Termination of the breeding season in the Suffolk ewe: involvement of an endogenous rhythm of reproduction

Two studies were performed to determine if the transition into anestrus in the Suffolk ewe results from the lack of a decrease in photoperiod, a signal suggested to be important in maintaining the breeding season, or from an obligatory turn-off that reflects the expression of an endogenous rhythm of reproduction. Shortly after the autumnal equinox, three groups of ovariectomized ewes bearing s.c. Silastic implants of estradiol were placed in different lighting environments. A control group was exposed to normal variations in day length until the winter solstice and held on that day length thereafter. The two experimental groups experienced either a continuously decreasing day length or a continuously increasing duration of elevated melatonin levels during each 24-h period until mid-March. Reproductive activity, assessed by circulating levels of luteinizing hormone (LH), was marginally extended (2-3 wk) in the experimental groups. In a second experiment, two groups of ovary-intact ewes were exposed to photoperiodic treatments shortly after the winter solstice. A control group was held on the winter solstice day length (10L:14D) until the end of the study in mid-March. The experimental group experienced a 3-h photoperiodic reduction to 7L:17D. It remained to determine if that abrupt decrease could maintain reproductive induction. Again, the cessation of reproductive induction was marginally delayed in the experimental group (2-3 wk). This marginal delay in the arrest of reproductive activity seen in both experiments indicates that the lack of decrease in day length around and after the winter solstice may play some role in timing the end of the breeding season. However, our inability to prevent or markedly delay the termination of reproductive activity leads to the conclusion that the primary reason for the transition into anestrus is an obligatory turn-off. This obligatory process may be the expression of an underlying endogenous rhythm of reproduction.     

Social cues can play a role in timing onset of the breeding season of the ewe

Female Suffolk sheep were pinealectomized around the vernal equinox to eliminate the major environmental input to the reproductive system (photoperiod) and then either isolated from, or maintained with, pineal-intact gonad-intact sheep. The ewes were ovariectomized and treated with constant-release oestradiol implants and reproductive state was monitored by measuring serum LH concentrations. Pinealectomized ewes that were isolated from the normal flock showed a 2 1/2-month delay in onset of the seasonal rise in LH values compared with that of pineal-intact controls (18 November vs 5 September). On the other hand, pinealectomized ewes that were maintained with the flock showed an onset of the seasonal rise in LH that was not delayed. These results suggest a timekeeping role for social cues for timing onset of the breeding season in an animal that normally relies on photoperiodic signals for temporal regulation of the seasonal reproductive cycle.     

A study of the relationship between photoperiod and pinealocyte granulated vesicles in the golden Syrian hamster

Summary Previous studies in rabbits and mice have revealed distinct circadian rhythms in the number of pinealocyte granulated vesicles (PGVs) and control of their synthesis and/or secretion by sympathetic nerves. The present study demonstrates the absence of a circadian rhythm in PGV content in hamsters functionally pinealectomized by maintenance under long photoperiod (L/D=14/10 h). On the other hand, a highly significant rhythm of low amplitude was noted in PGVs of hamsters placed in photoperiods (<12.5 h) which are known to initiate pineal antigonadotropic activity. Bilateral optic enucleation, which also leads to pineal-mediated gonadal atrophy in the hamster, produced a significant decrease in the number of perivascular PGVs when compared to intact control animals. Daily late afternoon injections of melatonin produced no significant difference in the number of PGVs between treated and control animals at any sample time examined.Supported in part by N.I.H. Grant#HD08759     

Seasonal change in the locomotor activity rhythm of the medaka,Oryzias latipes

A group of the medaka,Oryzias latipes (Cyprinodontidae, orange-red variety, 25 males and 25 females), was kept in an aquarium, which was placed outdoors under natural conditions from December 1984 to January 1986. Locomotor activity at three layers (upper, middle, and lower layers) was recorded with a phototransistor system in each season. In summer, the fish showed typical diurnal activity at all three layers and the activity was greater than in other seasons. However, in autumn and winter, the fish became less active and showed relatively high activity at night at the upper or middle layer and diurnal activity at the lower layer. Nocturnal activity seemed to appear when the water temperature was decreased and the photoperiod was shortened. A free-running activity rhythm was also recorded under continuous darkness (DD) in each season; however, the fish showed clear free-running activity rhythms under DD only in summer.     

