Long-day Photoperiod Research Articles

Variation of photoperiod response in moss gametangial formation

Photoperiod duration has been shown to induce reproduction in angiosperms and liverworts. In general, moss gametangial production has been considered non-respondent to photoperiod, yet has been insufficiently tested. Here, we tested the response of gametangial formation to day length cues in California populations of Pohlia nutans using controlled light levels and variable day length treatments. Surprisingly, we found that gametangia induction in these P. nutans populations responded to changes in day lengths (long-day to short-day) rather than constant short- or long-day photoperiod regimes, as has been previously reported in a few moss species. We discuss our results with respect to photoperiod induction of gametangia in mosses.

Photoperiodic regulation of the orexigenic effects of ghrelin in Siberian hamsters

Animals living in temperate climates with predictable seasonal changes in food availability may use seasonal information to engage different metabolic strategies. Siberian hamsters decrease costs of thermoregulation during winter by reducing food intake and body mass in response to decreasing or short-day lengths (SD). These experiments examined whether SD reduction in food intake in hamsters is driven, at least in part, by altered behavioral responses to ghrelin, a gut-derived orexigenic peptide which induces food intake via NPY-dependent mechanisms. Relative to hamsters housed in long-day (LD) photoperiods, SD hamsters consumed less food in response to i.p. treatment with ghrelin across a range of doses from 0.03 to 3 mg/kg. To determine whether changes in photoperiod alter behavioral responses to ghrelin-induced activation of NPY neurons, c-Fos and NPY expression were quantified in the arcuate nucleus (ARC) via double-label fluorescent immunocytochemistry following i.p. treatment with 0.3 mg/kg ghrelin or saline. Ghrelin induced c-Fos immunoreactivity (-ir) in a greater proportion of NPY-ir neurons of LD relative to SD hamsters. In addition, following ghrelin treatment, a greater proportion of ARC c-Fos-ir neurons were identifiable as NPY-ir in LD relative to SD hamsters. Changes in day length markedly alter the behavioral response to ghrelin. The data also identify photoperiod-induced changes in the ability of ghrelin to activate ARC NPY neurons as a possible mechanism by which changes in day length alter food intake.

Temperature and Photoperiodic Effects on Induction and Termination of Diapause in Female Leptocorisa chinensis (Hemiptera: Alydidae)

Abstract The effects of temperature and photoperiod on diapause induction and termination in Leptocorisa chinensis Dallas (Hemiptera: Alydidae) were studied under constant conditions or by using transfer experimental protocols. Nymphs were reared either under a long-day (16:8 [L:D] h) or a short-day (12:12 [L:D] h) photoperiod at 25°C in the laboratory. Females oviposited at 25 and 20°C under the long-day photoperiod. However, females did not lay eggs within 100 d at 15°C under the long-day photoperiod or at 20 and 15°C under short-day conditions. At 25°C, when nymphs were reared under a long-day photoperiod and transferred to a short-day photoperiod on the day of adult emergence, females started oviposition in 10 d but stopped shortly thereafter. When nymphs were reared under a short-day photoperiod and transferred to a long-day photoperiod on the day of adult emergence, females started oviposition in ≈40 d. Females that had been transferred from the field on 1 February and 29 March to long-day laboratory conditions at 25°C started oviposition in ≈40 d. However, females that had overwintered in the field were transferred to a short-day photoperiod at 25°C on 1 February and 29 March did not start oviposition in the laboratory. Both the nymphal and adult stages of L. chinensis are considered to be sensitive to reproductive diapause induction and termination signals both before and after overwintering. Female L. chinensis require not only a long-day photoperiod and >40 d at temperature of 20°C or higher but also threshold temperatures for start of oviposition, even after the winter.

Effect of body condition score of does and use of bucks subjected to added artificial light on estrus response of Alpine goats

The effects of body condition score of does and exposure to sexually active bucks after exposure to long-day artificial photoperiod were examined in mature anovulatory French Alpine goat in Northern Mexico. In June, goats in good (2.3 +/- 0.2, scale 1 to 4; n = 10) or poor (1.6 +/- 0.3; n = 10) body condition were exposed during 15 day to sexually active bucks, which had been exposed to long photoperiod (16:8-h light-dark cycle, starting in December). A third group of goats in good body condition was exposed to bucks kept under the natural photoperiod of this region (26 degrees N). All goats in good body condition exposed to bucks treated with prolonged photoperiod exhibited estrus behavior, whereas only 50% of the does in poor body condition showed estrous behavior during the 15-day buck exposure. None of the does in good body condition showed estrus when exposed to bucks under natural photoperiod. These results revealed that a good body condition is required for maximum estrus response in anestrous Alpine goats and that exposure of bucks to long photoperiod in winter is essential for an adequate stimulus to reestablish estrus cycles in anovulatory Alpine does in Northern Mexico.

