Change in duration of elevated concentrations of melatonin is the major factor in photoperiod response of the tammar, Macropus eugenii

In Exp. 1, 10 quiescent non-lactating tammars were exposed to 15L:9D (Days -41 to -1), 24L:0D (Days 0 to 14), 15L:9D (Days 15 to 34) and then to ambient increasing daylength from 13L:11D on Day 35. From Days 0 to 22 they received a s.c. injection of melatonin (400 ng/kg, N -5) on the arachis oil vehicle (N = 5) in the evening (19:30 h) 2.5 h before dark. Exposure to 24L:0D abolished the nocturnal plasma melatonin rise but this was reinstated by subsequent exposure to 15L:9D. Of 5 melatonin-treated tammars, 4 gave birth on Day 45, so had failed to respond to the melatonin injection alone but reactivated when this was combined with the endogenous melatonin rise during exposure to 15L:9D. Of 5 control tammars, 4 remained quiescent until reactivated by the decrease in daylength to 13L:11D, and gave birth significantly later (Day 63.7 +/- 2.2, mean +/- s.e.m., P less than 0.05). In Exp. 2, 6 tammars were exposed to 15L:9D (Days -15 to -1) and then to 12L:12D (Days 0 to 15) by extending the dark phase by 3 h in the morning. This extended the nocturnal melatonin rise by 2-3 h in the morning and all 6 tammars gave birth on Day 31.2 +/- 1.0. A transient pulse of peripheral plasma prolactin (81.5 +/- 31.0 ng/ml) was detected at dawn during 15L:9D in all 6 tammars but was not observed in any of them 5 days after exposure to 12L:12D. Together these results do not support the time of day hypothesis but indicate that increase in duration of the nocturnal melatonin rise mediates the effects of decreased daylength on reactivation of the corpus luteum, and that the first detectable result of this may be the abolition of a transient prolactin pulse at the end of the dark phase.     

Concentrations of plasma melatonin and luteinizing hormone in domestic gilts reared under artificial long or short days.

Plasma melatonin concentrations were measured every 1-2 h over 24 h and plasma luteinizing hormone (LH) concentrations every 15 min over 12 h in domestic gilts reared under artificial light regimens that had previously been used to demonstrate photoperiodic effects on puberty. In Expt 1, the light regimens both commenced at 12 h light: 12 h dark (12L:12D) and either increased (long-day) or decreased (short-day) by 15 min/week until the long-day gilts were receiving 16L:8D and the short-day gilts 8L:16D at sampling. In Expt 2, both light regimens commenced at 12L:12D and either increased (long-day) or decreased (short-day) by 10 or 15 min/week to a maximum of 14.5L:9.5D or a minimum of 9.5L:14.5D before being reversed. Sampling took place when daylength had returned to 14L:10D (long-day) or 10L:14D (short-day). In immature gilts housed at 12L:12D (Expt 1) and in postpubertal (Expt 1) and prepubertal (Expt 2) gilts reared under long-day or short-day light regimens, mean plasma melatonin concentrations were basal (3.6 pg/ml) when the lights were on and increased to peak concentrations greater than 15 pg/ml within 1-2 h after dark, before declining gradually to basal concentrations at or near the end of the dark phase. In prepubertal gilts bearing subcutaneous melatonin implants and reared under long-days (Expt 2), mean plasma melatonin concentration in the 6 h before dark was 91.9 +/- 5.26 pg/ml and 125.0 +/- 6.66 pg/ml 1 h after dark, but this increase was not statistically significant. In Expt 2, the short-day gilts had fewer LH pulses (2.6 +/- 0.25 vs. 4.6 +/- 0.24; P less than 0.01) in the 12-h sampling period than the long-day gilts, but the amplitude of the pulses (2.28 +/- 0.23 vs. 1.26 +/- 0.16 ng/ml; P less than 0.01) and the area under the LH curve (78.8 +/- 5.60 vs. 47.3 +/- 6.16; P less than 0.01) was greater in the short-day gilts. In the short-day, but not in the long-day, gilts LH pulses were more frequent (2.0 +/- 0.0 vs. 0.6 +/- 0.25; P less than 0.01), but had a smaller area (61.9 +/- 7.2 vs. 120.2 +/- 23.6; P less than 0.05) in the 6 h of dark than in the 6 h of light, which together made up the 12-h sampling period.(ABSTRACT TRUNCATED AT 400 WORDS)     

