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PubMed1995

Prenatal androgens modify the reproductive response to photoperiod in the developing sheep.

In most seasonal breeders, photoperiod influences the timing of the transition to sexual maturity. In sheep, males and females express reproductive maturity under different photoperiods. Spring-born males begin the maturational process during lengthening days (spring), whereas females do so during shortening days (autumn). We hypothesized that photoperiod differentially influences the transition to sexual maturity in each sex, and that this difference results from the presence or absence of androgens prenatally. We monitored the timing of sexual maturity in male and female lambs (n = 8 each) and in prenatally masculinized female lambs (n = 7) maintained under controlled photoperiods (natural-simulate or reverse natural-simulate). Circulating LH was analyzed to reveal the timing of the pubertal gonadotropin rise; lambs were gonadectomized and implanted with estradiol to provide a constant feedback on LH secretion. Under natural-simulate photoperiod, LH increased in males at 7.0 +/- 0.3 wk when days were lengthening. In females treated similarly, sexual maturity occurred at 27.0 +/- 0.8 wk when day lengths were decreasing. The reverse photoperiod had no effect on males, but it delayed the expression of sexual maturity in females. Thus, LH also increased in males at 7.1 +/- 0.9 wk, while none of the females maintained under the same photoperiod had elevated LH secretion when the experiment was terminated (32 wk of age). Prenatal treatment with androgens masculinized the reproductive response to photoperiod; as in the males, LH increased in the androgenized females maintained under a reverse natural-simulate photoperiod at 7.1 +/- 0.4 wk.(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗
PubMed1995

Influence of prenatal and postnatal photoperiods on postnatal testis development in the Siberian hamster (Phodopus sungorus).

In Siberian hamsters, juvenile testicular development is regulated to a large extent by photoperiod. Mother hamsters are able to pass photoperiodic information to their male fetuses, and this information can influence their postnatal gonadal development. In this study, we investigated the effects of gestation in long (16L:8D) and short (10L:14D) day lengths on the rates of juvenile testicular growth in several different postnatal photoperiods. On the day of parturition, parents and young from each gestation photoperiod were raised in 14L:10D through Day 13 of life and then were exposed to one of six photoperiods--16L:8D, 15L:9D, 14L:10D, 13L:11D, 12L:12D, or 10L:14D--until Day 32 of age. The data indicated that 15L and 14L are the minimal day lengths required to prevent complete inhibition of testis growth in long (16L) and short day (10L)-gestated hamsters, respectively. These results support earlier findings suggesting that gestation photoperiod can influence the rate of reproductive development in a certain range of "intermediate" postnatal day lengths (14L to 15L), but that gestation photoperiod does not alter the pattern of testis development in hamsters exposed to other (i.e., longer or shorter) postnatal photoperiods. Thus, both the absolute length and the direction of change of photoperiods experienced in early life can influence prepubertal testis growth.

Aging↗
PubMed1998

Effects of photoperiod and age on secretory patterns of luteinizing hormone and testosterone and semen production in male domestic turkeys.

The objective of this study was to determine effects of photoperiod and age on the circulating concentrations of LH, testosterone (T), thyroxine (T4), and semen production in male turkeys. Male turkeys from 10 or 12 wk of age were maintained under either a long-day (LD) photoperiod of 16L:8D up to 35 wk (LL), or a short-day (SD) photoperiod of 6L:18D to 29 wk and then an LD photoperiod of 16L:8D up to 35 wk of age (SL). Plasma concentrations of both LH and T increased by 17 or 18 wk of age under both photoperiods, but higher levels were attained in the LL group prior to 29 wk of age. Both LH and T levels increased significantly within days in the SL group after the group was switched to LD at 29 wk of age. Higher levels of T4 were present in the LL group prior to sexual maturation. No differences were observed in T4 concentration between lighting treatments after sexual maturation. The LL group first produced semen at 20-22 wk of age, which was about 1 wk earlier than first semen production in the SL group. A significantly larger volume of semen was produced in the LL group at most ages. No further increase in semen production was observed in the first 6 wk after the SL group was switched to the LD photoperiod at 29 wk of age. Pulsatile patterns of LH and T were characterized by serial blood sampling at 13, 23, and 35 wk of age under both the LL and SL photoperiods. The baseline levels of both LH and T in male turkeys were influenced by age and photoperiod. However, pulse characteristics (numbers, duration, and amplitude) of LH did not change with age or lighting treatment, while pulse characteristics of T did change with age. We conclude that exposing male turkeys to an LD photoperiod from 10 or 12 wk of age advanced the age of sexual maturation and induced earlier increased concentrations of LH and T.

