Ultrafast folding and molecular dynamics of a linear hydrophobic β-hairpin

The first computational study of the folding and dynamics of a hydrophobic β-hairpin containing a central heterochiral diproline segment is reported. Linear hydrophobic sequences containing centrally positioned diproline motifs, heterochiral (DL/LD) and homochiral (LL/DD)), are investigated for their ability to form β-hairpins. Heterochiral diproline motifs (LD/DL) reveal the formation of stable β-hairpins with the backbone adopting β-turn conformation and the formation of backbone hydrogen bonds with antiparallel cross-strand registry, whereas the homochiral diproline (LL/DD) containing sequences tend to adopt PP_II helix conformation. The competition between the β-turn formation and the backbone H-bond ladder of the antiparallel β-strands in heterochiral diproline containing sequences is employed to validate the hypothesis that β-turn formation precedes inter-strand registry in the folding of a β-hairpin (“zipper” mechanism). The observation of noncanonical hydrogen bonds leads to a folded β-hairpin-like conformation and points to the existence of relatively stable transition state intermediates, between the unfolded (extended) and folded (β-hairpin) states. The MD simulations are in excellent agreement with the experimental studies on the model system and constitute the very first computational investigation of the folding and dynamics of a completely hydrophobic synthetic β-hairpin containing heterogeneous residues of mixed chirality.     

Signification differentielle des photoperiodes pour l'horloge biologique de Pieris brassicae (Lepidoptera)

Abstract

Photoperiodic insects are able to distinguish between long days and short days. In various models the long day response is classifically considered the “actively” induced state. The short day response is thought to be “passive”, caused by failure of light to coincide with a photosensitive part of the night or failure of coincidence of constituent oscillators. The photoperiodic response curve of Pieris brassicae showed that diapause is induced by short days (4–14 h), and non‐diapause state by several conditions (natural and non‐natural): long days (16 h or more), LL, DD and ultrashort days (0.1 h). By reciprocal transfers of larvae between non‐diapausing determining and diapause determining conditions, it was proved possible to estimate the differential capacity of four non‐diapausing conditions vs. the diapausing action of LD 8: 16 in decreasing sequence: LD 16:8 > LL > DD = LD 0.1: 23.9. DD may be considered a “neutral” condition. In darkness the development seems to be determined by an endogenous program without external influence. LL, although beingan aperiodic signal as DD, has a weak antidiapausingeffect.Thebiological clock of Pieris differentiates between two constant conditions. The four non‐diapausing conditions have the same effect on the development when applied during the entire larval life, but have different effects when only applied during a few days. Both ecological conditions LD 16:8 and LD 8:16 have an action on the development but in an opposite way. There was not a “passive” state caused by failure of another inductive photoperiod. Ultra‐short days, DD and LL are without ecological meaning. Nevertheless, in these experiments, they provided informations in attempts to determine the mechanism of the time measurement. The external coincidence model of Pittendrigh and Minis (1964) was the more adequate to explain theearlier results on the biological clock of Pieris. However, this model has to be modified to account for the differential significance of several non‐diapausing conditions.     

Diurnal and circadian variations in intraocular pressure in goats exposed to different lighting conditions

ABSTRACT

The effect of constant light and constant darkness on intraocular pressure (IOP) in goats has not been investigated. We hypothesized that IOP variations would differ between goats kept under a cycle of 12 hours of light and 12 hours of darkness (LD), constant darkness (DD), and constant light (LL). To test this hypothesis, goats were exposed to these conditions for five days (LD, 30 goats; DD, 10 goats; LL, 10 goats). IOP was measured by applanation tonometry at 9 a.m. (beginning of photophase in LD) and 9 p.m. (beginning of scotophase in LD) on the fourth and fifth days of exposure. We found that changes in mean IOP from 9 a.m. to 9 p.m. differed significantly between groups (χ²(2) = 23.04, p < .0001). Most goats in LD showed a regular pattern of higher IOP in the morning and lower IOP in the evening, whereas those in DD and LL did not follow this pattern. In LD conditions, mean IOP was 2.4 mm Hg lower at 9 p.m. than at 9 a.m. (95% confidence interval for the difference (CI): ?2.8 to ?1.9 mm Hg, p < .0001). In DD conditions, mean IOP did not differ between 9 p.m. and 9 a.m. (CI: ?0.9 to 0.8 mm Hg, p = .90). In LL conditions, it was 0.6 mm Hg lower at 9 p.m. (CI: ?1.5 to 0.2 mm Hg, p = .12). Our results indicate that IOP in goats kept in LD is higher in the morning than in the evening, and that IOP variations are reduced in goats kept in DD and LL. These results suggest that exposure to alternating periods of light and darkness is important for maintaining rhythmic variations in IOP in this species.     