The molecular physiology of increased egg desiccation resistance during diapause in the invasive mosquito,Aedes albopictus

Photoperiodic diapause is a crucial adaptation to seasonal environmental variation in a wide range of arthropods, but relatively little is known regarding the molecular basis of this important trait. In temperate populations of the mosquito Aedes albopictus, exposure to short-day (SD) lengths causes the female to produce diapause eggs. Tropical populations do not undergo a photoperiodic diapause. We identified a fatty acyl coA elongase transcript that is more abundant under SD versus long-day (LD) photoperiods in mature oocyte tissue of replicate temperate, but not tropical, A. albopictus populations. Fatty acyl CoA elongases are involved in the synthesis of long chain fatty acids (hydrocarbon precursors). Diapause eggs from a temperate population had one-third more surface hydrocarbons and one-half the water loss rates of non-diapause eggs. Eggs from a tropical population reared under SD and LD photoperiods did not differ in surface hydrocarbon abundance or water loss rates. In both a temperate and tropical population, composition of hydrocarbon chain lengths did not differ between eggs from SD versus LD conditions. These results implicate the expression of fatty acyl coA elongase and changes in quantity, but not composition, of egg surface hydrocarbons as important components of increased desiccation resistance during diapause in A. albopictus.

The interactions of season, leptin and melatonin levels with thyroid hormone secretion, using an in vitro approach

Leptin's actions on the hypothalamic–pituitary–thyroid axis occur both centrally and peripherally. In addition, the thyroid activity may also be stimulated by melatonin. The mechanisms through which leptin, melatonin (MT) and the thyroid hormones co-operate in the regulation of the seasonal physiology in sheep, however, remains unclear. The aim of the study was to evaluate the interactions of season, leptin and melatonin levels with thyroid hormone secretion in sheep, using an in vitro approach. Thyroid glands from 18 ewes were collected during long-day (LD, n = 9) and short-day (SD, n = 9) photoperiods. The glands were dissected into approximately 30 mg samples. Each sample was equilibrated in RPMI 1640 (Roswell Park Memorial Institute 1640) + F12 (Nutrient Mixture F-12) medium (1/1) for 90 min, followed by an additional 3 h incubation. At the end of the equilibration period, all tissue samples were treated with a medium containing either 0 or 50 ng/ml leptin, with or without MT (40 ng/ml) and a medium containing MT (40 ng/ml) only. Secretions of thyroxine (T4) and triiodothyronine (T3) were higher ( P < 0.05) in the control group during the short-day (SD) period, compared to the long-day (LD) period. Melatonin tented to reduce the T4 secretion during the LD and SD periods. However, leptin stimulated ( P < 0.001) T4 secretion in both seasons. Leptin, MT, and both leptin and MT increased the secretion of T3 during LD period ( P < 0.001). Results demonstrated leptin to have a stimulatory effect on T3 and T4 secretion in sheep, however the effect of melatonin is dependent on the season.

Proteomics analysis of the regulatory network involved in long‐distance signaling in potato

In potato (Solanum tuberosum), BEL5 mRNA is a mobile RNA which is involved in the signaling system that activates tuber formation. Short day (SD) induces tuberization and long day (LD) inhibits the process. The mobility of StBEL5 RNA is induced by a SD photoperiod. It is likely that the movement of StBEL5 is facilitated by the formation of a RNA‐protein complex. To verify this proposed mechanism we have undertaken a proteomic analysis. Proteins from potato petioles (as the transcriptional source of StBEL5 RNA is leaf veins and petioles) grown under LD and SD photoperiod conditions were separated by 2‐dimensional gel electrophoresis (2‐DE). Proteins which were differentially expressed in response to changes in photoperiods were analyzed by Progenesis SameSpots software and identified by MALDI MS/MS. Phosphoproteins (phosphorylation of proteins is central to signal transduction) and RNA binding proteins were also enriched from LD and SD potato petioles, separated on 2‐DE and analyzed by MALDI MS/MS. We have identified many proteins that are differentially expressed in response to LD or SD photoperiods. A comprehensive profile of the phosphoproteomes of LD and SD potato petioles has been established. Significantly, the presence of the RNA‐binding protein, elF‐5A, has been detected in multiple phosphorylation states only under LD conditions. Numerous RNA‐binding proteins have also been isolated and identified.