Aging↗
PubMed2005

Skeleton photoperiods alter delayed-type hypersensitivity responses and reproductive function of Siberian hamsters (Phodopus sungorus).

Photoperiod (day length) can modulate immune function. Whether these photoperiodic effects on immune function are mediated directly by a circadian photoperiodic time measurement system or indirectly by nonspecific (e.g. stressful) effects of light is unknown. To discriminate between these two possibilities, Siberian hamsters (Phodopus sungorus) were housed in either long or short photoperiods (LD 16 : 8 h or LD 8 : 16 h) or in 'skeleton' long or short photoperiods (LD 1 : 14 h: LD 1 : 8 h or LD 1 : 6 h: LD 1 : 16 h). In the skeleton photoperiods, both long- and short-day animals received 2 h of light per day. After 10 weeks in their respective photoperiods, hamsters were tested for an antigen specific immune response using a delayed type hypersensitivity (DTH) model. Reproductive and endocrine responses of hamsters in each of the skeleton photoperiods were equivalent to those in standard long or short days, respectively. Hamsters in skeleton short days and LD 8 : 16 increased DTH responses compared to hamsters in both long-day groups. DTH responses were equivalent in both long-day groups. These results suggest that the influences of day length on immune function potentially are due to circadian photoperiodic time measurement systems.

Animals↗
PubMed2005

Photoperiod regulates multiple gene expression in the suprachiasmatic nuclei and pars tuberalis of the Siberian hamster (Phodopus sungorus).

Photoperiod regulates the seasonal physiology of many mammals living in temperate latitudes. Photoperiodic information is decoded by the master circadian clock in the suprachiasmatic nuclei (SCN) of the hypothalamus and then transduced via pineal melatonin secretion. This neurochemical signal is interpreted by tissues expressing melatonin receptors (e.g. the pituitary pars tuberalis, PT) to drive physiological changes. In this study we analysed the photoperiodic regulation of the circadian clockwork in the SCN and PT of the Siberian hamster. Female hamsters were exposed to either long or short photoperiod for 8 weeks and sampled at 2-h intervals across the 24-h cycle. In the SCN, rhythmic expression of the clock genes Per1, Per2, Cry1, Rev-erbalpha, and the clock-controlled genes arginine vasopressin (AVP) and d-element binding protein (DBP) was modulated by photoperiod. All of these E-box-containing genes tracked dawn, with earlier peak mRNA expression in long, compared to short, photoperiod. This response occurred irrespective of the presence of additional regulatory cis-elements, suggesting photoperiodic regulation of SCN gene expression through a common E-box-related mechanism. In long photoperiod, expression of Cry1 and Per1 in the PT tracked the onset and offset of melatonin secretion, respectively. However, whereas Cry1 tracked melatonin onset in short period, Per1 expression was not detectably rhythmic. We therefore propose that, in the SCN, photoperiodic regulation of clock gene expression primarily occurs via E-boxes, whereas melatonin-driven signal transduction drives the phasing of a subset of clock genes in the PT, independently of the E-box.

Animals↗
PubMed1994

Photoperiodic time measurement in Djungarian hamsters evaluated from T-cycle studies.

We investigated the photoperiodic response to T-cycles (0.5 h of light at intervals ranging from 23.0 h to 25.3 h) of two phenotypes of Djungarian hamsters that either exhibit or lack physiological short-day adjustments under a photoperiod of 9 h light:15 h darkness. Illumination of the same circadian time caused a similar photoperiodic response in both phenotypes. Thus hamsters found to be insensitive under a full short-day photoperiod can exhibit short-day adjustments after exposure to certain T-cycles. Given these results we conclude that the absence of photoperiodic adjustments normally found in short-day-insensitive hamsters results from their atypical entrainment under a full short-day photoperiod. We further suggest that the photoperiodic phenomena seen in Djungarian hamsters cannot be adequately explained by an external coincidence model of photoperiodic time measurement. As a more suitable model, we propose one form of internal coincidence where duration of daily motor activity reflects the phasing of multiple, endogenous oscillators. This conclusion is supported by the close relationship between duration of activity and the photoperiodic response as well as by the observation that a light pulse modulates duration of activity in a phase-dependent manner.