Exposure to light at night accelerates aging and spontaneous uterine carcinogenesis in female 129/Sv mice

The effect of the constant illumination on the development of spontaneous tumors in female 129/Sv mice was investigated. Forty-six female 129/Sv mice starting from the age of 2 mo were kept under standard light/dark regimen [12 h light (70 lx):12hr dark; LD, control group], and 46 of 129/Sv mice were kept under constant illumination (24 h a day, 2,500 lx, LL) from the age of 5 mo until to natural death. The exposure to the LL regimen significantly accelerated body weight gain, increased body temperature as well as acceleration of age-related disturbances in estrous function, followed by significant acceleration of the development of the spontaneous uterine tumors in female 129/Sv mice. Total tumor incidence as well as a total number of total or malignant tumors was similar in LL and LD group (p > 0.05). The mice from the LL groups survived less than those from the LD group (χ² = 8.5; p = 0.00351, log-rank test). According to the estimated parameters of the Cox’s regression model, constant light regimen increased the relative risk of death in female mice compared with the control (LD) group (p = 0.0041). The data demonstrate in the first time that the exposure to constant illumination was followed by the acceleration of aging and spontaneous uterine tumorigenesis in female 129/Sv mice.     

Circadian rhythm in endogenous nerve activity in the eye of Musca dornestica L.

The frequency of occurrence of endogenous bursts of spikes was monitored by external electrode placed on the surface of housefly eyes in darkness. In LD 16:8 the frequency of these bursts showed an entrained rhythm, with a c. 10-fold change in level from rest to active periods. The rate began to increase in anticipation of dawn. The free-running period in DD was c. 21 h and in LL, 16–17 h. The active/rest ratio was 1.0 in DD and 2.5 in LL, the active phase being 10.4 h in DD and 12.3 h in LL. In these respects the rhythm conforms to Aschoff's rule. In groups of flies, the entrained rhythm was apparently lost 4–6 days after transfer from LD to LL, because the individual flies' rhythms changed from the 24 h entrained state to the LL, free-running state at differing rates, leading to asynchrony. After four cycles the phase angles in a sample of ten flies differed by 120 (8 h). In contrast, when flies were transferred from LD to DD, the phase angle variation did not differ markedly, even after 9 days, from that of entrained flies. The findings are discussed in terms of Truman's (1972) clock types.     

Oscillations in the Activities of Enzymes of Nitrate Reduction and Ammonia Assimilation in Glycine max and Zea mays

The activities of glutamate dehydrogenase (GDH), glutamine synthetase (GS), and nitrate reductase (NR) and the levels of soluble protein and NO^-₃ were assayed in soybean (Glycine max [L.] Merr.) leaves over a 48-h period with the initial 24 h under a light-dark cycle (LD 16:8) followed by 24 h of continuous light (LL). Plants had been entrained for 30 days under the LD regime. Maize (Zea mays) leaves (10 days old) under a LD 15:9 cycle were assayed only for NR and nitrite reductase (NiR). Data were subjected to frequency analysis by the least squares method to determine probabilities for cosine function periods (τ's) between 10 and 30 h. NR activities for both soybean and Zea leaves had 24 h τ's with P values < 0.05 indicating circadian periodicity. GDH in soybeans had a 24-h rhythm under LD conditions which lengthened under LL conditions. The 24-h rhythm of GDH displayed maximal activity toward the end of the dark period of the LD cycle whereas the highest activity of NR was early in the light period. Total soluble protein displayed a rhythm with a best fitting τ of greater than 24 h under both LD and LL. GDH, GS, NR, NO₃, and soluble protein in soybeans and NiR in Zea, all displayed that were ultradian (10–18 h), indicating that a τ of about one half a circadian periodicity may be a common characteristic of the enzymes of primary nitrogen metabolism in higher plants. These data also demonstrate that although both NR and GDH are circadian in their activity, the 24-h rhythm may be greatly influenced by ultradian oscillations in activity.     

