Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Photoperiod”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 55 records · Page 3Linked to original sources
PubMed1999

Effects of long daily photoperiod and bovine somatotropin (Trobest) on milk yield in cows.

Bovine somatotropin (bST) and exposure to long daily photoperiod increase milk yield of dairy cattle. We tested the hypothesis that long daily photoperiod and bST treatment would increase milk yield in an additive manner in lactating cows. At winter solstice, 40 lactating cows were started on a 140-d experiment; cows were greater than 70 d in milk (DIM) and were balanced for uniformity of DIM and milk yield within parity. Cows were randomly assigned to one of four treatments (10/treatment): 1) natural photoperiod, 2) natural photoperiod + bST (14 mg/d Trobest i.m.), 3) long daily photoperiod (18 h of light and 6 h of darkness/d), or 4) long daily photoperiod + bST. Long daily photoperiod increased fat-corrected milk (FCM) yield 1.9 kg/d versus natural photoperiod. Treatment with bST increased FCM 5.7 kg/d versus natural photoperiod, and long daily photoperiod + bST increased FCM 5.8 kg/d versus long daily photoperiod. Long daily photoperiod + bST was additive, increasing FCM 7.7 kg/d versus natural photoperiod. Serum somatotropin increased with bST, but not photoperiod, and bST increased serum insulin-like growth factor-I. Long daily photoperiod tended to increase prolactin; bST had no effect. Long daily photoperiod + bST increased dry matter intake (DMI) relative to natural photoperiod and natural photoperiod + bST; long daily photoperiod increased DMI relative to natural photoperiod + bST. Photoperiod had no effect on net energy balance; however, bST decreased net energy balance. Generally, body weight and milk composition did not differ among treatments. In conclusion, combination of bST with long-daily photoperiod tended to amplify the increases in milk yield observed with either treatment individually.

Animals↗
PubMed2000

Effect of an inverse subtropical (19 degrees 13'N) photoperiod on ovarian activity, melatonin and prolactin secretion in Pelibuey ewes.

Twenty-one Pelibuey ewes were used from December 21, 1996 to December 21, 1998. Fourteen of them had never been exposed to artificial photoperiod, and they were maintained on natural photoperiod until March 21, 1997, when they were assigned to natural photoperiod (control group, n=8) or to inverse photoperiod (n=6). The other seven animals had been kept on a long photoperiod (16L:8D) from October 21, 1996 to December 21, 1996, when they entered the present study and were subjected to a gradual decrease in photoperiod, so that they reached an equinox photoperiod (12L:12 D) on March 21, 1997. At that time, they were assigned to natural photoperiod (n=3) or to inverse photoperiod (n=4). Blood samples for progesterone determination were taken twice a week from all the animals. During the second year of the study, prolactin was measured in the samples from five animals in inverse photoperiod and from five control ewes. Hourly samples were obtained to determine the 24-h melatonin profile of five animals from each group on September 21, 1997, December 21, 1997, March 21, 1997, and June 21, 1997. Exposure to inverse photoperiod resulted in a gradual shift on the annual reproductive cycle, so that the second ovulatory season was advanced by 5 months in the ewes kept on inverse photoperiod as compared to the control ewes (P<0.05). There were wide variations in the dates for the onset and the end of the ovulatory season within the inverse photoperiod groups, and three animals in this groups maintained ovulatory activity for at least 18 consecutive months. The duration of melatonin secretion was directly related to the length of the dark period (P<0.05), and this response was not affected by the calendar date. Prolactin concentrations were directly related to daylength, however, they were also affected by calendar date, being lower in the inverse group as compared to the corresponding time of the annual photoperiodic cycle of ewes on natural photoperiod. It is concluded that reproductive activity, melatonin secretion and prolactin secretion of Pelibuey ewes respond to the small variations in photoperiod that are present at 19 degrees 13'N, and that under natural conditions, photoperiod appears to be the main regulator of ovarian activity at this latitude. However, other factors such as temperature or humidity may act as modulators, and their relative importance could increase at more equatorial latitudes.