Geographic differences for delay of sexual maturation in Peromyscus leucopus: effects of photoperiod, pinealectomy, and melatonin

Effects of short-day photoperiod, pinealectomy, and melatonin on sexual maturation were tested in Peromyscus leucopus from either Connecticut (CT) or Georgia (GA). Laboratory reared-stocks from CT and GA were exposed to short daylength (photoperiod) from birth or 25 days of age. At 12 wk of age, delay in sexual maturation was indicated in most CT mice by decreased testis length, combined testes weight, and seminal vesicle weight. Conversely, GA animals did not delay sexual maturation when exposed to short-day photoperiod from either birth or 25 days of age. These results indicate that responses to short daylengths differ for juvenile CT and GA populations. In a second experiment, pinealectomized or sham-operated CT males were exposed to short-day (9L:15D) or long-day (16L:8D) photoperiod from birth. Pinealectomy blocked the effect of short daylength on reproduction. Therefore, the pineal must be involved in the delay of sexual maturation observed for short-day CT mice. The effects of melatonin, a pineal gland hormone, were tested with chronic s.c. implants or daily injections. In CT mice given either melatonin implants or afternoon injections, sexual maturation was delayed. GA mice were insensitive to all melatonin treatments. Further, no differences in circadian organization (phase angle, duration of activity, period under constant dark) between GA and CT animals were apparent. Collectively, these studies indicate that melatonin is involved in the mechanism responsible for delay of sexual maturation in CT mice. Short-day insensitivity of GA Peromyscus leucopus probably results from a deficiency in the melatonin effector pathway and is not due to a disruption of circadian organization.     

Light/dark patterns of interleukin-6 in relation to the pineal hormone melatonin in patients with acute myocardial infarction

AIMS: Atherosclerosis is a chronic disease that, from its origin to its ultimate complications, involves inflammatory cells, inflammatory proteins, and inflammatory responses from vascular cells. It has been demonstrated that cytokine activities are under neuroendocrine control, in part exerted by the pineal gland through the circadian secretion of its main product melatonin. Melatonin is mainly released during the night, but the precise relationship between melatonin and the light/dark rhythm of interleukin-6 in patients with acute myocardial infarction is still unclear. METHODS AND RESULTS: The study included 60 patients diagnosed with acute myocardial infarction and 60 healthy volunteers whose venous blood samples were collected at 09:00 h (light period) and 02:00 h (dark period). Our results demonstrate that interleukin-6 concentrations presented a light/dark pattern with mean serum concentrations being higher in the acute myocardial infarction group than in the control group (101.26 +/- 13.43 and 52.67 +/- 7.73 pg/ml at 02:00 h, 41.93 +/- 5.90 and 22.98 +/- 4.49 pg/ml at 09:00 h, respectively, p < 0.05). Differences in the day/night changes in melatonin levels in control subjects (48.19 +/- 7.82 at 02:00 h, 14.51+/- 2.36 at 09:00 h, pg/ml) and acute myocardial infarction patients (25.97 +/- 3.90 at 02:00 h, 12.29 +/- 4.01 at 09:00 h, pg/ml) (p < 0.05) were a result of a reduced nocturnal elevation of melatonin in the acute myocardial infarction group. CONCLUSIONS: The current findings suggest that the circadian secretion of melatonin may be responsible at least in part for light/dark variations of endogenous interleukin-6 production in patients with acute myocardial infarction. In this study, the melatonin seems to have an anti-inflammatory effect.     

