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PubMed2006

Photoperiod affects daily torpor and tissue fatty acid composition in deer mice.

Photoperiod and dietary lipids both influence thermal physiology and the pattern of torpor of heterothermic mammals. The aim of the present study was to test the hypothesis that photoperiod-induced physiological changes are linked to differences in tissue fatty acid composition of deer mice, Peromyscus maniculatus ( approximately 18-g body mass). Deer mice were acclimated for >8 weeks to one of three photoperiods (LD, light/dark): LD 8:16 (short photoperiod), LD 12:12 (equinox photoperiod), and LD 16:8 (long photoperiod). Deer mice under short and equinox photoperiods showed a greater occurrence of torpor than those under long photoperiods (71, 70, and 14%, respectively). The duration of torpor bouts was longest in deer mice under short photoperiod (9.3 +/- 2.6 h), intermediate under equinox photoperiod (5.1 +/- 0.3 h), and shortest under long photoperiod (3.7 +/- 0.6 h). Physiological differences in torpor use were associated with significant alterations of fatty acid composition in approximately 50% of the major fatty acids from leg muscle total lipids, whereas white adipose tissue fatty acid composition showed fewer changes. Our results provide the first evidence that physiological changes due to photoperiod exposure do result in changes in lipid composition in the muscle tissue of deer mice and suggest that these may play a role in survival of low body temperature and metabolic rate during torpor, thus, enhancing favourable energy balance over the course of the winter.

Activity Cycles↗
PubMed2006

Seasonal and photoperiodic regulation of secretion of hormones associated with reproduction in Magang goose ganders.

This study examined the reproductive endocrine profile under natural and artificial photoperiods in Magang goose ganders. Group 1 ganders (n=8) served as non-treated controls and were exposed to natural photoperiod throughout the experiment from 13th January to 17th December 2004. Group 2 ganders (n=8) were exposed to 18 h long daily photoperiod for 60 days from 13 January till 15 March 2004 and again to 16 h photoperiod for 75 days till 10th October 2004, and the 11h short photoperiod in the remainder periods of the experiment. In control ganders, plasma LH concentrations were high in normal breeding seasons (August-March) and decreased to low levels in non-breeding season from April to July. Testosterone concentrations changed similarly to that of LH throughout the seasons. Seasonal pattern of PRL concentrations was opposite to those of LH and testosterone, with low values in breeding season and high values in non-breeding season. In artificial photoperiod treated ganders, increasing photoperiod increased PRL and decreased LH and testosterone concentrations, while decreasing photoperiod reversed these changes. There were no seasonal or photoperiod caused changes in plasma T3 concentrations in both control ganders and artificial photoperiod treated ganders. These results demonstrated that in Magang goose ganders that long photoperiod stimulates PRL secretion and decreases LH secretion, which terminates reproductive season in spring and early summer, and short photoperiod stimulates LH secretion and inhibits PRL secretion rendering ganders enter into reproductive season.

Animals↗
PubMed2004

Effect of photoperiod on vasopressin-induced aggression in Syrian hamsters.

Syrian hamsters are photoperiodic and become sexually quiescent when exposed to short "winter-like" photoperiods. In short photoperiods, male hamsters display significantly higher levels of aggression than males housed in long photoperiods. Arginine-vasopressin (AVP) within the anterior hypothalamus (AH) has been reported to modulate aggression in hamsters housed in long photoperiods. Previous studies have shown that AVP can facilitate aggression and its effects appear to be mediated by AVP V(1a) receptors (V(1a)R). In the present study, we investigated whether the increased levels of aggression observed after exposure to short photoperiod were the result of an increased responsiveness to AVP within the AH. Injections of AVP into the AH significantly increased aggression in hamsters housed in a long photoperiod, but had no effect in hamsters housed in a short photoperiod. In addition, injection of a V(1a)R antagonist into the AH significantly inhibited aggression in hamsters housed in long photoperiod, but had no effect in hamsters housed in a short photoperiod. These findings indicate that AVP within the AH increases aggression in hamsters housed in long photoperiods, but not in hamsters housed in short photoperiods.

