EFFECTS OF LIGHT AND MELATONIN TREATMENT ON BODY TEMPERATURE AND MELATONIN SECRETION DAILY RHYTHMS IN A DIURNAL RODENT,THE FAT SAND RAT

Many mammals display predictable daily rhythmicity in both neuroendocrine function and behavior. The basic rest-activity cycles are usually consistent for a given species and vary from night-active (nocturnal), those mostly active at dawn and dusk (i.e., crepuscular), and to day-active (diurnal) species. A number of daily rhythms are oppositely phased with respect to the light/dark (LD) cycle in diurnal compared with nocturnal mammals, whereas others are equally phased with respect to the LD cycle, regardless of diurnality/nocturnality. Pineal produced melatonin (MLT) perfectly matches this phase-locked feature in that its production and secretion always occurs during the night in both diurnal and nocturnal mammals. As most rodents studied to date in the field of chronobiology are nocturnal, the aim in this study was to evaluate the effect of light manipulations and different photoperiods on a diurnal rodent, the fat sand rat, Psammomys obesus. The authors studied its daily rhythms of body temperature (T_b) and 6-sulphatoxymelatonin (6-SMT) under various photoperiodic regimes and light manipulations (acute and chronic exposures) while maintaining a constant ambient temperature of 30°C?±?1°C. The following protocols were used: (A) Control (CON) conditions 12L:12D; (A1) exposure to one light interference (LI) of CON-acclimated individuals for 30?min, 5?h after lights-off; (A2) short photoperiod (SP) acclimation (8L:16D) for 3 wks; (A3) 3 wks of SP acclimation with chronic LI of 15?min, three times a night at 4-h intervals; (A4) chronic exposure to constant dim blue light (470nm, 30 lux) for 24?h for 3 wks (LL). (B) The response to exogenous MLT administration, provided in drinking water, was measured under the following protocols: (B1) After chronic exposure to SP with LI, MLT was provided once, starting 1?h before the end of photophase; (B2) after a continuous exposure to dim blue light, MLT was provided at 15:00?h for 2?h for 2 wks; (B3) to CON animals, MLT was given intraperitoneally (i.p.) at 14:00?h. The results demonstrate that under CON acclimation, Psammomys obesus has robust T_b and 6-SMT daily rhythms in which the acrophase (peak time) of T_b is during the photophase, whereas that of 6-SMT is during scotophase. LI resulted in an elevation of T_b and a reduction of 6-SMT levels. A significant difference in the response was noted between acute and chronic exposure to LI, particularly in 6-SMT levels, which were lower than CON after LI and higher after chronic LI, implying an acclimation process. Constant exposure to blue light abolished T_b and 6-SMT rhythms in all the animals. MLT administration resumed the T_b daily rhythm in these animals, and had a recovery effect on the chronic LI-exposed animals, resulting in a T_b decrease. Altogether, the authors show in this study the different modifications of T_b rhythms and MLT levels in response to environmental light manipulations. These series of experiments may serve as a basis for establishing P. obesus as an animal model for further studies in chronobiology. (Author correspondence: hagitsc@research.haifa.ac.il)     

LIGHT INTENSITY AND THE TIMING OF DAILY ACTIVITY OF FINCHES (FRINGILLIDAE)

The prevailing general theory of entrainment of endogenous circadian rhythms explains variation in the timing of activity with season, latitude and weather conditions on the basis of the dependence of spontaneous frequency of the rhythm on the intensity of constant illumination. In an experiment designed to test the validity of this theory, Greenfinches and chaffinches were exposed to the natural light-dark cycle alternately in full illumination and in reduced daylight. Contrary to prediction by current hypotheses for these species, in which the spontaneous frequency decreases with decreasing light intensity, their midpoint of daily activity shifted forward when the intensity of natural daylight was reduced. This result refutes the hypothesis that light affects the timing of activity in nature in a manner predictable from its effect in constant conditions.
Both species of finches have a bimodal daily distribution of perch-hopping activity. The morning peak and evening peak of activity are of about equal strength in winter, but the morning peak increases sharply in the reproductive season. The possibility that the two peaks represent two pacemaker systems, under differential endocrine control, is discussed.
The precision in the timing of daily onset and end of activity is positively correlated with the estimated average rate of change of light intensity at these times of day. Thus, day-to-day variations are markedly increased in reduced daylight when activity begins late after sunrise and terminates well before sunset.     

