Illumination Schedule Research Articles

Dual color optogenetic tool enables heart arrest, bradycardic, and tachycardic pacing in Drosophila melanogaster

In order to facilitate cardiovascular research to develop non-invasive optical heart pacing methods, we have generated a double-transgenic Drosophila melanogaster (fruit fly) model suitable for optogenetic pacing. We created a fly stock with both excitatory H134R-ChR2 and inhibitory eNpHR2.0 opsin transgenes. Opsins were expressed in the fly heart using the Hand-GAL4 driver. Here we describe Hand > H134R-ChR2; eNpHR2.0 model characterization including bi-directional heart control (activation and inhibition) upon illumination of light with distinct wavelengths. Optical control and real-time visualization of the heart function were achieved non-invasively using an integrated light stimulation and optical coherence microscopy (OCM) system. OCM produced high-speed and high-resolution imaging; simultaneously, the heart function was modulated by blue (470 nm) or red (617 nm) light pulses causing tachycardia, bradycardia and restorable cardiac arrest episodes in the same animal. The irradiance power levels and illumination schedules were optimized to achieve successful non-invasive bi-directional heart pacing in Drosophila larvae and pupae.

Green Synthesis of Selenium Nanoparticles by Cyanobacterium Spirulina platensis (abdf2224): Cultivation Condition Quality Controls.

Selenium nanoparticles (SeNPs) are well-known bioactive compounds. Various chemical and biological methods have been applied to SeNP synthesis. Spirulina platensis is a widely used blue-green microalgae in various industries. In this study, the biosynthesis of SeNPs using sodium selenite and Spirulina platens has been developed. The SeNP synthesis was performed at different cultivation condition including pH and illumination schedule variation. The SeNPs were characterized by FT-IR, XRD, size, and zeta potential measurements, and the antioxidant activities of selected SeNPs were evaluated by DPPH and FRAP assays. FT-IR analysis showed the production of SeNPs. The 12 h dark/12 h light cycles and continuous light exposure at pH 5 led to the production of stable SeNPs with sizes of 145 ± 6 and 171 ± 13 nm, respectively. Antioxidant activity of selected SeNPs was higher than sodium selenite. It seems that green synthesis is a safe method to produce SeNPs as well as a convenient method to scale-up this production.

Intermittent Lighting Schedule effects on Broiler Production Performance and Carcass Traits

The current research aim is to examine the impact of light rhythm on development characteristics in broiler chicken before and after slaughter. One hundred and eighty-eight 11-day Ross 308 broilers were picked and reared between 11 to 42 days under an intermittent illumination schedule of either control illumination 6 hours of light: 18 hours of darkness T1 (6L:18D) or 2 hours of light: 2 hours of darkness T2(2L:2D) or 4 hours of light: 4 hours of darkness T3(4L:4D) or 6 hours of light: 6 hours of darkness T3(6L:6D). The results show that there are no significant differences for body weight and body weight gain at 23-42 days and body weight gain at 11-22days of age between treatments, but body weight in intermittent light (2L:2D) was significantly better than control group with other treatments group (P<0.05). The results also demonstrate that here is no significant difference between treatments for feed intake. Use of intermittent lighting schedule improved feed conversion ratio but not significantly (P<0.05). Also for mortality, there is no significant difference between treatments. Similarly, the chest and thigh percentage in birds reared in all photoperiods are not significantly different from each other. In addition, the dressing percentage of birds reared in the (2L:2D) treatment group is greater than measurements observed in the control or other lighting program. Therefore, we can conclude that in broiler managing, the (2L:2D) lighting schedule was preferable compared to 4L:4D, 6L:6D photoperiod and control.

Influence of light quality on leaf physiology of sweet pepper plants grown under drought

The application of artificial light to improve crop production in greenhouses is widely used in the horticultural sector. In this study, we evaluated the impact of light quality on sweet pepper plants’ physiology during a period of water deficit. Pepper plants were cultivated in a climate chamber and exposed to three different light regimes; (compact fluorescent lamps [CFL], continuous intensity from light emitting diodes [LED] [LEDcont] and bell-like shape illumination schedule from LEDs [LEDday]). The effect of temporary water shortage under these light treatments on plant height, chlorophyll and proline concentration, the maximum efficiency of photosystem II (Fv/Fm), the electron transport rate (ETR), and the non-photochemical quenching (NPQ), were studied. In general, plants exposed to CFL showed higher growth rates as compared to those exposed to LED under well-watered conditions. However, the lighting source did not induce significant effects on plant growth and chlorophyll concentration during water deficit, even though proline concentration was higher in plants exposed to CFL and to drought when compared to those exposed to LEDcont and LEDday. LED radiation led to a higher ETR and an early onset of NPQ under water deficit, suggesting an activation of the cyclic electron transport. As outcome, plants grown under LEDcont showed the highest photochemical performance. Overall, the results suggest that pepper plants grown under CFL radiation perform better, even under water deficit, possibly due to the more balanced light spectrum.

