DD Conditions Research Articles

Influence of Constant Light and Darkness, Light Intensity, and Light Spectrum on Plasma Melatonin Rhythms in Senegal Sole

Light is the most important synchronizer of melatonin rhythms in fish. This paper studies the influence of the characteristics of light on plasma melatonin rhythms in sole. The results revealed that under long‐term exposure to constant light conditions (LL or DD), the total 24 h melatonin production was significantly higher than under LD, but LL and DD conditions influenced the rhythms differently. Under LL, melatonin remained at around 224 pg/ml throughout the 24 h, while under DD a significant elevation (363.6 pg/ml) was observed around the subjective evening. Exposure to 1 h light pulses at MD (mid‐dark) inhibited melatonin production depending on light intensity (3.3, 5.3, 10.3, and 51.9 µW/cm2). The light threshold required to reduce nocturnal plasma melatonin to ML (mid‐light) values was 5.3 µW/cm2. Melatonin inhibition by light also depended on the wavelength of the light pulses: while a deep red light (λ>600 nm) failed to reduce plasma melatonin significantly, far violet light (λmax=368 nm) decreased indoleamine's concentration to ML values. These results suggest that dim light at night (e.g., moonlight) may be perceived and hence affect melatonin rhythms, encouraging synchronization to the lunar cycle. On the other hand, deep red light does not seem to inhibit nocturnal melatonin production, and so it may be used safely during sampling at night.

Selection for early and late adult emergence alters the rate of pre-adult development in Drosophila melanogaster

BackgroundCircadian clocks have been implicated in the regulation of pre-adult development of fruit flies Drosophila melanogaster. It is believed that faster clocks speed up development and slower clocks slow it down. We established three sets of D. melanogaster populations (early, control and late). The early and late populations were raised by selecting for flies that emerged either in the morning or in the evening under 12:12 hr light/dark (LD) cycles. After 75 generations of selection, the time course and waveform of the adult emergence and activity rhythms of the early and the late populations diverged from each other as well as from the controls. In this paper, we report the consequence of this selection on the rate of pre-adult development.ResultsWe assayed the pre-adult development time of the selected and control populations under 12:12 hr LD cycles and constant darkness (DD). Under LD cycles, the early populations develop faster than the controls, while the late populations develop slower than the controls. Although flies take longer to develop under DD than in LD, the relative differences between the mean development times of the selected and control populations remain unaltered in DD. In a separate experiment designed to investigate the effect of time of egg collection and experimental conditions on the duration of pre-adult stage, we assayed the development time of the selected and control populations by collecting eggs at different times of the day (morning and evening) and by assaying their pre-adult development time under constant light (LL), LD, and DD conditions. Irrespective of the time of egg collection and assay light regime, the late flies continue to develop slower than the early flies.ConclusionThe results of our study clearly indicate that selection on the timing of adult emergence alters the rate of pre-adult development in D. melanogaster. The timing of egg collection as well as assay light regime does not have any measurable effect on the relative differences between the developmental rates of the early and the late flies. Taken together these results appear to suggest that pleiotropic effects of clock genes mediate correlated changes in the timing of adult emergence and the rate of pre-adult development in D. melanogaster.

Circadian rhythm of locomotor activity in the Japanese honeybee, Apis cerana japonica

Abstract To reveal circadian characteristics and entrainment mechanisms in the Japanese honeybee Apis cerana japonica, the locomotor‐activity rhythm of foragers is investigated under programmed light and temperature conditions. After entrainment to an LD 12 : 12 h photoperiodic regime, free‐running rhythms are released in constant dark (DD) or light (LL) conditions with different free‐running periods. Under the LD 12 : 12 h regime, activity offset occurs approximately 0.4 h after lights‐off transition, assigned to circadian time (Ct) 12.4 h. The phase of activity onset, peak and offset, and activity duration depends on the photoperiodic regimes. The circadian rhythm can be entrained to a 24‐h period by exposure to submultiple cycles of LD 6 : 6 h, as if the locomotive rhythm is entrained to LD 18 : 6 h. Phase shifts of delay and advance are observed when perturbing single light pulses are presented during free‐running under DD conditions. Temperature compensation of the free‐running period is demonstrated under DD and LL conditions. Steady‐state entrainment of the locomotor rhythm is achieved with square‐wave temperature cycles of 10 °C amplitude, but a 5 °C amplitude fails to entrain.