Changes of glycogen metabolism in the gills and hepatic tissue of tilapia (Oreochromis mossambicus) during short-term Cd exposure

The aim of the study was to test the hypothesis that the mechanism of glycogen metabolism has taken place in gills rather than in liver during Cd exposure. Male tilapia were exposed to 44.45 μM ambient Cd for 12 h, and we found blood glucose significantly increased, however, lactate levels showed no significant changes. The glycogen phosphorylase (GP) activity increased immediately after 0.75 to 3 h of Cd exposure in the gills, and after 1 to 6 h in the liver, respectively. In addition, the glycogen level depleted faster in the gills than in the liver. Plasma cortisol level increased from 0.25 to 1 h and recovered after 3 h, while the glucagon did not significantly change during Cd exposure. Glucocorticoid receptor (GR) mRNA expression decreased after 0.75 h in the gills, while it significantly increased after 6 h in the liver. Ca²⁺, Na⁺, Cl⁻, and K⁺ significantly decreased upon Cd exposure within 6 h following Cd-induced toxic stress. We suggested that the cortisol is the spontaneous stimulation of glycogen metabolism in the gills, and it triggers a subsequent energy supply later in the liver. Taken together, the profile of glycogen metabolism between gills and liver during Cd-exposure stress provide good support to our hypothesis.     

DIURNAL EXPRESSION OF CLOCK GENES IN PINEAL GLAND AND BRAIN AND PLASMA LEVELS OF MELATONIN AND CORTISOL IN ATLANTIC SALMON PARR AND SMOLTS

In Atlantic salmon, the preadaptation to a marine life, i.e., parr-smolt transformation, and melatonin production in the pineal gland are regulated by the photoperiod. However, the clock genes have never been studied in the pineal gland of this species. The aim of the present study was to describe the diurnal expression of clock genes (Per1-like, Cry2, and Clock) in the pineal gland and brain of Atlantic salmon parr and smolts in freshwater, as well as plasma levels of melatonin and cortisol. By employing an out-of-season smolt production model, the parr-smolt transformation was induced by subjecting triplicate groups of parr to 6 wks (wks 0 to 6) under a 12?h:12?h light-dark (LD) regime followed by 6 wks (wks 6 to 12) of continuous light (LL). The measured clock genes in both pineal gland and brain and the plasma levels of melatonin and cortisol showed significant daily variations in parr under LD in wk 6, whereas these rhythms were abolished in smolts under LL in wk 12. In parr, the pineal Per1-like and Cry2 expression peaked in the dark phase, whereas the pineal Clock expression was elevated during the light phase. Although this study presents novel findings on the clock gene system in the teleost pineal gland, the role of this system in the regulation of smoltification needs to be studied in more detail. (Author correspondence: ti.hu@hotmail.com)     

SYNCHRONIZATION OF CHLOROPLAST DIVISION IN THE ULTRAMICROALGA CYANIDIOSCHYZON MEROLAE (RHODOPHYTA) BY TREATMENT WITH LIGHT AND APHIDICOLIN

A system of highly synchronized chloroplast divisions was developed in the unicellular red alga Cyanidioschyzon merolae De Luca, Taddei, & Varano. Chloroplast divisions were examined by epifluorescence microscopy following treatments with light and inhibitors. When the cells during stationary phase were transferred into a new medium under a 12:12 h LD cycle, chloroplasts, mitochondria, and cell nuclei divided synchronously in that order soon after the initiation of dark periods. More than 40% of the cells contained dividing chloroplasts. To obtain a system of highly synchronized cell division and chloroplast division, the cells synchronized by a 12:12 h LD cycle were treated with various inhibitors. Nocodazole and propyzamide did not affect cell and organelle divisions, whereas aphidicolin markedly inhibited cell-nuclear divisions and cytokinesis and induced a delay in chloroplast division. More than 80% of the cells contained dividing chloroplasts when cells synchronized by light were treated with aphidicolin for 12 h. This synchronized system will be useful for studies of the molecular and cellular mechanisms of organelle divisions .     

真鲷视网膜结构及其视觉特性研究：Ⅱ视网膜光感受细胞超微结构研究

对真鲷光感受细胞的超微结构进行观察,结果表明：视杆外段膜盘为游离膜盘,视锥外段膜盘则为连续的膜结构,视锥和视杆均含有连接纤毛和辅助外段。花萼状突起起源于内段。椭体内充满线粒体,无球状小体。双锥椭圆体并生膜为六层,视锥内段无鳍状突起,视锥突触带,在明适应视网膜中数量增多,在暗适应视网中数量减少,视杆突触带在这两种适应网膜中数量不变,每一杆小球只有一个突触带,而锥小足有４－６个突触带。     

