Photoperiodic induction in quail as a function of the period of the light-dark cycle: implications for models of time measurement

Impact of dichromatic lighted incubation on hatching result and post-hatch performance of broiler chickens

This study was planned to evaluate the impact of dichromatic lights during incubation on the hatching and post-hatch performance of broiler chickens. A total of 500 eggs of broiler breeder (Ross 308; Age 44 weeks) were evenly divided according to a completely randomized design into 4 treatments having 5 replicates and 25 eggs each. Treatments consisted of dichromatic lights Blue + Red (BR), Green + Red (GR) and Green + Blue (GB) provided at an intensity of 250 lx for 12 h a day along with a Dark (D) environment. After hatching 200 chicks (50 from each respective light group) were divided into 4 treatments with 5 replicates each having 10 chicks. Results indicated a higher embryo index (13.12%) in the GR group on the 12th day of incubation; while an ideal hatch window was observed in GR and GB (98.18% and 96.00% hatched chicks) lighting groups. In hatching traits, higher hatchability (86.15) and hatch of fertile (93.85) percentages were observed in GR lighting followed by GB, BR and Dark treatment groups; while dead-in shell embryos were lowest in the GR group. In growth performance, higher feed intake (513.20 g) and body weight (479.20 g) were observed in the GB group followed by GR, BR and dark group; and feed conversion ratio (FCR) was better in the GR group (1.06). In welfare parameters, improved physical asymmetry (0.90 mm) and tonic immobility (54.40 s) were measured in the GR group followed by GB, BR and the dark group. It was concluded that under experimental conditions when broiler breeder eggs are provided with GR lighting during incubation, it can help to improve hatchability, growth performance and welfare traits in chicks.

Effects of prenatal dichromatic light exposure on hatching results and post-hatch performance of Japanese quail

Present study evaluated the effect of lighted incubation on pre- and post-hatch performance of Japanese quail. In a completely randomized design, 1200 eggs were evenly divided into 4 treatments groups having six replicates (each tray was considered as replicate), 50 eggs each. Different dichromatic lights (Green + Red; GR, Green + Blue; GB, and Blue + Red; BR) of 250 lux were provided during incubation for 12 h daily and effects of these lights very evaluated on hatching results and post-hatch growth. After hatch, 600 quail chicks were divided into 4 treatments, 6 replicates, and 25 birds each. Regarding hatching traits, better hatchability was found in the GR group compared to GB, BR, and dark group; while early embryonic mortality was lower in BR, GB, and dark group than GR; mid embryonic mortality was lower in dark group and late embryonic mortality was noted in the GR group than those of other treatment groups. In addition, moisture loss during incubation was minimum in BR and dark groups; however, chick spread was better in the GR group. In terms of growth performance, weight gain was better in the GR group; feed intake in dark, feed conversion ratio in BR, and livability were better in BR and GR group. In morphometrics, keel and shank length were higher in all the colored groups (GB, BR, and GR) whereas body length, wing spread, shank circumference, drumstick length, and circumference were higher in the GR group. Regarding serum chemistry, glucose, albumin, and globulin levels were higher in the GR group. It was concluded that under the experimental conditions, GR light at the prenatal stage to Japanese quail eggs positively influenced hatching performance and post-hatch growth.

Functional inhibition of deep brain non-visual opsins facilitates acute long day induction of reproductive recrudescence in male Japanese quail