Acclimatization↗
PubMed2000

c-Fos rhythm in subdivisions of the rat suprachiasmatic nucleus under artificial and natural photoperiods.

Recent studies have shown that the waveform of the rhythm of c-Fos photoinduction in the ventrolateral (vl) part of the suprachiasmatic nucleus (SCN) and that of the rhythm in the spontaneous c-Fos production in the dorsomedial (dm) part of the SCN in rats released into constant darkness depend on the photoperiod under which the animals were previously maintained. The aim of the present study was to find out how the rhythms of c-Fos immunoreactivity in both SCN subdivisions are affected by actual light-dark (LD) cycles with various photoperiods, either artificial or natural ones, that animals may usually experience. Rats were maintained under artificial LD cycles, with either a long (16-h photoperiod) or a short (8-h photoperiod) or under natural daylight. In the latter case, c-Fos rhythms were followed in the summer when the photoperiod lasted about 16 h or in winter when it lasted only 8 h. The rhythms of c-Fos immunoreactivity under natural daylight did not differ significantly from those under corresponding artificial photoperiods. Under a long photoperiod, the morning c-Fos rise in the dm- as well as in the vl-SCN occurred about 4 h earlier than under a short one. In both SCN subdivisions, the interval when the nighttime c-Fos immunoreactivity was low, was shorter under a long than under a short photoperiod by roughly 6 h. The morning c-Fos rise in the dm-SCN always preceded that in the vl-SCN. Whereas in the former one the rise was due to the endogenous dm-SCN rhythmicity, in the latter one the rise was induced by the morning light onset. The results show that whereas c-Fos rhythmicity under actual LD cycles is affected by the photoperiod in both SCN subdivisions, mechanism of c-Fos induction in the dm-SCN differs from that in the vl-SCN.

Animals↗
PubMed1999

Formal properties of the circadian and photoperiodic systems of Japanese quail: phase response curve and effects of T-cycles.

A role for the circadian system in photoperiodic time measurement in Japanese quail is controversial. The authors undertook studies of the circadian and photoperiodic system of Japanese quail to try to identify a role for the circadian system in photoperiodic time measurement. The circadian studies showed that the circadian system acts like a low-amplitude oscillator: It is readily reset by light without significant transients, has a Type 0 phase response curve (PRC), and has a large range of entrainment. In fact, a cycle length that is often used in resonance protocols (LD 6:30) is within the range of entrainment. The authors employed T-cycle experiments; that is, LD cycles with 6- and 14-h photoperiods and period lengths ranging from 18 to 36 h to test for circadian involvement in photoperiodic time measurement. The results did not give evidence for circadian involvement in photoperiodic time measurement: T-cycles utilizing 6-h photoperiods were uniformly noninductive (that is, did not stimulate the reproductive system), whereas T-cycles utilizing 14-h photoperiods were inductive (stimulatory). A good match was observed between the phase-angles exhibited on the T-cycles employing 6-h photoperiods and the predicted phase-angles calculated from a PRC generated from 6-h light pulses.

Animals↗
PubMed1996

Short photoperiod-dependent down-regulation of thyrotropin-alpha and -beta in hamster pars tuberalis-specific cells is prevented by pinealectomy.