FAILURE OF EXTRAOCULAR LIGHT TO FACILITATE CIRCADIAN RHYTHM REENTRAINMENT IN HUMANS

Although extraocular light can entrain the circadian rhythms of invertebrates and nonmammalian vertebrates, almost all studies show that the mammalian circadian system can only be affected by light to the eyes. The exception is a recent study by Campbell and Murphy that reported phase shifts in humans to bright light applied with fiber-optic pads behind the knees (popliteal region). We tested whether this extraocular light stimulus could accelerate the entrainment of circadian rhythms to a shift of the sleep schedule, as occurs in shift work or jet lag. In experiment 1, the sleep/dark episodes were delayed 8h from baseline for 2 days, and 3h light exposures were timed to occur before the temperature minimum to help delay circadian rhythms. There were three groups: (1) bright (about 13,000 lux) extraocular light from fiber-optic pads, (2) control (dim light, 10–20 lux), and (3) medium-intensity (about 1000 lux) ocular light from light boxes. In experiment 2, the sleep/dark episodes were inverted, and extraocular light was applied either before the temperature minimum to help delay circadian rhythms or after the temperature minimum to help advance rhythms. Circadian phase markers were the salivary dim light melatonin onset (DLMO) and the rectal temperature minimum. There was no evidence that the popliteal extraocular light had a phase-shifting effect in either experiment. Possible reasons for phase shifts in the Campbell and Murphy study and not the current study include the many differences between the protocols. In the current study, there was substantial sleep deprivation before the extraocular light was applied. There was a large shift in the sleep/dark schedule, rather than allowing subjects to sleep each day from midnight to noon, as in the Campbell and Murphy study. Also, when extraocular light was applied in the current protocol, subjects did not experience a change from sleeping to awake, a change in posture (from lying in bed to sitting in a chair), or a change in ocular light (from dark to dim light). Further research is necessary to determine the conditions under which extraocular light might produce phase shifts in human circadian rhythms. (Chronobiology International, 17(6), 807–826, 2000).     

HYPERSENSITIVITY OF MELATONIN SUPPRESSION IN RESPONSE TO LIGHT IN PATIENTS WITH DELAYED SLEEP PHASE SYNDROME*

Patients with delayed sleep phase syndrome (DSPS) experiencea chronic mismatch between the usual daily schedule required by the individual'senvironment and their circadian sleep-wake pattern, resulting in major academic,work, and social problems. Although functional abnormalities of the circadianpacemaker system have been reported in patients with DSPS, the etiology ofDSPS has not been fully elucidated. One hypothesis proposed to explain whypatients with DSPS fail to synchronize their 24h sleep-wake cycle to theirenvironment is that they might have reduced sensitivity to environmental timecues, most notably light-dark cycles. Therefore, we compared the sensitivityof melatonin suppression in response to light in patients with DSPS and normalcontrol subjects. Fifteen patients with DSPS and age- and sex-matched healthycontrols were studied. As the melatonin secretion rhythm in patients withDSPS was expected to be delayed compared to the controls, the time of peakmelatonin secretion was determined in each subject in the first session. Inthe second session, each subject was exposed to light with an intensity of1000 lux for 2h beginning 2h prior to his or her peak melatonin secretion.Melatonin was measured by radioimmunoassay in saliva sampled every 30 minutesduring the period of light exposure. Suppression of the melatonin concentrationin saliva was dependent on duration of light exposure. In addition, the suppressiveeffect of light on the melatonin concentration was significantly greater inpatients with DSPS than in control subjects. The results suggest hypersensitivityto nighttime light exposure in patients with this syndrome. Our findings thereforesuggest that evening light restriction is important for preventing patientswith DSPS from developing a sleep phase delay. (ChronobiologyInternational, 18(2), 263–271, 2001)     