Influence of melatonin on the testicular regression induced by subcutaneous testosterone pellets in male rats kept in long or short photoperiod

Daily afternoon injections of 25 micrograms melatonin for 12 weeks had no effect on testicular weights of male rats kept in long photoperiod (14L:10D); similarly, exposure of rats to short photoperiod (2L:22D) had no effect on gonadal weight. However, rats maintained in a long or short photoperiod and implanted every 2 weeks with a 15 mm Silastic pellet containing testosterone showed a significant reduction in testicular weight; this effect was more pronounced in rats exposed to a short photoperiod. Melatonin injections in testosterone-treated rats in a long photoperiod exacerbated the inhibitory effects of testosterone alone. Subcutaneous 2-weekly implants of a beeswax pellet containing 1 mg melatonin reversed the effects of the melatonin injections on relative testicular weights but not those due to short photoperiod exposure. Testosterone implants significantly reduced pituitary LH values in long and short photoperiod-exposed animals, more particularly in those exposed to short photoperiod. Melatonin injections alone or in combination with melatonin pellets did not further exaggerate the depression in pituitary LH due to testosterone alone in long photoperiod-exposed animals; similarly melatonin pellets did not reverse the depression in pituitary LH observed. No significant differences in plasma prolactin concentrations or in thyroxine concentrations or free thyroxine index were observed after any combination of treatments. We therefore suggest that the effects observed with short photoperiod may be due to melatonin.     

Effect of maternal pinealectomy and reverse photoperiod on the circadian melatonin rhythm in the sheep and fetus during the last trimester of pregnancy

The present study tested the hypothesis that the nocturnal melatonin rhythm in the fetal sheep results from transfer across the placenta of melatonin from maternal circulation. Pregnant ewes were exposed to an artificial reverse photoperiod at about 100 days gestation (n = 6; lights on 10 h, 2200-0800 h PST). This treatment tested for entrainment in the ewe and its fetus of the 24-h pattern of melatonin production from the pineal gland. Other ewes were pinealectomized at 55 days post-breeding (n = 6), and similarly treated. Catheters were implanted and blood samples were collected between 117 and 142 days gestation at two 48-h periods, about every 0.5-4 h, to assess the pattern of melatonin in maternal and fetal circulations. In pineal-intact ewes and their fetuses, melatonin rhythms conformed to the reverse photoperiod, i.e. plasma melatonin concentrations were relatively low during the light period and significantly increased for the duration of darkness. In contrast, maternal pinealectomy abolished the melatonin rhythms in both the ewe and fetus; melatonin concentrations remained at or below the limits of detection. Pineal-intact sheep gave birth about 139 +/- 2 days (mean +/- SE, n = 4) at 1915 +/- 0.7 h and pinealectomized ewes (n = 5 of 6) lambed at 149 +/- 2 days at 0424 +/- 0.5 h. Finally, in lambs (n = 3) born to pinealectomized ewes, typical melatonin rhythms were present within the first week of life. The findings indicate that the maternal pineal gland is responsible for the 24-h pattern of melatonin in the ewe and its fetus during the last trimester of pregnancy.     

Maternal plasma catecholamines in the rhesus macaque during late gestation: effect of photoperiod and timed melatonin infusion.

This study tested the hypothesis that changes in photoperiod alter plasma catecholamine concentrations in the rhesus monkey during late gestation. Twelve chronically catheterized pregnant rhesus macaques were acclimated to a 12-h photoperiod (lights-on, 0700-1900 h). Under the control L:D cycle, blood samples were collected at 3-h intervals over 24 h for catecholamine analysis. Plasma concentrations (mean +/- SEM, pg/ml) ranged from 678 +/- 90 to 928 +/- 142 for norepinephrine; 230 +/- 22 to 631 +/- 141 for epinephrine; and 282 +/- 70 to 1090 +/- 362 for dopamine. A diurnal rhythm was observed in epinephrine with peak concentrations during lights-on (0900-1800 h; p less than 0.05, compared to lights-off). After the first sampling protocol, the animals were divided equally between two groups: phase shift, in which lights-on was shifted 11 h (2000-0800 h) and constant light, with lights on continuously. After the phase shift, a parallel shift in the plasma epinephrine rhythm was noted, with peak levels observed between 2200 and 0700 h (p less than 0.05). Constant light abolished the rhythm in epinephrine, with an overall reduction in mean basal levels of all three catecholamines. Daily melatonin infusions (0.2 micrograms/kg/h, 1900-0630 h) under constant light failed to restore the epinephrine rhythm or to return basal catecholamine concentrations to control photoperiod levels. These data suggest that photoperiod entrains the rhythm in epinephrine secretion, but the rhythm is ablated under constant conditions. Further, melatonin does not appear to play a role in the regulation of catecholamine secretion in the pregnant rhesus macaque.     

