Disease relevance of Photoperiod

• The target site(s) and mechanism(s) of action for the pineal/melatonin-independent effect of photoperiod on body weight in Syrian hamsters are also unknown [1].
• Short photoperiod and melatonin-induced BAT hypertrophy was not accompanied by any change in noradrenaline (NA) turnover in this tissue [2].
• Under the conditions employed, rats kept in short daylength throughout or kept on long photoperiod and given late-afternoon melatonin injections showed evidence of delayed puberty (seminal vesicle, ventral prostate, and testis weight decreased by 45%, 55%, and 60% respectively, compared to control rats) [3].
• Interestingly, melatonin injections administered during an inhibitory photoperiod (L10 : D14) caused greater inhibition of both reproduction and weight gain than short photoperiod alone [4].
• After 20 days of SP or long photoperiod (LP) exposure, all animals were sacrificed by decapitation and their sera and pituitaries saved for hormonal determinations [5].

Psychiatry related information on Photoperiod

• Food deprivation (48 h) reduced SOCS3 gene expression in hamsters acclimated to either long (LD) or short (SD) photoperiods, suggesting that leptin signals acute starvation regardless of photoperiod [6].
• Because both the pattern and level of locomotor activity are affected by day-length, we investigated whether photoperiod also affects calbindin expression [7].
• We tested whether genetic variability in reproductive seasonality is related to individual differences in the neuronal function of the gonadotropin-releasing hormone network, as assessed by the number and location of mature gonadotropin-releasing hormone-secreting neurons under inhibitory and excitatory photoperiods [8].
• In turkey hens, PR may be defined as a lack of responsiveness to photoperiods that previously induced or maintained egg production and is characterized by a spontaneous cessation of lay, usually followed by molt, as well as an absence of nesting behavior [9].

High impact information on Photoperiod

• The pineal hormone melatonin is involved in photic regulations of various kinds, including adaptation to light intensity, daily changes of light and darkness, and seasonal changes of photoperiod lengths [10].
• The onset of flowering is promoted by long photoperiods, but the constans (co) mutant flowers later than wild type under these conditions [11].
• Here we describe the gene EARLY FLOWERING 4 (ELF4), which is involved in photoperiod perception and circadian regulation [12].
• Loss of FT causes delay in flowering, whereas overexpression of FT results in precocious flowering independent of CO or photoperiod [13].
• Flowering in cry2/fha mutant plants is only incompletely responsive to photoperiod [14].

Chemical compound and disease context of Photoperiod

• Those hamsters that delayed puberty in response to this short photoperiod had a daily rhythm of FSH and progesterone secretion [15].
• It appears the total amount of daily locomotor activity in the hamster is modulated by circulating testosterone levels in a manner which is dependent upon the environmental photoperiod [16].
• Oestradiol-implanted, castrated male sheep were kept 16 weeks in SD (8 h light/day) or LD (16 h light/day) and then transferred to the opposite photoperiods for 8 weeks, during which food was restricted to 90% requirement to maintain body weight (maintenance) [17].
• Delayed puberty in the male Djungarian hamster: effect of short photoperiod or melatonin treatment on the GnRH neuronal system [18].
• 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 [19].

Biological context of Photoperiod

• Highest synthesis and assembly rates are confined to the photoperiod (mid-to-late G1) and support chlorophyll and carotenoid accretion before M-phase [20].
• Hd1, a major photoperiod sensitivity quantitative trait locus in rice, is closely related to the Arabidopsis flowering time gene CONSTANS [21].
• Syrian hamsters display a robust and transient peak of Per1 and ICER gene expression 3 h after lights-on (Zeitgeber time 3) in the PT, under both long (16 h light/8 h dark) and short (8 h light/16 h dark) photoperiods [22].
• Down-regulation of these genes was associated with reduced hypothalamic T4 uptake, which was reversed by long-day photoperiod treatments that restored responsiveness to short days [23].
• Phytochrome-mediated photoperiod perception, shoot growth, glutamine, calcium, and protein phosphorylation influence the activity of the poplar bark storage protein gene promoter (bspA) [24].