Hamster hypophyseal pars tuberalis (PT)-specific cells are characterized by the expression of common alpha-chain and TSH beta. Immunoreactivity for these subunits and the morphology of these cells are known to exhibit remarkable seasonal changes. The high density of melatonin (Mel) receptors on PT-specific cells leads to the supposition that fluctuations in circulating Mel levels induced by photoperiodic signals are a crucial factor for the morphological alterations. To more closely investigate transcriptional and translational activities in PT-specific cells, we cloned and sequenced hamster alpha and TSH beta complementary DNA fragments and assessed messenger RNA/protein formation by in situ hybridization and immunocytochemistry under short and long photoperiod and in pinealectomized animals kept in short photoperiod. Hamster common alpha-chain and TSH beta exhibited high sequence homology with the corresponding rat hormones [94% (alpha-chain) and 90% (TSH beta) on the nucleotide level and 100% (alpha-chain) and 96% (TSH beta) on the amino acid level]. Immunocytochemical staining with antibodies directed against the common alpha-chain and TSH beta revealed a reduced immunoreactivity of PT-specific cells under short photoperiod, but this was not altered in pinealectomized animals exposed to short photoperiod. In situ hybridization against both hormonal subunits paralleled these changes, with a dramatic decrease in hormonal messenger RNA in short photoperiod. This regulatory influence was also blocked in pinealectomy. Taken together, these results demonstrate that transcription and translation of hormonal subunits are regulated by photoperiod in hamster PT-specific cells, whereas expression remained unchanged in short photoperiod if pinealectomy was performed. We, therefore, conclude that in hamsters, the Mel Signal not the light regimen per se, is a direct or indirect Zeitgeber for the transduction of photoperiodic information to the secretory activity in this pituitary cell type.

Amino Acid Sequence↗
PubMedDate not supplied

Neuroanatomical approaches to the study of insect photoperiodism.

The anatomical locations of three components of insect photoperiodism--the photoperiodic photoreceptor, photoperiodic clock and hormonal effector--are summarized and compared between species. Among photoperiodic photoreceptors, either the retinal or extraretinal types or both are operative, and there is no general relationship between phylogeny and photoreceptor type. The photoperiodic clock comprises time measurement and counter systems. Currently, it is generally accepted that circadian oscillators are involved in the photoperiodic clock. Several recent studies have raised the possibility that timeless, a circadian clock gene, plays a role in the photoperiodic clock in flies. The dorsal protocerebrum has been identified as an important region regulating the endocrine system for adult, pupal and embryonic diapause controlled by photoperiod. In the blow fly Protophormia terraenovae, neural connections between circadian clock neurons and indispensable neurons in the pars lateralis for diapause induction in the dorsal protocerebrum have been demonstrated. This neural network may provide the access needed to investigate the neural components of the photoperiodic clock.

Animals↗
PubMed2007

Immune responses of piglets to weaning stress: impacts of photoperiod.

An acute stress response can be provoked by abrupt social, nutritional, and environmental changes associated with weaning, and this may disrupt homeostasis and thus compromise well-being. Manipulating environmental factors, such as photoperiod, might provide a simple way to reduce the physiological consequences that piglets experience due to weaning stress. The objective of this study was to evaluate the impacts of photoperiod manipulation across various weaning ages on leukocyte populations, lymphocyte proliferation, natural killer cytotoxicity (NK), chemotaxis, phagocytosis, and immunoglobulin G, cortisol, and BW of piglets during the nursery phase. Sixty-eight crossbred piglets were obtained from sows kept on a short-day (8 h of light/d) photoperiod from d 90 of gestation until weaning. Piglets were weaned at 14, 21, or 28 d of age and kept on a short or long (16 h of light/d) photoperiod until 10 wk of age. Piglet BW and blood samples were collected at weaning and at 6, 8, and 10 wk of age. Pigs weaned at 28 d had reduced neutrophil counts (P < 0.001), phagocytosis (P < 0.001), and lymphocyte proliferation (P < 0.05) at weaning compared with those weaned at 14 and 21 d. Pigs weaned at 21 d tended to have lower (P = 0.08) lymphocyte counts than did pigs weaned at 14 or 28 d. Pigs weaned at 14 d had reduced (P < 0.01) NK relative to those weaned at 21 or 28 d. Photoperiod also influenced pig BW and immune status. Generally, those pigs on the long-day photoperiod and weaned at 28 d were heavier (P < 0.001) than their counterparts weaned at 14 or 21 d. At 6 wk of age, NK was greater (P = 0.002) in pigs kept on a long day and weaned at 14 or 21 d than in pigs weaned at 28 d. Phagocytosis was less (P = 0.005) at 6 wk of age, but was greater at 8 wk, in piglets kept on the long day and weaned at 28 d than in long-day pigs weaned at 14 or 21 d. These results suggest that photoperiod differentially influences immune responses in piglets weaned at different ages and indicate an inverse relationship between growth and immune status. Here, weaning at 28 d and a long-day photoperiod was the treatment combination that was most physiologically beneficial to piglets, whereas a 14-d weaning and short-day photoperiod was least physiologically beneficial.