In vivo singlet molecular oxygen measurements: Sensitive to changes in oxygen saturation during PDT.

Direct singlet molecular oxygen detection is known to be a valuable tool for understanding photodynamic action. It could become useful for optimizing illumination schedules in photodynamic therapy. The method of time resolved singlet molecular oxygen luminescence detection can give insights into generation of singlet oxygen and its interaction with the environment and therefore possibly allows monitoring the treatments efficacy. Due to high requirements for sensitivity as well as time resolution it has not yet been used in situ. The latest improvements in the detection system make in vivo time resolved singlet molecular oxygen luminescence detection possible. In this work, blood vessels in the chicken embryo CAM-model were scanned after injection of the photosensitizer Foslip®, yielding time resolved singlet molecular oxygen luminescence. A custom-made trifurcated fiber in combination with a dye laser, a photomultiplier tube and a fiber spectrometer was utilized for simultaneous excitation, singlet molecular oxygen luminescence and photosensitizer fluorescence detection. Singlet oxygen luminescence kinetics for mixed venous and arterialized blood in chicken embryos using the CAM-model were recorded. The data analysis resulted in two distinct and distinguishable photosensitizer triplet lifetimes corresponding to the high and low oxygen partial pressures in the oxygen-rich arterialized blood and oxygen-poor mixed venous blood. The sensitivity of direct singlet molecular oxygen luminescence detection to different oxygen partial pressures could be shown in vivo. Therefore, this study is a first step towards optimizing the illumination conditions of photodynamic treatment in situ by real time monitoring of the oxygen partial pressure within the target tissue.

Effects of light-emitting diode treatments on Brevicoryne brassicae performance mediated by secondary metabolites in Brussels sprouts

Although short-wavelength light and especially UV radiation can induce resistance in plants against herbivorous insects, the optimal wavelengths, light intensities (photon flux rates), and illumination schedules for inducing resistance have not been previously determined. Light-emitting diode (LED) illumination enables researchers to subject insects and plants to narrow-banded light treatments. In this study, we assessed how the metabolite-based defense response in Brussels sprout plants (Brassica oleracea var. gemmifera) against the cabbage aphid, Brevicoryne brassicae (Hemiptera: Aphididae), was affected by the following LED-generated wavelengths of light: 300 nm (UV-B), 365 nm (UV-A), 470 nm (blue light), and 660 nm (red light). Ambient greenhouse light supplemented with light from sodium vapor lamps served as the control treatment. The results showed a significant reduction in B. brassicae performance in the UV-A treatment compared to the blue light treatment; the reduction in the UV-A treatment was accompanied by a significant increase in glucosinolate concentrations. The UV-B treatment induced significant changes in plant flavonoid concentrations but did not affect B. brassicae performance.

Using Movable Light-emitting Diodes for Electricity Savings in a Plant Factory Growing Lettuce

In this study, the effects of light-emitting diode (LED) panels with different illumination schedules and mounted above butterhead lettuce (Lactuca sativa var. capitata) seedlings on lettuce growth and photosynthesis were examined, and the performance of the vertical and horizontal movable system on energy savings was evaluated. The illumination schedules used were fixed LED [F-LED (four LED panels illuminated the area below)] and movable LED [M-LED (two LED panels moved left and right once per day to illuminate the same area as F-LED)] at distances of 10 and 30 cm above the seedlings. The plant yields were uniform in all LED treatments. The highest light utilization efficiencies and lowest electricity consumption were found for the treatments with irradiation from a shorter distance above the seedlings. The true leaf numbers and ascorbic acid concentrations were the highest in the M-LED and F-LED treatments at a distance above the seedlings of 10 cm, while the leaf lengths and sucrose concentrations in these groups were significantly lower than those in the 30-cm treatment. These results indicate that illumination with M-LED can halve the initial light source input while maintaining yield and that sustained illumination from a shorter distance above the seedlings is the main factor in electricity savings.