For nearly a century, we have known that brain photoreceptors regulate avian seasonal biology. Two photopigments, vertebrate ancient opsin (VA) and neuropsin (OPN5), provide possible molecular substrates for these photoreceptor pathways. VA fulfills many criteria for providing light input to the reproductive response, but a functional link has yet to be demonstrated. This study examined the role of VA and OPN5 in the avian photoperiodic response of Japanese quail (Coturnix japonica). Non-breeding male quail were housed under short days (6L:18D) and received an intracerebroventricular infusion of adeno-associated viral vectors with shRNAi that selectively inhibited either VA or OPN5. An empty viral vector acted as a control. Quail were then photostimulated (16L:8D) to stimulate gonadal growth. Two long days significantly increased pituitary thyrotrophin-stimulating hormone β-subunit (TSHβ) and luteinizing hormone β-subunit (LHβ) mRNA of VA shRNAi treated quail compared to controls. Furthermore, at one week there was a significant increase, compared to controls, in both hypothalamic gonadotrophin releasing hormone-I (GnRH-I) mRNA and paired testicular mass in VA shRNAi birds. Opn5 shRNAi facilitated the photoinduced increase in TSHβ mRNA at 2 days, but no other differences were identified compared to controls. Contrary to our expectations, the silencing of deep brain photoreceptors enhanced the response of the reproductive axis to photostimulation rather than preventing it. In addition, we show that VA opsin plays a dominant role in the light-dependent neuroendocrine control of seasonal reproduction in birds. Together our findings suggest the photoperiodic response involves at least two photoreceptor types and populations working together with VA opsin playing a dominant role.

Effect of early photostimulation at 15-weeks of age and everyday spin feeding on broiler breeder performance

To prevent broiler breeders from growing too quickly and becoming too large for optimum reproduction, their dietary intake is restricted. While current restricted feeding programs, such as skip-a-day feeding (SAD), improve the economic efficiency of broiler breeder operations, this management practice impacts bird welfare. There is an interest in finding strategies that could reduce the impact of feed restriction during broiler breeder rearing. This research investigated the effects of feeding pullets on an advanced growth curve for early photostimulation at 15 wk (15P) or standard growth curve for photostimulation at 21 wk (21P), using either an every-day-spin feeding program (EDS) or SAD feeding, on the reproductive parameters of broiler breeder hens in a 2 × 2 factorial arrangement. Overall, advancing the growth curve (15P) decreased blood corticosterone levels compared to 21P, but EDS resulted in higher blood corticosterone levels compared to SAD. At the end of rearing in both 15P and 21P, EDS pullets weighed less than SAD pullets. The onset of egg production was 20 and 24 wk of age for the 15P and 21P hens, respectively. Despite an earlier onset, 15P hens did not produce more eggs than 21P hens through 65 wk of age. Egg weight was reduced for 15P compared to 21P until 30 wk of age. The 15P hens had a greater number of double yolk eggs than the 21P hens. Fertility and hatch were not impacted by the advanced growth curve and early photostimulation. Although the current research indicates the potential to reduce feed restriction associated welfare issues by rearing broiler breeder pullets for an earlier photostimulation onset, further research in needed to determine if this management technique can be improved to optimize hen reproductive efficiency.

Effect of pre-hatch incubator lights on the ontogeny of CNS opsins and photoreceptors in the Pekin duck

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Incubated eggs with and without light had no effect on post-hatch production.

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Light does not influence the ontogeny of retinal rod and cone photoreceptors.

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Brain OPN4 mRNA is increased the later stages of embryonic development.

The Pekin duck is a valuable agricultural commodity globally and in the United States. Pekin ducks are seasonal breeders; they are sensitive to light and thus, research on the neuroendocrine and behavioral responses are needed to maximize production and to improve their welfare. There is compelling evidence that specific wavelengths of light may adversely alter the growth and welfare of meat (grow out) ducks. However, despite a birds’ dependence upon light, in commercial poultry hatcheries, incubators almost exclusively hold eggs in the dark. Therefore, our objective was to determine the effects of lighting on the expression of retina photoreceptors (RPs) and deep brain photoreceptors (DBPs) during duck embryological development. Two groups of ducks were raised with and without light over 21 d from egg laying, embryonic day 0. Brain and retinal tissues were collected at embryonic days 3, 7, 11, 16, and 21 of a 24 d incubation period. qRT-PCR was performed on RPs (OPN1LW, OPN2SW, OPN1SW, MAFA, RHO, and RBP3) and the DBP OPN4M from retinal and brain samples, respectively. We find that the presence and absence of light during pre-hatch incubation, had no influence on the expression of any retinal photoreceptor. However, a late embryological increase in DBP OPN4M expression was observed. Taken together, the impact of light during pre-hatch incubation does not impact the overall post-hatch production. However, future directions should explore how OPN4M pre-hatch activation impacts Pekin duck post-hatch development and growth.