Animals↗
PubMed1992

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.

Anestrus↗
PubMed1991

Effect of photoperiod on body weight and food intake of obese and lean Zucker rats.

Although the rat is usually not considered to be sensitive to photoperiod, under some experimental conditions photoperiod responses are unmasked. In addition, we have observed photoperiod-induced changes in body weight gain in lean and obese Zucker rats. In this experiment, body mass, food intake, body composition, brown adipose tissue (BAT) thermogenic state, and blood concentrations of corticosterone, insulin, and glucose were evaluated under one of two lighting conditions: a short (10 h light: 14 h dark) or a long (14 h light: 10 h dark) photoperiod. Plasma corticosterone and glucose concentrations measured under fasting conditions were unaffected by photoperiod in either genotype. The amount of BAT mitochondrial protein isolated was less in long photoperiod rats. BAT mitochondrial GDP binding was unaffected by photoperiod in the lean rats, but tended to be lower in long photoperiod obese rats than in short photoperiod obese rats. Although, photoperiod had no effect on daily food intake of rats exposed to the short versus long photoperiod, body mass was heaviest in obese rats raised in long photoperiod. Plasma insulin was increased in both lean and obese rats in long photoperiod. In addition, fat storage appeared to shift to internal depots in the lean rats exposed to long photoperiod. Our data demonstrate that photoperiod does have an effect on male Zucker rats with respect to body weight and fat distribution, with the obese rats being more sensitive to changes in photoperiod than the lean rats.

Adipose Tissue, Brown↗
PubMed1993

Development of collared lemmings, Dicrostonyx groenlandicus, is influenced by pre- and postweaning photoperiods.

We examined the role of pre- and postweaning photoperiod on postweaning development of collared lemmings. Lemmings were gestated and reared to weaning (19 days of age) in one of three photoperiods: 22L:2D (22 hr of light:2 hr of dark), 16L:8D, and 8L:16D. At weaning, lemmings were either maintained in their natal photoperiod or transferred to one of the other two photoperiods. At the termination of the experiment (10 weeks postweaning) data were collected on somatic characters (body weight, bifid claw width, pelage stage, and guard hair length), serum prolactin (PRL), and reproductive parameters (testes, seminal vesicle, and uterine weights). Somatic characters were predominantly influenced by postweaning photoperiod, when that photoperiod was either long (22L:2D) or short (8L:16D). When lemmings were exposed to an intermediate postweaning photoperiod (16L:8D), development of somatic characters was significantly influenced by the preweaning photoperiod; animals reared in 8L:16D regarded 16L:8D as a long day, whereas those reared in 22L:2D regarded 16L:8D as a short day. Serum PRL responded to photoperiod changes, often reflecting either the increase or decrease in day length, rather than simply the absolute number of light hours per day. Whereas reproductive indices in both sexes were stimulated by transfer from short to long photoperiod, chronic exposure to long photoperiod inhibited male development. No other photoperiod manipulations significantly influenced reproductive parameters. These observations suggest that, in the collared lemming, the neural and/or humoral factors regulating somatic and reproductive characters differ in their response to photoperiod. These results also suggest that the postweaning responses to photoperiod are programmed by earlier (gestational and/or neonatal) photoperiod exposure of the mother and/or the neonates.

Animals↗
PubMed1996

Effect of constant and of changing photoperiods on age at first egg and related traits in pullets.