Reproductive photorefractoriness in rams and accompanying changes in the patterns of melatonin and prolactin secretion

Exposure of rams to alternating 16-week cycles of long and short days (16L:8D and 8L:16D) results in periods of testicular regression followed by testicular redevelopment, and there is an inverse relationship between the blood levels of prolactin and testis activity. In this study, two groups of rams were held under long or short day lengths for a period of 94 weeks. When held under either long or short days for more than 16 weeks, the animals showed spontaneous changes in gonadal activity and in the secretion of prolactin, both of which were no longer correlated with the prevailing photoperiod, i.e., they became photorefractory. The photorefractoriness was characterized by cyclical changes in testis function which were independent of day length. The period of these spontaneous cycles was similar during both treatment regimens (long days: 40.9 +/- 1.5 weeks; short days: 38.1 +/- 0.33 weeks), suggesting the presence of an endogenous pacemaker for the reproductive system. The changes in blood prolactin levels during photorefractoriness were no longer correlated with testis activity, and though cyclical, the period lengths differed under the two regimens (long days: 31.8 +/- 1.4 weeks; short days: 48.6 +/- 0.3 weeks). The rates of change in testis function and prolactin secretion were slower during the refractory state than during the photosensitive state. Upon switching the rams to a different photoperiod after the 94 weeks of exposure to fixed day lengths, the rams showed relatively rapid testicular and prolactin responses. Photoperiodic information appears to be relayed to the endocrine system through the daily pattern of melatonin secretion by the pineal. We measured the daily blood levels of melatonin on several occasions during phases of photosensitivity and photorefractoriness in the same group of rams. During the first 21 weeks under both lighting treatments, the rams showed synchronized daily patterns in their blood levels of melatonin, with elevated levels occurring mainly during the daily period of darkness. Similar synchronized daily rhythms were also seen when the rams were switched to a different photoperiod following 94 weeks of exposure to either long or short days. Between Weeks 21 and 94, the daily rhythms of melatonin did not occur consistently in all rams; often, the patterns differed markedly between individual rams held under the same day length and peak levels of melatonin were not always confined to periods of darkness.(ABSTRACT TRUNCATED AT 400 WORDS)     

Photoperiod, melatonin secretion, and sexual maturation in a tropical rodent

Descendants of a sample of cane mice (Zygodontomys brevicauda) trapped at 8 degrees latitude in Venezuela were tested for reproductive photoresponsiveness. This species breeds continuously, year around, despite living in a seasonally harsh habitat. At 50 days of age there were no differences in the weights of the testes or seminal vesicles or in sperm counts of males born and reared on 16L:8D, 13L:11D, 11L:13D, or 8L:16D photoperiods, although there were small differences in body weight. Females born and reared on 16L:8D vs. 8L:16D cycles became pregnant at the same rates and ages when paired with males at 21 or 31 days of age. The daily duration of melatonin secretion depended on the length of the dark phase of the cycle in both sexes. Circulating levels of melatonin were elevated for 8 h on a 16L:8D cycle and for between 9 and 16 h on an 8L:16D cycle. In this tropical species, the neuroendocrine pathway that links photoperiod to reproduction apparently is disconnected somewhere between melatonin and gonadotropin secretion, causing cane mice to be reproductively unresponsive to variation in photoperiod.     