Lack of Food Anticipation in Per2 Mutant Mice

Predicting time of food availability is key for survival in most animals. Under restricted feeding conditions, this prediction is manifested in anticipatory bouts of locomotor activity and body temperature. This process seems to be driven by a food-entrainable oscillator independent of the main, light-entrainable clock located in the suprachiasmatic nucleus (SCN) of the hypothalamus . Although the SCN clockwork involves self-sustaining transcriptional and translational feedback loops based on rhythmic expression of mRNA and proteins of clock genes , the molecular mechanisms responsible for food anticipation are not well understood. Period genes Per1 and Per2 are crucial for the SCN's resetting to light . Here, we investigated the role of these genes in circadian anticipatory behavior by studying rest-activity and body-temperature rhythms of Per1 and Per2 mutant mice under restricted feeding conditions. We also monitored expression of clock genes in the SCN and peripheral tissues. Whereas wild-type and Per1 mutant mice expressed regular food-anticipatory activity, Per2 mutant mice did not show food anticipation. In peripheral tissues, however, phase shifts of clock-gene expression in response to timed food restriction were comparable in all genotypes. In conclusion, a mutation in Per2 abolishes anticipation of mealtime, without interfering with peripheral synchronization by feeding cycles.

Circadian Intraocular Pressure Rhythm Is Generated by Clock Genes

The present study in a mouse model was undertaken to reveal the role of the circadian clock genes Cry1 and Cry2 in generation of 24-hour intraocular pressure (IOP) rhythm. IOP was measured at eight time points daily (circadian time [CT] 0, 3, 6, 9, 12, 15, 18, and 21 hours), using a microneedle method in four groups of C57BL/6J mice (groups 1 and 3, wild-type; groups 2 and 4, Cry-deficient [Cry1-/-Cry2-/-]). During the IOP measurements, mice in groups 1 and 2 were maintained in a 12-hour light-dark cycle (LD), whereas mice in groups 3 and 4 were kept in a constant darkness (DD) that started 24 to 48 hours before the measurements. Circadian IOP variations in each group were evaluated by one-way analysis of variance (ANOVA) and Scheffé tests. In wild-type mice living in LD conditions, pressures measured in the light phase were significantly lower than those in the dark phase. This daily rhythm was maintained under DD conditions with low pressure in the subjective day and high pressure in the subjective night. In contrast, Cry-deficient mice did not show significant circadian changes in IOP, regardless of environmental light conditions. These findings demonstrate that clock oscillatory mechanisms requiring the activity of core clock genes are essential for the generation of a circadian rhythm of intraocular pressure.

Daily expression patterns for mRNAs of GH, PRL, SL, IGF-I and IGF-II in juvenile rabbitfish, Siganus guttatus, during 24-h light and dark cycles

Most animals respond to changes in the external environment in a rhythmic fashion. In teleost fishes, daily rhythms are observed in plasma concentrations of some hormones but it is not clear whether these rhythms are exogenous or are entrained by predictable cues. We investigated whether the expression patterns for the mRNAs of growth hormone (GH), prolactin (PRL) and somatolactin (SL) in the pituitary gland, and insulin-like growth factor-I and II (IGF-I and IGF-II) in the liver, follow a daily rhythm when juvenile rabbitfish ( Siganus guttatus) are reared under a normal 24-h light and dark cycle (LD), and when they are exposed to either continuous light (LL) or darkness (DD). Hormone mRNA levels were determined by real time PCR. Under LD conditions, GH mRNA expression in the pituitary was significantly lower during the light phase than during the dark phase suggesting a diurnal rhythm of expression. The rhythm disappeared when fish were exposed to LL or DD conditions. PRL mRNA expression pattern was irregular in all 3 conditions. Very low levels of SL mRNA were observed during the mid day under LD conditions. The expression pattern of SL mRNA became irregular under LL and DD conditions. No pattern could be observed in the expression profile of IGF-I and II mRNA in the liver during LD and LL conditions but a single peak in mRNA level was observed under DD conditions in both IGF-I and II. The results indicate that except for GH, the daily expression pattern for the mRNAs of the hormones examined do not seem to follow a rhythm according to light and dark cycles.

