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At least 19 recordsLinked to original sources

PubMed1984

Seasonal changes in the circadian activity rhythm of light-dark (LD) and completely dark (DD) regimen in the mouse submandibular gland in the presence of light-dark (LD) and completely dark (DD) regimen.

Influence of seasons on circadian activity changes and the influence of one and six weeks of DD upon these changes of acid phosphatase (AP) and beta-acetylglucosaminidase (AM) was studied in the submandibular gland of sexually mature male mice. Total enzyme activity was determined in tissue homogenates at four-hour intervals in March, June, October, and February under standard LD12/12 conditions and after one and six weeks of the DD regime. The rhythms were analysed according to cosinor method. Under constant lighting conditions the seasonal differences in the AM circadian activity rhythm were found. AP activity was considerably less influenced by seasonal changes. Both enzyme activity changes were independent of each other and each rhythm was differently influenced by DD. In the case of AM the most pronounced circadian activity changes had the highest amplitude and mesor occurred in summer. The strongest influence of DD upon this enzyme activity rhythm was observed in spring and summer especially after the first week, after six weeks the acrophase returned to the LD group value (spring). In autumn and winter the reaction to DD was different to that of summer and spring. For AP the circadian changes of activity were non-rhythmic in spring, whereas in all other seasons the acrophases occurred almost at the same time in the afternoon. In DD the activity rhythm significantly changed after six weeks. In all seasons, except spring the circadian rhythm of activity was not observed after six weeks of DD. An attempt was made to explain the observed results by the certain kind of genetic memory present in laboratory animals the neurohormonal system of which is influenced by seasonal changes.

Acetylglucosaminidase↗

PubMed1995

Dark Leaf Respiration in Light and Darkness of an Evergreen and a Deciduous Plant Species.

Dark respiration in light as well as in dark was estimated for attached leaves of an evergreen (Heteromeles arbutifolia Ait.) and a deciduous (Lepechinia fragans Greene) shrub species using an open gas-exchange system. Dark respiration in light was estimated by the Laisk method. Respiration rates in the dark were always higher than in the light, indicating that light inhibited respiration in both species. The rates of respiration in the dark were higher in the leaves of the deciduous species than in the evergreen species. However, there were no significant differences in respiration rates in light between the species. Thus, the degree of inhibition of respiration by light was greater in the deciduous species (62%) than in the evergreen species (51%). Respiration in both the light and darkness decreased with increasing leaf age. However, because respiration in the light decreased faster with leaf age than respiration in darkness, the degree of inhibition of respiration by light increased with leaf age (from 36% in the youngest leaves to 81% in the mature leaves). This suggests that the rate of dark respiration in the light is related to the rate of biosynthetic processes. Dark respiration in the light decreased with increasing light intensity. Respiration both in the light and in the dark was dependent on leaf temperature. We concluded that respiration in light and respiration in darkness are tightly coupled, with variation in respiration in darkness accounting for more than 60% of the variation in respiration in light. Care must be taken when the relation between respiration in light and respiration in darkness is studied, because the relation varies with species, leaf age, and light intensity.

Journal Article↗

PubMed2001

Heterophoria measured with white, dark-grey and dark-red Maddox rods.

BACKGROUND: Heterophoria is defined as a deviation from orthovergence position when no fusional contours are provided. It has been suggested that darkening one eye effects the phoric angle between the two eyes. We tested this assumption by comparing the phoric angles with white, dark-grey and dark-red Maddox rods. METHODS: In a first group of 14 subjects horizontal heterophoria was measured with white, dark-grey and dark-red Maddox rods. In a second group of 43 different subjects horizontal heterophoria was measured with white and dark-red Maddox rods. Subjects were asked to continually correct any perceived deviation, using Herschel prisms. Readings were taken after 1 min. RESULTS: Group 1 (n=14): No significant difference between white, dark-grey and dark-red Maddox rods (Friedmann test). Correlation between white and dark-grey Maddox rods r=0.97 (P<0.0001), slope of regression line 0.92 (95% confidence interval 0.78-1.06). Correlation between white and dark-red Maddox rods r=0.94 (P<0.0001), slope of regression line 0.67 (95% confidence interval 0.53-0.82). Group 2 (n=43): No significant difference between white and dark-red Maddox rods (Wilcoxon signed rank tests). Correlation r=0.96 (P<0.0001), slope of regression line 0.95 (95% confidence interval 0.87-1.03). CONCLUSION: Our study revealed no significant difference and a high correlation among the phoric angles obtained with white, dark-grey and dark-red Maddox rods. The close match suggests that darkening one eye does not effect the phoric angle between the two eyes.

Diagnostic Techniques, Ophthalmological↗

PubMed1996

Dark focus and dark vergence: an experimental verification of the configuration of the dual-interactive feedback model.