Annual gonadal cycles in birds: modeling the effects of photoperiod on seasonal changes in GnRH-1 secretion

This paper reviews current knowledge of photoperiod control of GnRH-1 secretion and proposes a model in which two processes act together to regulate GnRH1 secretion. Photo-induction controls GnRH1 secretion and is directly related to prevailing photoperiod. Photo-inhibition, a longer term process, acts through GnRH1 synthesis. It progresses each day during daylight hours, but reverses during darkness. Thus, photo-inhibition gradually increases when photoperiods exceed 12h, and reverses under shorter photoperiods. GnRH1 secretion on any particular day is the net result of these two processes acting in tandem. The only difference between species is their sensitivity to photo-inhibition. This can potentially explain differences in timing and duration of breeding seasons between species, why some species become absolutely photorefractory and others relatively photorefractory, why breeding seasons end at the same time at different latitudes within species, and why experimental protocols sometimes produce results that appear counter to what happens naturally.

Avian circadian organization: a chorus of clocks

In birds, biological clock function pervades all aspects of biology, controlling daily changes in sleep: wake, visual function, song, migratory patterns and orientation, as well as seasonal patterns of reproduction, song and migration. The molecular bases for circadian clocks are highly conserved, and it is likely the avian molecular mechanisms are similar to those expressed in mammals, including humans. The central pacemakers in the avian pineal gland, retinae and SCN dynamically interact to maintain stable phase relationships and then influence downstream rhythms through entrainment of peripheral oscillators in the brain controlling behavior and peripheral tissues. Birds represent an excellent model for the role played by biological clocks in human neurobiology; unlike most rodent models, they are diurnal, they exhibit cognitively complex social interactions, and their circadian clocks are more sensitive to the hormone melatonin than are those of nocturnal rodents.

Daily light regulates seasonal responses in the migratory male redheaded bunting (Emberiza bruniceps)

This study analyzed the role of day length in regulation of seasonal body fattening and testicular growth in a latitudinal Palaearctic-Indian migrant, the redheaded bunting (Emberiza bruniceps). When exposed to increasing photoperiods (hours of light: hours of darkness; 11.5L:12.5D, 12L:12D, 12.5L:11.5D, 13L:11D, 14L:10D, and 18L:6D) for 9-12 weeks, buntings responded in a photoperiod-dependent manner and underwent growth and regression cycle under photoperiods of > or =12 hr per day. Also, the response to a long photoperiod of birds that were held under natural photoperiods at 27 degrees N for 2 years was similar to those who arrived the same year from their breeding grounds ( approximately 40 degrees N), suggesting that the experience of higher amplitude day-night (light-dark, LD) cycles during migratory and breeding seasons were not critical for the subsequent response (initiation-termination-reinitiation) cycle. Another experiment examined entrainment of the circadian photoperiodic rhythm in buntings by subjecting them to T=24+/-2 hr LD-cycles with 8 hr photophase and to T=22 and 24 hr with 11 hr photophase. The results showed a reduction in critical day length under T=22 hr LD-cycle. In the last experiment, we constructed an action spectrum for photoperiodic induction by exposing birds for 4.5 weeks to 13L:11D of white (control), blue (450 nm), or red (640 nm) light at irradiances ranging from 0.028 to 1.4 W m(-2). The threshold light irradiance for photoinduction was about 10-fold higher for blue light, than for red and white lights. These results conclude that the daily light of the environment regulates the endogenous program that times seasonal responses in body fattening and testicular cycles of the redheaded bunting.