PHYSIOLOGICAL AND MORPHOLOGICAL MODIFICATIONS OF PLANTAGO MAJOR (PLANTAGINACEAE) IN RESPONSE TO LIGHT CONDITIONS

Physiological and morphological differences between Plantago major L. (Plantaginaceae) growing in full sunlight and shaded conditions were examined. Photosynthesis of isolated leaves was saturated by irradiance around 300 μE m^−-2 sec^−-1 and 170 μE m^−-2 sec^−-1, respectively. In contrast to previous studies of sun/shade leaf responses, initial slopes of curves from shaded plants are significantly less than those taken from full-sun plants. Within the 400–500 nm and 600–700 nm ranges, leaves 5.0 cm or longer are essentially opaque, transmitting less than 1.25% of incident light. Chlorophyll content per unit leaf area is nearly equivalent for leaves from plants growing under the two extremes in light levels. Morphometric comparisons indicate shaded plants bear fewer leaves, have less leaf overlap, lower total leaf area, and longer petioles than full-sun plants. Leaf elongation rates are lower and the duration between the emergence of successive leaves is longer in shaded plants. Computer analyses of both types of rosette morphology reveal shaded plants have an equal or greater capacity to intercept light than full-sun plants, principally because of the minimization of leaf overlap and the large variation in the deflection angles of leaves in shaded rosette morphologies. Simulations, calculated on the basis of light interception, and taking into account the transition between photosynthate-importing and -exporting leaves, predict relative growth rates for full-sun and shaded rosette morphologies that are in reasonable agreement with empirically determined leaf growth rates. However, the data indicate that significant physiological and morphological differences exist among leaves from a single rosette, and among developmentally comparable leaves from rosettes growing under different ambient light environments. Differences among leaves on a single plant must be accommodated in computerized techniques attempting to simulate light interception and its consequences on potential growth rates.     

CIRCADIAN ACTIVITY RHYTHMS AND SENSITIVITY TO NOISE IN THE MONGOLIAN GERBIL (MERIONES UNGUICULATUS)

Since consistent data on endogenous circadian rhythms of Mongolian gerbils are not available, the main aim of our study was to identify suitable conditions to receive stable and reproducible free-running rhythms of activity under different light intensities. Another objective was to determine the role of social cues as an exogenous zeitgeber in the absence of a light-dark (LD) cycle. We performed two long-term sets of experiments with adult male gerbils kept in climatic chambers under various photoperiods of at least 30 days each. In all cases, the time of lights on in the chambers differed from the daily starting hour of work in the animal house. Always, two animals per chamber were kept separately in cages with a running wheel while their activity was monitored continuously. During the first set, only three of eight animals developed intra- and interindividual variable free-running rhythms. The activity patterns seemed to be influenced by human activities outside, indicating high sensitivity to external factors. Subsequently, we damped the chambers and the room and restricted access to the room. In the following noise-reduced set, all gerbils developed comparable free-running rhythms of activity. We determined the mean of the free-running period τ, the activity-rest relationship α/θ and the amount of running wheel activity per day: τ = 23.7h ± 0.08h under low light (5 lux) and 25.5h ± 0.19h under high light intensities (450 lux); α/θ = 0.53 ± 0.08 under 5 lux and 0.34 ± 0.04 under 450 lux. The amount of daily activity was 12 times as high under 5 lux as under 450 lux. There was no indication that the two animals in one chamber socially synchronized each other. In conclusion, the pronounced rhythm changes in accordance with Aschoff's theory support the view that gerbils are mainly nocturnal animals. (Chronobiology International, 17(2), 137–145, 2000)     

BEHAVIORAL AND PHYSIOLOGICAL MEASUREMENTS OF MATERNAL INVESTMENT IN THE STELLER SEA LION, EUMETOPIAS JUBATUS

The onshore and at-sea cycles of females, suckling behavior of pups and their milk intake were studied in Steller sea lions ( Eumetopias jubatus ) during 1983 at Año Nuevo Island, California. Females averaged approximately 21 h ashore and 36 h at sea. The trips to sea lengthened as pups aged, resulting in an overall decline in female time ashore to 30% by the sixth week following parturition. Activity budgets of pups showed no significant differences among suckling time, age and sex. Milk intake, estimated using labeled water studies, revealed that heavier pups consumed more milk than lighter ones (milk ingestion in ml/d = 4.26 + 0.0687 [Pup Mass in kg]). Mean milk intake was 1.78 ± 0.33 liters/d. Mean pup growth rate was 0.38 ± 0.1 kg/d. The results suggest that female attendance patterns are shaped by the increasing nutritional demands of growing pups and their increasing efficiency at suckling.     

三种免疫制剂对真鲷弧菌病的免疫保护性

菌体疫苗按不同的方式对真鲷进行免疫2周后,对实验鱼均具有免疫保护性,免疫保护性最好的免疫组,免疫保护率在初次免疫后高达60%,强化免疫后免疫保护率可提高到80%;粗制LPS经去毒处理后初次免疫真鲷,不同浓度的LPS对实验鱼具有不同程度的免疫保护性,强化免疫后,免疫保护率均有明显的提高,浓度越高,免疫保护性越强,对真鲷的免疫保护率最高可达90%,最小弧菌产生的外毒素经福尔马林灭活后制成毒素苗,这种毒素苗能产生较好的免疫保护性,其免疫保护率可达80%,这表明外毒素不仅是最小弧菌产生的毒力因子,同时也是菌体产生的有效保护性抗原。     