Seasonal effects on the freerunning rhythm of circadian activity of longnose dace (Rhinichthys cataractae)

Synopsis Freerunning circadian rhythms of locomotor activity in individual longnose dace sampled from a population at 41°N latitude were recorded under constant darkness throughout the year. There was an annual cycle in the length of the circadian period, with maximum and minimum lengths of mean period of 23.6 and 21.6 h recorded during summer (June) and winter (December), respectively. These annual changes in period length may have resulted from seasonal changes in entrainment by natural light-dark cycles and their after-effects on endogenous circadian rhythms. The possibility of an endogenous circannual rhythm was also considered.     

Search for Seasonal Rhythmicity of Pineal Melatonin Production in Rats Under Constant Laboratory Conditions: Spectral Chronobiological Analysis,and Relation to Solar and Geomagnetic Variables

Earlier we reported that in a number of experiments pineal melatonin production in rats under constant laboratory conditions displayed seasonal rhythms but subsequently were not always able to confirm this. Since there was no indication under which conditions such rhythms may be present, we performed four consecutive identical experiments with untreated female Sprague–Dawley rats within the same animal room during 1997–2006. Nocturnal urine samples (19–23, 23–3, 3–7 h) were collected at monthly intervals over 494–658 d with 12 animals each in experiments I and II (1997–1999, 1999–2000), 30 animals in experiment III (2002–2004), and 15 in experiment IV (2005–2006). 6-Sulfatoxymelatonin (aMT6s) was measured by ELISA. The excreted aMT6s at each time interval as well as total nocturnal aMT6s-excretion (19–7 h) was submitted to standard statistical analyses as well as to a spectral chronobiological analysis to determine the period lengths of the components involved which was followed by processing with the single cosinor method. Seasonal rhythm components (circannual period length: 360 ± 60 d) were detected in experiment III (2002–2004) for the overall nocturnal excretion as well as for two sub-intervals (23–3 and 3–7 h) and in one night interval of experiment II (23–3 h). Multiple components with mostly short period lengths of around 100 d and some long ones of 500–650 d were found in the other experiments. Systematic MESOR and amplitude variations were observed during the experiments, being highest in experiment II (19–7 h, also 23–3 h and 3–7 h) and lowest in experiments I and IV. These results illustrate that seasonal melatonin rhythms are not a general phenomenon in female laboratory rats indicating an involvement of unknown environmental cues. As an extension of our earlier hypothesis regarding a seasonal Zeitgeber function of the horizontal intensity H of the geomagnetic field showing circannual variations, we assume further modulation by the 11-yrs' sunspot cycle which leads to geomagnetic disturbances and could facilitate seasonal aMT6s rhythmicity during specific years. (Author correspondence: christian.bartsch@uni-tuebingen.de)     

Refractoriness to short and long days determines the end and onset of the breeding season in subtropical goats

The objective was to determine whether refractoriness to short and long days were involved in the end and onset of the breeding season, respectively, in goats adapted to subtropical latitudes. Ovariectomized does given a subcutaneous implant constantly releasing estradiol-l7 β (OVX+E) were used in two experiments. Plasma LH concentrations were determined twice weekly. In Experiment 1, the control group remained in an open-shed pen (natural day length and ambient temperature). Two experimental groups were placed in light-proof buildings (with natural temperature variations). One group was exposed to natural simulated increasing days (winter to spring), whereas the other was exposed to a winter solstice photoperiod (10 h of light) from December 21 to April 28. In Experiment 2, the control group remained under natural day length and ambient temperature. One experimental group was exposed to natural simulated decreasing days (summer to autumn), whereas the other group was exposed to a summer solstice photoperiod (14 h of light) from June 21 to October 20. In Experiment 1, the breeding season was not prolonged in does maintained in the winter solstice day length. Mean dates of decrease in LH secretion (end of the breeding season) did not differ significantly between does exposed to natural (February 3 ± 5 d) or natural simulated photoperiod (January 26 ± 14 d) and those exposed to constant short days of winter solstice (February 4 ± 10 d). In Experiment 2, the onset of the breeding season was not delayed in does maintained in the summer solstice day length. Mean dates of increase in LH secretion (onset of the breeding season) did not differ significantly between does exposed to natural (September 7 ± 8 d) or natural simulated photoperiod (September 18 ± 10 d) and those exposed to constant long days photoperiod of summer solstice (September 24 ± 4 d). In goats adapted to a subtropical environment, we concluded that: 1) the end of breeding season was due to refractoriness to short days, and not the inhibitory effect of increasing day length; and 2) the onset of the breeding season was due to refractoriness to long days, and not a stimulatory effect of decreasing day length.     