Wavelength dependency of light-induced effects on photoperiodic clock in the migratory blackheaded bunting (Emberiza melanocephala)

The effects of light wavelength on photoperiodic clock were determined in the migratory male blackheaded bunting (Emberiza melanocephala). We constructed an action spectrum for photoperiodic induction (body fattening, gain in body mass, and gonadal recrudescence) by exposing birds for 4.5 weeks to 13 h light per day (L:D = 13:11 h) of white (control), blue (450 nm), or red (640 nm) color at irradiances ranging from 0.028 to 1.4Wm(-2). The threshold light irradiance for photoinduction was about 10-fold higher for blue, compared to red and white light. Phase-dependent effects of light wavelength on the photoperiodic clock were further examined in the next two sets of skeleton photoperiods (SKPs). In the first set of SKPs, birds were exposed for four weeks to asymmetrical light periods (L:D:L:D= 6:6:1:11 h) at 0.25+/-0.01 W m(-2); two light periods applied were of the same (450nm: blue:blue, B:B; 640nm, red:red, R:R) or different (blue:red, B:R or red:blue, R:B) wavelengths, or of white:white (W:W, controls). Photoperiodic induction occurred under R:R and B:R, but not under B:B and R:B light conditions; the W:W condition induced an intermediate response. The second set of SKPs used symmetrical light periods (L:D:L:D = 1:11:1:11 h), and measured effects also on the activity rhythm. Birds were first exposed to one of the four SKPs (R:R, B:B, R:B, or B:R) for three weeks, subsequently were released into dim constant light (LLdim; approximately 0.01 Wm(-2), the night light used in an L:D cycle) for two weeks, and then were returned to respective SKPs for another three weeks. Activity was greater in the R:R compared to B:B, and in B:R compared to R:B light condition. Zugunruhe (intense nighttime activity, indicating migratory restlessness in a caged situation) developed under the R:R and B:R, but not the B:B and R:B, light condition. Under LLdim, all birds free-ran with a period >24h, the Zugunruhe had a circadian period longer than the daytime activity, and the re-entrainment to SKPs was influenced by the position of light periods relative to circadian phase of the activity rhythm. Photoperiodic induction at the end of 8 weeks was found in the R:R and B:R, but not in B:B, light conditions; in the R:B condition only one bird had initiated testes. Taken together, these results suggest that in the blackheaded bunting, the circadian photoperiodic clock is differentially responsive to light wavelengths; this responsiveness is phase-dependent, and the development of Zugunruhe reflects a true circadian function. Wavelength-dependent response of the photoperiodic clock could be part of an adaptive strategy in evolution of the seasonality in reproduction and migration among photoperiodic species under wild conditions.

Effect of one or two pre-pubertal long days on age at first egg in domestic pullets

1. Two trials were conducted, using 288 brown-egg hybrid pullets in each, to determine the effect on age at first egg (AFE) of exposure to one or two 'long days' during the rearing period. In the first trial, birds were given a single 'long day' of 10, 12 or 14 h at 75, 89 or 103 d of age, with controls maintained on 8-h photoperiods. All treatment groups were transferred to cages at 110 d, and half the birds from each treatment combination given a 6-h increment in photoperiod at 116 d, with the remainder held on 8-h photoperiods. In the other trial, birds were given one or two long days of 14 or 16 h at 96, 107, 117 or 128 d of age; controls were again held on 8-h photoperiods. All groups were moved to cages at 130 d but maintained on 8-h photoperiods. 2. AFE was not significantly affected by one or two pre-pubertal long days, irrespective of when the long day was given or its length. AFE was advanced by 2 to 3 weeks following a transfer from 8 to 14 h at 116 d, independently of whether or not the birds had received a previous long day exposure. 3. It appears that a full-fed egg-type hybrid requires more than two cycles of long days to initiate rapid gonadal development, and that exposure to a single long day during the rearing period will have minimal effect on the timing of sexual maturation and no influence on the response to a subsequent permanent transfer to long days.

Supplementary dim light differentially influences sexual maturity, oviposition time, and melatonin rhythms in pullets