SEGREGATIVE MIGRATION OF DALL'S PORPOISE (PHOCOENOIDES DALLI) IN THE SEA OF JAPAN AND SEA OF OKHOTSK

Dall's porpoises from the Sea of Japan population taken by a dolphin fishery vessel were examined. Estimated body lengths at sexual maturity were similar to those for the truei -type population off the Pacific coast of Japan but larger than those for the offshore dalli -type in the North Pacific. The Sea of Japan population is known to migrate to the Pacific coast of Japan through Tsugaru Strait and to the Sea of Okhotsk through Soya Strait in summer. From the difference of catch composition, individuals of different reproductive status in this population are considered to have different patterns of summer migration. Most of the individuals which migrate into the Pacific Ocean through Tsugaru Strait are sexually immature, while those migrating into the Sea of Okhotsk are mature. The Sea of Okhotsk is thought to be a breeding area for this population. The calving season is estimated to be May through June, which is earlier than that of the truei -type off the Pacific coast of northern Japan. This may be an adaptation to lower water temperatures in the Sea of Japan during winter.     

GROWTH RATES OF PSEUDOPEDINELLA PYRIFORME (CHRYSOPHYCEAE) IN RESPONSE TO 75 COMBINATIONS OF LIGHT,TEMPERATURE AND SALINITY1

Clonal cultures were established of single cells of Pseudopedinella pyriforme Carter isolated from the Chesapeake Bay. Axenic cultures were incubated at 5, 10 and 15 C; in 2 1/2, 5, 7 1/2, 10 and 15‰; and at 143, 285, 428, 571 and 714 μW/cm² white light. Maintainable growth rates were calculated from absorbance readings taken for 3 to 5 days from acclimated cultures. The maximum number of doublings per day was 0.9 at 2 1/2‰ salinity, 571 μW/ cm² and 15 C. A salinity of 5 ‰ produced the fastest growth at most light intensities up to 428μW/cm² and temperatures of 5, 10 and 15 C.     

DIET AND FORAGING BEHAVIOR OF SEA OTTERS IN SOUTHEAST ALASKA

Abstract: Direct observations of feeding sea otters ( Enhydra lutris ) at 11 sites in southeast Alaska showed infaunal clams to be the primary prey utilized by otters throughout the region. Foraging dive times associated with clam and sea urchin prey were significantly longer than those for more easily captured prey (crabs and mussels). Dive times and surface intervals were also generally correlated with water depth or apparent difficulty in obtaining buried prey. Male otters, which fed more extensively on clams than females, made significantly longer foraging dives than females. Foraging success remained high, even at sites where prey numbers were found to be very low during a related study. The very deeply burrowing geoduck clam ( Panope abrupta ), while common at several otter feeding sites, was rarely captured by otters. These results, combined with those of a companion study on prey numbers, indicate that butter clams ( Saxidomus giganteus ) account for the majority of the sea otter diet in southeast Alaska, and that sea urchins may represent relatively short-term prey in comparison to infaunal bivalves in regions where both prey types co-exist. Furthermore, the importance of butter clams in the sea otter diet and the tendency for this bivalve to retain chronically high levels of paralytic shellfish poisoning toxins in southeast Alaska increases the probability that toxic phytoplankton blooms influence sea otter distribution in this region.     

PHYSIOLOGICAL AND ULTRASTRUCTURAL RESPONSES OF CYCLOTELLA MENEGHINIANA (BACILLARIOPHYTA) TO LIGHT INTENSITY AND NUTRIENT LIMITATION1

Photosynthetic characteristics and chloroplast ultrastructure of Cyclotella meneghiniana Kütz. were quantified while the organism was simultaneously adjusting to light and nutrient stress. Cells were grown in batch culture at either low or high light intensity on medium with a nitrogen/phosphorus molar ratio of 2:1 as a control, or with nitrogen or phosphorus deleted from the medium to create nutrient deficiencies. Analysis of variance indicated that light intensity, nutrient deficiency and duration of nutrient deficiency all had significant effects on cell growth, chlorophyll (Chl) concentration/cell, cellular fluorescence capacity (CFC), chloroplast volume and thylakoid surface density. Because interactions existed among nutrient deficiency, extent of nutrient deficiency, and light intensity, all three must be considered together in order to describe accurately the physiology and chloroplast ultrastructure of the diatom. Significant correlations were found between the Chl/cell or CFC/cell and chloroplast volume and thylakoid surface density. Through an increase in Chi concentration, chloroplast volume and thylakoid surface density, the cells successfully adapted to the conditions of low light intensity even while under nutrient stress. In contrast, less Chl/cell, smaller chloroplast volume and less thylakoid surface density were found at high light intensity.