Animals↗
PubMed1996

Identifying yield-optimizing environments for two cowpea breeding lines by manipulating photoperiod and harvest scenario.

Photoperiod and harvest scenario of cowpea (Vigna unguiculata L. Walp) canopies were manipulated to optimize productivity for use in future controlled ecological life-support systems. Productivity was measured by edible yield rate (EYR:g m-2 day-1), shoot harvest index (SHI: g edible biomass [g total shoot dry weight]), and yield-efficiency rate (YER:g edible biomass m-2 day-1 per[g nonedible shoot dry weight]). Breeding lines 'IT84S-2246' (S-2246) and "IT82D-889' (D-889) were grown in a greenhouse under 8-, 12-, or 24-h photoperiods. S-2246 was short-day and D-889 was day-neutral for flowering. Under each photoperiod, cowpeas were harvested either for leaves only, seeds only, or leaves plus seeds (mixed harvest). Photoperiod did not affect EYR of either breeding line for any harvest scenario tested. Averaged over both breeding lines, seed harvest gave the highest EYR at 6.7 g m-2 day-1. The highest SHI (65%) and YER (94 mg m-2 day-1 g-1) were achieved for leaf-only harvest of D-889 under an 8-h photoperiod. For leaf-only harvest of S-2246, both SHI and YER increased with increasing photoperiod, but declined for seed-only and mixed harvests. However, photoperiod had no effect on SHI or YER for D-889 for any harvest scenario. A second experiment utilized the short-day cowpea breeding line 'IT89KD-288' (D-288) and the day-neutral breeding line 'IT87D-941-1' (D-941) to compare yield parameters using photoperiod extension under differing lamp types. This experiment confirmed the photoperiod responses of D-889 and S-2246 to a mixed-harvest scenario and indicated that daylength extension with higher irradiance from high pressure sodium lamps further suppressed EYR, SHI, and YER of the short-day breeding line D-288.

Agriculture↗
PubMed1999

Transfer from long to short photoperiods affects production efficiency of day-neutral rice.

The day-neutral, semidwarf rice (Oryza sativa L.) cultivar Ai-Nan-Tsao was grown in a greenhouse under summer conditions using high-pressure sodium lamps to extend the natural photoperiod. After allowing 2 weeks for germination, stand establishment, and thinning to a consistent planting density of 212 plants/m2, stands were maintained under continuous lighting for 35 or 49 days before shifting to 8- or 12-h photoperiods until harvest 76 days after planting. Non-shifted control treatments consisting of 8-, 12-, or 24-h photoperiods also were maintained throughout production. Tiller number increased as duration of exposure to continuous light increased before shifting to shorter photoperiods. However, shoot harvest index and yield efficiency rate were lower for all plants receiving continuous light than for those under the 8- or 12-h photoperiods. Stands receiving 12-h photoperiods throughout production had the highest grain yield per plant and equaled the 8-h-photoperiod control plants for the lowest tiller number per plant. As long as stands were exposed to continuous light, tiller formation continued. Shifting to shorter photoperiods late in the cropping cycle resulted in newly formed tillers that were either sterile or unable to mature grain before harvest. Late-forming tillers also suppressed yield of grain in early-forming tillers, presumably by competing for photosynthate or for remobilized assimilate during senescence. Stands receiving 12-h photoperiods throughout production not only produced the highest grain yield at harvest but had the highest shoot harvest index, which is important for resource-recovery strategies in advanced life-support systems proposed for space.

Biomass↗
PubMedDate not supplied

[Functional organization of a photoperiodic brain system].