1. The effects of constant photoperiods and of single (5 h) changes in photoperiod applied at 12 or 17 weeks of age upon age at first egg (AFE) were studied using ISA Brown and Shaver 288 pullets. 2. Birds reared from 2 d of age until after maturity on constant 10 h photoperiods matured 8 d earlier than birds reared on constant 8 h and 5 d earlier than the average for 13 or 18 h photoperiods. 3. A single increment in photoperiod from 8 to 13 h advanced AFE by 23 d (compared to 8 h constant day controls) when applied at 84 d, but by only 6 d when given at 119 d. An increase in photoperiod from 13 to 18 h advanced AFE by only 4 d, averaged across breeds and age at increase. A reduction in photoperiod from 13 to 8 h delayed AFE by 22 d when given at 84 d and by 16 d at 119 d. A similar 5 h reduction in photoperiod, but from 18 to 13 h, retarded maturity by 11 d in ISA Brown pullets, but only when given at 84 d, and delayed AFE in Shaver 288 by 12 d, but only when given at 119 d. This interaction may be partly explained by the different physiological stages reached by the two breeds when the photoperiod was changed. 4. Under constant daylengths cumulative food intake before first egg was positively correlated with photoperiod, but the early AFE for birds on 10 h photoperiods resulted in this group having the lowest cumulative food intake to first egg. 5. A 5 h increase in photoperiod at 84 d significantly reduced the food consumed to first egg, but had no effect when given at 119 d. A 5 h decrease in photoperiod generally increased the food consumed to first egg, but the effect was only significant when the daylength was reduced from 13 to 8 h at 119 d. Food intake to first egg in birds subjected to a change in photoperiod was highly correlated with AFE. 6. The data confirm that sexual development in growing pullets responds more to changes in photoperiod than to the absolute daylength, that changes made at different daylengths are not equivalent and that sensitivity changes with age.

Aging↗
PubMed2002

Reduced body mass, food intake, and testis size in response to short photoperiod in adult F344 rats.

BACKGROUND: Although laboratory rats are often considered classic nonseasonal breeders, peripubertal rats of two inbred strains, F344 and BN, have both reproductive and nonreproductive responses to short photoperiods. Unmanipulated adult rats have not been reported to have robust responses to short photoperiod alone, although several treatments can induce photoperiodic responses in adults. In this study, we tested the hypotheses that unmanipulated F344 rats retain responses to short photoperiod as adults and that they have the necessary elements for an endogenous circannual rhythm of sensitivity to short photoperiod. RESULTS: Relative to rats kept in long photoperiods (L16:D8), adult F344 rats transferred at 4.5 months of age to short photoperiods (L8:D16) had significantly lower testis size, food intake, and body weight. In a second experiment, newly weaned F344 rats underwent an initial period of inhibition of reproductive maturation, lower food intake, and lower body weight in short photoperiod or intermediate photoperiod (L12:D12) relative to rats in long photoperiod. By 18 weeks of treatment, rats in the two inhibitory photoperiods no longer differed from long photoperiod controls. In short photoperiod, rats underwent a second period of slight reproductive inhibition between weeks 35 and 48, but there was an effect on body weight and slight inhibition of food intake only in an intermediate photoperiod. CONCLUSION: Male F344 rats retain photoresponsiveness as adults, with less reproductive inhibition but equivalent nonreproductive responses. There was only weak evidence for an endogenous timer controlling a circannual cycle of sensitivity to short photoperiod.

Aging↗
PubMed1986

Decreased testosterone levels do not mediate short-photoperiod-induced brown fat changes.

Previous studies showed that short photoperiod increased brown fat (BAT) mass and reduced gonadal size and gonadal hormone secretion in hamsters. The present study investigated the possibility that the effects on BAT were dependent on reduced levels of gonadal hormones. BAT from male Syrian hamsters exposed to short photoperiod for 10 wk was significantly greater in mass, protein content, and total maximal citrate synthase and beta-hydroxyacyl-CoA dehydrogenase activities than was BAT from long-photoperiod hamsters, These differences between short- and long-photoperiod exposure were observed in hamsters housed at 21 as well as at 8 degrees C. Short photoperiod also increased the total recovered mitochondrial GDP binding, a finding consistent with increased BAT thermogenic capacity. These short-photoperiod effects were neither mimicked by castration of long-photoperiod hamsters nor prevented by high levels of testosterone administered to short-photoperiod animals. Castration did attenuate the effects of short photoperiod on BAT growth if, after surgery and prior to short-photoperiod exposure, the animals were housed at a long photoperiod for 2-3 wk. In contrast, in hamsters immediately placed at short photoperiod after surgery, castration did not inhibit short-photoperiod effects. The present three experiments demonstrate that, in addition to increasing BAT mass, short photoperiod elevates the thermogenic capacity of BAT, and this elevation does not require the absence or a much reduced testosterone level.