Daily rhythms of clock gene expression and feeding behavior during the larval development in gilthead seabream,Sparus aurata

Light is the main environmental time cue which synchronizes daily rhythms and the molecular clock of vertebrates. Indeed, alterations in photoperiod have profound physiological effects in fish (e.g. reproduction and early development). In order to identify the changes in clock genes expression in gilthead seabream larvae during ontogeny, three different photoperiods were tested: a regular 12L:12D cycle (LD), a continuous light 24L:0D (LL) and a two-phases photoperiod (LL?+?LD) in which the photoperiod changed from LL to LD on day 15 after hatching (dph). Larvae were sampled on 10, 18, 30 and 60 days post-hatch (dph) during a 24?h cycle. In addition to the expression of clock genes (clock, bmal1, cry1 and per3), food intake was measured. Under LD photoperiod, larvae feed intake and clock genes expression showed a rhythmic pattern with a strong light synchronization, with the acrophases occurring at the same hour in all tested ages. Under LL photoperiod, the larvae also showed a rhythmic pattern but the acrophases occurred at different times depending on the age, although at the end of the experiment (60 dph) clock genes expression and feed intake rhythms were similar to those larvae exposed to LD photoperiod. Moreover, the expression levels of bmal1 and cry1 were much lower than in LD photoperiod. Under the LL?+?LD photoperiod, the 10 dph larvae showed the same patterns as LL treatment while 18 and 30 dph larvae showed the same patterns as LD treatment. These results revealed the presence of internal factors driving rhythmic physiological responses during larvae development under constant environmental conditions. The LL?+?LD treatment demonstrates the plasticity of the clock genes expression and the strong effect of light as synchronizer in developing fish larvae.     

Role of light in the mediation of acute effects of a single afternoon melatonin injection on steroidogenic activity of testis in the rat

Young adult male rats, maintained either in an LD 12: 12 or in continuous illumination (LL) for one week, were given a single injection of 25 μg melatonin/100 g body wt or ethanolic-saline (control) at 17.00 h. Animals from each group were sacrificed at 11.00 h on the following day. The activity of two important steroidogenic enzymes, 17β-hydroxysteroid dehydrogenase (17β-HSD) and Δ⁵-3β-hydroxysteroid dehydrogenase (Δ⁵-3β-HSD), and serum concentrations of testosterone, were measured following highly specific and sensitive spectrophotometric techniques and RIA, respectively. A significant decrease in the activity of both the steroidogenic enzymes was noted in the testes of melatonin-treated rats maintained under normal light-dark schedules, but this response was found to be lacking in the LL rats. However, no significant changes in the level of serum testosterone were noted in either group of melatonin-treated rats from the values in respective groups of ethanolic saline-administered LD and LL rats. Exposure of ethanolic saline-injected rats to continuous light also did not cause any change in the steroidogenic activity of the testis from those in LD rats. The study indicates that continuous light as such does not affect the endocrine function of testis but abolishes suppressive effects of melatonin on the steroidogenic activity of the testis in rat.     

\4 integrin expression on<Emphasis Type="Italic">in vitro</Emphasis> and<Emphasis Type="Italic">in vivo</Emphasis> metastatic variants of lewis lung carcinoma

The expression of β4, α6, and β1 integrin subunits has been investigated on somein vitro andin vivo murine metastatic variants derived from Lewis lung carcinoma (3LL). By the use of monoclonal antibodies which recognizes different epitopes of α6, β1, and β4 subunits we demonstrate that α6 and β1 subunits are expressed in all metastatic variants of 3LL irrespective of their metastatic potential, whereas β4 subunit is expressed only in highly metastasizing cells of 3LL. Northern blots of different metastatic variants probed with β1 and β4 subunits demonstrate thata) significant amounts of β1 mRNA were detected in all metastatic variants of 3LL;b) mRNA corresponding to the described entire coding sequence of β4 subunit is expressed only on highly metastasizing cells of 3LL. We conclude that β4 subunit is specifically expressed in highly metastasizig cells of 3LL while is undetectable in lower metastasizing ones.     

