Distribution by Scientific Domains
Distribution within Life Sciences

Kinds of Darkness

  • complete darkness
  • constant darkness
  • continuous darkness

  • Selected Abstracts


    ART HISTORY, Issue 1 2008
    This study locates Velázquez's Supper at Emmaus (c. 1617/18) within early seventeenth-century debates on the Christian conversion of Seville's African slaves. Through a careful analysis of writings by Sevillian clerics, the essay argues that Velázquez gave pictorial form to discourse on African spiritual ,illumination' and developing theories of skin colour. Treatises by Seville's ecclesiastics also provide crucial insight into the original, elite audience for whom Velázquez surely constructed his African subject. In Supper at Emmaus, Velázquez presented his male beholder with one possession encompassed within another: a female slave in a painting by Seville's most promising young artist. [source]

    Adapting to the dark side: a review of Cave Biology: Life in Darkness, by Aldemaro Romero

    William R. Jeffery
    No abstract is available for this article. [source]

    To Rise in Darkness: Revolution, Repression, and Memory in El Salvador, 1920,1932

    Ellen Moodie
    First page of article [source]

    In Conrad's Footsteps: Critical Approaches to Africanist Travel Writing

    Robert Burroughs
    Travel writing about Central Africa in English reverberates with the language of Joseph Conrad's Heart of Darkness. This essay considers how that canonical text, in shaping twentieth-century travellers' understandings of Central Africa and the travel genre, also shapes literary critics' understandings of the same subjects. [source]

    Novel Findings Regarding Photoinduced Commitments of G1-, S- and G2-phase Cells to Cell-cycle Transitions in Darkness and Dark-induced G1-, S- and G2-phase Arrests in Euglena

    Shin-ya Hagiwara
    No abstract is available for this article. [source]

    Response of superoxide dismutase isoenzymes in tomato plants (Lycopersicon esculentum) during thermo-acclimation of the photosynthetic apparatus

    Daymi Camejo
    Seedlings of Lycopersicon esculentum Mill. var. Amalia were grown in a growth chamber under a photoperiod of 16 h light at 25°C and 8 h dark at 20°C. Five different treatments were applied to 30-day-old plants: Control treatment (plants maintained in the normal growth conditions throughout the experimental time), heat acclimation (plants exposed to 35°C for 4 h in dark for 3 days), dark treatment (plants exposed to 25°C for 4 h in dark for 3 days), heat acclimation plus heat shock (plants that previously received the heat acclimation treatment were exposed to 45°C air temperature for 3 h in the light) and dark treatment plus heat shock (plants that previously received the dark treatment were exposed to 45°C air temperature for 3 h in the light). Only the heat acclimation treatment increased the thermotolerance of the photosynthesis apparatus when the heat shock (45°C) was imposed. In these plants, the CO2 assimilation rate was not affected by heat shock and there was a slight and non-significant reduction in maximum carboxylation velocity of Rubisco (Vcmax) and maximum electron transport rate contributing to Rubisco regeneration (Jmax). However, the plants exposed to dark treatment plus heat shock showed a significant reduction in the CO2 assimilation rate and also in the values of Vcmax and Jmax. Chlorophyll fluorescence measurements showed increased thermotolerance in heat-acclimated plants. The values of maximum chlorophyll fluorescence (Fm) were not modified by heat shock in these plants, while in the dark-treated plants that received the heat shock, the Fm values were reduced, which provoked a significant reduction in the efficiency of photosystem II. A slight rise in the total superoxide dismutase (SOD) activity was found in the plants that had been subjected to both heat acclimation and heat shock, and this SOD activity was significantly higher than that found in the plants subjected to dark treatment plus heat shock. The activity of Fe-SOD isoenzymes was most enhanced in heat-acclimated plants but was unaltered in the plants that received the dark treatment. Total CuZn-SOD activity was reduced in all treatments. Darkness had an inhibitory effect on the Mn-SOD isoenzyme activity, which was compensated by the effect of a rise in air temperature to 35°C. These results show that the heat tolerance of tomatoplants may be increased by the previous imposition of a moderately high temperature and could be related with the thermal stability in the photochemical reactions and a readjustment of Vcmax and Jmax. Some isoenzymes, such as the Fe-SODs, may also play a role in the development of heat-shock tolerance through heat acclimation. In fact, the pattern found for these isoenzymes in heat-acclimated Amalia plants was similar to that previously described in other heat-tolerant tomato genotypes. [source]

