensitive pineal hormone melatonin can be suppressed by facial light exposure in subjects with closed eyelids.Eight healthy volunteers participated in 3 nightly sessions: a dim-light control session (10 lux) and two light-exposure sessions (2000 lux, 60 min between 2400 and 0200 h). One light exposure occurred with eyes open and the other with eyes closed. Saliva samples were collected at least every hour from 1900 to 0300 h. Melatonin concentrations were measured by radioimmunoassay.Salivary melatonin concentrations decreased only in 2 of the 8 volunteers during light-exposure sessions with eyes closed. On average, light exposure did not decrease the salivary melatonin concentration.Because indoor illuminance is usually much lower than 2000 lux, light is probably ineffective in regulating the neuroendocrine hypothalamic functions in people during their sleep. Nevertheless, the possibility remains that higher illuminances, often used for therapeutic purposes, can inhibit the secretion of melatonin even in sleeping patients.

Melatonin was tested as a sleeping pill in five patients with neuronal ceroid lipofuscinoses. The single-blind, placebo-controlled study consisted of motor activity recordings, sleep logs, and administration of placebo or melatonin (2.5 or 5 mg). Daily motor activity rhythms were measured by wrist actigraphy during four 7-day periods (baseline, placebo, melatonin 2.5 mg, and melatonin 5 mg). The placebo or melatonin was administered in the evenings for 3 weeks, and the recordings were made during the last week of the 3-week treatment. Sleep logs were kept by the caregivers during the recordings. Based on period analyses, the activity recordings were evaluated to display a normal (24-h) or fragmented rhythm. Three patients had normal motor activity patterns during the baseline recordings, and administration of placebo or melatonin did not affect their rest/activity rhythms. Two patients had abnormally fragmented activity rhythms during the baseline periods, and administration of placebo or melatonin did not induce synchronization. According to the actigraphic data, there were no changes in activity rhythms resulting from administration of melatonin. However, based on the observations, three families reported that melatonin slightly improved the sleep quality of the patients. These controversial findings show the difficulties involved in specifying the role of melatonin in modulating sleep. Thus, we conclude that more evidence is required before the significance of melatonin as a sleeping pill is defined.

We studied whether light information can reach the pineal glands of clinically blind patients with neuronal ceroid-lipofuscinoses. The suppression of melatonin by light was used as an indicator. Seven patients and seven control subjects were exposed to 3,000-lux light for 60 minutes at the rising phase of the melatonin synthesis. Most patients were not cooperative, and their eyelids were opened by a researcher every 2 minutes for 2 seconds. The control subjects opened and closed their eyes similarly by themselves. Light suppressed melatonin in three of seven control subjects and in all patients. The average postlight levels were 80% (control subjects) and 51% (patients) of the corresponding levels during the dim-light session. Despite degenerated retinas of the blind patients, light can penetrate their visual system to the hypothalamic and pineal levels and regulate neuroendocrine function.

The adjustment of pineal melatonin and locomotor activity rhythms to 10:10-h light:dark (LD) or 14:14-h LD cycles was studied in male Wistar rats. Both lighting conditions were thought to be outside the limits of entrainment of the rest-activity rhythm in this species. We assumed that the rhythm of pineal melatonin synthesis might be more adaptable. As expected, the locomotor activity rhythm was not adjusted to the 10:10-h LD cycles. Under these conditions, a free-running component (25 h) became dominant. Under the 14:14-h LD cycles, however, an unexpected adaptation occurred within 10 days. The profiles of the pineal melatonin contents measured on days 5 and 30 under the 10:10-h LD and on day 7 under the 14:14-h LD schedule were in line with the estimated free-running oscillations, but the profile on day 21 under the 14:14-h LD schedule was not. This melatonin pattern fitted the LD-adjusted activity rhythm. Thus, the melatonin rhythm did not adapt better than the activity rhythm to the exotic LD cycles. Instead, parallel changes were found.