Effect of frontal hypothalamic deafferentation on duration of breeding season and melatonin secretion in the ewe

The objectives of this study were to determine if ewes subjected to frontal hypothalamic deafferentation (FHD) during anestrus remained anestrus or began to have estrous cycles, and if melatonin secretion was disrupted by FHD. Ovary-intact ewes in Group 1 were subjected to either FHD (n = 10) or sham FHD (n = 5) in early July 1983. Estrous cycles were monitored by measuring circulating progesterone concentrations from before FHD until September 1985. Group 2 ewes (n = 4) were subjected to FHD in October 1984. In late April 1985, blood samples were taken from all ewes at 1- to 4-h intervals from 1100 h to 0700 h of the following day to monitor diurnal changes of melatonin. Hypothalami were collected for histological evaluation of lesions. All Group 1 ewes (sham FHD and FHD) initiated normal estrous cycles in August and September 1983, and all ceased cycles by mid-February 1984. All sham FHD and 4 FHD ewes remained anestrus until August or September of 1984 and then resumed normal cycles. In contrast, 5 FHD ewes resumed cycles as early as April 1984 and then cycled intermittently or almost continuously. Two Group 2 ewes cycled continuously after FHD and 2 cycled infrequently. FHD ewes that showed prolonged breeding seasons had cuts that damaged the suprachiasmatic nucleus (SCN) and adjacent structures. Mean nocturnal (2000 h-0500 h) melatonin concentrations did not differ (p greater than 0.05) between sham FHD, FHD "normal season," and FHD "continuous cycle" ewes. In summary, damage to the SCN region by FHD during anestrus had no detectable effect on either onset or cessation of the next breeding season but greatly prolonged subsequent breeding seasons. Thus, the environmental signals that both initiated and terminated the 1983 breeding season apparently had been given before FHD was performed in midsummer. Damage to the SCN region during the breeding season caused some ewes to cycle continuously. The effects of FHD apparently were not due to disruption of melatonin secretion. FHD ewes that showed prolonged breeding seasons had normal seasonal changes of plasma prolactin concentrations. This suggests that different neural structures control seasonal patterns of gonadotropin and prolactin secretion.     

Evidence for an endogenous circadian rhythm of feeding in the trout (Oncorhynchus mykiss)

Abstract

The possible endogenous circadian rhythm in the feeding activity of rainbow trout (Oncorhynchus mykiss) was investigated using individual fish previously trained for self‐feeding. Under LD 12:12 conditions, the fish showed a diurnal behaviour, in many cases with a feeding rhythm with two main peaks of food demand at dawn and dusk, with an 8h interval of low feeding activity, and the actograms showed an expected 24 h rhythm. Fish kept under constant conditions (L : L, 15°±0.5°C), showed free‐running feeding activity for about 12 days. Food demands were concentrated at dawn, with a periodogram of 25.3 hour, under continuous environmental conditions. Results showed evidence for the endogenous origin of the circadian rhythm of feeding in this species.     