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed1989

Differential effects of photoperiodic history on the responses of gonadotrophins and prolactin to intermediate daylengths in the male Syrian hamster.

The effect of photoperiodic history on the neuroendocrine response to intermediate daylengths (11-13.5 hr of light) was investigated in the male Syrian hamster. The duration of the nocturnal peak of pineal melatonin content was inversely proportional to photoperiod and independent of photoperiodic history. Serum levels of prolactin were lower in animals exposed to shorter photoperiods. Photoperiodic history had little effect on the response of serum prolactin to intermediate daylengths. Serum luteinizing hormone (LH) concentrations were also lower in shorter photoperiods, but in addition were sensitive to the direction of photoperiodic change, so that a single photoperiod could be interpreted as either stimulatory or inhibitory to LH secretion. This effect of photoperiodic history was expressed at intermediate photoperiods with 12-13.5 hr of light. The sensitivity of serum follicle-stimulating hormone (FSH) levels to photoperiodic history was masked by an early onset of photorefractoriness. Testicular size and serum testosterone levels revealed weaker effects of photoperiodic history; these were attributed to the dissociation between gonadotrophin and prolactin secretion induced by intermediate daylengths. The contrasting effects of photoperiodic history on the secretion of LH and prolactin may represent the expression of multiple photoperiodic time-measuring systems.

Aging↗
PubMed2004

Effects of photoperiod history on immune responses to intermediate day lengths in Siberian hamsters (Phodopus sungorus).

Seasonal changes in day length enhance or suppress immune function in individuals of several mammalian species. Siberian hamsters (Phodopus sungorus) are long-day breeders that adjust reproductive physiology and behavior, body mass, and immune function following exposure to short photoperiods. Photoperiods of intermediate-duration, encountered in nature by juvenile hamsters born in early-spring and by those born in mid-summer, trigger gonadal development in the former cohort and inhibit the onset of puberty in the latter. Divergent reproductive responses to the same intermediate photoperiod depend on a photoperiod history, communicated during gestation. These experiments assessed whether photoperiod history during gestation likewise impacts immunological responses to intermediate photoperiods. Male hamsters were gestated in long photoperiods and remained in long photoperiods postnatally, or were transferred to an intermediate-duration or a short-duration photoperiod; other males were gestated in short days and transferred to an intermediate-duration photoperiod at birth. Long days stimulated, and short days inhibited, somatic and reproductive development; intermediate day lengths either accelerated or inhibited somatic and reproductive development, depending on whether hamsters were gestated in short days or long days, respectively. By contrast, photoperiod during gestation did not affect most immune endpoints. The data suggest that photoperiodic mechanisms that enhance and suppress several aspects of immunity in young-adult hamsters are not responsive to prenatally communicated photoperiod history information.

Age Factors↗
PubMed2005

Indoleamines and 5-methoxyindoles in trout pineal organ in vivo: daily changes and influence of photoperiod.