Morning pulse of prolactin maintains seasonal quiescence in the tammar, Macropus eugenii

The pulse of prolactin, present in female tammars kept in an inhibitory photoperiod and absent 5 days after a change to a stimulatory photoperiod, was artificially maintained during stimulatory photoperiods (Exps 1A and 1B) or abolished during an inhibitory photoperiod (Exp. 2). In Exp. 1A, thyrotrophin-releasing hormone (TRH) was injected i.v. for 8 consecutive mornings and in Exp. 1B ovine prolactin was injected i.v. for 10 consecutive mornings beginning on the day the photoperiod was changed from 15L:9D to 12L:12D. In Exp. 1A, in 5 of 6 control females the prolactin pulse was present until the 3rd morning after the lighting was changed, and absent thereafter. In both experiments the early progesterone peak and the interval to birth in the treated females was significantly delayed compared to the control females; reactivation of the CL did not occur until treatment ceased. In Exp. 2, for 5 consecutive mornings, before the prolactin pulse was expected to occur, bromocriptine was injected i.m. In 2/4 treated animals the prolactin pulse was abolished and these animals showed an early progesterone peak and gave birth 28 and 29 days after treatment began. The remaining 2 animals and the controls (N = 4) did not show reactivation until after they experienced a stimulatory photoperiod. The results indicate that the prolactin pulse is the critical factor in the maintenance of the inhibition of the CL of the tammar during seasonal quiescence.     

Effects of haloperidol and melatonin on the in situ activity of nigrostriatal tyrosine hydroxylase in male Syrian hamsters

Haloperidol, an antipsychotic drug, was tested for its effects on the in situ activity of nigrostriatal and hypothalamic tyrosine hydroxylase, in control male Syrian hamsters and in those receiving a high daily dose of melatonin. After receiving daily ip injections (1.25 mg/kg ip) of haloperidol for 21 days, the animals were sacrificed and brain tissue collected for analysis of dopamine and metabolites by HPLC with electrochemical detection. In situ activity of tyrosine hydroyxlase (TH) activity was determined by measuring the accumulation of L-Dopa after administration of the L amino acid decarboxylase inhibitor, mhydroxybenzylhydrazine. Tissue content of dopamine and its metabolites, DOPAC and HVA, was depressed in striatum of animals receiving haloperidol, and tyrosine hydroxylase (TH) activity was significantly decreased 20-24 h after the last injection (from 1823 +/- 63 to 1139 +/- 85 pg l-dopa/mg tissue). The decrease in TH activity in striatum was significantly inhibited by daily injections of a high dose of melatonin (2.5 mg/kg ip) (from 1139 +/- 85 to 1560 +/- 116 pg L-dopa/mg tissue). In the substantia nigra and in the hypothalamus, on the other hand, haloperidol significantly increased the activity of tyrosine hydroxylase. Melatonin administration did not significantly influence TH activity in the substantia nigra, but inhibited TH activity in the hypothalamus and in the pontine brainstem. One explanation for these data is that chronic haloperidol administration in Syrian hamsters increases TH activity in hypothalamus and substantia nigra, but decreases TH activity in striatum by a mechanism involving D2 presynaptic receptors and a melatonin sensitive kinase which regulates TH phosphorylation.     

A comparison of the efficiency of melatonin treatments in advancing oestrus in ewes

Early oestrous cycles were induced in adult, maiden, 18-month-old Suffolk-cross ewes, maintained from birth in natural photoperiod by the following treatments applied from mid-June: subcutaneous implantation of melatonin (1 g) in Silastic packets, daily, oral, melatonin administration (3 mg/ewe) at 15:30 h, an artificial photoperiod of 8L:16D (lights on 07:30 h). Ovarian cycles began 5-10 weeks before those of control ewes maintained in a natural photoperiod. In contrast, the onset of ovarian cycles in ewes given s.c. implants of melatonin (1 g) in April, and a further group in May, was highly variable, and not significantly different from that of the control ewes. Plasma melatonin profiles in sheep with implants showed a night-time rise super-imposed on a constant level, which was itself within the physiological night-time range. Implant-derived melatonin declined with time but remained at or above physiological night-time levels for at least 3 1/2 months. These results indicate that melatonin implants in June, but not in April or May, advance onset of oestrus in the non-lactating, adult ewe. The effects of melatonin implants in June on onset of ovarian cycles were indistinguishable from those of melatonin feeding or artificial short photoperiod initiated at this time of year.     