Variation in levels of luteinizing hormone and reproductive photoresponsiveness in a population of white-footed mice (Peromyscus leucopus)

Natural genetic variation in reproduction and life history strategies is a manifestation of variation in underlying regulatory neuronal and endocrine systems. A test of the hypothesis that genetic variation in luteinizing hormone (LH) level could be related to a life history trait, seasonal reproduction, was conducted on artificial selection lines from a wild-source population of white-footed mice (Peromyscus leucopus). Variation exists in the degree of suppression of reproduction by winter short-day photoperiods (SD) in wild-source individuals and in the laboratory population. In this population, most individuals from a photoperiod-responsive (R) artificial selection line are strongly suppressed reproductively in SD, while most individuals from a photoperiod-nonresponsive (NR) artificial selection line are only weakly reproductively suppressed in SD. We assayed levels of LH to test for genetic variation between lines that could contribute to variation in reproductive status in SD. Females from both lines were raised in long-day photoperiods (LD) or SD, ovariectomized under isoflurane anesthesia, and given estradiol implants. Levels of LH were significantly higher in the NR line than in the R line, indicating genetic variation for levels of LH. Levels of LH were higher in LD than in SD, indicating that levels of LH were sensitive to photoperiod treatment even with a controlled level of estradiol negative feedback. The results indicate that there is genetic variation in levels of LH that could be functionally important both in the laboratory in SD and in the wild population in winter. Thus genetic variation in levels of LH is a plausible causal factor determining winter reproductive phenotype in the wild population.

A transcriptional element of the diapause program in the Asian tiger mosquito, Aedes albopictus, identified by suppressive subtractive hybridization

Many temperate insects cope with the unfavorable conditions of winter by entering a photoperiodic diapause, but the molecular basis of this crucial adaptation is not well understood. In temperate populations of Aedes albopictus, exposure to short-day lengths causes the adult female to oviposit diapausing eggs. Suppressive subtractive hybridization (SSH) and quantitative reverse transcription PCR (qRT-PCR) were performed on RNA isolated from mature (stage V) oocytes of a temperate population of Ae. albopictus. A total of 438 inserts were sequenced from the SSH library and 324 unique (non-redundant) sequences were identified. QRT-PCR experiments were performed for 53 transcripts using a novel experimental design that included replicate temperate populations that do undergo photoperiodic diapause and replicate tropical populations that do not undergo a photoperiodic diapause. There was greater abundance of an epithelial membrane protein transcript under short-day versus long-day photoperiods in multiple temperate, but not tropical, populations. This gene may function during the diapause program by increasing desiccation resistance or energy reserves. The expression of a phosphatidylethanolamine- binding protein transcript in response to SD versus LD photoperiod differed between temperate and tropical populations but does not appear to be causally involved in diapause. Rapid Amplification of cDNA Ends (RACE) was performed to determine the entire cDNA sequence of both transcripts.

Effects of photoperiod on daily locomotor activity, energy expenditure, and feeding behavior in a seasonal mammal

The objective of this study was to determine whether the previously observed effects of photoperiod on body weight in Siberian hamsters were due to changes in the daily patterns of locomotor activity, energy expenditure, and/or feeding behavior. Adult males were monitored through a seasonal cycle using an automated comprehensive laboratory animal monitoring system (CLAMS). Exposure to a short-day photoperiod (SD; 8:16-h light-dark cycle) induced a significant decline in body weight, and oxygen consumption (Vo(2)), carbon dioxide production (Vco(2)), and heat production all decreased reaching a nadir by 16 wk of SD. Clear daily rhythms in locomotor activity, Vo(2), and Vco(2) were observed at the start of the study, but these all progressively diminished after prolonged exposure to SD. Rhythms in feeding behavior were also detected initially, reflecting an increase in meal frequency but not duration during the dark phase. This rhythm was lost by 8 wk of SD exposure such that food intake was relatively constant across dark and light phases. After 18 wk in SD, hamsters were transferred to a long-day photoperiod (LD; 16:8-h light-dark cycle), which induced significant weight gain. This was associated with an increase in energy intake within 2 wk, while Vo(2), Vco(2), and heat production all increased back to basal levels. Rhythmicity was reestablished within 4 wk of reexposure to long days. These results demonstrate that photoperiod impacts on body weight via complex changes in locomotor activity, energy expenditure, and feeding behavior, with a striking loss of daily rhythms during SD exposure.