Based on the dual-interactive feedback model, dark focus and dark vergence designate a point on a line describing the response AC/A ratio. In order to verify the relationship between dark focus and dark vergence, we predicted the dark vergence from the measured dark focus when the measurements were based on the response-based calculated and gradient AC/A ratios. For 10 subjects, the correlations between predicted and measured dark vergence values were high. The prediction was better when using the gradient AC/A ratio.

Accommodation, Ocular↗

PubMed2003

Direct detection of weakly interacting massive particles using non-cryogenic techniques.

A flux of weakly interacting neutral particles incident on the Earth would produce occasional nuclear-recoil events in any material. These could be detected as scintillation or ionization pulses in suitable target materials. Expected rates are in the range 1-10(-4) events kg(-1) d(-1). These must be distinguished from much higher rates due to backgrounds from gamma and beta background, even in deep underground locations. Methods of uniquely identifying nuclear recoils are described using crystal scintillators, scintillation and ionization processes in liquid xenon, and ionization tracks in gases. World progress on these techniques and future prospects are summarized. A possible future weakly interacting massive particle detector based on mechanical recoil of suspended microgranules is proposed which, with advances in nanotechnology, could eventually be extended to the detection of low-energy relic neutrinos.

Journal Article↗

PubMed2003

Entrainment of 2 subjective nights by daily light:dark:light:dark cycles in 3 rodent species.

Recent work with exotic 24-h light:dark:light:dark (LDLD) cycles indicates surprising flexibility in the entrainment patterns of Syrian hamsters. Following exposure to an LDLD cycle, hamsters may adopt a form of rhythm splitting in which markers of subjective night (e.g., activity, melatonin) are expressed in each of the twice daily scotophases. This pattern contrasts markedly with that of conventionally entrained hamsters in which markers of subjective night are expressed once daily in only 1 of the 2 dark periods. The "split" entrainment pattern was examined further here in Syrian and Siberian hamsters and in mice exposed to LDLD 7:5:7:5, a condition that reliably induces split activity rhythms in all 3 species. The phase angle of entrainment and activity duration were generally similar comparing the 2 daily activity bouts in each species. The stability of this split entrainment state was assessed by deletions of photophases on individual days, by exposure to skeleton photoperiods, and by transfer to constant darkness. As in Syrian hamsters, the one-time substitution of darkness for one 7-h photophase did not grossly alter activity patterns of Siberian hamsters but acutely disrupted the split rhythms of mice. Skeleton light pulses of progressively shorter duration did not significantly alter split entrainment patterns of either Syrian or Siberian hamsters. Both species continued to exhibit stable entrainment with activity expressed in alternate scotophases of an LD 1:5 cycle presented 4 times daily. In contrast, the split activity rhythms of mice were not maintained under skeleton pulses. In constant darkness, rhythms of Siberian hamsters remained distinctly split for a minimum of 2 cycles. Split entrainment to these novel LDLD and 4-pulse skeleton lighting regimes demonstrates a marked degree of plasticity common to the circadian systems of several rodent species and identifies novel entrainment patterns that may be reliably elicited with simple environmental manipulations. Inter- and intraspecific differences in the stability of split activity rhythms likely reflect differences in coupling interactions between the component circadian oscillators, which, adopting separate phase relations to these novel LD cycles, yield a split entrainment pattern.

Animals↗

PubMed2001

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.

Effects of light and darkness on cell-cycle progression were studied in the log-linear photoautotrophic growth mode of Euglena gracilis. We found that there are light-dependent restriction points in the post-G1 phases, quite in contrast to Chlamydomonas, where a light-dependent restriction is known to exist only in the G1 phase. Thus, in E. gracilis, there are photoinduced commitments of G1-, S- and G2-phase cells that allow them to progress to the G1, S and G2 phases in darkness, and there are dark-induced G1-, S- and G2-phase arrests. In darkness, only committed cells were able to progress to the committed phases (G1, S or G2), whereas uncommitted cells were unable to undergo a cell-cycle transition. Whether or not cells were induced to commit by irradiation, they were eventually arrested somewhere in the G1, S or G2 (but not M) phase within 14 h of being transferred to darkness. We also describe the dependence of photoinduced commitment on light intensity and discuss the results as they relate to cell-cycle progression in continuous light.

Animals↗

PubMedDate not supplied

[A decreased frequency of peeking out from the dark compartment--the only constant index of the effect of anxiogens on the behavior of mice in a "light-darkness" chamber].