A 15-minute light pulse during darkness prevents the antigonadotrophic action of afternoon melatonin injections in male hamsters

When adult male Syrian hamsters were maintained under 14 h light and 10 h darkness daily (lights on from 0600-2000 h), peak pineal melatonin levels (705 pg/gland) were attained at 0500 h. When the dark phase of the light:dark cycle was interrupted with a 15 min pulse of light from 2300–2315 h (3 h after lights out), the highest melatonin levels achieved was roughly 400 pg/gland. Finally, if the 15 min pulse of light was given at 0200–0215 h (6 h after lights out) the nocturnal rise in pineal melatonin was completely abolished. Having made these observations, a second experiment was designed to determine the ability of afternoon melatonin injections to inhibit reproduction in hamsters kept under an uninterrupted 1410 cycle or under the same lighting regimen where the dark phase was interrupted with a 15 min pulse of light (0200–0215 h). In the uninterrupted light:dark schedule the daily afternoon injection of 25 g melatonin caused the testes and the accessory sex organs to atrophy within 11 weeks. Conversely, if the dark phase was interrupted with light between 0200–0215 h, afternoon melatonin injections were incapable of inhibiting the growth of the reproductive organs. The findings suggest that exogenously administered melatonin normally synergizes with endogenously produced melatonin to cause gonadal involution in hamsters.     

Effect of photoperiod on LH, FSH, prolactin and melatonin patterns in ovariectomized prepubertal heifers

Angus and Angus crossbred prepubertal heifers were ovariectomized and randomly assigned to either increasing light simulating the photoperiod of the vernal equinox to the summer solstice (I) or decreasing light simulating the photoperiod of the autumnal equinox to the winter solstice (D) for 43 degrees N latitude. Three blood samples were taken each week for 14 weeks, the first at 11:00 h and two others 2 days later, 1 h before lights on (dark), 1 h before lights off (light). At the end of 14 weeks 4 heifers from each treatment group were cannulated and samples were taken for 12 h at 15-min intervals, 6 h in the light and 6 h in the dark. All sera were assayed for LH, FSH and prolactin. In addition, the samples taken at 15-min intervals were assayed for melatonin. In samples taken weekly at 11:00 h circulating concentrations of LH and prolactin were higher among animals in Group I, while FSH concentrations were not different between Groups D and I. In samples collected weekly in the light or the dark, LH and prolactin concentrations were higher in Group I animals. However, prolactin concentrations were higher and LH concentrations tended to be higher in samples taken in the dark. FSH concentrations were not different between either D or I or dark and light. In samples taken at 15-min intervals the prolactin baseline was higher and pulse amplitude tended to be higher for Group I animals. Neither LH nor FSH pulse characteristics differed between I and D; however, LH baseline and LH pulse amplitude were higher in the dark. Melatonin pulse amplitude was higher among animals in Group D and higher in serum collected in the dark. These results suggest that photoperiod alters circulating concentrations of LH and prolactin and alters pulsatile release of LH, prolactin and melatonin in the prepubertal heifer.     