Method for studying behavioural activity patterns during long-term recordings using a force-plate actometer

The motor activity (MA) patterns of rodents are commonly detected in the laboratory using infrared photo-beams or running wheels. In chronobiological studies, the MA rhythm is considered as a behavioural output of the circadian pacemaker. This paper describes a method to obtain long-term records of MA in rodents, with a 1 mm spatial resolution and a 1 s temporal resolution. The device comprised a square platform laid on top of three force transducers, allowed the calculation of the coordinates of the centre of force exerted by a freely moving rodent, and continuously monitored its displacements. A specific computer program processed the trajectories, providing an exhaustive analysis of motion. To test this method, motor behavioural activity was studied in rats exposed to conditions that favoured rhythmicity: light–dark cycles of both 24 h (LD) and 22 h (T22), and constant darkness (DD). In addition, arrhythmicity patterns were studied under constant light (LL) conditions, and in animals with permanent lesions of the hypothalamic suprachiasmatic nucleus (SCNx). A single description of the general MA distribution at 24 h was obtained using infrared photo-beams. By contrast, under LD conditions, a 24-h rhythm with ultradian components was seen in the total distance travelled, whereas that detected in the number of slow motions showed less ultradian components. In addition, a regional preference in the nesting place was detected under both LD and DD conditions. In one SCNx animal and another exposed to LL conditions, both showing arrhythmicity in photo-beam-detected MA, a 24 h rhythm was observed in regional preference; other LL animal presented a 24 h rhythm in the number of slow motions. This method has capabilities lacking in commonly used techniques. The potential uses of this approach, principally in cronobiological studies, are discussed.

Accumulation of sense–antisense transcripts of the rice catalase gene CatB under dark conditions requires signals from shoots

The amount of mRNA of the Oryza sativa L., cv. Nipponbare (rice) catalase gene, CatB, was decreased in the roots of intact seedlings kept in continuous darkness (DD). In contrast, sense and antisense unspliced CatB transcripts accumulated in the same tissue. Both strands cover the entire CatB-coding region, and form double-stranded RNA (dsRNA). The results of RNA dot-blot hybridization analysis using low molecular weight RNAs suggested that the sense and antisense CatB transcripts were more stable under DD conditions than under a light–dark regimen (LD). After shifting the lighting conditions from DD to LD, both the sense and antisense CatB transcripts were hardly detected, and the amount of CatB mRNA was restored. From these results, the antisense CatB transcripts might play a role in suppressing the normal processing of sense CatB transcript and also CatB protein synthesis by dsRNA formation, under conditions unsuitable for plant growth such as DD. This study indicates that signals transmitted from shoots are associated with the accumulation of sense and antisense CatB transcripts in roots under DD conditions, and that auxin is one of the possible signals.

Individual variability and photic entrainment of circadian rhythms in golden spiny mice

Golden spiny mice are diurnally active in most of their natural habitat. Their diurnal activity is ascribed to non-photic cues: competitive exclusion from the nocturnal niche, or thermoregulatory considerations. Here we studied the entrainment of golden spiny mice to light. In the laboratory, golden spiny mice were primarily nocturnal and displayed an unusual variety of rhythm patterns, with activity bursts occurring during both activity and rest periods. Spontaneous shifts of activity rhythms between light phases were sometimes recorded. In all cases but one, body temperature shifted in parallel with activity. Under DD conditions, the free running period (tau) of all individuals but one was shorter than 24 h, and in all individuals but the same one it was shorter than tau under LL conditions. In response to a 6 h phase delay, all individuals entrained to the new LD cycle in a relatively uniform way. During phase advance four out of the twelve individuals further delayed their activity and body temperature rhythms, and eight individuals advanced their activity rhythm, but the re-entrainment took them over twice as long as to re-entrain to the phase delay. We suggest that the golden spiny mouse is a nocturnal rodent whose circadian system developed the flexibility to be nocturnal or diurnal according to environmental conditions, or a nocturnal rodent in the process of turning diurnal, and that it has low sensitivity to the immediate masking effect of light on activity.

The daily rhythms of melatonin and free fatty acids in goats under varying photoperiods and constant darkness