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Endogenous nitric oxide (NO) is an important mediator in the processes that control biological clocks and circadian rhythms. The present study was designed to elucidate if NO synthase (NOS) activity in the brain, kidney, testis, aorta, and lungs and plasma NO_x levels in mice are controlled by an endogenous circadian pacemaker. Male BALB/c mice were exposed to two different lighting regimens of either light–dark 14:10 (LD) or continuous lighting (LL). At nine different equidistant time points (commencing at 09:00h) blood samples and tissues were taken from mice. The plasma and tissue homogenates were used to measure the levels of NO₂+ NO₃^? (NO_x) and total protein. The NO_x concentrations were determined by a commercial nitric oxide synthase assay kit, and protein content was assessed in each homogenate tissue sample by the Lowry method. Nitric oxide synthase activity was calculated as pmol/mg protein/h. The resulting patterns were analyzed by the single cosinor method for pre-adjusted periods and by curve-fitting programs to elucidate compound rhythmicity. The NOS activity in kidneys of mice exposed to LD exhibited a circadian rhythm, but no rhythmicity was detected in mice exposed to LL. Aortic NOS activity displayed 24h rhythmicity only in LL. Brain, testis, and lung NOS activity and plasma NO_x levels displayed 24h rhythms both in LD and LL. Acrophase values of NOS activity in brain, kidney, testis, and lungs were at midnight corresponding to their behavioral activities. Compound rhythms were also detected in many of the examined patterns. The findings suggest that NOS activity in mouse brain, aorta, lung, and testis are regulated by an endogenous clock, while in kidney the rhythm in NOS activity is synchronized by the exogenous signals.     

Variations in the esterase expression pattern with respect to different light regimes in Drosophila agumbensis and Drosophila nagarholensis

Circadian clock enables organism’s to adapt under fluctuating environmental conditions by coupling of behavioral, physiological and molecular processes in a wide variety of organisms including bacteria, fungi, plants, birds and mammals. The endogenous circadian system functions to organize behavior and physiology to adapt to and anticipate environment changes in light and temperature. The present study is an attempt to understand enzyme profiles (alpha- and beta-esterases) of Drosophila agumbensis and Drosophila nagarholensis under light/dark (LD), constant dark (DD) constant light (LL), conditions over twenty generations. A polyacrylamide gel electrophoresis (7.5% – Native gel) was used to study the esterase expression patterns in two species of the montium subgroup of Drosophila. Alpha- and beta-esterase expression was significantly decreased in LL when compared to LD and DD at both the generations and species. In all the light regimes, females were found to have significantly higher level of α- and β-esterase expression than males. Flies were maintained under different light regimes showed difference in their expression patterns with respect to alpha- and beta-esterases. The present study showed that constant light conditions affect the expression of esterases in D. agumbensis and D. nagarholensis.     

State-dependent effects of light-dark cycle on somatosensory and visual cortex EEG in rats

Somatosensory (SSctx) and visual cortex (Vctx) EEG were evaluated in rats under a 12:12-h light-dark (LD) cycle and under constant light (LL) or constant dark (DD) in each sleep or wake state. Under LD conditions during light period, relative Vctx EEG slow-wave activity (SWA) was higher than that of the SSctx, whereas during dark period, relative Vctx EEG SWA was lower than in the SSctx. These effects were state specific, occurring only during non-rapid eye movement sleep (NREMS). Under LL conditions, the duration of REMS and NREMS during the period that would have been dark if the LD cycle had continued (subjective dark period) was greater than under LD conditions. DD conditions had little effect on the duration of NREMS and REMS. SSctx and Vctx EEG SWA were suppressed by LL during the subjective dark period; however, the degree of Vctx SWA suppression was smaller than that of the SSctx. DD conditions during the subjective light period enhanced SSctx SWA, whereas Vctx SWA was suppressed. Under LL conditions during the subjective dark period, Vctx EEG power was higher than that of the SSctx across a broad frequency range during NREMS, REMS, and wakefulness. During DD, SSctx EEG power during NREMS was higher than that of the Vctx in the delta wave band, whereas SSctx power during REMS and wakefulness was higher than that of the Vctx in frequencies higher than 8 Hz. We concluded that the SSctx and Vctx EEGs are differentially affected by light during subsequent sleep. Results provide support for the notion that regional sleep intensity is dependent on prior regional afferent input.     

Effects of ultraviolet radiation on carotenoid-containing and albino strains of Neurospora crassa

To determine the influence of carotenoids on UV sensitivity of Neurospora crassa conidia, the dose-response curves of 3 albino strains were compared to that of the wild type. In a control experiment the genetic background effects were eliminated by irradiating the wild type in which carotenoid synthesis had been inhibited by β-ionone, and comparing the dose-response curve to that of untreated wild type. All strains used had similar γ-ray survival curves and nuclei per conidium which precluded differences in UV sensitivity due to morphological differences.The albinos and β-ionone-treated strains showed a greater sensitivity (mean LD50 4.35·10³ erg/mm²) to UV irradiation than the wild type (LD50 7.30·10³ erg/mm²).     