    A Beam of Intense Darkness,

    Antonino Ferro
    First page of article [source]

    A Beam of Intense Darkness: Wilfred Bion's Legacy to Psychoanalysis by Grotstein, James

    Judith Pickering
    No abstract is available for this article. [source]

    Darkness and UV radiation provoked compensatory growth in marine phytoplankton Phaeodactylum tricornutum (Bacillariophyceae)

    Zhuoping Cai
    First page of article [source]

    A Beam of Intense Darkness: Wilfred Bion's Legacy to Psychoanalysis , By James Grotstein

    Meg Harris Williams
    First page of article [source]

    Throwing Some Light on the Vast Darkness that is Analysis: Niels Henrik Abel's Critical Revision and the Concept of Absolute Convergence

    CENTAURUS, Issue 1 2010
    Henrik Kragh Sørensen
    During the first half of the nineteenth century, mathematical analysis underwent a transition from a predominantly formula-centred practice to a more concept-centred one. Central to this development was the reorientation of analysis originating in Augustin- Louis Cauchy's (1789,1857) treatment of infinite series in his Cours d'analyse. In this work, Cauchy set out to rigorize analysis, thereby critically examining and reproving central analytical results. One of Cauchy's first and most ardent followers was the Norwegian Niels Henrik Abel (1802,1829) who vowed to shed some light on the vast darkness in analysis. This paper investigates some important aspects of Abel's contribution to the reorientation in analysis. In particular, it stresses the role for critical revision in the process of rigorization. By critically examining past practice, the new practice sought to explain the relative success of the previous,now outdated,approach. This is illustrated by discussing a number of issues related to Abel's new proof of the binomial theorem (1826) including his reactions to the exception that he encountered to one of the central theorems of Cauchy's theory. Following this discussion, the formation of new concepts as the result of critical revisions is illustrated by analysing the early history of the concept of absolute convergence. Thereby, it is shown how a new concept was distilled, investigated, put to use and eventually superseded. [source]

    Effects of locomotor stimulation and protein synthesis inhibition on circadian rhythms in size changes of L1 and L2 interneurons in the fly's visual system

    Elzbieta Kula
    Abstract Axons of monopolar cell interneurons L1 and L2 in the first optic lobe (lamina) of the fly Musca domestica undergo cyclical changes in diameter. These axons swell during the day and shrink during the night. In addition, the axons' size depends on light conditions since they are largest in continuous light (LL), somewhat smaller under day/night (LD) conditions, and smallest under constant darkness (DD). In this study we found that sizes of both cells can further increase in free flying flies under LD conditions, while the visual stimulation alone does not have significant effect on the cross-sectional area of L1 and L2 axons. The stimulation of free flying had no effect on L1 and L2 sizes if it was performed at the beginning of subjective day in LL or DD. Our results indicate that a maximal increase in size of L1 and L2 is observed when stimulation of free flying is synchronized with a fly' daily peak of activity. We also found that protein synthesis is needed to increase size of monopolar cell axons during the day when they normally swell. © 2007 Wiley Periodicals, Inc. Develop Neurobiol, 2007. [source]

    Circadian changes in Drosophila motor terminals

    Kerstin I. Mehnert
    Abstract In Drosophila melanogaster, as in most other higher organisms, a circadian clock controls the rhythmic distribution of rest/sleep and locomotor activity. Here we report that the morphology of Drosophila flight neuromuscular terminals changes between day and night, with a rhythm in synaptic bouton size that continues in constant darkness, but is abolished during aging. Furthermore, arrhythmic mutations in the clock genes timeless and period also disrupt this circadian rhythm. Finally, these clock mutants also have an opposing effect on the nonrhythmic phenotype of neuronal branching, with tim mutants showing a dramatic hyperbranching morphology and per mutants having fewer branches than wild-type flies. These unexpected results reveal further circadian as well as nonclock related pleiotropic effects for these classic behavioral mutants. © 2007 Wiley Periodicals, Inc. Develop Neurobiol, 2007. [source]