Aggression↗
PubMed1997

Effect of size and timing of photoperiod increase on age at first egg and subsequent performance of two breeds of laying hen.

1. ISA Brown and Shaver 288 pullets were changed from 8 h to 8, 10, 13 or 16 h photoperiods at 42, 63, 84, 105, 126 or 142 d of age. 2. Age at first egg (AFE) was curvilinearly affected by the size and timing of the change in photoperiod. AFE was advanced most by a photoperiod change from 8 to 13 h made at 63 or 84 d. ISA birds were generally more responsive than Shaver to the photoperiod changes. 3. Longer photoperiods significantly increased survivors' egg production, but decreased liveability to 504 d. so that eggs per hen housed were unaffected. Retarding AFE by 10 d reduced survivors' egg numbers by 7.0, but increased mean egg weight by 1.26 g. Egg output by Shaver birds was unaffected by AFE, but that of ISA was curvilinearly affected, with an apogee at an AFE of 135 d. In both breeds, egg weight and egg output were greater following an early or late, rather than a mid-term photostimulation. 4. Photoperiod significantly increased mean daily food intake during lay by 1.26 g/h. A 10 d retardation in AFE resulted in a reduction in food intake of 1 g/d. Efficiency of food conversion deteriorated according to the square of the photoperiod, and changed curvilinearly according to age at photostimulation. Food conversion efficiency improved by 0.05 g/g for each 10 d delay in AFE. 5. Shell quality was unaffected by AFE, but deteriorated with increasing photoperiod and was curvilinearly affected by age at photostimulation with the smallest shell weights associated with photostimulation at 63 d. The incidence of double-yolked (DY) egg production increased with photoperiod and decreased with delayed photostimulation. There was an exponential regression of DY eggs on AFE. 6. Body weight at first egg increased by 75 g/d delay in AFE, but body weight at 504 d of age was unaffected by AFE, photoperiod or age at photostimulation. Body weight gain during lay increased by 15 g/h increase in photoperiod, decreased by 6 g per 10 d delay in photostimulation and by 40 g per 10 d delay in AFE. Fat content at 504 d increased by about 10 g/kg and by 23 g/bird for each 10 d delay in AFE. 7. Mortality in lay increased by 0.8%/h increase in photoperiod, but was unaffected by either age at photostimulation or AFE.

Aging↗
PubMed1993

Photoperiodic time measurement and a graded response in a cockroach.

Almost exclusively, photoperiodic insects respond to a given photoperiod in one of two ways: a "long-day" response or a "short-day" response. Intermediate responses occur only at a very restricted range of photoperiods (often less than 30 min) and are generally population phenomena rather than intermediate responses of individuals. In contrast, individuals of the wood roach, Parcoblatta pennsylvanica, show intermediate responses over a broad range of photoperiods. We examined the effect of constant light, constant darkness, and photoperiods ranging from 10 to 18 hr of light per 24 hr on growth rate as measured by weight gain, and found a robust photoperiodic response. Nymphs raised in photoperiods with light periods (photophases) from 0 to 12 hr gained little weight, whereas those in LD 18:6 were almost 15 times heavier. This is the first report of a photoperiodic response curve for a cockroach. Interestingly, there was a linear relationship between the duration of the photophase and weight gain over a broad range of photoperiods (LD 12:12 to LD 18:6; r2 = 0.99). Statistical analysis showed that the intermediate responses were attributable to individuals' growing at an intermediate rate. Another interesting observation was that all larval stages appeared to be capable of perceiving and responding to photoperiodic signals. The results of further experiments using non-24-hr photoperiods were consistent with the existence of a circadian component in the photoperiodic time measurement in this species.

Analysis of Variance↗
PubMed2003

Photoperiod and bromocriptine treatment effects on expression of prolactin receptor mRNA in bovine liver, mammary gland and peripheral blood lymphocytes.