Lactate dehydrogenase activity of rat epididymis and spermatozoa: effect of constant light.

During its passage through the epididymis, the gamete undergoes a process of "maturation" leading to the acquisition of its fertilizing ability. The epididymis displays regional variations in the morphology and metabolic properties of its epithelium which are relevant for the progressive development of mature sperm characteristics. The epididymis has spontaneous peristaltic contractions and receives sympathetic innervation that is modulated by melatonin, a hormone synthesized and released by the pineal gland. Constant lighting disrupts melatonin synthesis and secretion. We have studied the effect of constant light on lactate dehydrogenase (LDH; EC 1.1.1.27) and its isozyme C4 activities and protein content in whole epididymis, epididymal tissue and in spermatozoa from caput and cauda segments. Animals were exposed from birth to an illumination schedule of 14 h light:10 h dark (group L:D). At 60 days of age one group of animals was submitted to constant light over 50 days (group L:L). In order to test the fertilizing ability, the rats of each group were mated with soliciting estrous females. The percentage of pregnancies in females mated with males maintained in L:L was remarkably lower than those in females mated with males maintained in the L:D photoperiod (44% and 88% respectively). Constant light increased protein concentration and LDH activity in caput as well as in cauda of total epididymis. On the contrary, in epididymal tissue, the protein content decreased in both epididymal sections compared with controls. When enzymatic activity was expressed in Units per spermatozoa, constant light induced a significant reduction of total LDH and LDHC4 in caput and cauda spermatozoa while LDH activity of epididymal tissue was not affected. In spite of the decrease in LDH per sperm cell when rats were exposed to constant light, in total epididymis (epididymis tissue plus sperm cells content) and in spermatozoa, values of enzyme activities expressed per weight unit were higher than those of controls. This is explained by the increase in the amount of stored spermatozoa, both in caput and cauda, produced by exposure of animals to constant light. Our results confirm that in rats, chronic exposure to constant light promotes a reduction of fertilizing ability and indicates that continuous lighting reduces the total LDH and LDHC4 activities, possibly due to moderate aging of spermatozoa within the duct by lengthening of the sperm transit through the epididymis.

Chemotoxicity and survival of tumor-bearing mice under exposure to randomized photoperiodic regimen

Although disruption of the circadian rhythm had been traditionally considered as a pathological sign, there is an increasing recognition that an existence of internal disorder (or chaos) in the organism's homeostasis is, to some degree, essential to the organism's well being. In this study we explored the effects of rhythm scrambling by exposure to random light/dark (RLD) alternation or by hydrocortisone administration. The variables measured were the toxicity of Adriamycin, Vincristin, Cisplatinum and Cyclophosphamide in C57Bl/6J mice and the survival of EL4 lymphoma-bearing mice, before and after chemotherapy. Rhythm alterations were determined by WBC counts and plasma Alkaline Phosphatase activity. Injections of Adriamycin, Cisplatinum and Vincristin in RLD conditions resulted in a better survival than in control groups of mice kept in LD illumination regimen, although the differences between the groups were significant only for injection of Adriamycin. RLD conditions imposed a “protective” effect on survival of tumor-bearing mice. On the 94th day, 20% of the injected mice in RLD conditions still survived while, there were no survivors beyond 38 days in control group. Chemotherapy had a more prominent beneficial effect on survival in RLD group, as compared to LD group. The injections of hydrocortisone had detrimental effect on survival in both illumination schedules. However, the survival in the RLD group was still better than in the LD group. These experiments indicate that temporal disorganization has beneficial effects on lymphoma-bearing mice and could be used for development of new therapeutic modalities.