    Growth in relation to microclimatic conditions and physiological characteristics of four Lobaria pulmonaria populations in two contrasting habitats

    ECOGRAPHY, Issue 1 2004
    Gisela Gaio-Oliveira
    The aim of the present study was to compare the physiological characteristics of various populations of the lichen Lobaria pulmonaria in Portugal and Sweden. For this, indirect markers of algal (photobiont) and fungal (mycobiont) activity were measured, as well as their CO2 gasexchange characteristics. Microclimatic conditions and the lichens growth performance in the two countries were compared using reciprocal transplantation. Two populations of L. pulmonaria represented each country: one collected from forest interior conditions and one from forest edge habitats. A non-transplanted "wild" population was also studied in each country, in order to evaluate any transplantation effects per se. The main hypothesis were that; 1) growth should be faster in Portugal due to higher light availability; 2) the energy use efficiency of lichen biomass gain should be similar for the native populations in their respective native habitat; 3) if the lichens were able to adapt to the environmental conditions in the foreign habitat this should be revealed as similar growth rates among all thalli transplanted at the same site, regardless of their origin. Physiologically, the Portuguese and Swedish populations were very similar, both concerning their CO2 gas exchange characteristics and distribution of resources between photo- and mycobiont tissue. Environmental conditions were more advantageous for L. pulmonaria growth in Portugal, i.e. higher photon flux densities and ambient temperatures when the lichens were wet and active, and a lower fraction of the active time occurring in darkness. However, despite similar physiological characteristics of all the studied populations, the Swedish lichens were not able to grow as well in Portugal as the native, while all populations had similarly low growth rates in Sweden. [source]

    Illumination influences the ability of migrating juvenile salmonids to pass a submerged experimental weir

    P. S. Kemp
    Abstract,,, The downstream migration of juvenile salmonids has previously been considered predominantly passive. It has been argued that passive displacement during periods of darkness is, partially at least, a result of an inability to maintain a fixed position in the absence of visual cues. In this study, behaviour of juvenile Pacific salmonids was assessed under conditions of light and dark as they passed through an artificial channel and encountered a submerged weir. Results indicated that when light, fish formed schools and actively explored the channel. Conversely, when dark (infrared illumination only) they did not form schools, but maintained randomly distributed positions holding station against the flow. As a consequence, more fish approached and either passed, or rejected, the weir when light. The majority of fish that passed the weir did so within the first minute of each trial. Fish predominantly passed through the channel facing downstream and changed orientation prior to passing tail first over the weir crest in the presence and absence of visual cues. The orientation switch was less common when dark. This study shows, at a fine-resolution scale, that downstream movement of juvenile salmonids can be inhibited as fish exhibit alternative behaviours in the absence of visual cues. Downstream movement was not predominantly passive. Fish passage design should not be based on the assumption that downstream migration is passive. [source]

    Determination of melatonin in wine and plant extracts by capillary electrochromatography with immobilized carboxylic multi-walled carbon nanotubes as stationary phase

    ELECTROPHORESIS, Issue 13 2010
    Patricia W. Stege
    Abstract The finding of melatonin, the often called "hormone of darkness" in plants opens an interesting perspective associated to the plethora of health benefits related to the moderate consumption of red wine. In this study, the implementation of a new method for the determination of melatonin in complex food matrices by CEC with immobilized carboxylic multi-walled carbon nanotubes as stationary phase is demonstrated. The results indicated high electrochromatographic resolution, good capillary efficiencies and improved sensitivity respect to those obtained with conventional capillaries. In addition, it was demonstrated highly reproducible results between runs, days and columns. The LOD for melatonin was 0.01,ng/mL. The method was successfully applied to the determination of melatonin in red and white wine, grape skin and plant extracts of Salvia officinalis L. [source]