We show that the pineal melatonin synthesis of rats can be uncoupled from the circadian regulation by exposing the animals to abnormally long light periods. Male rats were kept 7 days under 22.5 1.5- h light/dark conditions and then exposed to darkness at different times of the day. After a 60-min dark exposure, the melatonin synthesis increased independently of the time of the day (Expt. 1). During 22 h in darkness, the mean melatonin content did not return to the low daytime level (Expt. 2). A dark-induced, time-independent increase of melatonin was also found after the rats had been 3–7 days under constant light (Expts. 3 and 4).

Pineal melatonin is a putative humoral coordinator of various circadian body rhythms. Rather few loci in the brain contain such a density of melatonin receptors that specific binding can be demonstrated by autoradiography. In this study we measured, using in vitro receptor autoradiography, displaceable binding of iodomelatonin to the anteroventral and anterodorsal thalamic nuclei of Wistar rats (0.6–1.4 fmol/mg protein at 100 pM ligand concentration). These nuclei of the limbic system have direct connections with the retina and they participate in learning and memory functions.

Several studies in the late seventies characterized insensitivity to light as a feature of human melatonin synthesis. Later it has shown that bright light does suppress human melatonin secretion (Lewy et al. 1980). More recently it has been reported that even lower illuminances decrease the nighttime melatonin levels in humans (e.g. Bojkowski et al. 1987, McIntyre et al. 1989a). Technical and experimental differences may serve as an explanation for the deviating results. It is also possible that interindividual differences of sensitivity obtained from small groups of subjects distort the results. In the present preliminary study we attempted to find such individual differences.

Daily Melatonin Injections Have Only Minor Effects on Gonadotropins of Intact or Castrated Male Rats Kept Under Constant or Periodic Light Intact and castrated adult male Wistar rats were kept under constant or periodic (lights on 0600 and off 1800 h) light for 1 wk. During the study they received melatonin or saline injections daily either at 0900 or 1600 h. After each experiment, serum samples and the adenohypophyses were collected between 1000 and 1100 h and the gonadotropin concentrations were measured radioimmunologically. We had previously found changes in light sensitivity of the hypothalamo-pituitary axis of castrated rats and hypothesized that this axis could also involve changes in sensitivity to exogenous melatonin. However, the results of the present study do not support the hypothesis.

The mechanism by which laser phototherapy (Low Level Laser Therapy - LLLT) induces analgesia in the treatment of chronic pain is not understood. To investigate a possible role for opioids in this treatment, a double-blind, placebo-controlled study was designed to compare the effect of two dosages (1 J/cm and 5 J/cm ) of an infrared (IR) laser (820 nm), a visible red laser (670 nm) and a near-monochromatic light emitting device (660 nm, 30 nm bandwidth) on trigger points. Fifty-six consenting subjects with chronic pain conditions exhibiting myofascial trigger points in the neck and upper trunk region underwent six experimental sessions over a two week period. Blood samples were withdrawn before and after treatment on three of six appointments. Plasma was assayed for β-endorphin (radioimmunoassay, RIA) and adrenocorticotropic hormone (ACTH -two-site immunoradiometric assay, IRMA) to assess opioid response. ACTH was shown to have a cumulative response to treatment with a significant response to a 1 J/cm infrared laser (p < 0.001) and a 5 J/cm red laser (p < 0.05). β-endorphin was noted to be significantly elevated between days one and four (p < 0.05) in subjects who received IR (5 J/cm) laser therapy. Results indicated that the analgesic response to phototherapy may be mediated through hormonal/opioid mechanisms, and that responses to LLLT are dose and wavelength dependent. A mechanism is proposed by which peripheral stimulation using LLLT may elicit activity in the central pathways.

Plasma levels of TSH and thyroid hormones in 22 male and 27 female medical students were determined by radioimmunoassay before and after an academic examination. The plasma values of TSH were slightly higher in both sexes on the examination day than on the control days. The values were lower after the examination than before it in females but not in males. Plasma levels of T3 were higher in males than in females on the examination day. In contrast, the plasma rT3 values were higher for females on the examination day than on control days. The plasma levels of T4 were similar in both sexes. The results suggest that during psychic stress, the pituitary-thyroid endocrine system of the female reacts differently from that of the male.