The addition of two 3-h periods of very dim light, one before and one after a normal 8-h photoperiod, advances sexual maturity in pullets by about a week. This trial tested the hypothesis that dim light given before a short day of normal intensity is linked to form a more stimulatory day length and that dim light given after it is photosexually ignored. Pullets were reared from 2 d of age on 8-h photoperiods. From 10 wk, they were continued on 8-h photoperiods, transferred to 16 h, or given an 8-h period of dim light (0.09 lx) immediately before or after the main 8-h photoperiod. The bright/dim and dim/ bright groups matured at the same age, thus disproving the hypothesis tested. Both groups matured 1 wk earlier than the 8-h controls but 5 wk later than birds transferred to 16-h photoperiod. Oviposition time was similar for 8-h controls and bright/dim hens and delayed by 3 h for 16-h birds, but phase advanced by 2.4 h for dim/bright hens. Plasma melatonin rhythm was phase-advanced by about 5 h in the dim/bright hens and retarded by about 5 h in the bright/dim hens, suggesting a 13-h subjective day. However, these treatments were not regarded as fully stimulatory, as a transfer to a normal 13-h photoperiod at this age advances maturity by 5 to 6 wk. These findings show that the addition of a period of dim light to a normal nonstimulatory photoperiod differentially affects the clocks that control sexual maturation, plasma melatonin concentration, and oviposition time.

Photostimulation affects gonadotropin-releasing hormone immunoreactivity and activates a distinct neuron population in the hypothalamus of the mallard

To reveal central mechanisms that transduce photic stimuli to sexually related neuroendocrine changes, Fra-2-ir, an inducible immediate-early gene marker of neuronal activation has been consecutively localized with that of GnRH-I in the brain of mallards that were triggered by artificial light at the photosensitive phase of the reproductive cycle. Strong neuronal activation was found in the POM and PVN in response to 1x or 4x 20 h light exposure that was accompanied with an increase of GnRH-ir in the hypothalamus and a dramatic depletion of GnRH-ir from terminals in the median eminence. The Fra-2 and GnRH-ir profiles, however, were not co-localized in any region at any phase of photostimulation. These results demonstrate profound changes of GnRH-ir in the hypothalamus and reveal a distinct, photoresponsive cell population in the anterior hypothalamic area of the mallard.

Effect of delayed step-up lighting on plasma luteinizing hormone and reproductive function in broiler breeders

The aim of the study was to establish, in contemporary broiler breeders, whether delayed photostimulation at 313 d results in a reproductive response similar to that after photostimulation at 134 d (standard practice). The standard lighting program was compared with a novel program in which daily hours of light were reduced to 3 h during rearing and kept at 3 h until photostimulation at 264 d (8 h) or at 313 d (16 h). This experiment was done with hens fed ad libitum or feed-restricted hens. In photostimulated and nonphotostimulated hens, feed restriction delayed the onset of egg production and enhanced the subsequent rate of laying. Standard photostimulation advanced the onset of lay and increased the subsequent rate of lay in hens fed ad libitum and feed-restricted hens. Delayed photostimulation of hens did not impair the photoinduced increase in the concentration of plasma luteinizing hormone (LH) or egg production. Delayed photostimulation in cockerels failed to stimulate LH secretion. Unexpectedly, for feed-restricted hens, transfer from 3 to 8 h light/d at 264 d resulted in an increased in plasma LH and increased egg production. A similar increase in plasma LH was observed for cockerels subjected to the same lighting treatment. We concluded that, in broiler breeder hens, the reproductive response to photostimulation is not impaired if photostimulation is delayed for up to 313 d. Cockerels may not respond well to delayed photostimulation.

Pharmacological characterization, anatomical distribution and sex differences of the non-NMDA excitatory amino acid receptors in the quail brain as identified by CNQX binding