Recent evidence suggests that photoperiod influences immune function. Interestingly, photoperiod has profound effects on concentrations of prolactin (PRL), a hormone also known to be involved in fluctuations of the immune system. However, the impact of photoperiod on PRL receptor (PRL-R) expression is poorly understood, particularly in tIssues of the immune system. Two experiments were performed to increase the general understanding of how photoperiod interacts with the immune system. Our first objective was to determine the effects of photoperiod on PRL-R mRNA expression and cellular immune function. Lymphocytes were isolated from blood collected from calves (n=10) and PRL-R mRNA expression of both long and short forms was quantified using real-time PCR. Lymphocytes expressed PRL-R mRNA, suggesting that PRL could act directly on these cells. To determine the relationship between photoperiod and PRL-R mRNA expression in other tIssues, hepatic and mammary biopsies were collected after calves were exposed to long days (LDPP; 16 h light:8 h darkness) or short days (SDPP; 8 h light:16 h darkness). Relative to LDPP, SDPP decreased circulating PRL, but increased expression of both forms of PRL-R mRNA in liver, mammary gland and lymphocytes. Short days also increased lymphocyte proliferation compared with long days. Reversal of photoperiodic treatments reversed the effects on circulating PRL, PRL-R mRNA expression and lymphocyte proliferation. Our second objective was to manipulate PRL concentration in photoperiod-treated animals, using bromocriptine. Concentrations of PRL in LDPP animals injected daily with bromocriptine for 1 week were decreased compared with LDPP controls, to a level similar to SDPP animals. Receptor expression was increased in LDPP+bromocriptine-treated animals relative to LDPP controls, as was lymphocyte proliferation. Overall, our results indicate that photoperiodic effects on PRL-R mRNA expression were inverse to those on circulating PRL, with short days stimulating expression of both forms of PRL-R mRNA. Expression of PRL-R mRNA changed in the same direction as lymphocyte proliferation with regard to photoperiod treatment, suggesting a link between photoperiodic effects on PRL sensitivity and immune function. Thus, PRL signaling may mediate photoperiodic effects on immune function.

Animals↗
PubMed1984

Photoperiod perception in the blind mole rat (Spalax ehrenbergi, Nehring): involvement of the Harderian gland, atrophied eyes, and melatonin.

The involvement of the Harderian gland, atrophied eyes, and melatonin in the perception of photoperiodic changes has been studied in the mole rat, a fossorial blind mammal the thermoregulatory capacity of which is photoperiod-dependent. When transferred from a long photoperiod to a short one, mole rats increase their resistance to cold, a perfectly reversible phenomenon. After 2 weeks under short photoperiod the thermoregulatory capacities of animals without Harderian glands are less than those of the controls. The Harderian gland appears thus to be implicated in the detection of photoperiodic changes. After 5 weeks, however, the Harderianectomized animals had perfectly integrated the photoperiodic change, so demonstrating that other photoreceptor organs exist. The atrophied eyes, which, under these conditions, do not seem to play an important role, are involved when the animals are transferred from short photoperiod to long photoperiod. Melatonin, but not 5-methoxytryptamine, appears to be a crucial compound in such a phenomenon. These results, which demonstrate that in mammals (at least in the mole rat, as in nonmammalian vertebrates), nonocular photoreceptors exist, suggest that the mechanism by which mammals integrate photoperiodic changes is not the same when the animals are transferred from long to short photoperiod as when transferred from short photoperiod to long photoperiod.

5-Methoxytryptamine↗
PubMed1993

Photoperiodic and pineal influences on estrogen-stimulated behaviors in female Syrian hamsters.

Three experiments investigated the effects of short photoperiod exposure on the estrogenic facilitation of locomotor activity and lordosis. In Experiment 1, ovariectomized female hamsters were administered exogenous estrogen to stimulate locomotor activity in running wheels. Estrogen was effective in the long photoperiod group but did not stimulate running-wheel activity in the short photoperiod group. In Experiment 2, the role of the pineal gland in mediating photoperiodic influences on female hamster behavior was examined. Both estrogen-induced locomotor activity and estrogen+progesterone-stimulated lordosis behavior were significantly reduced in short photoperiod females. Both these photoperiodic effects were absent in pinealectomized hamsters. Sham-pinealectomized, short photoperiod females expressed behavioral deficits; pinealectomized hamsters in the short photoperiod did not. Experiment 3 investigated lordosis only and used hormone injections rather than silastic implants to administer estrogen. The photoperiodic and pineal effects observed in Experiment 2 were replicated in Experiment 3. Additionally, the suppression of lordosis responsiveness by short photoperiod exposure was estrogen dose dependent. Photoperiodic effects were present when 2 micrograms estradiol cypionate was used but absent when higher estrogen doses were used. These findings are discussed in the context of other results that suggested photoperiodic effects on hamster lordosis were pineal independent.