This study describes the diel rhythms in several indoleamines, melatonin, and related 5-methoxyindoles in the pineal organ of rainbow trout in vivo. In addition, the effect of different photoperiod conditions was evaluated. Melatonin levels displayed clear daily rhythms in the pineal organ of rainbow trout kept experimentally under long (LD 16:08), neutral (LD 12:12), and short (LD 08:16) photoperiods. Duration of melatonin signal was dependent on the night length of prevailing photoperiod, while peak amplitude was higher when lengthening the photoperiod. Significant daily rhythms in 5-HT content, the precursor of melatonin synthesis, were found in neutral and short photoperiod with increases of the amine content just after the light-dark interphase and decreases in the middle of the night, which were more important under short photoperiod. In contrast, no significant 24-h cyclic variation was found in pineal 5-HT content under long photoperiod. Daily profiles in the content of the main 5-HT oxidative metabolite, the 5-hydroxyindoleacetic acid (5-HIAA), outlined those of the amine precursor. The chronograms of both aminergic compounds contrast with those of 5-hydroxytryptophan content, which displayed a net tendency to increase at night. This study also provides evidence for the existence of daily cyclic changes in the content of 5-methoxytryptamine (5-MT), 5-methoxyindoleacetic acid (5-MIAA), and 5-methoxytryptophol (5-MTOL) in trout pineal organ, which were also dependent on photoperiod. The 24-h profiles in 5-MT content correlated well with those of 5-HT, showing a peak at the first hour of darkness in all photoperiodic conditions, and a decay at midnight only in both neutral and long photoperiods. Similarly, the content of 5-MTOL also displayed high values during the day-night transition in trout kept under neutral and long photoperiods, followed by a slow decay all along the night. Finally, levels of 5-MIAA increased in all photoperiods when lights were turned off, being this nocturnal increase maximal in fish kept under LD 16:08. These results suggest that light-dark cycle modulates daily rhythms in pineal indoles and non-melatonin 5-methoxyindoles by acting mainly through the melatonin synthesis activity, which limits the availability of 5-HT for the oxidative and direct methylation pathways. In addition, it seems that a nocturnally increased synthesis of 5-HT might be a requirement for the optimal formation of melatonin and other 5-methoxyindoles in the pineal organ when trout remain under short photoperiods.

5-Methoxytryptamine↗
PubMed2001

Photoperiodic modulation of GnRH mRNA in the male Syrian hamster.

Male Syrian hamsters (Mesocricetus auratus) are seasonal breeders. They show marked testicular regression when exposed to short autumnal photoperiods, and then remain sexually quiescent for several months. By mid-winter, however, they show a loss in responsiveness to the inhibitory influence of short photoperiods and their testes begin to recrudesce. To shed light on the neuroendocrine mechanism responsible for mediating these reproductive changes, we examined the influence of photoperiod on the expression of GnRH mRNA in the hamster forebrain. Adult males were either exposed to short photoperiods (6L:18D) for 16 weeks or were maintained under long photoperiods (14L:10D); additional animals were exposed to short or long photoperiods for 22 weeks. As expected, exposure to short photoperiods for 12 weeks resulted in a marked decrease (P<0.01) in testicular mass and serum testosterone levels, but after 22 weeks these reproductive parameters were once again significantly elevated (P<0.01). In contrast, quantitative in situ hybridization histochemistry revealed no difference (P>0.05) between the GnRH mRNA levels of the short-photoperiod hamsters and their aged-matched long-photoperiod controls, although an age-related decrease (P<0.05) was evident in both photoperiod-treatment groups. These data emphasize that GnRH mRNA is highly expressed in hamsters even when their reproductive axis has been rendered sexually quiescent by exposure to short photoperiods, and that photoperiod-induced changes in GnRH secretion, rather than synthesis, are more likely to regulate the timing of the breeding season. On the other hand, the data indicate that GnRH mRNA levels show an aging-related decrease, regardless of photoperiod, suggesting that in the long term a decrease in GnRH gene expression may contribute to the reduced fertility of old hamsters.

Aging↗
PubMed2001

Photoperiodic control of seasonality in birds.