Special measurements of the effects of anxiolytics and anxiogens on the commonly used parameters of behavior of mice in a dark-light chamber (the rate of transitions and time spent in a dark and light compartments) demonstrated their low reproducibility in consecutive experiments. Therefore, these indices are not reliable (Lapin, 1992). One more parameter was tested in the present study. A decrease in the rate of leanings out of the dark compartment appeared to be a constant effect of standard anxiety-inducing drugs: caffeine, pentylenetetrazole, yohimbine, and a putative endogenous anxiogen phenylethylamine. Increase in the rate of leanings out, like increase in the rate of transitions and shortening of the time spent in a dark compartment produced by anxiolytics diazepam, chlordiazepoxide, hydroxyzine, phenibut and baclofen were not significant in the majority of experiments. That is why these effects of anxiolytics are not reliable for measuring the activity of anxiolytics in a dark-light chamber.

Analysis of Variance↗

PubMed1989

[Study on choroidal blood flow at dark and light adaptation. 1. Choroidal blood flow at dark adaptation].

The effect of dark adaptation on choroidal blood flow (CBF) was studied in albino rabbits. CBF was measured by the hydrogen clearance method. There was no significant change of CBF at dark adaptation in both short term dark adaptation, in which CBF had been expected to increase due to increased oxygen demand of the outer retina, and long term dark adaptation, in which CBF had been expected to decrease due to depressed function of visual cells and retinal pigment epithelium. The results show that dark adaptation does not influence CBF, in spite of the close relationship between the outer retina and the choroidal circulation. The large blood flow of the choroidal circulation may not need the reaction mechanism for the functional changes of the outer retina.

Animals↗

PubMed1988

Arousal-related changes in dark focus accommodation and dark vergence.

Dual-innervation theory suggests that dark focus (DF; the accommodation in effect in total darkness) reflects a balance between sympathetic and parasympathetic inputs. Since it is assumed that relaxation of accommodation is sympathetically innervated, and that accommodative increases are parasympathetically innervated, stimulation that leads to sympathetic activation should produce lower DF values than is the case when there is greater parasympathetic influence. In addition, the synkinesis between accommodation and vergence, and the known effects of fatigue, injury and drugs on fusion, promote an interest in the effects of arousal on dark vergence (DV; the vergence in effect in total darkness). Twenty-three young adult males experienced a variety of stimulus conditions. The conditions, selected because of their likely autonomic effects, included deep muscle relaxation, cold pressor and mental activity, among others. During each condition, measurements were made of DF (with a laser optometer) and DV (with a Nonius alignment system). Results for DF were consistent with dual innervation theory; manipulations expected to induce sympathetic activation (eg, cold pressor) produced lower DF values than did conditions expected to induce more parasympathetic (or less sympathetic) activation (eg, relaxation). DV tended to be influenced in the opposite direction, in that relaxation led to smaller DV angles than did the other conditions. Several analyses confirmed a lack of synkinesis between accommodation and vergence during darkness.

Accommodation, Ocular↗

PubMed2000

Collisional Dark Matter and the Structure of Dark Halos.

We study how the internal structure of dark halos is affected if cold dark matter particles are assumed to have a large cross section for elastic collisions. We identify a cluster halo in a large cosmological N-body simulation and resimulate its formation with progressively increasing resolution. We compare the structure found in the two cases in which dark matter is treated as collisionless or as a fluid. For the collisionless case, the overall ellipticity of the cluster, the central density cusp, and the amount of surviving substructure are all similar to those found in earlier high-resolution simulations. Collisional dark matter results in a cluster that is more nearly spherical at all radii, has a steeper central density cusp, and has less-but still substantial-surviving substructure. As in the collisionless case, these results for a "fluid" cluster halo are expected to carry over approximately to smaller mass systems. The observed rotation curves of dwarf galaxies then argue that self-interacting dark matter can only be viable if intermediate cross sections produce structure that does not lie between the extremes we have simulated.

Journal Article↗

PubMed1992

'Dark' cell formation under protein malnutrition: process of conversion and concept of 'semi-dark' type Purkinje cells.

This paper deals with some deleterious effects of protein malnourishment in rat cerebellum. Severe protein deprivation enhanced the formation of 'dark' cells in white rats. It is postulated that abnormal changes in the neuronal contents induced by nutritional stress play a vital role in the formation of the 'dark' cells through an intermediary stage, 'semi-dark' cells. Centrophenoxine a lipofuscinolytic agent, however, seems to interfere with the process of formation of 'dark' cells and/or helps reconversion of the 'dark' cells into the normal or 'light' type Purkinje cells.

Animals↗

PubMed1995

Confrontation of developing melanophore bars of dark and white axolotls with endogenous dark-embryo mannose-binding lectin correlates with melanophore bar disruption.