Animals↗
PubMed1988

The effect of photoperiod on diurnal rhythms of serum gonadotrophins, prolactin and melatonin in ovariectomized heifers.

Fourteen heifers, ovariectomized prepubertally, were used in two experiments to test the hypotheses that (1) there are diurnal patterns in circulating concentrations of luteinizing hormone (LH), follicle stimulating hormone (FSH), prolactin and melatonin and (2) that these diurnal patterns would be altered by changing photoperiod. In experiment 1 (Exp. 1) animals were randomly assigned to either increasing photoperiod (I) (n = 7) or decreasing photoperiod (D) (n = 7) for a period of 8 weeks. In the second experiment (Exp. 2) four heifers from each photoperiod group were assigned to the opposite treatment for another 4 weeks forming four subgroups; continued increasing photoperiod (II) (n = 3), increasing followed by decreasing photoperiod (ID) (n = 4), decreasing followed by increasing photoperiod (DI) (n = 4) and continued decreasing photoperiod (DD) (n = 3). At weeks 4, 8 (Exp. 1) and 12 (Exp. 2) the animals were cannulated and blood samples were taken hourly from 1030 hr to 0830 hr (23 samples). In Exp. 1, animals exposed to either I or D did not differ in circulating concentrations of LH, FSH, prolactin and melatonin. Concentrations of LH and melatonin but not FSH or prolactin were higher in animals during the scotophase than the photophase. In Exp. 2 LH, FSH and prolactin, but not melatonin concentrations were higher in animals exposed to I (II and ID) than D (DI and DD). Animals exposed to I had higher circulating concentrations of FSH and animals exposed to both I and D had higher concentrations of melatonin during the scotophase. Neither LH nor prolactin concentrations differed between scotophase and photophase. The abrupt switch from one photoperiod treatment to the other did not significantly affect LH, FSH or prolactin but did alter the patterns and concentrations of circulating melatonin. Animals that remained in the same photoperiod treatment had similar melatonin concentrations; but animals changed from I to D had higher serum melatonin concentrations than those changed from D to I. These data support the hypothesis that there are diurnal changes in circulating concentrations of melatonin in the prepubertal bovine female, with concentrations higher during scotophase than photophase. In addition, under certain photoperiodic conditions there were diurnal rhythms in gonadotropins. These data also support the hypothesis that changing photoperiod alters the diurnal pattern in circulating melatonin concentrations.

Animals↗
PubMed1998

Effect of constant and of changing photoperiod on plasma LH and FSH concentrations and age at first egg in layer strains of domestic pullets.