Seasonal influence on the response of the somatotropic axis to nutrient restriction and re‐alimentation in captive Steller sea lions (Eumetopias jubatus)

Fluctuations in availability of prey resources can impede acquisition of sufficient energy for maintenance and growth. By investigating the hormonal mechanisms of the somatotropic axis that link nutrition, fat metabolism, and lean tissue accretion, we can assess the physiological impact of decreased nutrient intake on growth. Further, species that undergo seasonal periods of reduced intake as a part of their normal life history may have a differential seasonal response to nutrient restriction. This experiment evaluated the influence of season and age on the response of the somatotropic axis, including growth hormone (GH), insulin-like growth factor (IGF)-I, and IGF-binding proteins (BP), to reduced nutrient intake and re-alimentation in Steller sea lions. Eight captive females (five juveniles, three sub-adults) were subject to 28-day periods of food restriction, controlled re-feeding, and ad libitum recovery in summer (long-day photoperiod) and winter (short-day photoperiod). Hormone concentrations were insensitive to type of fish fed (low fat pollock vs. high fat herring), but sensitive to energy intake. Body mass, fat, and IGF-I declined, whereas GH and IGFBP-2 increased during feed restriction. Reduced IGF-I and IGFBP with increased GH during controlled re-feeding suggest that animals did not reach positive energy balance until fed ad libitum. Increased IGF-I, IGFBP-2, IGFBP-3, and reduced GH observed in summer reflected seasonal differences in energy partitioning. There was a strong season and age effect in the response to restriction and re-alimentation, indicating that older, larger animals are better able to cope with stress associated with energy deficit, regardless of season.

Preliminary characterization of floral response of Xerophyta humilis to desiccation, vernalisation, photoperiod and light intensity

Xerophyta humilis is a monocotyledonous resurrection plant found in arid and semi-arid summer rainfall areas of Southern Africa, which undergoes desiccation to survive periods of extreme drought. In order for X.humilis to thrive in their natural habitat, correct timing of the floral transition, coincident with wet periods of sufficient duration, is essential. In this study, the environmental cues involved in the regulation of the floral transition in X.humilis were analysed. No single parameter tested was sufficient to induce flowering, but it was found that flowering was promoted by a combination of a cool period experienced while plants were hydrated, followed by transfer to long-day photoperiods of relatively high light intensity. Plants retained competence to flower if desiccated during exposure to cold, but no flowering occurred if dried prior to this exposure. These data suggest that exposure to cold temperature facilitates vernalisation and subsequent exposure to high light and long days are inductive for floral initiation in X. humilis.

KALANCHOE × HOUGHTONII SSH AND MICROARRAY ANALYSIS TO SCREEN GENES INVOLVED IN VIVIPARY

Vivipary, referred here as the formation of novel complete plantlets on mature organs, has been reported in many families as an asexual propagation strategy. In K. × houghtonii (Crassulaceae), viviparous plantlets are formed on leaf margin notches in response to a long day photoperiod and their appearance follow a basipetal fashion. To identify genes involved in this process, suppression subtractive hybridisation libraries (SSH) were prepared. Two hundred c-DNA clones were classified and grouped into 14 functional categories according to Goldberg database (http://estdb.biology.ucla.edu/PcEST). Six hundred thirty sequences (200 SSH library, 48 database Kalanchoe genus, 382 other species database genes) were used as probes for microarray analysis according to the CombiMatrix technology and a 4x2K Custom Array ™ was synthesized. RNA was extracted from margin of leaves at 7 stages of development before buds emission (5 to 50 mm) during long-day photoperiod (permissive conditions). Three replications for each sample were prepared. From double strand cDNAs antisense RNAs (a RNA) were synthesized and amino-allil-UTP incorporated and coupled with Alexa Fluor ® 647. Microarray was hybridized according to CombiMatrix protocol. Data were extracted with CombiMatrix Microarray Imager software and exported into Microsoft Excel for computing of mean, median and standard deviation. Person's correlation was computed and data normalized. After background removal, probes were reduced to 484. Fold change method (FC=2) was used to compare different levels of gene expression of samples. Significance Analysis of Microarrays Statistic (SAM method) generated 263 significant modulated genes with a False Discovery Rate (FDR) of 5%.