Comparative uptake of nitrate by intact seedlings of C3 (barley) and C4 (corn) plants: Effect of light and exogenously supplied sucrose

The effect of light and exogenously supplied sucrose on NO₃ ⁻ uptake was studied in 9-day-old intact C₃ (barley) and C₄ (corn) seedlings. The seedlings used were uninduced for nitrate uptake system (i.e. had never seen nitrogen during germination and growth) and were exposed to continuous light for 3 days to avoid any diurnal variation and to load the seedlings fully with photosynthates. The uptake assay was conducted either in light or in darkness. Prior to assay, seedlings were treated with darkness or light for 24 h. Accordingly, four sets of seedlings, i.e. pretreated with light and assayed in light (LL); pretreated and assayed in darkness (DD); pretreated with light and assayed in darkness (LD); and pretreated with darkness and assayed in light (DL) were formed. Barley exhibited 55% higher NO₃ ⁻ uptake than corn during light (LL) and 91% higher during darkness (DD). Shifting barley seedlings from light to dark (LD) or dark to light (DL) for uptake assay, did not affect NO₃ ⁻ uptake, i.e. in LD the uptake was similar to LL and in DL it was similar to DD. However, in corn, the light conditions during the assay determined the uptake regardless of the conditions during the period preceding the assay. One percent sucrose in the medium increased NO₃ ⁻ uptake by 31% in barley and 70% in corn during light (LL). The corresponding increase during darkness (DD) was 38% in both barley and corn. Removal of the corn residual endosperm decreased NO₃ ⁻ uptake by 40% during darkness. Etiolated seedlings (those having never seen light) of both barley and corn were able to take up significant amount of NO₃ ⁻ during darkness. Externally supplied sucrose in the assay medium of etiolated seedlings increased the NO₃ ⁻ uptake to about 4 and 2 fold in barley and corn, respectively. The data presented here provide evidence that: 1. In intact seedlings, light per se is not obligatory for NO₃ ⁻ uptake and that the carbohydrate supply may mimic light. 2. Light affected the NO₃ ⁻ uptake differently in barley and corn. This revised version was published online in June 2006 with corrections to the Cover Date.     

Solvatochromism and solvation of water-soluble molybdenum(O)-tetracarbonyl diimine-complexes

Solvatochromic behaviour is described for the water-soluble molybdenum(0)-carbonyl-diimine complexes [Mo(CO)₄(LL)]ⁿ⁻, where LL=fz (ferrozine;3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine-p,p′-disulphonate) and n = 2 or LL = sb (Schiff base from 2-acetyl pyridine plus β-alanine) and n = 0, in water and in a range of non-aqueous solvents, and in water-isopropanol solvent mixtures. The possibility of using solvatochromic compounds of this type to probe selective solvation in solvent mixtures is assessed, with particular reference to water-isopropanol and acetone-chloroform mixtures, and to microemulsions.     

Postnatal Constant Light Compensates Cryptochrome1 and 2 Double Deficiency for Disruption of Circadian Behavioral Rhythms in Mice under Constant Dark