1. ISA Brown pullets were transferred from 8 to 14 h or from 14 to 8 h photoperiods at 35 or 56 d of age. Controls were maintained on constant 8 or 14 h photoperiods from day 1. 2. Blood samples were obtained immediately before each daylength change and subsequently at 7 d intervals until 1st egg in the treated groups and at 70 d of age and then at 14 d intervals until 1st egg in the constant photoperiod controls. Plasma luteinising hormone (LH) and follicle stimulating hormone (FSH) concentrations were determined using homologous radioimmunoassays. 3. Prior to 16 weeks, LH was consistently higher in birds on constant 14 h photoperiods than in those on constant 8 h, but was down-regulated as birds approached maturity so that LH concentrations in the 2 groups were similar during the final 10 d before the first egg was laid. FISH concentrations rose steadily with age but with a tendency for concentrations to be higher in the 8 h than in the 14 h treatment. Birds on constant 8 h daylengths matured 18.3 d later than those on constant 14 h photoperiods. 4. A 6 h increment in photoperiod given at 35 d or 56 d, resulted in an increase in LH within 7 d in both cases. FSH concentration did not respond to an increase in photoperiod at 35 d but rose following the same increase at 56 d. This was associated with a 3-week advance in sexual maturity, whilst age at 1st egg in birds photostimulated at 35 d was similar to the age with a constant 14 h photoperiod. 5. LH concentration fell when photoperiod was reduced from 14 to 8 h at either 35 or 56 d and remained below the constant 8 h controls for many weeks before rising to a concentration not significantly different from other groups in the final 10 d before 1st egg. FSH concentrations in birds exposed to a decreased daylength at 35 d, although more oscillatory, were similar to the constant 8 h photoperiod controls. In birds exposed to the same decrease at 56 d, FSH concentration initially tumbled but was similar in the 2 groups during the latter stages of rearing; neither differed significantly from the constant daylength controls during the 60 d before 1st egg. Sexual maturity in both groups given a reduction in photoperiod was delayed by about 2 weeks compared with constant 8 h controls. 6. Change in FSH concentration following an increase in daylength was a better predictor of age at 1st egg than change in LH. However, FSH concentrations after 14 weeks of age were rather similar in short day and long day controls and in the 2 groups given reductions in photoperiod at 35 d and 56 d, despite differences of nearly 5 weeks in mean age at 1st egg amongst these 4 treatments.

Animals↗
PubMed1986

Functional maturation of the gonads of Turkish hamsters under various photoperiods.

The golden hamster, Mesocricetus auratus, is the only photoperiodic rodent to date that has been shown to fail to respond to inhibitory (i.e., short, less than 12.5 h/day) photoperiods until after pubertal onset. In other photoperiodic hamsters, mice, and voles, short photoperiods greatly retard gonadal maturation. The Turkish hamster, Mesocricetus brandti, is a photoperiodic rodent that as an adult is reproductively competent only on photoperiods of 15-17 h of light per day; photoperiods of less than 15 or greater than 17 h of light promote gonadal regression. In this report we addressed two questions: a) are prepubertal M. brandti photoperiodic, and b) if so, is gonadal maturation enhanced or suppressed by exposure to photoperiods of greater than 17 h of light per day? Turkish hamsters were raised on photoperiods of 12, 16, 20, or 24 (= LL) h of light per day. Testicular growth was retarded for 16 wk by 12L:12D. Very long days, 20L:4D, or LL did not retard testicular development. In females, pubertal onset, as indicated by first vaginal estrus, was delayed in young raised on 12L:12D and in 2 of 18 and 4 of 19 young raised on 20L:4D and LL, respectively. These results demonstrate that prepubertal Turkish hamsters are photoperiodic, but respond differently from adults to photoperiods greater than 17 h of light per day.

Aging↗
PubMed2001

The effect of maternal photoperiod on seasonal dormancy in Arabidopsis thaliana (Brassicaceae).

The maternal photoperiod at the time of seed maturation can predict the seasonal conditions of newly dispersed seeds. We investigated the effects of maternal photoperiod on seasonal dormancy in Arabidopsis thaliana using a set of F6 recombinant inbred lines derived from a cross between individuals from two natural populations (Cal-0 and Tac-0) differing in cold requirements for germination. We grew 40 Cal × Tac lines in a long-day photoperiod (8 h of full spectrum light plus 8 h of low-fluence incandescent light) and a short-day photoperiod (8 h full spectrum light). We then exposed seeds from each family and maternal photoperiod to either a cold stratification treatment (4°C, 21 d) or no cold stratification. Both maternal photoperiod and progeny stratification influenced the percentage of seeds that germinated and the speed of germination. The short-day photoperiod caused increased responsiveness to stratification, with higher germination percentages and speeds in stratified seeds. Stratification influenced the expression of maternal photoperiod effects, such that short days increased germination percentage and speed in stratified seeds but inhibited germination in unstratified seeds. Families differed significantly in their plasticity to maternal photoperiod and stratification, but genetic variation for plasticity to maternal photoperiod was expressed only in unstratified seeds. Because the expression of maternal photoperiod effects and genetic variation for photoperiod effects depended on progeny stratification, the evolution of these maternal effects will depend on the seasonal environment experienced by progeny.