Melatonin Stimulates the Release of Gonadotropin-Inhibitory Hormone by the Avian Hypothalamus

Gonadotropin-inhibitory hormone (GnIH), a neuropeptide that inhibits gonadotropin synthesis and release, was first identified in quail hypothalamus. GnIH acts on the pituitary and GnRH neurons in the hypothalamus via GnIH receptor to inhibit gonadal development and maintenance. In addition, GnIH neurons express melatonin receptor and melatonin induces GnIH expression in the quail brain. Thus, it seems that melatonin is a key factor controlling GnIH neural function. In the present study, we investigated the role of melatonin in the regulation of GnIH release and the correlation of GnIH release with LH release in quail. Melatonin administration dose-dependently increased GnIH release from hypothalamic explants in vitro. GnIH release was photoperiodically controlled. A clear diurnal change in GnIH release was observed in quail, and this change was negatively correlated with changes in plasma LH concentrations. GnIH release during the dark period was greater than that during the light period in explants from quail exposed to long-day photoperiods. Conversely, plasma LH concentrations decreased during the dark period. In contrast to LD, GnIH release increased under short-day photoperiods, when the duration of nocturnal secretion of melatonin increases. These results indicate that melatonin may play a role in stimulating not only GnIH expression but also GnIH release, thus inhibiting plasma LH concentrations in quail. This is the first report describing the effect of melatonin on neuropeptide release.

Influence of nutritional and socio-sexual cues upon reproductive efficiency of goats exposed to the male effect under extensive conditions

This study evaluated the effect of nutritional supplementation and socio-sexual cues upon reproductive efficiency of goats exposed to the male effect under rangeland grazing conditions (22°N). Criollo goats (n = 73) were distributed in four experimental groups: (1) continuous males (CM, n = 19) in which males (n = 2) remained together with females from 7 March to 28 July; (2) supplemented males (SM, n = 16) in which males (n = 2) were kept separately and were individually supplemented with 18% crude protein and 2.77 Mcal ME kg–1 DM, during a 30-day period; (3) supplemented males exposed to the female effect (SM + FE, n = 19), in which supplemented males (n = 2) were maintained with females induced to oestrus before being used for male effect; and (4) supplemented males and supplemented females (SM + SF, n = 19) in which males (n = 2) were supplemented as in group SM, and females received the same supplementation as males 30 days before and 30 days after male introduction. Grazing was performed from 0900 to 1900 hours; liveweight (LW) was registered weekly before grazing and (or) supplementation. Ovarian activity was evaluated (serum P4 concentrations) in the four groups before and after male introduction. At the beginning of the study and supplementation, female LW did not differ among treatments (P &gt; 0.01). However, during the supplementation phase, LW increased in a different fashion among groups (P &lt; 0.002), favouring the SM, SM + FE and SM + SF groups. A positive correlation between female LW at the beginning of the rainy season and the onset of ovulatory activity was observed (r = +0.90; P &lt; 0.01). The average date for the onset of ovarian activity differed (P &lt; 0.001) among groups, being earlier in the SM + SF group (9 May ± 4.3 days), which also depicted the shortest interval between the introduction of males until the onset of ovulatory activity (P &lt; 0.001). Results of the present study indicate that nutritional signalling of the reproductive activity of both female and male Criollo goats reared under marginal conditions surmounts the inhibitory effects of long-day photoperiods during the non-reproductive season. An increased level of nutrition during the anestrous season may be used to increase reproductive function of both male and female goats reared in harsh nutritional conditions and applied as a green, clean, and ethical reproductive tool at these latitudes.

Down-regulation of the OsPDCD5 gene induced photoperiod-sensitive male sterility in rice

Programmed cell death (PCD) is a crucial process for plants during development and environmental stress. OsPDCD5, is an ortholog to mammalian programmed cell death 5 gene. Here we report that decreased expression of OsPDCD5 caused by antisense technology could induce pollen sterility in photoperiod-sensitive rice. The male sterility of transgenic plants is reversible, determined mainly by photoperiod. Transgenic plants are sterile under long-day photoperiod (≥13.5 h sunlight) with postponed heading time, while they can restore fertility under short-day photoperiod (below 13 h sunlight). Analysis of tissue sections of anthers displays the tapetum cells of the anther wall retard PCD process in transgenic plants under long-day photoperiod. The retarded PCD was also confirmed by DNA fragmentation. In F 1 hybrids made from transgenic plants with antisense- OsPDCD5 and japonica rice varieties, lower transcript inhibition could restore fertility, under certain photoperiod and temperatures. The surprising discovery of the photosensitive male fertility suggested that by using specific photoperiods, the male sterility (PGMS) could be used for commercial production of hybrid rice using a two-line breeding system. The transgenic hybrid strategy was easy to apply, reduced costs and shortened the breeding period. It provides great advantages for commercial applications in rice and other crops.