The neurofunctional system, which receives a photoperiod, is a photoperiodic brain system. As a part of chronoperiodic system of organism it is involved in perception and transfer of information about the main external Zeitgeber to the peripheral tissues. Such role of photoperiodic system allows it not only synchronize the chronorhythms of different somatic and visceral functions, but also realize the coordination and the modulation of adaptation mechanisms to the stressors influence. The present review is focused on the ways of conduction of photoperiodic information, role of suprachiasmatic nuclei of hypothalamus in endogenous oscillation of chronorhythms and pineal gland as a neuroendocrinal transducer; and also on characteristics of circadian and circannual parts of photoperiodic system. Special attention is given to vegetative part of photoperiodic system and melatonin--"the hormone of dark". It is supposed that adenosine, one of the humoral elements of photoperiodic system, is involved in transfer of duration of the light part of photoperiod. Due to presented data we have come to the conclusion that septohippocampal system is one of the center for saving photoperiodic information.

Adaptation, Physiological↗
PubMed2004

Immune and stress responses in C57BL/6 and C3H/HeN mouse strains following photoperiod manipulation.

OBJECTIVES: The purpose of this study was to determine whether two different strains of mice, that are reproductively unresponsive to photoperiod, adjust immune function in response to photoperiod. SETTING AND DESIGN: Adult male C3H/HeN (C3H) and C57BL/6 (C57) mice were each placed into either a long (LD 16:8) or short (LD 8:16) photoperiod for 10 weeks (n = 15/ group). METHODS: Blood was collected for flow cytometry and radioimmunoassay analysis of leukocyte numbers and corticosterone concentrations, respectively. In addition, all mice were sensitized to, and challenged with the antigen, 2,4-dinitro-1-fluorobenzene. Pinnae measurements were obtained for 7 days following challenge to determine the magnitude of the inflammatory response. RESULTS: Photoperiod did not affect leukocyte cell numbers in either C3H or C57 mice. C3H mice displayed higher neutrophil numbers than C57 mice (p< 0.0001), whereas C57 mice displayed higher lymphocyte numbers than C3H mice (p< 0.01). C3H mice housed in LD 16:8 had higher corticosterone concentrations than those housed in LD 8:16 (p< 0.005) and C57 mice housed in either photoperiod (p< 0.05). Photoperiod did not affect the inflammatory response, though C57 mice displayed an overall higher magnitude of response than C3H mice (p<0.05). MAIN FINDINGS: Our results suggest that photoperiod does not alter immune function in C3H and C57 mice. Strain differences in immune function, however, were observed. CONCLUSIONS: Immune function is unresponsive to photoperiod in these laboratory mice, possibly indicating; a link between immune and reproductive responsiveness to photoperiod, the decreased predictive value of this annual cue to domesticated animals, or both.

Analysis of Variance↗
PubMed2005

[Analysis of heading time genotype for a rice photoperiod and thermo--sensitive male sterile line PeiAi64S].

PeiAi64S, a photoperiod and thermo-sensitive genic male sterile, has been wildly applied to hybrid rice seed production in China, but its photoperiod-sensitivity gene for heading date in this sterile line was still unknown. This definitely limited the further use of this sterile line in breeding practice and re-production of hybrid seeds. To solve this problem, using heading time nearly isogenic lines EGO - EG7, ER - LR, T65 - T65m and six heading date QTL-isogenic lines, NIL (Hd1) - NIL (Hd6) with the genes of Nipponbare but Hd1 - Hd6 genes from Kasalath respectively, we performed a genetic analysis of PeiAi64S with special reference to photoperiod-sensitivity loci, in natural long days at Nanjing (32 degrees N) where the average day-length is about 14 h and in natural short days at Linshui county, Hainan province(18 degrees 29'N), where the average day-length is about 11.6 h during the course of rice growing respectively. The F1 and F2 generations from the crosses 'PeiAi64S x heading time nearly isogenic lines' were subjected to genetic analyses. Experimental results showed that PeiAi64S carries photoperiod-sensitivity allele gene E1 and E3 and dominant earliness gene Ef-1 in E1 and E3 and Ef-1 loci, respectively, and a photoperiod insensitivity allele Se-1 degrees in Se-1 locus. Meanwhile, the photoperiod-sensitivity gene E1 and photoperiod-insensitivity gene Se-1e in PeiAi64S were also identified by crossing with the NIL(Hd1) and NIL(Hd4). In addition, a recessive inhibitor for photoperiod-sensitive gene E1 or Se-1(n) and other modified photoperiod-sensitive genes: i-Se-1, E3, Hd3 (En-Se-1), Hd5 and Hd6, were identified in PeiAi64S by crossing with QTL nearly isogenic lines: NIL(Hd2), NIL (Hd3), NIL (Hd5) and NIL( Hd6), The results indicated that the genotype of PeiAi64S's heading date was: E1E1e2e2E3E3Se-1(e)Se-1(e)Ef-1 Ef-1 i-Se-1 i-Se-1.