Journal Article↗
PubMed1975

Effect of photoperiod on reproductive activity and hair in mares.

The effects of photoperiod on reproductive activity and hair changes in pony mares were studied in 2 experiments. In experiment I, the effect of a fixed daily photoperiod on the onset of the breeding season was studied in 36 mares from Nov 13, 1973, to June 13, 1974. The 4 treatment groups were as follows: daily photoperiod equivalent to the normal day length (control group); constant light 24 hours a day with no dark (L24:D0 group); 16-hour daily photoperiod with 8 hours of dark (L16:D8 group); and 9-hour daily photoperiod with 15 hours of dark (L9:D15 group). The intervals from beginning of experiment to 1st ovulation of breeding season, to shedding of hair in tufts, and to appearance of a smooth coat were shorter (P less than 0.05) for L16:D8 group (107.1 +/- 11.1, 56.0 +/- 0, and 145.8 +/- 4.0 days, respectively) than for control, L24:D0, and L9:D15 groups and were shorter (P less than 0.05) for L24:D0 group (less than 156.1 +/- 12.2, 99.5 +/- 9.5, and 173.9 +/- 9.9 days, respectively) than for control group (192.1 +/- 3.3, 134.9 +/- 8.9, and 205.0 +/- 0 days, respectively) or L9:D15 group (less than 200.3 +/- 5,8, 150.6 +/- 12.9, and 201.7 +/- 3.3 days, respectively). These intervals were not significantly different between the control group and the L9:D15 group, but fewer (P less than 0.05) mares in the L9:D15 group had at least 1 ovulation by termination of the project. In experiment II, the effect of photoperiod on onset of anestrus was studied in 3 groups of 7 mares each. Mares in group A, as part of a previous experiment, were induced to enter the breeding season earlier than normal by a gradual increase in daily photoperiod beginning on Oct 13, 1972. From Feb 16, 1973, to June 22, 1973, group A mares were maintained at a fixed daily photoperiod of 15 hours 23 minutes. Mares in group B, as part of a previous experiment, were kept under environmental conditions simulating normal conditions in southern Wisconsin. On June 22, 1973 (beginning of the present experiment), the following treatments began: groups A and B were exposed to natural day length. In addition, 7 mares (group C) were allotted from a band of mares that had been exposed to natural day length and were exposed to 15-hour 23-minute daily photoperiod from the beginning of the present experiment (June 22, 1973) to the end (June 22, 1974). The interval to onset of anestrus was longer (P less than 0.05) for group C mares (234.6 +/- 35 days) than for group B mares (133.6 +/- 16.5 days). Significant difference did not exist between group A (144.0 +/- 45.9 days) and group B. A fixed daily photoperiod of 16 or 24 hours induced early onset of the breeding season and early shedding of hair, with development of a smooth coat. A photoperiod of 9 hours retarded the onset of the breeding season. Mares induced to begin the breeding season earlier than normal did not become anestrous earlier than normal. Mares kept on a long daily photoperiod in the fall became anestrous later than normal.

Anestrus↗
PubMed1993

Threshold photoperiods for the induction of short day traits in collared lemmings (Dicrostonyx groenlandicus).

When exposed to short photoperiod collared lemmings undergo a number of physiological and morphological changes including an increase in body weight, a change in body composition, development and enlargement of the bifid "digging" claw, and a molt to a white winter pelage. We investigated the threshold photoperiods for the induction of these traits in male and female lemmings born and raised under a 22L:2D photoperiod and transferred at weaning (19 days of age) to various other photoperiods. Male lemmings showed the characteristic increase in body weight when exposed to 16 hr of light or less per day whereas females required a photoperiod of 14 hr of light or less per day to elicit an increase in body weight. The threshold photoperiods for the increase in bifid claw size were 16 and 18 hr of light per day in male and female lemmings, respectively. The molt to the white winter pelage began under a longer photoperiod in females (16L:8D) than in males (14L:10D). Testes and seminal vesicles were significantly inhibited by photoperiods of 22L:2D and 20L:4D. Likewise, uterine weights were inhibited by maintenance on a photoperiod of 22L:2D. Taken together, these data show that the threshold photoperiods for the induction of the short day traits in collared lemmings are both trait- and sex-dependent. These observations also suggest that under some conditions, exposure to long photoperiods can inhibit sexual maturation.