Plasma levels of LH and FSH in male rats were compared in blood samples collected by decapitation or through permanently implanted aortic cannulae. The hormone levels were higher in the samples taken by decapitation. After cannulation, the gonadotropin levels remained unchanged when sampling occurred only once a day and each rat was bled 1-3 times over a period of 7 days (sample volume 2.3 ml). The hematocrits of these rats decreased from 42% to 34% after two samplings. In another experiment the LH and FSH levels increased when seven samples had been taken during 24 h. In this experiment the blood cells were reinfused into the circulation, and as a result after 5 samples the hematocrit decreased only from 45% to 40%. A drop in food consumption was observed after cannulation. It is suggested that the increase in gonadotropin levels may be due to the acute stress caused by handling during and before decapitation or decrease in gonadotropin levels may be due to the chronic stress caused by the implanted cannula. The frequent bleedings and cell infusions into the cannulated rats may stimulate the secretion of gonadotropins, opposing the effect of chronic stress.

The 24-h patterns of melatonin, PRL, and gonadotropins in male rats maintained under natural lighting conditions have been found to differ from the patterns in rats kept under artificial lighting. In the present experiments we studied the role of different daily illuminances as a possible causative factor for the variation of the hormonal patterns. Three groups of male rats were kept under artificial lighting conditions (12 h on/12 h off), where the daily illuminance was 550, 110 or 25 lux. After a 7-day adaptation period the pineal content of melatonin, the serum levels of LH, FSH and PRL, and the pituitary content of these hormones were measured by RIAs in samples taken at 10.00, 13.00, 22.00 and 01.00 h. The patterns of pineal melatonin were equal in all three groups. The variation of daily illuminance did not change the serum levels of LH, FSH and PRL or the pituitary content of the gonadotropins. However, the pituitary content of PRL during the light phase was inversely related to the illuminance. The results suggest that the intensity of daily lighting in the studied range does not affect the patterns of melatonin or gonadotropins, but the synthesis of prolactin may be significantly regulated by the daily illuminance level.

We studied the role of nocturnal illuminance as a possible regulatory factor in the production and secretion of reproductive hormones. Adult male rats were kept under artificial lighting conditions (LD 12/12 hours) where the daily illuminance was 520-550 lx and the nocturnal illuminance 0, less than 0.1, or 1-1.5 lx. After a 7 day adaptation period, the pineal contents of melatonin, the serum levels of LH, FSH, and prolactin, and the pituitary contents of these hormones were measured by radioimmunoassay in samples taken 4 and 7 hours after the onset of light and onset of darkness. When the rats were kept in full darkness or under the minimal nocturnal iluminance (less than 0.1 lx), the patterns of pineal melatonin were equal. When nocturnal illuminance was 1-1.5 lx, the pineal melatonin contents at night were lower than in complete darkness. However, this illuminance level did not totally abolish the nocturnal increase of melatonin synthesis. The serum levels of LH, FSH, and prolactin were all affected by the increase of nocturnal illuminance so that the difference between the daytime and nighttime levels increased (higher values during the night). The variation of nocturnal illuminance did not change the pituitary contents of gonadotropins. The effects on pituitary prolactin were negligible as well. The results are interpreted to support the concept that nocturnal illuminance levels may regulate the secretion of the studied hormones in male rats.