Responsiveness to photoperiodic changes in the circannual rhythm of the varied carpet beetle, <Emphasis Type="Italic">Anthrenus verbasci</Emphasis>

The circannual pupation rhythm of Anthrenus verbasci is entrained to an environmental cycle by changes in photoperiod. Exposure of larvae reared under short-day conditions to 4 weeks of long days can induce phase-dependent phase shifts. In the present study, we examined the range of photoperiodic changes effective for phase shifts at 20°C. For larvae under light/dark (LD) 12:12 conditions, 4-week exposure to LD 14:10 caused a clear phase delay, as great an extent as that brought about by exposure to LD 15:9 and LD 16:8. In contrast, the delay brought about by exposure to LD 13:9 was slight. For larvae under LD 10:14, exposure to LD 14:10 and LD 16:8 for 4 weeks induced a phase delay, but exposure to LD 12:12 did not. These results indicate that a clear phase delay is induced when the photoperiodic change exceeds a critical value in the photophase between 13 and 14 h, regardless of the amplitude of the change. Although phase advances were smaller than phase delays, they depended on the amplitude of photoperiodic changes rather than the absolute photophase duration in contrast to the case of the phase delay.     

Nyctohemeral Rhythm in the Levels of S-Adenosylmethionine in the Rat Pineal Gland and Its Relationship to Melatonin Biosynthesis

Abstract: Liquid chromatographic techniques that permit the simultaneous analysis of S -adenosylmethionine, melatonin, and its intermediary metabolites N -acetyl-5-hydroxytryptamine and 5-hydroxytryptamine within individual pineal glands have been developed. S -Adenosylmethionine has been shown to undergo a marked nyctohemeral rhythm in the pineal gland of the rat, with maximal levels occurring during the light period and minimal levels during the dark period. Detailed studies of the temporal relationships between the levels of S -adenosylmethionine and those of melatonin and its intermediary metabolites suggest that an association exists between the levels of S -adenosylmethionine and the status of the biosynthesis of melatonin. Exposure of animals to continuous light and the administration of the β-adrenoreceptor antagonist propranolol were both found to inhibit the induction of melatonin synthesis and prevent the reduction in the levels of S -adenosylmethionine during the dark period. As a corollary the induction of melatonin biosynthesis following the administration of the β-adrenoreceptor agonist isoproterenol during the light period was accompanied by a marked decrease in the levels of S -adenosylmethionine in the pineal gland. The significance of the link between the nyctohemeral rhythms in the levels of S -adenosylmethionine and the biosynthesis of melatonin in the pineal gland is discussed in the context of the therapeutic efficacy of S -adenosylmethionine as an antidepressant.     

Comparison of the circadian eclosion rhythm between non-diapause and diapause pupae in the onion fly,Delia antiqua

The influence of pupal diapause on adult eclosion rhythm of Delia antiqua was investigated. When non-diapause and diapause pupae were exposed to various photoperiods at 15, 20 and 25 °C, both of them emerged as adults close to the light-on time, but the phase of eclosion varied with photoperiod and temperature. Moreover, there was a significant difference in the eclosion time between non-diapause and diapause pupae; the eclosion peak of diapause pupae was earlier than that of non-diapause pupae. When non-diapause and diapause pupae were transferred to constant darkness (DD) after having experienced LD 12:12 at 15, 20 and 25 °C, both showed circadian rhythmicity in eclosion. Although the free-running period (τ) decreased slightly as temperature increased in both non-diapause and diapause pupae, the latter tended to show shorter τ than the former. This observation suggests that the observed difference in eclosion time in LD cycles between non-diapause and diapause pupae is due to differences in τ.     

Photoperiodic Variation in CD45-Positive Cells and Cell Proliferation in the Mediobasal Hypothalamus of the Soay Sheep