Animals↗
PubMed2006

Positional relationships between photoperiod response QTL and photoreceptor and vernalization genes in barley.

Winterhardiness has three primary components: photoperiod (day length) sensitivity, vernalization response, and low temperature tolerance. Photoperiod and vernalization regulate the vegetative to reproductive phase transition, and photoperiod regulates expression of key vernalization genes. Using two barley mapping populations, we mapped six individual photoperiod response QTL and determined their positional relationship to the phytochrome and cryptochrome photoreceptor gene families and the vernalization regulatory genes HvBM5A, ZCCT-H, and HvVRT-2. Of the six photoreceptors mapped in the current study (HvPhyA and HvPhyB to 4HS, HvPhyC to 5HL, HvCry1a and HvCry2 to 6HS, and HvCry1b to 2HL), only HvPhyC coincided with a photoperiod response QTL. We recently mapped the candidate genes for the 5HL VRN-H1 (HvBM5A) and 4HL VRN-H2 (ZCCT-H) loci, and in this study, we mapped HvVRT-2, the barley TaVRT-2 ortholog (a wheat flowering repressor regulated by vernalization and photoperiod) to 7HS. Each of these three vernalization genes is located in chromosome regions determining small photoperiod response QTL effects. HvBM5A and HvPhyC are closely linked on 5HL and therefore are currently both positional candidates for the same photoperiod effect. The coincidence of photoperiod-responsive vernalization genes with photoperiod QTL suggests vernalization genes should also be considered candidates for photoperiod effects.

Alleles↗
PubMed2005

Fos-related antigen 2 (Fra-2) memorizes photoperiod in the rat pineal gland.

As the physiological role of fos-related antigen-2 (Fra-2) is largely unknown and since the pineal plays an important role in the photoperiodic control of the body, we have tested the hypothesis that Fra-2 expression is photoperiod-dependent and may be involved in imprinting photoperiod on the pineal gland and the body as a whole. To this end, we have investigated Fra-2 mRNA expression and Fra-2 protein expression under various light/dark (LD) cycles. A clear nocturnal increase occurs for both monitored parameters under all photoperiodic conditions studied. The level of Fra-2 protein expression clearly depends on photoperiod, because the amount of protein at dark onset and during the night negatively correlates with the length of the photoperiod. Further, high-phosphorylated Fra-2 isoforms are abundant under all photoperiods tested, with the exception of LD 20:4. Because Fra-2 phosphorylation depends on cGMP, a depressed cGMP response to adrenergic stimulation under LD 20:4 appears to explain this finding. We conclude that photoperiod is imprinted on Fra-2 in terms of both protein amount and protein phosphorylation in the rat pineal gland. This imprinting becomes fully manifest after about 7 days only, suggesting that a number of altered photoperiodic cycles are required for pineal Fra-2 to "learn" that the photoperiod has changed. Reportedly, Fra-2 limits expression of the enzyme iodothyronine deiodinase type II, which catalyzes the intracellular deiodination of thyroxine prohormone to the active 3,3',5-triiodothyronine. We have found that the extent of Fra-2 expression inversely correlates with the dII gene response to cAMP; hence the photoperiodic regulation of Fra-2 may affect the body by changing pineal thyroid hormone metabolism.

Acetyltransferases↗
PubMed1998

Photoperiodic regulation of hypothalamic neuropeptide messenger RNA expression: effect of pinealectomy and neuroanatomical location.