Breeding↗
PubMed1997

Photoperiodism in higher vertebrates: an adaptive strategy in temporal environment.

Life on earth is subjected to strict regimen of cyclical changes. Of all geophysical changes, the most prominent are the daily changes between day and night and the regular succession of annual seasons. Synchronization to environmental day-night and seasonal cycles is key to survival. Night-time and day-time environments differ in illumination, temperature, food supplies and predators. Organisms have, therefore, developed highly specialized temporal programmes to get better adapted to activity either during night or during the day. Many species use annual cycle of changes in daylength as "calendar" to synchronize and/or to time their daily and seasonal physiological and behavioral functions. This is described as photoperiodism. The minimum daylength (photoperiod) that will induce a physiological response is the "critical daylength" (CD). CD requirement is quite stringent. CD is species-specific; CD may be response-specific as well. Switching 'on' and 'off' the seasonal responses in many species is regulated by the development of photorefractoriness-a phenomenon when organism remains no longer capable to continue its stimulatory response to a photoperiod. Photorefractoriness may be qualitatively different between species. Broadly, two categories of photorefractoriness are described: absolute refractoriness and relative refractoriness. What causes photorefractoriness and at what level in the brain photorefractoriness occurs are unknown. A photoperiodic response system has three principal components: a photoreceptor that interprets photic input, a clock that measures photic signal, and a neurosecretory system that translates photic signal into endocrine secretions. Both retinal and extra-retinal structures are involved in the photoperiodic photoreception. In insects, mollusks, crustaceans, fishes, amphibians, reptiles and birds, the photoreception occurs largely through extra-retinal photoreceptors (ERRs) localized in the hypothalamus. In adult mammals, brain photoreceptors are apparently absent and light input is only through eyes. Endogenous circa-rhythms believed to be involved in photoperiodism are synchronized to changes in illumination of the environment with either the time of day (circadian rhythm) or the season of the year (circannual rhythm). The Suprachiasmatic nuclei (SCN) of the hypothalamus in mammals function as the clock. The SCN monitors the photoperiodic message and decodes it by dictating the changes in rhythm in melatonin secretion in the pineal gland. The hypothalamic paraventricular nuclei (PVN) are also an integral component of the neural network mediating photoperiodism in mammals. The location of SCN homologue and the role of PVN in mediating photoperiodism in non-mammalian vertebrates is still unclear. Furthermore, how various components of photo-neuroendocrine circuitry are functionally linked together is unknown.

Adaptation, Physiological↗
PubMed1989

Reception of photoperiodic information by fetal Siberian hamsters: role of the mother's pineal gland.

The rate of reproductive development in juvenile male Siberian hamsters is strongly influenced by daylength (photoperiod). Recent studies indicate that reception of photoperiodic cues begins during fetal life. The present experiments yielded a further demonstration that developing male Siberian hamsters receive information about the photoperiod to which their mother is exposed during pregnancy. The possibility that photoperiodic information is transmitted from mother to young after birth was investigated by cross-fostering young gestated on 12L and 16L to mothers from the other photoperiod. Litters were cross-fostered on the day of birth and then were transferred, along with their foster mothers, to 14L. We found no influence of the mother after birth, indicating that transmission of photoperiodic information from mother to young must occur during gestation. To determine if the pineal gland of the mother is required for this response, adult females were pinealectomized or sham-operated and paired with intact males in 12L, 14L, or 16L. After parturition parents and offspring were exposed to 14L. The influence of prenatal photoperiod on postnatal testicular development in 14L was blocked by pinealectomy of the mother. Postnatal testicular development was retarded in offspring that experienced a photoperiod transfer from either 15L to 14L or 8L to 12L at birth. In contrast, the inhibitory effect of a transfer from 16L to 14L at birth was abolished when juvenile males were exposed to a single long photoperiod (16.3 h light) at age 17-21 days and then were returned to 14L.

Animals↗