This review examines how birds use the annual cycle in photoperiod to ensure that seasonal events--breeding, molt, and song production--happen at the appropriate time of year. Differences in breeding strategies between birds and mammals reflect basic differences in biology. Avian breeding seasons tend to be of shorter duration and more asymmetric with respect to changes in photoperiod. Breeding seasons can occur at the same time each year (predictable) or at different times (opportunistic), depending on the food resource. In all cases, there is evidence for involvement of photoperiodic control, nonphotoperiodic control, and endogenous circannual rhythmicity. In predictable breeders (most nontropical species), photoperiod is the predominant proximate factor. Increasing photoperiods of spring stimulate secretion of gonadotropin-releasing hormone (GnRH) and consequent gonadal maturation. However, breeding ends before the return of short photoperiods. This is the consequence of a second effect of long photoperiods--the induction of photorefractoriness. This dual role of long photoperiods is required to impart the asymmetry in breeding seasons. Typically, gonadal regression through photorefractoriness is associated with a massive decrease in hypothalamic GnRH, essentially a reversal to a pre-pubertal condition. Although breeding seasons are primarily determined by photoperiodic control of GnRH neurons, prolactin may be important in determining the exact timing of gonadal regression. In tropical and opportunistic breeders, endogenous circannual rhythmicity may be more important. In such species, the reproductive system remains in a state of "readiness to breed" for a large part of the year, with nonphotic cues acting as proximate cues to time breeding. Circannual rhythmicity may result from a temporal sequence of different physiological states rather than a molecular or cellular mechanism as in circadian rhythmicity. Avian homologues of mammalian clock genes Per2, Per3, Clock, bmal1, and MOP4 have been cloned. At the molecular level, avian circadian clocks appear to function in a similar manner to those of mammals. Photoperiodic time measurement involves interaction between a circadian rhythm of photoinducibility and, unlike mammals, deep brain photoreceptors. The exact location of these remains unclear. Although the eyes and pineal generate a daily cycle in melatonin, this photoperiodic signal is not used to time seasonal breeding. Instead, photoperiodic responses appear to involve direct interaction between photoreceptors and GnRH neurons. Thyroid hormones are required in some way for this system to function. In addition to gonadal function, song production is also affected by photoperiod. Several of the nuclei involved in the song system show seasonal changes in volume, greater in spring than in the fall. The increase in volume is, in part, due to an increase in cell number as a result of neurogenesis. There is no seasonal change in the birth of neurons but rather in their survival. Testosterone and melatonin appear to work antagonistically in regulating volume.

Animals↗
PubMed1998

Spontaneous testicular regression in collared lemmings (Dicrostonyx groenlandicus) exposed to prolonged long photoperiod.

Reproductive maturation and attainment of maximal gonadal size in collared lemmings (Dicrostonyx groenlandicus) is facilitated by transfer from a short photoperiod (8 h light: 16 h dark) to a long photoperiod (22 h light:2 h dark). However, reproductive maturation in lemmings born in 22 h light:2 h dark is impeded by exposure to the natal photoperiod of 22 h light:2 h dark. Data from adult lemmings suggest that prolonged exposure to a long photoperiod of 20 h light:4 h dark results in gonadal regression. The present experiments were conducted to test the hypothesis that adult lemmings exposed to a prolonged long photoperiod undergo testicular regression. Male collared lemmings were transferred at weaning (19 days of age) from the natal photoperiod of 8 h light:16 h dark to one of two long photoperiods: 22 h light:2 h dark or 24 h light:0 h dark (constant light). Gonadal mass was maximal in both groups 10 weeks after weaning. However, 20 weeks after weaning, gonadal mass in both groups was low (relative to that at 10 weeks), suggesting that regression had occurred. When testes mass was maximal 10 weeks after weaning, animals were transferred in groups from 22 h light:2 h dark to one of several shorter photoperiods: 20 h light:4 h dark, 18 h light:6 h dark, 16 h light:8 h dark, or 8 h light:16 h dark. Testes mass 20 weeks after weaning was greatest, that is, not different from maximal, in animals from the 20 h light:4 h dark and 18 h light:6 h dark groups, intermediate in animals from the 16 h light:8 h dark group, and low in animals from the 8 h light:16 h dark group. These observations indicate that transfer from 22 h light:2 h dark to a slightly shorter photoperiod permits maintenance of gonadal size, but transfer to a short photoperiod causes testicular regression. Body weight, bifid claw width and pelage colour did not change during spontaneous gonadal regression in animals housed in a long photoperiod for 20 weeks. These results suggest that prolonged exposure to an unchanging long photoperiod causes spontaneous testicular regression, and that photoperiod regulates reproductive and somatic parameters independently.

Animals↗
PubMed1994

Photoperiodic effects on puberty and specific 2-[125I]iodomelatonin binding sites in Siberian hamsters.