Seasonal changes in daylength (photoperiod) affect many aspects of mammalian physiology and behavior, including reproduction, metabolism, thermoregulation, and sleep. The circadian pacemaker in the hypothalamic suprachiasmatic nuclei (SCN) regulates these photoperiodic changes. Our studies of the Siberian hamster SCN have shown that two types of neuropeptide-containing neurons, vasopressin (AVP) and vasoactive intestinal peptide (VIP) neurons, respond to short photoperiod by decreasing mRNA expression. The present studies investigated whether photoperiodic inhibition of mRNA expression also occurs in somatostatin-synthesizing neurons in the SCN, depends upon the pineal gland, and occurs in neurons in other hypothalamic nuclei. Juvenile Siberian hamsters exposed to either long photoperiod (16 h light/day) or short photoperiod (10 h light/day) for 2 weeks after weaning, were used for these studies. Coronal sections throughout the SCN were prepared and processed for in situ hybridization. The results showed that photoperiod decreased the expression of AVP mRNA and VIP mRNA in the SCN, as seen previously, but not somatostatin mRNA. Furthermore, pinealectomy did not attenuate the short photoperiod inhibition of AVP mRNA and VIP mRNA expression in the SCN. Also, short photoperiod inhibition of AVP mRNA expression was found in the paraventricular and supraoptic nuclei, as well as in the SCN. These results show that short photoperiod inhibition of mRNA expression is partially selective among the neuropeptides, but is not restricted to the SCN. Furthermore, these findings suggest that photoperiodic regulation of neuropeptide mRNA expression is independent of pineal melatonin secretion and gonadal steroid secretion.

Animals↗
PubMed2002

The photoperiodic entrainment and induction of the circadian clock regulating seasonal responses in the migratory blackheaded bunting (Emberiza melanocephala).

The properties of the circadian photoperiodic oscillator have been investigated in detail only in the Japanese quail. While the study of the quail is clearly very important, one cannot simply assume that other species, especially passerines that seem to have a different circadian organization than quail, function the same way. The current set of experiments was conducted to understand the entrainment and photoinduction of the circadian photoperiodic oscillator in a passerine species, the blackheaded bunting (Emberiza melanocephala). The experimental paradigm used skeleton photoperiods with two light periods, the first called the "entraining light pulse" (E-pulse) and the second called the "inducing light pulse" (I-pulse). Three experiments were performed on photosensitive male birds (N = 6-8/group). Experiment 1 investigated the effects of the temporal relationship between E- and I-pulses on photoperiodic induction. Buntings entrained to 8h: 16h L:D for 4 wk were released into constant dim light (LLdim, approximately 1 lux). Beginning on subjective day 8, they received for 8 wk, E- and I-pulses only at alternate cycles. While I-pulse was 1h and always began at zt 11.5, E-pulse varied in duration and timing (the 1h E-pulse beginning either at zt 0, zt 5, or zt 9, the 4h one beginning at zt 0 or zt 6, and the 10 h one at zt 0; zeitgeber time 0 = time of lights-on under 8h: 16h L:D prior to release into LLdim). A photoperiodic response was induced only when the E-pulse began at zt 0, and thus the beginning of E- and 1-pulses were separated by 11.5h. Experiment 2 determined whether the duration of the E-pulse influences the position of the photoinducible phase (phii) of the circadian photoperiodic oscillator. Birds were entrained to 1h:23h L:D or 10h: 14h L:D for 2 wk, and then exposed to 1h I-pulse at zt 11.5, zt 15, or zt 18.5 for another 8 wk. Photoperiodic induction occurred at all 3 zts in birds entrained to 10h but only at zt 11.5 in birds entrained to 1h, which infers the circadian rhythm of photoinducibility (CRP) in buntings was re-entrained when I-pulse fell at zt 15 and after. The last experiment examined the possibility of the re-entrainment of the CRP to light pulses falling at zt 15 and after. Birds received 1h I-pulse for 8wk at zt 15 following 2wk of 2.5h:21.5h L:D or 3.5h:20.5h L:D, or at zt 21.5 or zt 22.5 following 2 wk of 10h: 14h LD. Photoperiodic induction was consistent with the hypothesis of the re-entrainment of the CRP under these light-dark cycles. The I-pulse appeared to be interpreted as a "new dawn", and so the photoperiodic induction was determined by the coincidence of phii with the E-pulse. These results suggest a phase-dependent action of light on the circadian oscillator regulating photoperiodic responses in the blackheaded bunting. This could be a useful strategy for a photoperiodic species to regulate its seasonal responses in nature.

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