Clock genes Cryptochrome (Cry1) and Cry2 are essential for expression of circadian rhythms in mice under constant darkness (DD). However, circadian rhythms in clock gene Per1 expression or clock protein PER2 are detected in the cultured suprachiasmatic nucleus (SCN) of neonatal Cry1 and Cry2 double deficient (Cry1 ^-/-/Cry2 ^-/-) mice. A lack of circadian rhythms in adult Cry1 ^-/-/Cry2 ^-/- mice is most likely due to developmentally disorganized cellular coupling of oscillating neurons in the SCN. On the other hand, neonatal rats exposed to constant light (LL) developed a tenable circadian system under prolonged LL which was known to fragment circadian behavioral rhythms. In the present study, Cry1 ^-/-/Cry2 ^-/- mice were raised under LL from postnatal day 1 for 7 weeks and subsequently exposed to DD for 3 weeks. Spontaneous movement was monitored continuously after weaning and PER2::LUC was measured in the cultured SCN obtained from mice under prolonged DD. Surprisingly, Chi square periodogram analysis revealed significant circadian rhythms of spontaneous movement in the LL-raised Cry1 ^-/-/Cry2 ^-/- mice, but failed to detect the rhythms in Cry1 ^-/-/Cry2 ^-/- mice raised under light-dark cycles (LD). By contrast, prolonged LL in adulthood did not rescue the circadian behavioral rhythms in the LD raised Cry1 ^-/-/Cry2 ^-/- mice. Visual inspection disclosed two distinct activity components with different periods in behavioral rhythms of the LL-raised Cry1^-/-/Cry2^-/- mice under DD: one was shorter and the other was longer than 24 hours. The two components repeatedly merged and separated. The patterns resembled the split behavioral rhythms of wild type mice under prolonged LL. In addition, circadian rhythms in PER2::LUC were detected in some of the LL-raised Cry1^-/-/Cry2^-/- mice under DD. These results indicate that neonatal exposure to LL compensates the CRY double deficiency for the disruption of circadian behavioral rhythms under DD in adulthood.     

Light Enhances Survival of Dinoroseobacter shibae during Long-Term Starvation

Aerobic anoxygenic phototrophs (AAPs) as being photoheterotrophs require organic substrates for growth and use light as a supplementary energy source under oxic conditions. We hypothesized that AAPs benefit from light particularly under carbon and electron donor limitation. The effect of light was determined in long-term starvation experiments with Dinoroseobacter shibae DFL 12^T in both complex marine broth and defined minimal medium with succinate as the sole carbon source. The cells were starved over six months under three conditions: continuous darkness (DD), continuous light (LL), and light/dark cycle (LD, 12 h/12 h, 12 µmol photons m⁻² s⁻¹). LD starvation at low light intensity resulted in 10-fold higher total cell and viable counts, and higher bacteriochlorophyll a and polyhydroxyalkanoate contents. This coincided with better physiological fitness as determined by respiration rates, proton translocation and ATP concentrations. In contrast, LD starvation at high light intensity (>22 µmol photons m⁻² s⁻¹, LD conditions) resulted in decreasing cell survival rates but increasing carotenoid concentrations, indicating a photo-protective response. Cells grown in complex medium survived longer starvation (more than 20 weeks) than those grown in minimal medium. Our experiments show that D. shibae benefits from the light and dark cycle, particularly during starvation.     

Solid-state synthesis of cyclo LD-diphenylalanine: A chiral phase built from achiral subunits

The solid-state structure of LL/DD or LD/DL diphenylalanine diluted in KBr pellets is studied by infrared (IR) absorption and vibrational circular dichroism (VCD) spectroscopy. The structure depends on the absolute configuration of the residues. The natural LL diphenylalanine exists as a mixture of neutral and zwitterionic structures, depending on the humidity of the sample, while mostly the zwitterion is observed for LD diphenylalanine whatever the experimental conditions. The system undergoes spontaneous cyclization upon heating at 125°C, resulting to the formation of a diketopiperazine (DKP) dipeptide as the only product. The reaction is faster for LD than for LL diphenylalanine. As expected, LL and DD diphenylalanine react to form the LL and DD enantiomers of cyclo diphenylalanine. Interestingly, the DKP dipeptides formed from the LD or DL diphenylalanine show unexpected optical activity, with opposite VCD spectra for the products formed from the LD and DL reagents. This is explained in terms of chirality synchronization between the monomers within the crystal, which retain the symmetry of the reagent, resulting to the formation of a new chiral phase made from transiently chiral molecules.     

Effect of continuous illumination of varying length on the reproductive rhythms in rats; after‐effects

Abstract

Permanent oestrus was induced in 24, 61 and 100% of 2‐months old Wistar rats under conditions of continuous light exposure (LL) for 1, 2 and 6 months, respectively. After cessation of 2 months LL, rhythmic fluctuations of oestrus activity were observed.

The weight of newborns produced by females under LL during pregnancy was increased by 7% as compared to controls (P < 0.05). LL before mating did not affect embryonic development.

20‐day old pups produced by females which were kept in LL for 1, 2 months and more were significantly heavier than controls by 5, 18 and 30%, respectively.

The stimulatory effect of LL for 1 and 2 months on pre‐ and postnatal development was maintained in the subsequent reproduction cycle, when these females were transferred to normal conditions of LD 14:10.