    Autoinducers extracted from microbial mats reveal a surprising diversity of N -acylhomoserine lactones (AHLs) and abundance changes that may relate to diel pH

    Alan W. Decho
    Summary Microbial mats are highly structured and diverse communities, and one of the earliest-known life assemblages. Mat bacteria interact within an environment marked by strong geochemical gradients and fluctuations. We examined natural mat systems for the presence of autoinducers involved in quorum sensing, a form of cell,cell communication. Our results revealed that a diverse array of N -acylhomoserine lactones (AHLs) including C4 - to C14 -AHLs, were identified from mat extracts using mass spectrometry (MS), with further confirmation by MS/MS-collision-induced dissociation (CID), and additions of external standards. Microelectrode measurements showed that mats exhibited diel pH fluctuations, ranging from alkaline (pH 9.4) during daytime (net photosynthesis) to acidic (pH 6.8) during darkness (net respiration/fermentation). Under laboratory conditions, AHLs having shorter acyl-chains were degraded within the time frame that daily alkaline pH (> 8.2) conditions exist in mats. Intensive sampling of mats after full day- or night-time incubations revealed that accumulations of extractable shorter-chain AHLs (e.g. C8 - and C10 -AHLs) were significantly (P < 0.001) diminished during daytime. Our study offers evidence that stabilities of AHLs under natural conditions may be influenced by the proximal extracellular environment. We further propose that the ancient periodicity of photosynthesis/respiration in mats may potentially drive a mechanism for diel differences in activities of certain autoinducers, and hence bacterial activities mediated through quorum sensing. [source]

    Polyphyletic photosynthetic reaction centre genes in oligotrophic marine Gammaproteobacteria

    Jang-Cheon Cho
    Summary Ecological studies indicate that aerobic anoxygenic phototrophic bacteria (AAP) that use bacteriochlorophyll to support phototrophic electron transport are widely distributed in the oceans. All cultivated marine AAP are alpha-3 and alpha-4 Proteobacteria, but metagenomic evidence indicates that uncultured AAP Gammaproteobacteria are important members of ocean surface microbial communities. Here we report the description of obligately oligotrophic, marine Gammaproteobacteria that have genes for aerobic anoxygenic photosynthesis. Three strains belonging to the OM60 clade were isolated in autoclaved seawater media. Polymerase chain reaction assays for the pufM gene show that these strains contain photosynthetic reaction centre genes. DNA sequencing and phylogenetic analysis indicate that the pufM genes are polyphyletic, suggesting multiple instances of lateral gene transfer. Peptide sequences from six photosynthesis genes (pufL, pufM, pufC, pufB, pufA and puhA) were detected by proteomic analyses of strain HTCC2080 cells grown aerobically in seawater. They closely match predicted peptides from an environmental seawater bacterial artificial chromosome clone of gammaproteobacterial origin, thus identifying the OM60 clade as a significant source of gammaproteobacterial AAP genes in marine systems. The cell yield and rate of growth of HTCC2080 in autoclaved, aerobic seawater increased in the light. These findings identify the OM60 clade as a source of Gammaproteobacteria AAP genes in coastal oceans, and demonstrate that aerobic, anoxygenic photosynthetic metabolism can enhance the productivity of marine oligotrophic bacteria that also grow heterotrophically in darkness. [source]

    Kleptoplasty in an Antarctic dinoflagellate: caught in evolutionary transition?