The purpose of the study was to explore parallel and divergent features of the daily rhythms of melatonin and plasma free fatty acids (FFA) in goats exposed to different lighting conditions. From these features, we attempted to analyze whether the endogenous melatonin rhythm plays any role in the maintenance of the FFA rhythm. Seven Finnish landrace goats were kept under artificial lighting that simulated the annual changes of photoperiod at 60°N (longest photoperiod, 18 h; shortest, 6 h). The ambient temperature and feeding regimen were kept constant. Blood samples were collected 6 times a year at 2 h intervals for 2 d, first in the prevailing light‐dark (LD) conditions and then after 3 d in constant darkness (DD). In LD conditions, the melatonin levels always increased immediately after lights‐off and declined around lights‐on, except in winter (18 h darkness), when the low daytime levels were restored clearly before lights‐on. The FFA levels also displayed a consistent rhythmicity, with low levels at night and a transient peak around lights‐on. In DD conditions, the melatonin profiles were very similar to those found in the habitual LD conditions, but the rhythm tended to advance. The FFA rhythm persisted also in DD, and the morning peak tended to advance. There was an overall parallelism between the two rhythms, with one significant exception. In winter in LD conditions, the morning rise in FFA levels coincided with lights‐on and not with the declining phase of melatonin, whereas in DD conditions, the FFA peak advanced several hours and coincided with the declining phase of melatonin. From this finding and comparisons of the calculated rhythm characteristics, i.e., phase‐shifts, phase differences, and correlations, we conclude that the daily rhythm of FFA levels is most probably generated by an endogenous oscillator, primarily adjusted by dawn, whereas the melatonin rhythm in this species is regulated by an oscillator primarily adjusted by dusk. The results did not exclude a modulatory effect of melatonin on the daily FFA profiles, but melatonin secretion, alone, does not explain the patterns sufficiently.

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.

Ser-557-phosphorylated mCRY2 Is Degraded upon Synergistic Phosphorylation by Glycogen Synthase Kinase-3β

Cryptochrome 1 and 2 act as essential components of the central and peripheral circadian clocks for generation of circadian rhythms in mammals. Here we show that mouse cryptochrome 2 (mCRY2) is phosphorylated at Ser-557 in the liver, a well characterized peripheral clock tissue. The Ser-557-phosphorylated form accumulates in the liver during the night in parallel with mCRY2 protein, and the phosphorylated form reaches its maximal level at late night, preceding the peak-time of the protein abundance by approximately 4 h in both light-dark cycle and constant dark conditions. The Ser-557-phosphorylated form of mCRY2 is localized in the nucleus, whereas mCRY2 protein is located in both the cytoplasm and nucleus. Importantly, phosphorylation of mCRY2 at Ser-557 allows subsequent phosphorylation at Ser-553 by glycogen synthase kinase-3beta (GSK-3beta), resulting in efficient degradation of mCRY2 by a proteasome pathway. As assessed by phosphorylation of GSK-3beta at Ser-9, which negatively regulates the kinase activity, GSK-3beta exhibits a circadian rhythm in its activity with a peak from late night to early morning when Ser-557 of mCRY2 is highly phosphorylated. Altogether, the present study demonstrates an important role of sequential phosphorylation at Ser-557/Ser-553 for destabilization of mCRY2 and illustrates a model that the circadian regulation of mCRY2 phosphorylation contributes to rhythmic degradation of mCRY2 protein.

Demand-feeding rhythms and feeding-entrainment of locomotor activity rhythms in tench ( Tinca tinca)

Tench ( Tinca tinca) has been described as a strictly nocturnal species whose locomotor activity rhythms, albeit strongly synchronised by light, have an endogenous nature. Aside from light, a number of other environmental factors, such as mealtime, can act as circadian system synchronisers in fish; however, there is a scarcity of information on tench feeding rhythms. This study describes daily self-feeding rhythms in tench, and analyses the role of feeding time on synchronisation of locomotor activity rhythms. Tench were able to operate string sensor-activated self-feeders, and they displayed a strictly nocturnal behavior, both under indoor and outdoor conditions. Locomotor activity remained strictly nocturnal irrespective of whether tench were fed only during the scotophase (D-feeding) or the photophase (L-feeding). However, no statistically significant differences were detected between both groups in terms of food intake or growth performance. Furthermore, unlike L-feeding, D-feeding elicited a clear anticipatory activity (FAA). When tench were given the possibility of feeding at both times of the day, they showed a clear preference for D-feeding. Finally, in fish exposed to constant darkness (DD), feeding time acted as a true zeitgeber and FAA was observed. When animals were fasted under DD conditions, locomotor activity free-run and 6 out of 12 individuals yielded significant results in the periodogram analysis. Under DD, fish resynchronised when regular food was resumed, with some tench displaying FAA. The obtained results indicated the existence of a feeding-entrainable oscillator (FEO) in tench.