Brain-independent development in the moth Sesamia nonagrioides

The caterpillars of Sesamia nonagrioides developing under long-day (LD) photoperiod pupate in the 5th or 6th instar whereas under short day (SD) conditions they enter diapause and undergo several extra larval molts. The diapause is terminated within 1–3 instars upon transfer of SD larvae to the LD conditions. Brain removal from the 6th instar larvae promotes pupation followed by imaginal development; however, one third of the SD larvae and 12% of the LD larvae debrained at the start of the instar first undergo 1–2 larval molts. The incidence of larval molts is enhanced by the brain implants. Exclusively pupal molts occur in the LD larvae debrained late in the 6th instar. Decapitation elicits pupation in both LD and SD larvae, except for some of the 4th and 5th and rarely 6th instar that are induced to a fast larval molt. The pupation of decapitated larvae is reverted to a larval molt by application of a juvenile hormone (JH) agonist. No molts occur in abdomens isolated from the head and thorax prior to the wandering stage. Abdomens isolated later undergo a larval (SD insects) or a pupal (LD insects) molt. Taken together the data reveal that in S. nonagrioides (1) several larval molts followed by a pupal and imaginal molt can occur without brain; (2) an unknown head factor outside the brain is needed for the pupal–adult molt; (3) brain exerts both stimulatory and inhibitory effect on the corpora allata (CA); (4) larval molts induced in CA absence suggest considerable JH persistence.

MT1 Melatonin Receptors Mediate Somatic, Behavioral, and Reproductive Neuroendocrine Responses to Photoperiod and Melatonin in Siberian Hamsters (Phodopus sungorus)

Environmental day length drives nocturnal pineal melatonin secretion, which in turn generates or entrains seasonal cycles of physiology, reproduction, and behavior. In mammals, melatonin (MEL) binds to a number of receptor subtypes including high-affinity (MT1 and MT2) and low-affinity (MT3, nuclear orphan receptors) binding sites, which are distributed throughout the central nervous system and periphery. The MEL receptors that mediate photoperiodic reproductive and behavioral responses to MEL have not been identified in a reproductively photoperiodic species. Here I tested the hypothesis that MT1 receptors are necessary and sufficient to engage photoperiodic responses by challenging male Siberian hamsters (Phodopus sungorus), a species that does not express functional MT2 receptors, with ramelteon (RAM), a specific MT1/MT2 receptor agonist. In hamsters housed in a long-day photoperiod, late-afternoon RAM treatment inhibited gonadotropin secretion, induced gonadal regression, and suppressed food intake and body mass, mimicking effects of MEL. In addition, chronic (24 h/d) RAM infusions were sufficient to obscure endogenous MEL signaling, and these treatments attenuated gonadal regression in short days. Together, the outcomes indicate that signaling at the MT1 receptor is sufficient and necessary to mediate the effects of photoperiod-driven changes in MEL on behavior and reproductive function in a reproductively photoperiodic mammal.

Correlation with Behavioral Activity and Rest Implies Circadian Regulation by SCN Neuronal Activity Levels