The Earth's solar orbit induces annual climatic changes challenging to survival. Many animals have evolved to cope with seasonal variability through compensatory annual changes in their physiology and behavior, which involve innate long-term timing and photoperiodic synchronization to anticipate the environmental seasonal cycles. Here we considered the potential involvement of cyclical histogenesis in seasonal timing mechanisms in the sheep. Adult Soay rams were established in three distinctive seasonal states by controlled photoperiod exposure. A first group, representing the condition in late spring (long-photoperiod [LP] group), was taken indoors in May and exposed to 4 wks of 16?h light/day (LP). A second group was exposed to 20 wks of LP to establish a late-summer/long-day refractory condition (LPR group). A third group of animals was brought indoors in August and exposed to 4 wks of LP followed by 4 wks of 8?h light/day (short photoperiod [SP]) to establish an autumn-like condition (SP group). At the end of these regimes, we injected 5-bromo-2-deoxyuridine (BrdU), and animals were killed 24?h or 4 wks later. When BrdU was administered 24?h before death, more BrdU-immunopositive cells were detected in the hilus of the hippocampus in LP compared with SP animals, indicative of a higher proliferation rate. When BrdU was administered 4 wks before death, more BrdU-positive cells were detected in the hippocampus under LP, compared with SP, indicating increased cell survival. These mitotic cells were occasionally seen to adopt a neuronal phenotype in the hippocampus, but not in the hypothalamus. Approximately 10% of BrdU-positive cells in the basal hypothalamus coexpressed the pan-leukocytic marker CD45, and showed morphological features and regional distribution consistent with ameboid microglia. Increased numbers of these cells were detected in the region of the median eminence and tuberoinfundibular sulcus of animals kept in SP compared with LP or LPR. These data suggest that neuroimmune mechanisms may be involved in photoperiod-dependent seasonal remodeling of the adult brain. (Author correspondence: d.hazlerigg@abdn.ac.uk)     

哺乳动物昼夜节律组构中的下丘脑视交叉上核和松果腺

哺乳动物下丘脑视交叉上核（SCN）是昼夜节律最主要的起搏器,控制着机体的生理和行为的节律。它具有自身内在的节律性,同时也受光照周期信号和一些内源性化学物质的调节。检查腺分泌裉黑素（MEL）受SCN的调控,MEL通过作用于SCN上高亲和性MEL受体,启动第二、第三信使系统,调整SCN的昼夜节律活动。这种调整具有时间敏感性。     

Maternal androgens in the pied flycatcher: timing of breeding and within-female consistency

Maternal hormones can have substantial phenotypic effects in the progeny of many vertebrates. It has been proposed that mothers adaptively adjust hormone levels experienced by particular young to optimize their reproductive output. In birds, systematic variation in egg hormone levels has been related to different female reproductive strategies. Because in many bird species prospects of the offspring change seasonally and with brood number, strategic adjustment of yolk androgen levels would be expected. To test this idea, we induced pied flycatcher (Ficedula hypoleuca) females to nest twice during the same season by removing their first clutches shortly after clutch completion. We collected eggs of first and replacement clutches to measure yolk concentrations of androstenedione (A4) and testosterone (T) and captured the females that laid these clutches for phenotypic measurements. Although average egg androgen levels were remarkably consistent within females, hormone patterns differed considerably between first and replacement clutches. Eggs of replacement clutches were heavier with larger yolks compared to first clutches, but they contained on average lower levels of androgens. Within clutches, androgen concentration increased over the laying sequence in the first clutch, but decreased or remained more constant over the laying sequence in the replacement clutch. Mean yolk T, but not A4 levels, were negatively associated with laying date for both breeding attempts. Moreover, females in good body condition produced eggs containing lower levels of androgens than females in poor condition. Our results are consistent with the idea that differences in yolk androgen levels may be one mechanism underlying seasonal variation in reproductive success and it is possible that changes in egg androgen patterns may reflect a change in female reproductive strategy. High within-female consistency also highlights the possibility that there may be some underlying genetic variation in yolk androgen levels.     

Variation in the timing of the reproductive season among breeds of sheep in relation to differences in photoperiodic synchronization of an endogenous rhythm.