Anatomical context of Photoperiod

• The results demonstrate that melatonin can exert either pro- or antigonadal effects and emphasize that the effects of melatonin on the testis cannot be properly assessed unless account is taken of the dosage and mode of melatonin administration and the photoperiod on which experimental animals are maintained [25].
• How photoperiod controls melatonin biosynthesis in organs containing mainly photoreceptor cells, remains unclarified [26].
• The photoreceptive pineal gland of the goldfish generates circulating melatonin rhythms according to a given photoperiod under light-dark cycles and in a circadian manner under continuous dark conditions [27].
• In birch (Betula pubescens) these events are triggered by short photoperiod, and involve the production of 1,3-beta-D-glucan containing sphincters on the plasmodesmata [28].
• Lesions of the iodomelatonin-binding sites of the mediobasal hypothalamus spare the lactotropic, but block the gonadotropic response of male Syrian hamsters to short photoperiod and to melatonin [29].

Associations of Photoperiod with chemical compounds

• The interactions among luteinizing hormone, gonadal steroids, and the photoperiod seem to set the appropriate conditions for neural processes triggering a complete and normal release of luteinizing hormone [30].
• In each family the characteristics of diapause differ, and the specific controls vary widely from lactational to seasonal, from estrogen to progesterone, or from photoperiod to nutritional [31].
• This robust Ca(2+) flux likely plays regulatory roles in the sensing of both light/dark transitions and photoperiod [32].
• Once critical weight is reached, juvenile hormone (JH) titers decline, resulting in the release of prothoracicotropic hormone (PTTH) at the next photoperiod gate and thereby inducing metamorphosis [33].
• Removal of the olfactory bulbs of male golden hamsters results in a marked increase in tonic gonadotropin, prolactin and testosterone secretion which counteracts inhibitory effects of manipulations such as maintenance on short photoperiod, food restriction or treatment with gonadal steroids [34].

Gene context of Photoperiod

• Interestingly, AGL20 expression is positively regulated not only by the redundant vernalization and autonomous pathways of flowering but also by the photoperiod pathway [35].
• We found that Vip(-/-) and Vipr2(-/-) mice showed two daily bouts of activity in a skeleton photoperiod and multiple circadian periods in constant darkness [36].
• Null mutations in ARP6 caused numerous defects, including altered development of the leaf, inflorescence, and flower as well as reduced female fertility and early flowering in both long- and short-day photoperiods [37].
• Surprisingly, the phyA cry1 cry2 triple mutant flowered earlier and showed better response to photoperiod than the cry1 cry2 double mutant, indicating that phyA is involved in light repression of flowering [38].
• High training activity and a dark photoperiod appeared to independently suppress ovarian activity and were not associated with chronic changes in anterior pituitary hormone or SHBG concentrations [39].

Analytical, diagnostic and therapeutic context of Photoperiod

• The results reported herein of "skeleton photoperiod" experiments indicate that the efficacy of phototherapy may not depend on its timing or its effect on melatonin secretion [40].
• Serum gonadotropin concentrations increased following castration in both long and short photoperiods, but gonadotropin secretion was inhibited by much smaller doses of testosterone in the males maintained on the short photoperiod as compared to males kept on a long photoperiod [41].
• Melatonin was measured over 24 hr in the eyestalks of Uca pugilator by means of radioimmunoassay; crabs were acclimatized either to a LD 12:12 photoperiod or constant darkness [42].
• Twenty-one-day-old female BALBc mice were treated with daily subcutaneous injections of aMT (200 micrograms) or diluent, 3 hr before the onset of darkness (photoperiod LD 12:12) [43].
• To exclude the possibility that the lesion to the MBH prevented gonadal regression through disruption of nocturnal melatonin production, MBH-X animals were switched to a long day photoperiod, pinealectomized, and fitted with a sc cannula for the infusion of either melatonin (500 ng/10 h) or saline (50 microliters/h) once daily for 6 weeks [29].

References