The SCN of the hypothalamus contains a major pacemaker, which exhibits 24-h rhythms in electrical impulse frequency. Although it is known that SCN electrical activity is high during the day and low during the night, the precise relationship between electrical activity and behavioral rhythms is almost entirely unknown. The authors performed long-term recordings of SCN multiple unit activity with the aid of implanted microelectrodes in parallel with the drinking activity in freely moving mice. The animals were kept in a 12h:12h light-dark cycle (LD 12:12) and in short-day (LD 8:16) and long-day photoperiods (LD 16:8). Onsets and offsets of behavioral activity occurred when SCN discharge was around half-maximum value. Of the onsets 80%, and of the offsets 62%, occurred when SCN electrical activity differed less than 15% from the half-maximum electrical activity levels. Transitions between rest and activity could be described by a sigmoid shaped probability curve with Hill coefficients of 7.0 for onsets and 5.7 for offsets. The similarity in the onset and offset levels shows an absence of hysteresis in the control of behavioral activity by the SCN. Exposure to short- or long-day photoperiods induced significant alterations in the waveform of electrical activity but did not affect SCN electrical activity levels at which behavioral transitions occurred. In all photoperiods, the SCN signal was skewed with more rapid discharge changes during onsets (19% per hour) than offsets (11% per hour). The precision of the circadian system appears optimized, as transitions between behavioral activity and rest occur when the change in SCN electrical activity is maximal, both during the declining and rising phase. The authors conclude that transitions in behavioral state can be described by a probability function around half-maximum electrical activity levels and that the parameters of the SCN, predicting onset and offset of behavior, are remarkably insensitive to environmental conditions.

Corrigendum

CorrigendaCorrigendumPublished Online:01 Nov 2009https://doi.org/10.1152/ajpregu.zh6-7009-corr.2009Original articleMoreSectionsPDF (529 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInEmailWeChat Volume 65, May 2009Herwig A, Wilson D, Logie TJ, Boelen A, Morgan PJ, Mercer JG, Barrett P. Photoperiod and acute energy deficits interact on components of the thyroid hormone system in hypothalamic tanycytes of the Siberian hamster. Am J Physiol Regul Integr Comp Physiol 296: , 2009. First published March 18, 2009; doi:10.1152/ajpregu.90755.2008 (http://ajpregu.physiology.org/cgi/content/full/296/5/R1307).In the original Figure 1A, the lower left panel was mistakenly a copy of the one on the lower right. The corrected figure appears below with its original legend.Fig. 1.Quantification of type II (D2) and III (D3) deiodinase (Dio2 and Dio3) mRNA expression in the 3rd ventricular tanycyte layer of Siberian hamster in long-day (LD) or short-day (SD) photoperiod with or without 48 h of starvation. A and C: representative autoradiographs of coronal brain sections from each of the 4 treatment conditions hybridized with a probe for Dio2 and Dio3. B and D: quantification of autoradiograph signals for Dio2 and Dio3 mRNA expression. Expression was normalized to the highest value obtained for each probe. Solid bars, ad libitum-fed hamsters; gray bars, fold-restricted (48-h-starved) animals. *P < 0.05; ***P < 0.001 by 2-way ANOVA and Tukey's post hoc test for Dio2 and by t-test for Dio3.Download figureDownload PowerPointIn the original Figure 4E, the panel on the upper right was mistakenly a copy of the panel on the upper left side. The corrected figure appears below with its original legend.Fig. 4.Quantification of VGF, neuropeptide Y (NPY), and thyrotropin-releasing hormone (TRH) mRNA expression in the hypothalamus of the Siberian hamster. A: representative autoradiographs of coronal brain sections from each of the treatment conditions hybridized with a probe for VGF. B: quantification of VGF mRNA expression in the dorsal region of the medial posterior area of the arcuate nucleus (dmpARC) of hamsters in the SD photoperiod (no expression in LD) with and without 48 h of starvation. C: autoradiographs of coronal brain sections from each of the treatment conditions hybridized with a probe for NPY. D: quantification of NPY expression in the arcuate nucleus of hamsters held in LD and SD photoperiods with and without 48 h of starvation. E: autoradiographs of coronal brain sections from each of the treatment conditions hybridized with a probe for TRH. F: quantification of TRH mRNA expression in the paraventricular nucleus. Expression was normalized to the highest value for each probe. Solid bars, ad libitum-fed hamsters; gray bars, starved hamsters. *P < 0.05; ***P < 0.001 by 2-way ANOVA and Tukey's post hoc test.Download figureDownload PowerPointThis article has no references to display. Download PDF Previous Back to Top FiguresReferencesRelatedInformationRelated ArticlesPhotoperiod and acute energy deficits interact on components of the thyroid hormone system in hypothalamic tanycytes of the Siberian hamster 01 May 2009American Journal of Physiology-Regulatory, Integrative and Comparative Physiology More from this issue > Volume 297Issue 5November 2009Pages R1624-R1624 Copyright & PermissionsCopyright © 2009 American Physiological Societyhttps://doi.org/10.1152/ajpregu.zh6-7009-corr.2009History Published online 1 November 2009 Published in print 1 November 2009 Metrics