Diurnal and circadian retinomotor movements in zebrafish

Key indicators of circadian regulation include the persistence of physiological rhythmicity in the absence of environmental time cues and entrainment of this rhythmicity by the ambient light cycle. In some teleosts, the inner segments of rod and cone photoreceptors contract and elongate according to changes in ambient lighting and the circadian cycle. Pigment granules in the retinal pigment epithelium (RPE) disperse and aggregate in a similar manner. Collectively, these movements are known as retinomotor movements. We report the histological characterization of diurnal and circadian retinomotor movements in zebrafish, Danio rerio. Adult fish subjected to a 14:10 light:dark (LD) cycle, constant darkness (DD), or constant light (LL) were sacrificed at 1-13 h intervals and processed for semithin sectioning of the retina. Using bright-field microscopy, 15 measurements of pigment granule position and the inner segment lengths of 30 rods and 30-45 cones were collected from the central third of the dorso-optic retina per time point. In LD, rods and cones followed a clear diurnal rhythm in their inner segment movements. Short-single, UV-sensitive cones were found to contract significantly 1 h before light onset in LD conditions. In DD conditions, the inner segments movements of short-single and double cones displayed statistically significant rhythms. RPE pigment granule movements are rhythmically regulated in both LD and DD although fluctuations are damped in the absence of photic cues. No significant retinomotor movements were observed in LL. These findings indicate retinomotor movements in zebrafish are differentially regulated by an endogenous oscillator and by light-dependent mechanisms.

Toxicity and Bioaccumulation of Hexavalent Chromium in Green Paramecium, Paramecium bursaria

The effects of hexavalent chromium on the cell growth of green paramecium, Paramecium bursaria (P. bursaria), were investigated in this study. Two strains (MB-1 and F1 generation) of P. bursaria were incubated in lettuce media supplemented with different concentrations of potassium dichromate under LL (24 hr light), LD (12 hr light : 12 hr dark) and DD (24 hr dark) conditions, and the IC50 values were obtained. The IC50 7-day value showed that the toxicity of potassium dichromate was light-sensitive in both strains of P. bursaria. The results of the toxic effect of chromium on the cell shape of P. bursaria (BWK-4) showed that the body ratio of P. bursaria increased, even if the cells were incubated for 24 hr with 0.5 µM potassium dichromate solution, indicating that the cell shape of P. bursaria is very sensitive to potassium dichromate. The average amount of chromium accumulated in green paramecium ranged from 1.72 to 15.5 pg Cr/cell in a time- and concentration-dependent manner. This finding indicates the possibility of the use of P. bursaria as a biomonitor and bioaccumulator for chromium contaminants in aquatic environments. The experiment with electrical stimuli into the culture of P. bursaria indicated that cells accumulated at the negative electrode, suggesting that P. bursaria carried a positive charge. Thus, because the positive charge does not cause any significant absorption of chromium into the cells, P. bursaria may develop a variety of mechanisms for chromium accumulation in the cell. Further research studies are required to elucidate the mechanism of chromium uptake in P. bursaria.

Effects of moonlight exposure on plasma melatonin rhythms in the seagrass rabbitfish, Siganus canaliculatus.

Influences of light-dark (LD) cycle and moonlight exposure on plasma melatonin rhythms in the seagrass rabbitfish, Siganus canaliculatus, a lunar synchronized spawner, were determined by time-resolved fluoroimmunoassay (TR-FIA). When the fish were exposed to a natural LD (12:12) cycle, plasma melatonin levels exhibited a clear daily rhythm, with higher levels at midnight and lower levels during the day. These rhythms were not evident under either constant light (LL) or constant dark (DD) conditions. Plasma melatonin levels under LL condition were low and high under DD condition. These results indicate that plasma melatonin rhythms are driven by LD cycle in this species. When the fish were exposed to the 4 lunar phases, plasma melatonin levels around the new moon were significantly higher than during the first quarter moon and the full moon. Exposure to experimental new moon and full moon conditions caused significant increases and decreases of plasma melatonin levels, respectively. The synchronous rhythmicity of melatonin levels in the plasma support the hypothesis that the seagrass rabbitfish perceives moonlight intensity and responds with secretion of melatonin into the bloodstream.

Influence of light-dark and lunar cycles on the ocular melatonin rhythms in the seagrass rabbitfish, a lunar-synchronized spawner.