Photoperiod may regulate seasonal reproduction either by providing the primary driving force for the reproductive transitions or by synchronizing an endogenous reproductive rhythm. This study evaluated whether breed differences in timing of the reproductive seasons of Finnish Landrace (Finn) and Galway ewes are due to differences in photoperiodic drive of the reproductive transitions or to differences in photoperiodic synchronization of the endogenous rhythm of reproductive activity. The importance of decreasing photoperiod after the summer solstice in determining the onset and duration of the breeding season was tested by housing ewes from the summer solstice in either a simulated natural photoperiod or a fixed summer-solstice photoperiod (18 h light:6 h dark; summer-solstice hold). Onset of the breeding season within each breed did not differ between these photoperiodic treatments, but Galway ewes began and ended their breeding season earlier than Finn ewes. The duration of the breeding season was shorter in Galway ewes on summer-solstice hold than on simulated natural photoperiod; duration did not differ between photoperiodic treatments in Finn ewes. The requirement for increasing photoperiod after the winter solstice for initiation of anoestrus was tested by exposing ewes from the winter solstice to either a simulated natural photoperiod or a winter-solstice hold photoperiod (8.5 h light:15.5 h dark). Onset of anoestrus within each breed did not differ between these photoperiodic treatments, but the time of this transition differed between breeds. These observations suggest that genetic differences in timing of the breeding season in Galway and Finn ewes do not reflect differences in the extent to which photoperiod drives the reproductive transitions, because neither breed requires shortening days to enter the breeding season or lengthening days to end it at appropriate times. These findings are consistent with the hypothesis that photoperiod synchronizes an endogenous rhythm of reproductive activity in both breeds and that genetic differences in timing of the breeding season reflect differences in photoperiodic synchronization of this rhythm.     

Evidence for an endogenous circannual component in the control of the annual gonadal cycle in spotted munia

Abstract

For the first time evidence has been provided for a circannual gonadal cycle in any avian species (male spotted munia Lonchura punctulata, Estrildidae) held on continuous light. A model has thus been rendered available in which the “entraining effects” of photoperiod could be clearly distinguished from its direct “driving effects”.     

Circadian rhythm of adrenal glucocorticoid: Its regulation and clinical implications

Glucocorticoid (GC) is an adrenal steroid hormone that controls a variety of physiological processes such as metabolism, immune response, cardiovascular activity, and brain function. In addition to GC induction in response to stress, even in relatively undisturbed states its circulating level is subjected to a robust daily variation with a peak around the onset of the active period of the day. It has long been believed that the synthesis and secretion of GC are primarily regulated by the hypothalamus-pituitary-adrenal (HPA) neuroendocrine axis. However, recent chronobiological research strongly supports the idea that multiple regulatory mechanisms along with the classical HPA neuroendocrine axis underlie the diurnal rhythm of circulating GC. Most notably, recent studies demonstrate that the molecular circadian clockwork is heavily involved in the daily GC rhythm at multiple levels. The daily GC rhythm is implicated in various human diseases accompanied by abnormal GC levels. Patients with such diseases frequently show a blunted GC rhythmicity and, more importantly, circadian rhythm-related symptoms. In this review, we focus on recent advances in the understanding of the circadian regulation of adrenal GC and its implications in human health and disease.     

Ontogeny of the rhythmic melatonin production in a precocial and an altricial bird,the Japanese quail and the European starling

A distinct daily rhythm of melatonin production was found in the pineal gland of both precocial Japanese quail (Coturnix coturnix japonica) and altricial European starling (Sturnus vulgaris) during the first day of postembryonic life. Rhythmic melatonin production was reflected in a rhythmic profile in the general circulation. Significant day-night differences in melatonin content were also observed in the eyes of Japanese quail.The amplitude of the rhythm in the quail pineal gland increased steadily during the first two weeks of postem-bryonic life. A transient increase in maximum melatonin concentration was observed at the end of the first week of life in the plasma but not in the pineal gland of quail suggesting that a metabolizing pathway or a changed ocular contribution may influence the melatonin profile in the circulation and its availability to other tissues. There was no delay in the postembryonic development of melatonin rhythmicity in the altricial starling in comparison with the precocial quail. The amplitude of the plasma melatonin rhythm did not increase over the first week of life in starlings as it did in quail and the only significant increase was found between 6- and 17-day old starlings.In general, the development of the rhythm resulted from an increase of dark-time values. The day-time concentrations were low in all age groups of both species. A one-hour light pulse suppressed the high dark-time melatonin concentrations in 1-, 7- and 14-day old Japanese quail as well as in 7- and 14-day old European starlings. The manner in which the rhythm develops suggests that the circadian pacemaker(s) as well as the mechanisms of photoreception and entrainment are developed in hatchlings of both species in spite of their otherwise different developmental strategies.