Clock-controlled endogenous melatonin rhythms in Nile tilapia (Oreochromis niloticus niloticus) and African catfish (Clarias gariepinus)

The purpose of this work was to investigate the circadian melatonin system in two tropical teleost species characterized by different behavioral habits, Nile tilapia (diurnal) and African catfish (nocturnal). To do so, fish were subjected to either a control photoperiod (12L:12D), continuous light (LL) or darkness (DD), or a 6L:6D photoperiod. Under 12L:12D, plasma melatonin levels were typically low during the photophase and high during the scotophase in both species. Interestingly, in both species, melatonin levels significantly decreased prior to the onset of light, which in catfish reached similar basal levels to those during the day, demonstrating that melatonin production can anticipate photic changes probably through circadian clocks. Further evidence for the existence of such pacemaker activity was obtained when fish were exposed to DD, as a strong circadian melatonin rhythm was maintained. Such an endogenous rhythm was sustained for at least 18 days in Nile tilapia. A similar rhythm was shown in catfish, although DD was only tested for four days. Under LL, the results confirmed the inhibitory effect of light on melatonin synthesis already reported in other species. Finally, when acclimatized to a short photo-cycle (6L:6D), no endogenous melatonin rhythm was observed in tilapia under DD, with melatonin levels remaining high. This could suggest that the circadian clocks cannot entrain to such a short photocycle. Additional research is clearly needed to further characterize the circadian axis in teleost species, identify and localize the circadian clocks, and better understand the environmental entrainment of fish physiology.     

Entrainment of the melatonin rhythms in early postnatal lambs and their mothers

Although the developing sheep can produce an appropriately timed melatonin rhythm as early as 1 week after birth, it is not known whether the lamb is able to adjust its melatonin rhythm to a change in daylength. The ability of the young lamb to entrain its pattern of melatonin secretion to a new photoperiod was determined in the present study. Eight female lambs and their mothers were raised in long days (LD 16:8) beginning 2 weeks postpartum. At 7 weeks of age, the time of lights-off was advanced 8 hr, the short-day photoperiod then being LD 8:16; the time of lights-on remained unchanged. Concentrations of melatonin were measured in blood samples collected hourly on days - 1, 0, 2, 4, 6, and 13 relative to the light change. On day 0, all mothers and daughters had advanced the onset of melatonin secretion by at least 1 hr, and by day 13, 12 of 16 had completely entrained to the new photoperiod. The rate of entrainment among individuals varied; the mean rate for lambs and mothers did not differ. This study provides evidence that the melatonin-rhythm-generating system matures shortly after birth.     

Radioimmunoassay of melatonin: human serum and cerebrospinal fluid

Using a newly characterized anti-melatonin serum it has been possible to establish human serum melatonin concentrations at short time intervals during 24h. A clear circadian rhythm with peak values during the dark phase was demonstrated in both men and women. Values (pg/ml;mean +/- SE) were as follows: females 02.00h: 130 +/- 7, 18.00h: 45 +/- 5 males 02.00h: 140 +/- 11, 18,00H: 70 +/- 5. The estimation (pg/ml; mean +/- SE) of melatonin in human serum (males: 63 +/- 22 and females: 100 +/- 45) and cerebrospinal fluid simultaneously taken has shown that melatonin is lower in cerebrospinal fluid (males: 59 +/- 33 and females: 57 +/- 28). Blanks are not subtracted.     

Photomanipulation of sexual maturation and breeding cycle of the steppe polecat (Mustela eversmanni) and other techniques for more rapid propagation of the species

Twenty steppe polecats were divided into 2 groups, each consisting of 4 males and 6 females, and subjected to either a natural photoperiod (controls) or alternating periods of short (8 h light/16 hr dark for 8-9 weeks) and long days (16 h light/8 h dark for 16-20 weeks). The experimental photoperiod significantly accelerated sexual maturation in both sexes, with males developing maximal testis size within 57 days and females breeding after an average of 52 days exposure to 16L/8D. Males in the experimental group completed 2 1/2 testicular cycles and participated in mating during 3 successive breeding seasons during the 18 month period whereas males in the control group completed a single testicular cycle and only had an opportunity to mate during a single breeding season. Females in the experimental group produced 3 litters whereas females in the control group only gave birth to a single litter. Litter size averaged 6.9 +/- 2.0 (n = 23) and did not significantly differ with age, parity, or treatment. Pseudopregnant females returned to estrus within 12 days after the expected date of parturition, were bred, and gave birth to kits. Polecats which were subjected to the experimental photoperiods completed more molting cycles and underwent more photoperiod-induced changes in body weight than those in the control group. Death or removal of kits within 8 days after birth resulted in 12/12 females returning to estrus within 6-26 days. Eleven of these females were remated and gave birth to kits. Eight domestic ferrets readily accepted neonatal polecat kits and 5 successfully reared kits, although kit survival was quite poor.(ABSTRACT TRUNCATED AT 250 WORDS)     