The distribution of non-N-methyl-D-aspartate binding sites was studied in coronal and sagittal sections through the brain of adult Japanese quail by quantitative autoradiography, using tritiated 6-cyano-7-nitroquinoxaline-2,3-dione as a radioligand. Saturation binding experiments were, in addition, carried out in areas showing high levels of binding (cerebellar molecular layer, nucleus anterior medialis and nucleus infundibularis) and demonstrated that the binding of tritiated ligand was specific and saturable. Competition studies with alpha-amino-3-hydroxy-methyl-4-isoxazole propionic acid and kainic acid indicated that kainic acid strongly inhibited ligand binding in all brain areas. alpha-Amino-3-hydroxy-methyl-4-isoxazole propionic acid was only a weak inhibitor in the hypothalamic nuclei whereas in the cerebellar molecular layer both high and low affinity inhibitions were detected. The highest binding levels of tritiated ligand were observed in the molecular layer of the cerebellum. Very high levels of binding were detected in various preoptic/hypothalamic sites including the nucleus suprachiasmaticus pars medialis, nucleus anterior medialis hypothalami, nucleus infundibularis, nucleus mammillaris medialis, nucleus posteromediale hypothalami and nucleus hypothalami ventromedialis. High levels of binding were also detected in the bulbus olfactorius, bed nucleus commissuralis anterior, bed nucleus commissuralis pallii, nucleus accumbens, bed nucleus striae terminalis and nucleus interpeduncularis. In the preoptic area/hypothalamus, high levels of binding were clearly present in all areas that contain gonadotropin releasing hormone cells or fibers. In the pons and mesencephalon, moderate levels of binding were associated with catecholaminergic areas such as the area ventralis tegmentalis (area ventralis of Tsai) and the locus coeruleus. Saturation analysis demonstrated the presence of a higher number of binding sites in females than in males in the cerebellar molecular layer, nucleus infundibularis and nucleus anterior medialis. This latter difference was confirmed in the one point assays that also identified higher levels of specific binding in the nucleus suprachiasmaticus pars medialis of males as compared with females. These anatomical data suggest a possible implication of non-N-methyl-D-aspartate receptors in the synthesis and/or release of both gonadotropin releasing hormone and catecholaminergic neurotransmitters that should now be tested by pharmacological experiments.

A direct comparison of photoperiodic time measurement and the circadian system in European starlings and Japanese quail

The extent to which circadian rhythms are involved in photoperiodic time measurement in quail is enigmatic, and earlier investigations have produced results consistent with an hourglass clock or one involving damped circadian oscillators. To address the problem further, the present authors carried out a direct comparison between the clocks in quail and those in starlings. Starlings possess strongly self-sustaining circadian oscillators. In Experiment 1, comparisons of testicular growth were made between the two species when birds were exposed to light:dark (LD) 6:30, LD 6:18, and LD 18:6. Starlings grew their testes rapidly under both LD 6:30 and LD 18:6, and they became photorefractory (under LD 6:18, the testes remained undeveloped). Quail grew their testes rapidly under LD 18:6 but did not do so under LD 6:30 or LD 6:18. In Experiment 2, entrainment of the activity rhythm under cycles of LD 6:30 was investigated by measuring the phase of the rhythm after release into constant darkness (DD). Birds were exposed to either 10 cycles or 11 cycles of LD 6:30 prior to DD. Starlings maintained their 24-h rhythmicity under LD 6:30 and always free ran from the phase of the subjective day. By contrast, quail showed circadian activity approximately 24 h after every light pulse and free ran from the phase of the last light pulse received. In Experiment 3, phase response curves (PRCs) were generated to 6-h light pulses. The species were strikingly different; starlings produced a Type 1 PRC, whereas quail produced a Type 0 PRC. More important, in quail the 6-h light pulse had the same effect regardless of circadian time and in almost every case activity free ran from the position of the 6-h light pulse. The results in quail are consistent with the photoperiodic time measurement system being based on a weakly self-sustaining (rapidly damping) circadian system that is invariably reset by 6 h of light, whereas in starlings the pacemakers are strongly self-sustaining. The results support the notion that hourglass pacemakers can be highly damped circadian pacemakers.

The photoperiodic clock is blackheaded buntings (Emberiza melanocephala) is mediated by a self-sustaining circadian system

Three experimental protocols were employed to clarify whether the circadian system is involved in photoperiodic time-measurement in the blackheaded bunting, Emberiza melanocephala. In a single-pulse paradigm, one 8-h light pulse was delivered at different times to groups of birds across three days of constant darkness (DD). Photoperiodic induction, as measured by a rise in plasma luteinizing hormone (LH), showed clear circadian rhythmicity. The second experiment examined the LH responses in birds exposed to lighting cycles using a Nanda-Hamner type of protocol and confirmed full photostimulation under 6L:30D. The third experiment measured the time of the first photoinduced rise in LH in birds subjected to 30 h of continuous light following entrainment under short days (6L:18D). This experiment aimed to identify the position of the photoinducible phase (phi i). LH first rose at hour 18 following dawn indicating that phi i lies in the middle of the day. Plasma concentrations of melatonin were also measured under 6L:18D and 6L:30D light cycles as another physiological marker of the circadian systems in buntings. The pattern of melatonin secretion with the driving oscillator being circadian in nature. It is concluded that the circadian pacemaker driving the photoinducible rhythm in blackheaded bunting is strongly self-sustaining and free-runs under constant conditions.