    Rebecca J. Gast
    Summary Photosynthetic dinoflagellates contain a diverse collection of plastid types, a situation believed to have arisen from multiple endosymbiotic events. In addition, a number of heterotrophic (phagotrophic) dinoflagellates possess the ability to acquire chloroplasts temporarily by engulfing algae and retaining their chloroplasts in a functional state. These latter relationships typically last from a few days to weeks, at which point the chloroplasts lose function, are digested and replaced with newly acquired plastids. A novel and abundant dinoflagellate related to the icthyotoxic genera Karenia and Karlodinium was recently discovered by us in the Ross Sea, Antarctica. Sequencing of its plastid small subunit ribosomal gene indicated that it did not share evolutionary history with the plastids of Karenia or Karlodinium, but was closely related to the free-living haptophyte Phaeocystis antarctica, a species that often dominates phytoplankton blooms in the Ross Sea. Chloroplast uptake was observed to occur rapidly (within 2 days), with retention in cultures being long-lived (several months) but not permanent. The dinoflagellate was also incapable of growing indefinitely in continuous darkness with algae as prey. Our findings may indicate an emerging endosymbiotic event yielding a dinoflagellate that is presently neither purely phototrophic nor purely heterotrophic, but occupies a niche juxtaposed between these contrasting nutritional modes. [source]

    The responses of photosynthesis and oxygen consumption to short-term changes in temperature and irradiance in a cyanobacterial mat (Ebro Delta, Spain)

    Eric Epping
    We have evaluated the effects of short-term changes in incident irradiance and temperature on oxygenic photosynthesis and oxygen consumption in a hypersaline cyanobacterial mat from the Ebro Delta, Spain, in which Microcoleus chthonoplastes was the dominant phototrophic organism. The mat was incubated in the laboratory at 15, 20, 25 and 30°C at incident irradiances ranging from 0 to 1000 µmol photons m,2 s,1. Oxygen microsensors were used to measure steady-state oxygen profiles and the rates of gross photosynthesis, which allowed the calculation of areal gross photosynthesis, areal net oxygen production, and oxygen consumption in the aphotic layer of the mat. The lowest surface irradiance that resulted in detectable rates of gross photosynthesis increased with increasing temperature from 50 µmol photons m,2 s,1 at 15°C to 500 µmol photons m,2 s,1 at 30°C. These threshold irradiances were also apparent from the areal rates of net oxygen production and point to the shift of M. chthonoplastes from anoxygenic to oxygenic photosynthesis and stimulation of sulphide production and oxidation rates at elevated temperatures. The rate of net oxygen production per unit area of mat at maximum irradiance, J0, did not change with temperature, whereas, JZphot, the flux of oxygen across the lower boundary of the euphotic zone increased linearly with temperature. The rate of oxygen consumption per volume of aphotic mat increased with temperature. This increase occurred in darkness, but was strongly enhanced at high irradiances, probably as a consequence of increased rates of photosynthate exudation, stimulating respiratory processes in the mat. The compensation irradiance (Ec) marking the change of the mat from a heterotrophic to an autotrophic community, increased exponentially in this range of temperatures. [source]

    Cyst-based toxicity tests XII,Development of a short chronic sediment toxicity test with the ostracod crustacean Heterocypris incongruens: Selection of test parameters

    Belgis Chial
    Abstract Experiments were carried out with neonates of the freshwater ostracod Heterocypris incongruens hatched from cysts in order to develop a new culture/maintenance-free solid-phase microbiotest for the toxicity assessment of contaminated sediments. Based on preliminary investigations, a number of test parameters were investigated for a short-chronic assay: hatching time, size of the cups of the multiwell test plates, feeding of the test organisms prior to the test, amount of supplemental algal food, volume of sediment, and duration of the test. On the basis of the findings, a test protocol was formulated for a 6-day assay in 12-cup multiwell plates with 10 organisms per cup and 3 replicates. The test organisms were collected 52 h after the start of the incubation of the cysts in standard freshwater at 25°C under continuous illumination after a 4-h prefeeding with 1.3 mg/mL Spirulina. The test biota in the cups were exposed to 300 ,L of test sediment in 2 mL of standard freshwater with 3 × 107 live algal cells (Raphidocelis subcapitata) as food supplement. Calibrated sand was used as a reference sediment. Mortality and growth of the ostracods were determined after 6 days' incubation at 25°C in darkness. The selected test parameters for the new microbiotest were found adequate for toxicity determination of natural sediments compared with the 10-day contact test with the amphipod Hyalella azteca. © 2002 Wiley Periodicals, Inc. Environ Toxicol 17: 520,527, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/tox.10085 [source]