A note on simulating the `observer effect' using constant photoperiod on nursery pigs

Often, researchers using video cameras to record animal behavior must resort to illuminating the environment to obtain data during the night hours. This unnatural lighting during the night hours may change the behavior of experimental animals. Therefore, this study was designed to determine if the behavior of pigs is altered by constant illumination. Nursery pigs (24±0.95 days of age, 5.58±0.18 kg) were randomly assigned to one of two treatments. Treatment pigs were exposed to a constant photoperiod (24:0, light:dark cycle) while control pigs were exposed to a 12:12 light:dark cycle (lights on at 0600 h and off at 1830 h). The pigs for each treatment ( n=30) were randomly assigned to one of six pens, blocked by sex, so that each pen contained five pigs (two females and three males). Pigs were acclimated to the photoperiods for 1 week, and during this time, no observations were made. After this period, the activity of both treatments was recorded by video cameras for 6 days. Upon completion of this week of observation, the photoperiod for all pigs were reverted to the 12:12 light:dark illumination schedule for 1 week, after which observations resumed for an additional 6 days (days 14 to 19). The 24:0 pigs were more active than the 12:12 pigs ( P<0.001) between 1830 and 0630. This increase in night time activity resulted in a trend for 24:0 pigs to be more active during the entire day ( P<0.08). The 24:0 pigs were most active during the first 3 h and last 3 h of observation ( P<0.001) from 1830 to 0630. At no point during the study did we find that pigs exposed to constant illumination were less active than control pigs. Therefore, we conclude that constant illumination caused an alteration in the behavior of pigs during video recording effectively simulating the `observer effect'. Altering the activity budgets of experimental animals could have profound effects on experimental results as alterations in activity may lead to alterations in eating behavior, agonistic encounters, and levels of social stress.

Thyroliberin‐induced changes in the fluorescence of a membrane probe in individual bovine anterior pituitary cells.

1. We have investigated the use of TMA-DPH (1-[4-(trimethylammonio) phenyl]-6-phenylhexa-1,3,5-triene) as an indicator of exocytosis in individual bovine anterior pituitary cells using microfluorimetric imaging. 2. TMA-DPH was photolabile in artificial and cell membranes. In cells incubated in TMA-DPH the distribution of fluorescence depended both on the incubation time and the illumination schedule. If the dye was added while the cells were subjected to repeated cycles of 0.36 s light intermittent with 1-15 s dark, the fluorescence of the peripheral annulus and the central region of individual cells rose in parallel and reached a steady state within 200 s; the annulus was always brighter than the central region. However, using long intervening dark periods (200 s), the central region continued to incorporate dye after the annulus had reached a plateau. 3. When the cells were loaded with TMA-DPH using intermittent light with short dark periods, the dye washed out of the central region and the annulus in parallel when external dye was removed. However, if the cells had been loaded using long dark periods, the dye was washed out of the central region more slowly than from the annulus. 4. When cells were incubated in TMA-DPH in the dark for 1 min and then exposed to constant illumination in the presence of external dye, the fluorescence of the central region and the annulus both decayed in parallel to a new steady state. If the cells were incubated in TMA-DPH in the dark for 240 min the fluorescence from each region fell to a steady state but the falls were larger and were not in parallel. 5. We suggest that TMA-DPH fluorescence was derived from plasma membrane-associated and internalized dye and that the amount of fluorescence from the latter varied because TMA-DPH was photobleached. Thus, when illumination was interrupted by short dark intervals, annular fluorescence was high compared to central fluorescence because bleached dye in the plasma membrane was rapidly replaced by unbleached dye from the medium. However, long dark intervals permitted the dye to be internalized before it was bleached and fluorescence was therefore also present in central regions. 6. The total cell fluorescence, observed using 15 s dark intervals, was increased 5-40% (in single cells) in a dose-dependent fashion by addition of TRH (tripeptide thyrotrophin-releasing hormone; 1-200 nM).(ABSTRACT TRUNCATED AT 400 WORDS)

Glucose attenuation of deficits in memory retrieval in altered light:dark cycles

Previous studies in rats show that disrupting circadian light-dark rhythms leads to impairments in memory. In particular, both phase delays and phase advances of the light:dark cycle initiated after inhibitory (passive) avoidance training result in impaired retention. The present study examined this phenomenon in mice and, using a retrieval design, examined whether glucose or epinephrine could attenuate deficits in memory. Groups of mice were first trained on an inhibitory avoidance task during the light portion of the illumination cycle. They were then maintained for a 72-h train-test interval either under the same schedule of illumination or one with a phase advance of 4 h. Thirty minutes before testing, groups were injected with saline, glucose (1, 10, 100, 250, or 500 mg/kg), or epinephrine (0.1 mg/kg). The results showed that (1) retention was significantly impaired in phase-shifted mice relative to nonphase-shifted controls and (2) both glucose (100 mg/kg) and epinephrine attenuated the deficit in memory. These findings indicate that altered illumination schedules disrupt memory in mice as well as in rats. In addition, they suggest that glucose may be a useful treatment to attenuate deficits in memory associated with impaired biological rhythms.