Does unusual entrainment of the circadian system under T36h photocycles reduce the critical daylength for photoperiodic induction in Japanese quail?

In photoperiodic species, short daylength resonance cycles of modulo t + 1/2 (t = 24 h) behave like long days because they entrain the circadian system so that alternate light pulses coincide with the photoinducible phase (Oi) in castrated quail. However, while a long-day response after exposure to a single long daylength is readily detected by a rise in plasma LH (photoinduction), long-term exposure to LD 6:30 is ineffective in this respect. To discover whether this occurs because of unusual entrainment, circadian rhythms in quail and starlings were investigated. Whereas starlings entrained in the expected way with alternate pulses falling at different circadian phases, activity bouts in quail appeared to follow 24 h after successive light pulses. Because of this, activity was examined in free-running conditions to confirm that the pacemaker in quail was indeed being reset to a constant phase (reset to circadian time [CT] 0) by successive pulses. Examination of the circadian rhythms of plasma melatonin secretion under LD 6:30 also showed a resetting to CT 0. The positioning of all light pulses at the same circadian phase in the early subjective day explains the lack of photoinduction in quail since Oi in the early subjective night phase remains unilluminated. A second feature in quail is that when the length of the photophase is gradually increased within T36h cycles, there is a progressive increase in the degree of photoinduction although the photophase length remains well below the critical daylength for induction in normal T24h cycles. We therefore tested whether Oi is reset to a constant phase by successive pulses in LD 6:30, and that this phase is also advanced relative to light onset so that photophases shorter than the critical daylength can interact with Oi to cause induction. Such a reduction in critical daylength relative to successive LD 6:30 pulses was confirmed by transferring quail to various types of long day and measuring the change in LH secretion. When the long-day test was replaced with continuous light, stimulation of LH secretion occurred 5-7 h earlier in quail pretreated with LD 6:30 and LD 6:54 compared to quail pretreated with LD 6:18 or LD 6:42, implying that Oi had been markedly phase advanced under resonance cycle.

Photoperiodic activation of fos-like immunoreactive protein in neurones within the tuberal hypothalamus of Japanese quail

Photoperiodic stimulation of quail (Coturnix coturnix japonica) resulted in the appearance of a nuclear fos-like protein within neurones of the basal tuberal hypothalamus. On transfer to long days the number of neurones containing this fos-like immunoreactivity increased from about 150 to 700, the neurones being scattered throughout the length of the tubero-infundibular complex. This activation had occurred by early in the second long day and was maintained for at least three long days. Over this period circulating levels of LH increased seven-fold, indicating that photoperiodic induction had taken place in the birds. A similar time-course of fos-like induction occurred in castrated quail exposed to a single long day and then returned to short days. Activation mirrored the long-term changes in LH secretion found in this paradigm and fos-like immunoreactivity showed the same "carry-over" characteristics of photoperiodic induction, being maximal two days after the quail had been exposed to the single long day (and were again on short days) and when LH secretion was at its maximum. Activation of fos-like immunoreactive cells did not take place when long-day quail were transferred to short photoperiods. The evidence supports the view that the neurones being activated are involved in a specific fashion in the avian photoperiodic response.