When juvenile male Siberian hamsters are transferred from a long photoperiod to a short photoperiod, sexual maturation is greatly delayed by a pineal-dependent process. We hypothesized that the eventual onset of puberty during short photoperiod exposure may be caused by a loss of receptors for the pineal hormone, melatonin. This study quantitated specific 2-[125I]iodomelatonin binding sites in the suprachiasmatic nuclei and pars tuberalis of Siberian hamsters exposed to short photoperiod (10 h light per day) for either 12 or 30 weeks and in hamsters exposed to long photoperiod (16 h light per day) for the same time intervals. Photoperiodic exposure significantly affected testes weight. The hamsters exposed to long photoperiod for either 12 or 30 weeks had mean tests weights > 700 mg, in contrast to hamsters in short photoperiod for 12 weeks (mean testes weights < 30 mg) or 30 weeks (mean testes weights approximately 350 mg). The affinity of specific 2-[125I]iodomelatonin binding sites in both regions was significantly lower in hamsters exposed to short photoperiod as compared to hamster exposed to long photoperiod, at either 12 or 30 weeks. In contrast, there were no effects of photoperiod or duration of exposure on the density of specific 2-[125I]iodomelatonin binding sites in either the suprachiasmatic nuclei or the pars tuberalis. Furthermore, a change in the affinity of the specific 2-[125I]iodomelatonin binding sites in the suprachiasmatic nuclei was observed between the hamsters housed in short photoperiod for 12 weeks (sexually immature) and the hamsters housedin short photoperiod for 30 weeks (undergoing puberty).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2006

Control of annual reproductive cycle in the subtropical house sparrow (Passer domesticus): evidence for conservation of photoperiodic control mechanisms in birds.

BACKGROUND: In many birds, day length (= photoperiod) regulates reproductive cycle. The photoperiodic environment varies between different seasons and latitudes. As a consequence, species at different latitudes may have evolved separate photoperiodic strategies or modified them as per their adaptive need. We studied this using house sparrow as a model since it is found worldwide and is widely investigated. In particular, we examined whether photoperiodism in house sparrows (Passer domesticus) at 27 degrees N, 81 degrees E shared features with those exhibited by its conspecifics at high latitudes. RESULTS: Initial experiment described in the wild and captive conditions the gonad development and molt (only in captives) cycles over a 12-month period. Both male and female sparrows had similar seasonal cycles, linked with annual variations in day length; this suggested that seasonal reproduction in house sparrows was under the photoperiodic control. However, a slower testis and attenuated follicular growth among captives indicated that other (supplementary) factors are also involved in controlling the reproductive cycle. Next experiment examined if sparrows underwent seasonal variations in their response to stimulatory effects of long day lengths. When birds were transferred every month over a period of 1 year to 16 hours light:8 hours darkness (16L:8D) for 17-26 weeks, there was indeed a time-of-year effect on the growth-regression cycle of gonads. The final experiment investigated response of house sparrows to a variety of light-dark (LD) cycles. In the first set, sparrows were exposed for 31 weeks to photoperiods that were close to what they receive in between the period from sunrise to sunset at this latitude: 9L:15D (close to shortest day length in December), 12L:12D (equinox, in March and September) 15L:9D (close to longest day length in June). They underwent testicular growth and regression and molt in 12L and 15L photoperiods, but not in 9L photoperiod. In the second set, sparrows were exposed for 17 weeks to photoperiods with light periods extending to different duration of the daily photosensitivity rhythm (e.g. 2L:22D, 6L:18D, 10L:14D, 14L:10D, 18L:6D and 22L:2D). Interestingly, a slow and small testicular response occurred under 2L and 10L photoperiods; 6L:18D was non-inductive. On the other hand, 14L, 18L and 22L photoperiods produced testicular growth and subsequent regression response as is typical of a long day photostimulation. CONCLUSION: Subtropical house sparrows exhibit photoperiodic responses similar to that is reported for its population living at high latitudes. This may suggest the conservation of the photoperiodic control mechanisms in birds evolved over a long period of time, as a physiological strategy in a temporally changing environment ensuring reproduction at the best suited time of the year.