Neonatally androgenized and intact adult male Wistar rats received daily, during 1 week, either testosterone propionate or sesame oil injections in periodic or constant light. Serum and pituitary gonadotropins and hypothalamic LHRH were measured. In periodic light, neonatal androgenization did not change the serum concentration or pituitary contents of gonadotropins, or the hypothalamic content of LHRH. Testosterone injections decreased serum concentration and pituitary content of gonadotropin of intact rats but failed to decrease the pituitary gonadotropin content of neonatally androgenized rats. In constant light, serum FSH was decreased in neonatally androgenized rats. Testosterone injections decreased both serum LH and FSH concentrations of intact rats but only serum LH of androgenized rats. Pituitary gonadotropin and hypothalamic LHRH contents remained unchanged. We conclude that neonatal androgenization renders the male rat hypothalamo-pituitary axis more resistant to changes of testosterone concentration in adulthood. Constant light did not sensitize the neonatally androgenized rats to testosterone, but on the contrary, testosterone injections were less effective in constant than in periodical light.

Recently nighttime melatonin levels have been shown to be attenuated in depressive patients or patients with dementia of the Alzheimer type. On the other hand, depression can be transiently relieved by deprivation of rapid eye movement sleep. Since exogenous melatonin administration increases rapid eye movement sleep and slow wave sleep in the rat, could rapid eye movement sleep deprivation then inversely influence endogenous melatonin production? We found indices that in castrated Wistar rats 4 days of rapid eye movement sleep deprivation by the cuff pedestal method elevates the pineal content of melatonin by a factor of two at 1 to 2 h after light onset. Rapid eye movement sleep is thus suggested to influence pineal activity. This mechanism might be involved in the human depression-alleviating effect of rapid eye movement sleep deprivation.

It has been shown in the Syrian hamster that a short photoperiod sensitizes the hypothalamo-hypophyseal axis of castrated animals to the negative feedback effect of testosterone. There is some evidence that even the reproductive system of the rat, which is generally considered not to be very sensitive to light, can respond to changes in illumination. Therefore, we found it of interest to examine whether alterations in lighting conditions produce changes of sensitivity in the negative feedback effect of testosterone in the rat. We kept intact, castrated, and castrated testosterone-treated animals either in periodic (L:D 12:12) or constant light for 7 days starting 4 weeks after castration. In all 3 testosterone-injected groups, serum luteinizing hormone (LH) was lower in constant than in periodic light. Exogenous testosterone did not decrease the castration-induced elevations of pituitary LH and follicle-stimulating hormone (FSH). On the contrary, testosterone increased the pituitary contents of LH and FSH, especially in constant light. We conclude that, in constant light, the hypothalamo-hypophyseal axis of the castrated rat becomes more sensitive to the negative feedback action of testosterone.

In castrated Wistar rats four days of Rapid Eye Movement sleep (REMs) deprivation by the cuff pedestal method induced decrements in plasma LH and FSH. The adenohypophyseal levels of these hormones were decreased in the REMs-deprived rats and in the control rats kept on pedestals with the supporting cuff in the elevated position as compared with the home-cage control rats. The results are discussed in terms of regional brain metabolic activity and transmission.

Natural lighting differs from usual artificial lighting mainly as follows: it has larger spectral composition, fluctuations of intensity during the day, higher intensity levels during the night (moonlight, starlight), and gradual changes of illuminance at dawn and dusk. The present experiment was performed in order to study whether these features of lighting affect the 24-hour patterns of melatonin and prolactin in male rats. The rats were kept 7 days in 'natural' lighting (sunlight through windows) or in artificial lighting (cool white fluorescent lamps) of similar periodicities (13/11 h light/dark). The samples were collected at 3-hour intervals during a 24-hour period. Pineal melatonin contents, pituitary prolactin contents, and plasma prolactin concentrations were measured radioimmunologically. The nocturnal pineal melatonin contents were higher and the daytime contents lower in natural than in artificial lighting conditions. A corresponding 'strengthening of rhythm' of prolactin was found in natural lighting. A reason for the higher amplitude variation of melatonin in the natural lighting conditions may be the gradual changes of illuminance at dawn and dusk. The different pituitary and plasma prolactin patterns of the rats kept in the two lighting conditions might partly be explained by a stimulatory effect of melatonin on the production and secretion of prolactin, but other regulatory factors had to be involved, too.