Circadian rhythm in gamma glutamyltranspeptidase and leucine aminopeptidase urinary activity in rats.

Urinary gamma glutamyltranspeptidase (GGT) and leucine aminopeptidase (LAP), renal tubular brush border enzymes, have been shown to be sensitive indicators of renal tubular functions. This study documents circadian rhythms in the urinary activity of GGT and LAP, statistically validated and quantified by the cosinor method, in 15 male Wistar rats standardized to a LD 12:12 illumination schedule (light from 0800 hr to 2000 hr) and fed ad libitum. The acrophase of the circadian rhythms in urinary GGT and LAP activity occurred at the end of the rest span of the animals: between 1730 and 1915 for GGT (depending on the mode of expression of the activity) and between 1700 and 1910 for LAP. Of striking resemblance in their timing, both these rhythms were also of large amplitude (about 50% of the mesor for urinary GGT activity and about 45% for LAP one). The circadian acrophases of urinary GGT and LAP activity led in timing the circadian rhythms in urine volume and creatinine excretion by about 13 hr. Such findings consistent with the circadian variations found by other investigators in GGT in kidney homogenates or in LAP in human urine thus reflect a periodicity in renal tubular function. The reasons for these circadian variations, still unknown at this time, are discussed. The influence recently demonstrated of the hormonal context on protein and enzyme synthesis at the tubule, and its phase relations to urinary enzyme excretion emphasize how much the circadian rhythm in urinary GGT and LAP activity is well included in the murine time structure.(ABSTRACT TRUNCATED AT 250 WORDS)

Experimental study on the relationship between cardiac arrhythmias and sleep states by ambulatory ECG-EEC monitoring.

The relationship between cardiac arrhythmias and sleep states was investigated in rats using the ambulatory ECG-EEG monitoring system under the 14/10 light-dark illumination schedule. Records of 14 rats obtained over 94 days were analyzed. Bradyarrhythmias (SA block and AV block) and ventricular arrhythmias [ventricular premature contraction (VPC) and short run of VPCs (ventricular tachycardia, VT)] were observed. Average number of episodes of bradyarrhythmia per day was 7.5, and the ratio of SA block to AV block was 34.9% to 65.1%. Average VPC or VT occurrence per day was 0.9 or 0.1 times, respectively. Sleep states were divided into alertness, slow-wave sleep, and paradoxical sleep, and the relationship between sleep states and arrhythmias was investigated. Bradyarrhythmias appeared predominantly during paradoxical sleep, while ventricular arrhythmias appeared during alertness as well as paradoxical sleep. Bradyarrhythmic episodes decreased by right or left vagotomy 78% or 70%, respectively. Sinus bradyarrhythmias disappeared almost completely by the right vagotomy, while the occurrence of AV block decreased by the right or left vagotomy. Circadian rhythms in arrhythmias were also analyzed by the cosine-fitting technique, and significant circadian rhythms were demonstrated in both bradyarrhythmias and ventricular arrhythmias. Acrophases were 9:56 A.M. and 1:47 A.M., respectively. Occurrence of VT was rare, but the most frequent incidental time zone was immediately following transition from light effects (rest) to dark (activity). This knowledge of circadian rhythm effects in arrhythmias must be incorporated into improved treatment of arrhythmias.

The ACTH-(4–9) analog ORG 2766 and desglycinamide 9-(Arg 8)-vasopressin reverse the retrograde amnesia induced by disrupting circadian rhythms in rats

Disrupting circadian organization by exposing rats to a shifted illumination schedule after training for passive avoidance and shuttle box avoidance behavior resulted in retrograde amnesia as evidenced by impaired performance during retention and extinction testing respectively. A single treatment with either the ACTH-(4–9) analog ORG 2766 or desglycinamide 9-(Arg 8)-vasopressin (DGAVP) 1 hour prior to the retention of passive avoidance or extinction of shuttle box avoidance behavior restored the behavioral impairment. It is suggested that these peptides may be useful to relieve memory deficits induced by disturbances in circadian organization.

Role of the suprachiasmatic nuclei of the hypothalamus on diurnal rhythm in cardiac arrhythmias.