The aim of this study was to investigate the effects of light-dark (LD) cycles and lunar phases on ocular melatonin rhythms in the seagrass rabbitfish, Siganus canaliculatus, a lunar-synchronized spawner. Under a natural 24-hr LD (12.00:12.00) cycle, ocular melatonin levels were low during daylight hours. The levels significantly elevated to peak during the mid-dark phase at 24.00 hr and then declined sharply in the early morning around 06.00 hr. These rhythms disappeared under either constant light (LL) or constant dark (DD) conditions. Melatonin levels remained low in LL compared with those in DD condition. These results suggest that ocular melatonin rhythms in the seagrass rabbitfish are suppressed in the presence of light. When fish were exposed to natural moon phases, ocular melatonin concentrations were higher around the new moon than both the first quarter and full moon phases. Exposure to experimental new moon conditions caused a significant increase in melatonin levels while those of the fish exposed to experimental full moon conditions were decreased. These results suggest that the seagrass rabbitfish perceives moonlight through the eye and that moonlight directly causes melatonin suppression.

Daily and annual variations of free fatty acid, glycerol and leptin plasma concentrations in goats ( Capra hircus) under different photoperiods

The aim of the study was to differentiate the impact of lighting conditions and feeding times on the regulation of lipid metabolism of goats under different photoperiods throughout the year. Seven Finnish landrace goats were kept under artificial lighting that simulated the annual changes of photoperiod at 60°N (the longest light period 18 h, the shortest 6 h). Ambient temperature and feeding regime were kept constant. Blood samples were collected six times a year at 2-h intervals for 2 days, first in light/dark (LD) conditions and then after 3 days in constant darkness (DD). Significant daily variations were detected in the concentrations of plasma free fatty acids (FFA) and glycerol throughout the year. The nocturnal decrease and morning rise of FFA levels were related to the photoperiod, while the trough levels of glycerol were associated with the concentrate meal times. In DD conditions, FFA and glycerol rhythms were unstable. A significant seasonal variation was detected in the overall FFA and glycerol levels suggesting decreased lipogenesis in winter, increased lipolysis in spring and high lipogenesis in summer and fall. There was no significant daily rhythm in serum leptin levels, nor did the profiles in LD and DD conditions differ. The leptin level was slightly lower in early fall than in the other seasons, paralleling a small decrease of body mass in the goats after the grazing season. The daily or annual variations of FFA and glycerol levels were not clearly related to leptin concentrations. The results suggest that lipid metabolism of goats is regulated by light even in constant temperature and feeding conditions; however, no significant contribution of leptin levels could be shown.

Environmental light conditions alter gene expression of rat catecholamine biosynthetic enzymes and Neuropeptide Y: differential effect in superior cervical ganglia and adrenal gland

The hypothalamic suprachiasmatic nuclei (SCN) comprise the main site in the brain involved in the control of the homeostatic mechanism which respond to environmental daily light changes. The sympathetic nervous system and hypothalamic releasing or inhibiting factors mediate the SCN control of a number of peripheral organs and tissues. In this work we analyzed the involvement of two environmental light conditions, constant light (LL) and constant dark (DD) for 20 days, on the expression of mRNAs for catecholamines biosynthetic enzymes and neuropeptide Y (NPY) genes in rat superior cervical ganglia (SCG) and adrenal gland. The results of Northern blot analysis show that LL exposure reduces mRNA levels for tyrosine hydroxylase (TH) the rate limiting catecholamine biosynthetic enzyme and also of dopamine β-hydroxylase (DBH) as well as for NPY in SCG to about half the levels in control animals. In contrast, exposure of the rats to DD did not elicit any change in the SCG. In the adrenal gland, both, LL and DD conditions increased the TH, DBH as well as phenylethanolamine N-methyltransferase (PNMT) mRNA levels. Under the same conditions, adrenal NPY mRNA levels were decreased by either LL or DD. The results show, for the first time, that prolonged changes in environmental light can alter the gene expression of catecholamine biosynthetic enzymes and of NPY. There was differential response in SCG and adrenal gland.

Lack of nociceptin receptor alters body temperature during resting period in mice

The role of nociceptin (NOC) receptor on body core temperature (Tcore) control was examined using NOC receptor knockout mice. In homozygote NOC receptor-knockout, wild-type, and control C57BL/6J and 129/SV mice, Tcore was continuously recorded under 12:12 h light:dark (LD) and conditions of constant darkness (DD). The Tcore values during the resting period were higher in the NOC receptor-knockout mice than in both wild-type and control mice under both LD and DD conditions. Spontaneous activity during the resting period and plasma cortisol levels were not different between the NOC receptor-knockout and control mice. The findings herein indicate that the NOC receptor is involved in the control of Tcore during the resting period and is independent of light, physical activity and/or cortisol regulation.