    Metabolism of uniconazole-P in water-sediment systems under illumination

    Rika Kodaka
    Abstract Aerobic soil metabolism of uniconazole-P ([S]- E -1-[4-chlorophenyl]-4,4-dimethyl-2-[1,2,4-triazole-1-yl]-penten-3-ol) and the effect of illumination on metabolic profiles were studied in the water,sediment system when spiked to water. Uniconazole-P was gradually partitioned to the sediment with an aquatic half-life of 6.9 d in darkness with formation of bound residues. Illumination of the system from a xenon lamp (>290 nm) greatly accelerated the degradation of uniconazole-P via photoinduced isomerization between E- and Z-isomers with a subsequent intramolecular cyclization, and its aquatic half-life was greatly reduced to 0.6 d. Kinetic analysis based on compartment models suggested the possible contribution of photodegradation at the water-sediment interface, leading to more formation of the cyclized derivative in the sediment. [source]

    The Effects of Social Experience on Aggressive Behavior in the Green Anole Lizard (Anolis carolinensis)

    ETHOLOGY, Issue 9 2001
    Eun-Jin Yang
    To understand how context-specific aggression emerges from past experience, we examined how consecutive aggressive encounters influence aggressive behavior and stress responses of male green anole lizards (Anolis carolinensis). Animals were shown a video clip featuring an aggressively displaying conspecific male, which provoked aggressive responding, while control animals viewed a neutral video. After 5 d of interaction with the videos, both the subject and control groups were presented with a live conspecific. As a non-invasive assay of stress responses, we measured changes in body color and eyespot darkness, two features known to be strongly correlated with titers of stress hormones. Our results demonstrate that experience increased aggression in male anoles, but that increases in aggression to a repeated stimulus were transient. Tests with a novel conspecific indicate that the experienced animals remained aggressive when presented with novel stimuli. Although there were differences in the morphological indicators of the stress response between experimental and control groups during video presentations, there were no differences when presented with novel conspecifics. These data indicate that experience-dependent differences were not mediated by differences in the ,stressfulness' of aggressive interaction, as thought to be the case for animals in chronic subordinate/dominant dyads. We suggest that habituation and reinforcement interact to promote aggressive responding and to restrict it to novel individuals. Such context specificity is a hallmark of natural patterns of aggression in territorial species. [source]

    Roles of light and serotonin in the regulation of gastrin-releasing peptide and arginine vasopressin output in the hamster SCN circadian clock

    Jessica M. Francl
    Abstract Daily timing of the mammalian circadian clock of the suprachiasmatic nucleus (SCN) is regulated by photic input from the retina via the retinohypothalamic tract. This signaling is mediated by glutamate, which activates SCN retinorecipient units communicating to pacemaker cells in part through the release of gastrin-releasing peptide (GRP). Efferent signaling from the SCN involves another SCN-containing peptide, arginine vasopressin (AVP). Little is known regarding the mechanisms regulating these peptides, as literature on in vivo peptide release in the SCN is sparse. Here, microdialysis,radioimmunoassay procedures were used to characterize mechanisms controlling GRP and AVP release in the hamster SCN. In animals housed under a 14/10-h light,dark cycle both peptides exhibited daily fluctuations of release, with levels increasing during the morning to peak around midday. Under constant darkness, this pattern persisted for AVP, but rhythmicity was altered for GRP, characterized by a broad plateau throughout the subjective night and early subjective day. Neuronal release of the peptides was confirmed by their suppression with reverse-microdialysis perfusion of calcium blockers and stimulation with depolarizing agents. Reverse-microdialysis perfusion with the 5-HT1A,7 agonist 8-OH-DPAT ((±)-8-hydroxydipropylaminotetralin hydrobromide) during the day significantly suppressed GRP but had little effect on AVP. Also, perfusion with the glutamate agonist NMDA, or exposure to light at night, increased GRP but did not affect AVP. These analyses reveal distinct daily rhythms of SCN peptidergic activity, with GRP but not AVP release attenuated by serotonergic activation that inhibits photic phase-resetting, and activated by glutamatergic and photic stimulation that mediate this phase-resetting. [source]