Lectins are carbohydrate-binding proteins suggested to be important in embryonic cell adhesion/differentiation. Dark and white axolotls contain an endogenous mannose-binding lectin that is especially prevalent during larval melanophore pattern formation (Martha et al., 1990). To determine if this lectin can alter melanophore patterning, lectin extracts have been isolated from Dark embryos by affinity chromatography. The main protein band is 44K on SDS-PAGE. Dark and white embryos at the early chromatophore migration stage have been confronted with Dark lectin or its nonmetabolized inhibitor, 2-deoxyglucose (2-DG). The barred melanophore pattern of both genotypes is disrupted by lectin or 2-DG treatment suggesting that endogenous mannose-binding lectin and its receptor participate in bar formation.

Ambystoma↗

PubMed1976

Light peak to dark trough ratio in clinical electro-oculography: influence of dark oscillations on the following light peak.

In the clinical standard EOG procedure the light rise potential is influenced by the preceding dark troughs oscillation. This is apparent in the different configuration of the light rise potential when following a dark trough instead of a steady state. Uninfluenced responses can be obtained only under steady-state conditions. Recording of the light peak potential in this manner may be used on a trial basis for clinical routine examination. Experimental and more detailed clinical studies require separate recording of light peak and dark trough potential, each preceded by a steady state. The evaluation of these responses, expressing them in percent of the steady state, should reveal more information than can be expected from the standard light peak to dark trough ratio.

Adult↗

PubMed1987

Tryptamine and some related molecules block the accumulation of a light-sensitive pool of cyclic AMP in the dark-adapted, dark-incubated mouse retina.

Dark-adapted retinas of mice (C57BL/6J) incubated in the dark in media containing 1 mM 3-isobutylmethylxanthine (IBMX) or 5 mM Co2+ accumulate cyclic AMP (cAMP). A portion of this pool is light sensitive, as light can prevent or reverse its accumulation. Similarly, tryptamine, serotonin, 5-methoxytryptamine, bufotenine, and 5-methoxydimethyltryptamine can block the accumulation of the light-sensitive pool of cAMP, whereas tryptophan, melatonin, N-acetylserotonin, 5-methoxytryptophol, and tetrahydro-beta-carbolines are inactive. The phenomenon is not seen with mutant mouse retinas (rd/rd), which lack most photoreceptors, but persists in abnormal retinas containing photoreceptors but with extensive neuronal depletion in the inner retina. Tryptamine also inhibits cAMP accumulation in either dark or light-adapted retinas exposed to forskolin alone but not in media containing high levels of forskolin plus 1 mM IBMX. There is some suggestion that serotonin 5-HT-2 antagonists can partially reverse the action of the tryptamines, but hitherto undescribed receptors may be involved. Current data suggest that photoreceptors are the target for the action of the tryptamines.

1-Methyl-3-isobutylxanthine↗

PubMed1982

A method of dark-field and simultaneous light--dark-field illumination for photomacrography of autoradiographic preparations.

A technique is described for dark-field and light--dark-field illumination of autoradiographic preparations for photomacrogra. A right-angle prism is employed as a substrate through which illumination is introduced to the specimen. The technique permits uniform illumination of large fields of view, and also minimizes the image-degrading effects of chromatic dispersion and excessive noncoherent scatter which are often associated with conventional dark-field illumination.

Animals↗

PubMed1984

Darkly pigmented lesions in dark-skinned patients.

It is well known that fair-haired, fair-complected individuals have an increased risk of skin malignancies. Current literature, however, gives no aid in evaluating darkly pigmented lesions in the dark-skinned patient. Blacks have an incidence of malignant melanoma from 5 to 18 times less than whites, while Hispanics have a higher incidence than blacks, but 3.5 to 4.5 times less than whites. Basal-cell epitheliomas are more likely to be darkly pigmented in both groups, leading to erroneous diagnosis and treatment as melanomas.

Adult↗

PubMed1993

Effects of scheduled food and water access on circadian rhythms of hamsters in constant light, dark, and light:dark.

Wheel-running activity of 31 Syrian hamsters was monitored in constant light (LL), dark (DD), and light-dark (LD) under ad lib and restricted food and water access schedules. Free-running or damped circadian wheel-running rhythms of 26 hamsters in LL were entrained by exposure to the restriction schedule. The phase of entrainment was positive, i.e., wheel running anticipated access time. In LD, activity was nocturnal. When food and water were restricted to midlight, five hamsters showed additional activity in anticipation of access time. Thirty hamsters showed a small advance of the phase of nocturnal activity onset. In subsequent DD, anticipatory activity was revealed (unmasked) in several additional cases, and nocturnal activity shifted and entrained to the access schedule in 19 cases. The properties of food anticipation and entrainment under the three lighting conditions support a model of the hamster circadian system that incorporates separate but strongly coupled food/water- and light-entrainable pacemakers.

Animals↗