Functional similarity in relation to the external environment between circadian behavioral and melatonin rhythms in the subtropical Indian weaver bird

The present study investigated whether the circadian oscillators controlling rhythms in activity behavior and melatonin secretion shared similar functional relationship with the external environment. We simultaneously measured the effects of varying illuminations on rhythms of movement and melatonin levels in Indian weaver birds under synchronized (experiment 1) and freerunning (experiment 2) light conditions. In experiment 1, weaverbirds were exposed to 12h light: 12h darkness (12L:12D; L = 20 lx, D = 0.1 lx) for 2.5 weeks. Then, the illumination of the dark period was sequentially enhanced to 1-, 5-, 10-, 20- and 100 lx at the intervals of about 2 to 4 weeks. In experiment 2, weaver birds similarly exposed for 2.5 weeks to 12L:12D (L = 100 lx; D = 0.1 lx) were released in constant dim light (LL(dim), 0.1 lx) for 6 weeks. Thereafter, LL(dim) illumination was sequentially enhanced to 1-, 3- and 5 lx at the intervals of about 2 weeks. Whereas the activity of singly housed individuals was continuously recorded, the plasma melatonin levels were measured at two time of the day, once in each light condition. The circadian outputs in activity and melatonin were phase coupled with an inverse phase relationship: melatonin levels were low during the active phase (light period) and high during the inactive phase (dark period). This phase relationship continued in both the synchronized and freerunning states as long as circadian activity and melatonin oscillators subjectively interpreted synchronously the daily light environment, based on illumination intensity and/or photophase contrast, as the times of day and night. There were dissociations between the response of the activity rhythms and melatonin rhythms in light conditions when the contrast between day and night was much reduced (20:10 lx) or became equal. We suggest that circadian oscillators governing activity behavior and melatonin secretion in weaverbirds are phase coupled, but they seem to independently respond to environmental cues. This would probably explain the varying degree to which the involvement of pineal/melatonin in regulation of circadian behaviors has been found among different birds.     

Role of the pituitary gland in the development of photorefractoriness and generation of long-term changes in prolactin secretion in rams

Hypothalamo-pituitary disconnected Soay rams were exposed to two photoperiodic treatments: 1) constant long days (16L:8D) for 48 wk after pretreatment under short days (LD group), and 2) constant short days (8L:16D) for 48 wk after pretreatment under long days (SD group). In the LD group, plasma prolactin (PRL) concentrations increased from 0 to 8 wk (maximum: 143.3 +/- 8.4 microg/l; 8.8 +/- 1. 2 wk), decreased from 9 to 34 wk (minimum: 15.6 +/- 1.6 microg/l; 34. 5 +/- 1.5 wk), and finally increased again under the constant conditions, with a similar cyclical pattern for all individuals. In the SD group, PRL concentrations showed an inverse pattern (minimum: 8.6 +/- 2.6 microg/l; 17.1 +/- 2.0 wk; maximum: 46.4 +/- 5.5 microg/l; 30.2 +/- 3.2 wk), with more variability. Plasma concentrations of FSH were basal in both groups. The duration of the daily nocturnal melatonin peak (measured at 10, 24, and 44 wk) remained close to 8 h under long days (high-fidelity melatonin signal) but decreased significantly (13.8 h to 9.3 h) under short days (low-fidelity melatonin signal). The results support the conclusion that the melatonin signal encoding photoperiod acts within the pituitary gland to induce both acute (inductive) and chronic (refractory) effects photoperiod on PRL secretion.