    The role of the medial caudate nucleus, but not the hippocampus, in a matching-to sample task for a motor response

    Raymond P. Kesner
    Abstract A delayed-match-to-sample task was used to assess memory for motor responses in rats with control, hippocampus, or medial caudate nucleus (MCN) lesions. All testing was conducted on a cheeseboard maze in complete darkness using an infrared camera. A start box was positioned in the centre of the maze facing a randomly determined direction on each trial. On the sample phase, a phosphorescent object was randomly positioned to cover a baited food well in one of five equally spaced positions around the circumference of the maze forming a 180-degree arc 60 cm from the box. The rat had to displace the object to receive food and return to the start box. The box was then rotated to face a different direction. An identical baited phosphorescent object was placed in the same position relative to the start box. A second identical object was positioned to cover a different unbaited well. On the choice phase, the rat must remember the motor response made on the sample phase and make the same motor response on the choice phase to receive a reward. Hippocampus lesioned and control rats improved as a function of increased angle separation used to separate the correct object from the foil (45, 90, 135, and 180 degrees) and matched the performance of controls. However, rats with MCN lesions were impaired across all separations. Results suggest that the MCN, but not the hippocampus, supports working memory and/or a process aimed at reducing interference for motor response selection based on vector angle information. [source]

    Diurnal regulation of the gastrin-releasing peptide receptor in the mouse circadian clock

    Ilia N. Karatsoreos
    Abstract In mammals, circadian rhythms are generated by the suprachiasmatic nuclei (SCN) of the hypothalamus. SCN neurons are heterogeneous and can be classified according to their function, anatomical connections, morphology and/or peptidergic identity. We focus here on gastrin-releasing peptide- (GRP) and on GRP receptor- (GRPr) expressing cells of the SCN. Pharmacological application of GRP in vivo or in vitro can shift the phase of circadian rhythms, and GRPr-deficient mice show blunted photic phase shifting. Given the in vivo and in vitro effects of GRP on circadian behavior and on SCN neuronal activity, we investigated whether the GRPr might be under circadian and/or diurnal control. Using in situ hybridization and autoradiographic receptor binding, we localized the GRPr in the mouse SCN and determined that GRP binding varies with time of day in animals housed in a light,dark cycle but not in conditions of constant darkness. The latter results were confirmed with Western blots of SCN tissue. Together, the present findings reveal that changes in GRPr are light driven and not endogenously organized. Diurnal variation in GRPr activity probably underlies intra-SCN signaling important for entrainment and phase shifting. [source]

    Nerve growth factor-induced circadian phase shifts and MAP kinase activation in the hamster suprachiasmatic nuclei

    Gastón A. Pizzio
    Abstract Circadian rhythms are entrained by light and by several neurochemical stimuli. In hamsters housed in constant darkness, i.c.v. administration of nerve growth factor (NGF) at various times in their circadian cycle produced phase shifts of locomotor activity rhythms that were similar in direction and circadian timing to those produced by brief pulses of light. Moreover, the effect of NGF and light were not additive, indicating signalling points in common. These points include the immediate-early gene c-fos and ERK1/2, a component of the mitogen-activated protein kinases (MAPK) family. NGF activates c-FOS and ERK1/2-MAPK in the suprachiasmatic nuclei, the site of a circadian clock in mammals, when administered during the subjective night but not during the day. The effect of NGF on ERK1/2 activation was not inhibited by the administration of MK-801, a glutamate/NMDA receptor antagonist. These results suggest that NGF, acting through MAPK activation, plays a role in photic entrainment of the mammalian circadian clock. [source]