The circadian nature of melatonin secretion in Japanese quail (Coturnix coturnix japonica)

Plasma melatonin concentrations were measured in Japanese quail held under different photoperiods and constant darkness (< 1 lux). When subjected to LD6:18 (6 hr light: 18 hr darkness), levels rose approximately 2 hr after lights-off, attained a peak level 8 hr after lights off, and subsequently declined to low daytime levels before the next lights-on signal. This generated a distinct daily rhythm in melatonin secretion with a duration of approximately 13 h. On exposing quail to a range of photoperiods, containing 6, 9, 11, 12, 13, 15, 18, or 20 hr of light per day, the onset of melatonin secretion remained essentially similar with the rise occurring soon after lights-off. However, the offset of melatonin secretion was suppressed by the light of the next day and thus a much truncated rhythm was produced under long (> 12 hr) photoperiods. Importantly, between night lengths of 4 to 18 hr (i.e., LD 20:4 to LD 6:18) a linear relationship existed between the duration of night-length and secretion of melatonin with the duration increasing by about 0.8 hr for each additional hour of darkness. If quail were released into darkness following a short (LD 6:18) or long (LD 20:4) day schedule, the rhythm persisted for at least two cycles with peaks occurring at about 24 hr intervals. In those quail coming into darkness from long days (LD 20:4), the rhythm of melatonin secretion decompressed rapidly on both sides of the peak, indicating that both the onset and offset of melatonin secretion were suppressed under long days.(ABSTRACT TRUNCATED AT 250 WORDS)

Photoperiodic control of reproduction in the domestic hen

Egg laying in domestic hens exposed to natural lighting begins shortly after the winter solstice, peaks in early spring, begins to decrease before the fall equinox, and is at its lowest during the late fall and early winter. The seasonal cycle of egg production phase-leads that of the changes in day length. This seeming anomaly can be explained if it is accepted that 1) short days are photoperiodically neutral and do not actively inhibit gonadotropin-releasing hormone (GnRH)-I neurons; and 2) long days are photoperiodically active, transducing both stimulatory and inhibitory inputs to GnRH-I neurons. The development of a long day-induced inhibitory input results in a form of photorefractoriness. Around the winter solstice, photorefractoriness is dissipated by prolonged exposure to short days, allowing GnRH-I neurons to express a photoperiodic-independent, genotype-dependent, level of activity. This is sufficient to stimulate egg laying before the minimum photoperiod for photoinduced gonadotropin release is reached in early spring. When day length begins to decrease after the summer solstice, the photoinduced stimulatory input to GnRH-I neurons is reduced, unmasking the photoinduced inhibitory input. As a consequence, the activity of GnRH-I neurons decreases rapidly and the intensity of egg laying decreases. The minimum and maximum day lengths required to stimulate reproductive function in short-day hens, calculated from the photoperiodic response curves (PRC) for luteinizing hormone release are about 10 and 13 h, respectively, depending on genotype.(ABSTRACT TRUNCATED AT 250 WORDS)

Circadian nature of the photoperiodic clock in Japanese quail

The photoperiodic clock in quail (Coturnix coturnix japonica) is based upon a rhythm of photoinducibility (phi i) but the extent to which this rhythm is circadian remains unclear. Two types of experiment investigated this situation. In the first, gonadectomized quail were adapted to live in periods of darkness by training them on a schedule containing one short day and 3 days of darkness (SD/DD/DD/DD). They were then exposed to a single pulse of 6 or 10 h of light at different times across 3 days of darkness. The photoperiodic response, measured by the increase in LH secretion, showed clear rhythmicity, demonstrating unequivocally the circadian nature of phi i. The second set of experiments employed Nanda-Hamner cycles and varied the length of the photoperiod from 6 to 11 h. Responsiveness in a 36 h or a 60 h cycle was highly dependent upon the length of the photoperiod, something not predicted from theory. For instance, LD 6:30 was not photoperiodically inductive but LD 10:26 was clearly inductive. Close analysis of patterns of LH secretion indicated an unexpected delay before induction occurred and then a rapid rise to a stable level of induction. When LH was measured in every pulse under LD 10:26 there was no evidence that LH levels alternately increased and decreased. This is not consistent with the simplest interpretation of Nanda-Hamner experiments where alternate pulses of light are thought to "entrain" the rhythm or "induce" a photoperiodic response by coinciding with phi i. It is concluded that the quail's photoinducible rhythm is indeed based on a circadian rhythm but one that is only weakly self-sustaining.(ABSTRACT TRUNCATED AT 250 WORDS)