Ambulatory EGG and EEG recordings were recorded under a 14/10-h light-dark illumination schedule using rats. The rats consisted of two groups: a suprachiasmatic (Sch) lesioned group (n = 5) and a normal control group (n = 5). Bilateral Sch nuclei were lesioned electrically (DC, 2.5 mA, 30 s for each) using a pair of platinum electrodes 0.3 mm in diameter. After recovery from surgery, recordings of ECGs (leads I, II, and III) and EEGs from the cortex and the left dorsal hippocampus were continued for 6 days. Diurnal periodicity in bradyarrhythmia (sinoatrial block, atrioventricular block) and heart rate was analyzed by the least square fit of 24-h cosines. Significant diurnal rhythm was observed in control rats, whereas Sch-lesioned rats showed no significant diurnal rhythm. The integrity of the Sch nuclei, therefore, is necessary for the generation and/or the expression of diurnal periodicity in bradyarrhythmia in rats.

Effect of light on the acetylcholine concentrations of the suprachiasmatic nucleus in the rat

Acetylcholine concentrations were determined in suprachiasmatic nucleus of rats sacrificed by irradiation of microwave, using radioimmunoassay. No significant rhythmicity was observed over a 24-h period in rats blinded for two weeks. When the light was given at 22.00 h (illumination schedule L:07.00–19.00 h) in intact rats, acetylcholine concentration increased 30 and 60 min after light on in suprachiasmatic nucleus, but not in the other control site. These results suggest that endogenous circadian rhythm of acetylcholine concentration is absent in suprachiasmatic nucleus, but light may affect acetylcholine concentration of this site.

Light-dark and feeding regimens affect circadian phasing of blood-ethanol decay rates

Rats maintained on a 12 hour: 12 hour light-dark cycle, with food continuously available, exhibited a prominent and reproducible circadian rhythm in the slope of the linear blood-ethanol clearance curve. Peak values fell near the end of the dark period and trough values late in the light period. These phase relationships persisted with 4, 8 and 12 hour phase shifts of the illumination schedule. However, when food availability was restricted to 4 hours per day the feeding regimen became the dominant synhcronizer for the rhythms in blood-ethanol decay rate and body core temperature. With resumption of the ad lib feeding regimen, the L-D cycle again entrained these rhythms. Ethanol injections (1.5 g/kg, IP) did not alter the expected excursion of the circadian temperature curve, as measured 4 hours after dosing.

Endogenous nature of circadian rhythms in calcium metabolism.

Rats studied when the lights are on from 0600 to 1800 daily and fed only in the dark period displayed circadian rhythms in plasma calcium (ionized and total) and 45Ca concentrations, 6 and 8 days after 45Ca administration. In rats fed a calcium-deficient diet, the amplitude of daily variation of plasma ionized and total calcium increased markedly whereas plasma 45Ca daily fluctuation remained essentially unchanged. In the calcium-deficient rats, significant correlations between plasma calcium and 45Ca and between plasma calcium and magnesium were observed throughout the 24 h; circadian periodicity of calcium metabolism persisted in rats fasted overnight, regardless of the illumination schedule. Normal daily fluctuations in plasma 45Ca, lost after thyroparathyroidectomy (TPTX), were restored by feeding the TPTX rats a high-calcium diet. These results demonstrate clearly that circadian rhythms of calcium metabolism occurred irrespective of the light-dark schedule, the calcium supply through intestines and the thyroparathyroid system. An attractive suggestion is that circadian rhythmicity originates as a result of dynamic properties involving nonlinear processes of calcium metabolism.

Different direct effects of light intensity on the entrained activity rhythm in neotropical bats (Chiroptera, Phyllostomidae)

In the two neotropical Chiroptera species, Artibeus lituratus and Phyllostomus discolor, the influence of illumination intensity during the D-time of an LD 12:12 h on the locomotory activity rhythm was investigated by offering specific rectangular illumination schedules. In LD 12:12 (10 1:10 -4lux), A. lituratus and P. discolor exhibit a stable unimodal basic activity pattern. By increasing the light intensity during D-time to 10 -1 lux the activity pattern, especially in A. lituratus, can be modified in almost every way. This indicates a strong direct inhibitory effect of higher light intensities (> 10 -4 lux). Hereby light effects via the circadian system have practically no importance. The response of A. lituratus to changes of the D-light intensity is more pronounced than that of P. discolor. It is suggested that the different direct effects of light intensity on the activity pattern of the two bat species reflect specific ecological adaptations.