    Rat anterodorsal thalamic head direction neurons depend upon dynamic visual signals to select anchoring landmark cues

    Michaël B. Zugaro
    Abstract Head direction cells, which are functionally coupled to ,place' cells of the hippocampus, a structure critically involved in spatial cognition, are likely neural substrates for the sense of direction. Here we studied the mechanism by which head direction cells are principally anchored to background visual cues [M.B. Zugaro et al. (2001) J. Neurosci., 21, RC154,1,5]. Anterodorsal thalamic head direction cells were recorded while the rat foraged on a small elevated platform in a 3-m diameter cylindrical enclosure. A large card was placed in the background, near the curtain, and a smaller card was placed in the foreground, near the platform. The cards were identically marked, proportionally dimensioned, subtended the same visual angles from the central vantage point and separated by 90°. The rat was then disoriented in darkness, the cards were rotated by 90° in opposite directions about the center and the rat was returned. Preferred directions followed either the background card, foreground card or midpoint between the two cards. In continuous lighting, preferred directions shifted to follow the background cue in most cases (30 of the 53 experiments, Batschelet V -test, P < 0.01). Stroboscopic illumination, which perturbs dynamic visual signals (e.g. motion parallax), blocked this selectivity. Head direction cells remained equally anchored to the background card, foreground card or configuration of the two cards (Watson test, P > 0.1). This shows that dynamic visual signals are critical in distinguishing typically more stable background cues which govern spatial neuronal responses and orientation behaviors. [source]

    Opposing actions of neuropeptide Y and light on the expression of circadian clock genes in the mouse suprachiasmatic nuclei

    Elizabeth S. Maywood
    Abstract The circadian clockwork of the hypothalamic suprachiasmatic nuclei (SCN) is synchronized by light and by nonphotic cues. The core timing mechanism is cell-autonomous, based on an autoregulatory transcriptional/translational feedback loop of circadian genes and their products. This study investigated the effects of neuropeptide Y (NPY), a potent nonphotic resetting cue, and its interaction with light in regulating clock gene expression in the SCN in vivo. Injection of NPY adjacent to the SCN and transfer to darkness 7 h before scheduled lights out, shifted the circadian activity,rest cycle. Exposure to light for 1 h immediately after NPY infusion blocked this behavioural response. NPY-induced shifts were accompanied by suppression of both mPer1 and mPer2 mRNA in the SCN, assessed 3 h after infusion. mPer mRNAs were not altered 1 h after infusion. Levels of mClock mRNA or mCLOCK immunoreactivity in the SCN were not affected by NPY at either time point. In parallel to the behavioural response, the NPY-induced suppression of mPer genes in the SCN was attenuated when a light pulse was delivered immediately after the infusion. These results identify mPer1 and mPer2 as molecular targets for both photic and nonphotic (NPY-induced) resetting of the clockwork, and support a synthetic model of circadian entrainment based upon convergent up- and downregulation of mPer expression. [source]


    EVOLUTION, Issue 2 2002
    Wade N. Hazel
    Abstract Seasonal polyphenism, in which different forms of a species are produced at different times of the year, is a common form of phenotypic plasticity among insects. Here I show that the production of dark fifth-instar caterpillars of the eastern black swallowtail butterfly, Papilio polyxenes, is a seasonal polyphenism, with larvae reared on autumnal conditions being significantly darker than larvae reared on midsummer conditions. Both rearing photoperiod and temperature were found to have individual and synergistic effects on larval darkness. Genetic analysis of variation among full-sibling families reared on combinations of two different temperatures and photoperiods is consistent with the hypothesis that variation in darkness is heritable. In addition, the genetic correlation in larval darkness across midsummer and autumnal environments is not different from zero, suggesting that differential gene expression is responsible for the increase in larval darkness in the autumn. The relatively dark autumnal form was found to have a higher body temperature in sunlight than did the lighter midsummer form, and small differences in temperature were found to increase larval growth rate. These results suggest that this genetically based seasonal polyphenism in larval color has evolved in part to increase larval growth rates in the autumn. [source]