Journal Article↗
PubMed1987

Effect of photoperiod on LH, FSH and prolactin patterns in ovariectomized oestradiol-treated heifers.

Angus and Angus crossbred heifers were ovariectomized, treated with oestradiol implants and randomly assigned to the natural photoperiod of fall to spring for 43 degrees N latitude or extra light simulating the photoperiod of spring to fall. Weekly blood samples were taken for 6 months (fall to spring equinox). All heifers were cannulated every 4 weeks and blood samples were taken for 4 h at 15-min intervals. Sera were assayed for LH, FSH, prolactin and oestradiol. In samples taken weekly, serum LH and FSH concentrations were higher while serum prolactin was lower in heifers exposed to natural photoperiod. There was a photoperiod X time interaction for both FSH and prolactin with concentrations diverging as photoperiod diverged. Circulating concentrations of oestradiol were not different between groups. In samples taken every 4 weeks at 15-min intervals, baseline concentrations of LH and FSH and LH pulse amplitude were higher while prolactin pulse frequency was lower in heifers exposed to natural photoperiod. There was a photoperiod X time interaction for each of these pulsatile characteristics. The correlation between LH and prolactin concentrations estimated from the 15-min samples differed between the two photoperiod treatment groups. The pooled correlation coefficient (r) was -0.12 under natural photoperiod and +0.50 under extra light. There was also a photoperiod X time interaction with negative correlations occurring when photoperiod was decreasing and positive correlations occurring when photoperiod was increasing. These results support the hypothesis that photoperiod alters serum concentrations of LH, FSH and prolactin in cattle.

Animals↗
PubMed1986

Effects of photoperiod on growth, carcass composition, prolactin, growth hormone and cortisol in prepubertal and postpubertal Holstein heifers.

Effects of photoperiod on growth, carcass composition and serum concentrations of prolactin, growth hormone and cortisol were determined in prepubertal and postpubertal Holstein heifers. Forty-two prepubertal (avg body wt 84 +/- 3.0 kg) and 42 postpubertal (avg body wt 303 +/- 7.1 kg) Holstein heifers were utilized. Ten prepubertal and 10 postpubertal heifers were slaughtered before treatment began to obtain initial carcass data. The remaining 32 prepubertal and 32 postpubertal heifers were paired by body weight and randomly assigned to short-day (8 h of light: 16 h of dark) or long-day (16 h of light: 8 h of dark) photoperiods. After exposure to treatments for an average of 139 d, 10 prepubertal and 10 postpubertal heifers from each photoperiod treatment were slaughtered. In prepubertal heifers, photoperiod did not affect (P greater than .10) average daily body weight gain, carcass weight, carcass composition, accretion of carcass fat and carcass protein, or serum concentrations of prolactin, growth hormone or cortisol. However, prepubertal heifers exposed to long-day photoperiods had reduced (P less than .01) urinary N tau-methylhistidine excretion compared with heifers given short-day photoperiods. Postpubertal heifers exposed to short-day photoperiods had greater average body weight daily gain than animals exposed to long-day photoperiods. Although there was no effect of photoperiod (P greater than .10) on carcass or fat depot weights, postpubertal heifers exposed to short days had greater (P = .06) percentages of fat and reduced (P = .07) percentages of protein in the soft tissue of the 9-10-11 rib sections. Fat accretion was greater (P less than .05) in carcasses of postpubertal heifers exposed to short days than heifers given long-day photoperiods, but there was no effect (P greater than .10) of photoperiod on protein accretion. Photoperiod did not affect serum concentrations of growth hormone and cortisol, but serum prolactin tended (P less than .10) to be greater in postpubertal heifers exposed to long days. Under the conditions of this experiment, we conclude that exposure to short-day photoperiods stimulated body weight gain and fat accretion in postpubertal but not prepubertal Holstein heifers.

Animals↗