Effect of Aging on Circadian Activity in Gray Mouse Lemurs

Microcebus murinus s a very photoperiod-dependent primate with a potentially extended longevity (13 years). Reduction of artificial seasonal cycles allows acceleration of the aging process. Under these conditions, age is defined according to the number of seasonal cycles. We conducted experiments in order to assess the effects of aging upon (1) the main parameters (period: duration: ) of the circadian activity–rest rhythm; and (2) the plasticity of the response to light, which is the main entraining factor of the internal clock. We studied the evolution of and through two types of experiments: a transverse one comparing 36 males of various ages (1–13 seasonal cycles) and a longitudinal one following 2 pairs of males from the same litter (one from each pair was maintained under natural cycle while the other was submitted to a shortened cycle) over 54 months. Results from transverse experiments demonstrated no statistical difference in and with age except in 4 senescent (>10 cycles) subjects in which these two parameters were decreased. Longitudinal experiments confirmed this tendency. The plasticity of responses to light, resynchronization after a shift of the day–night cycle, or shift of activity onset after presentation of a light pulse at various circadian times was unaffected by aging. Taken together, the data demonstrate that the parameters of the circadian activity–rest rhythm remain stable over a long span of life and/or that light remains a powerful entraining parameter even in very old individuals.     

Circadian complexes: Circadian rhythms under common gene control

Summary Circadian rhythms for food and water consumption were measured in five inbred strains of mice under a photoperiod of 16 h light and 8 h dark (16:8 LD), and under constant light (LL).Significant strain differences were observed which indicate that a common gene difference, or set of differences inMus musculus influences both the phase angle () associating the rhythms with the light-dark cycle, and the periods (_LL) of circadian rhythms for food and water consumption. The biological clock mechanism influenced by this genetic variance is common to both food and water circadian rhythms, and differs among the five inbred strains. A positive genetic correlation was observed between the phase angle () and the period (_LL) of each rhythm. This observation can be understood in terms of a functional relationship between phase and period proposed by Pittendrigh and Daan (1976b) for the entrainment of a circadian oscillator by a light-dark cycle in nocturnal rodents.These results suggest that circadian rhythms for food and water consumption in mice are regulated by a common physiological mechanism, and would respond to natural selection as a single circadian complex under common gene control.     

Carotenogenesis and asparagine inLeptosphaeria michotii (West) Sacc.

Summary InLeptosphaeria michotii U¹⁴C-asparagine was incorporated into the coloured carotenoids, the synthesis of which carried on till day 8. The pigment turnover, obvious from day 6, was not modified by the light conditions used.Nicotine (0.25 to 4.5 mM) has been used to study carotenogenesis and sporulation rhythm regulation inL. michotii fed with asparagine 2.6 mM. Control cultures contained in darkness -carotene only and in continuous light -carotene 98% and lycopene 2%. The mold receiving nicotine 0.25 mM in darkness contained -carotene 98% and lycopene 2%. For nicotine 0.5 mM and upwards -carotene decreased, lycopene increased and -carotene appeared, the balance between these pigments also depending on the light conditions. Whereas period length () of the sporulation rhythm increased from one cycle to the next in control cultures in darkness, it was stabilized either by continuous light ( 27 h) or by nicotine 0.25 mM ( 30 h). For nicotine 0.5 mM sporulation was uniform in darkness or in light.     

Circadian control of oviposition in the codling moth, Laspeyresia pomonella, Lepidoptera: Olethreutidae

The oviposition rhythm in Laspeyresia pomonella (L.) is entrained by light-dark cycles and freeruns in continuous light with a period =25.9 hr and in continuous darkness with =21.8 hr. In the laboratory as well as in the field, the median of oviposition occurs on average 2.5 hr before the onset of darkness. The codling moth can adapt quickly to a new light regime. Oviposition was resynchronized with a normal light-dark cycle within 48 hr after freerunning for several days in continuous light.

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Circadiane steuerung der eiablage beim apfelwickler, Laspeyresia pomonella, lepidoptera, olethreutidae

Zusammenfassung Der Eiablagerhythmus von Laspeyresia pomonella (L.) wird von Licht-Dunkel-Zyklen gesteuert und läuft frei im Dauerlicht mit einer Periode =25.9 St. und im Dauerdunkel mit =21.8 St. Im Labor sowie unter natürlichen Bedingungen lag der 50%-Punkt der täglichen Eiablage jeweils 2.5 St. vor dem Beginn der Dunkelheit. Der Apfelwickler kann sich rasch an ein verändertes Lichtregime anpassen. Nach mehreren Tagen Freilauf im Dauerlicht synchronisierte sich der Eiablagerhythmus innerhalb von 48 St. mit einem normalen Licht-Dunkel-Zyklus.

     

The effects of pinealectomy and blinding on the circadian locomotor activity rhythm in the Japanese newt,Cynops pyrrhogaster

We examined the effects of pinealectomy and blinding (bilateral ocular enucleation) on the circadian locomotor activity rhythm in the Japanese newt, Cynops pyrrhogaster. The pinealectomized newts were entrained to a light-dark cycle of 12 h light and 12 h darkness. After transfer to constant darkness they showed residual rhythmicity for at least several days which was gradually disrupted in prolonged constant darkness. Blinded newts were also entrained to a 12 h light/12 h dark cycle. In subsequent constant darkness they showed free-running rhythms of locomotor activity. However, the freerunning periods noticeably increased compared with those observed in the previous period of constant darkness before blinding. In blinded newts entrained to the light/dark cycle the activity rhythms were gradually disrupted after pinealectomy even in the presence of the light/dark cycle. These results suggest that both the pineal and the eyes are involved in the newt's circadian system, and also suggest that the pineal of the newt acts as an extraretinal photoreceptor which mediates the entrainment of the locomotor activity rhythm.Abbreviations circadian period - DD constant darkness - LD cycle, light-dark cycle - LD 12:12 light-dark cycle of 12 h light and 12 h darkness     

Sodium channel opening as a precursor to inactivation

The time constant of the process producing the delay in Na inactivation development as determined by the two pulse method (_delay) was extracted and compared to that of the slowest Na activation process ₃ for the I _Na during the conditioning pulse of that same determination. _delay and two pulse inactivation _c values were computer generated using a nonlinear least squares algorithm. _h and single pulse inactivation _h values were independently generated for each determination also with the aid of the computer using the same non-linear least squares algorithm. In one determination at 2 mV, _c was 4.68 and _delay 0.494 ms while _h was 4.70 and ₃ 0.491 ms for a _c/_h of 0.996 and a _delay/₃ of 1.006. Mean _delay/₃ from five determinations in four axons, both Cs and K perfused, and spanning a potential range of-27 to 2mV was 1.068. The precursor process to inactivation is channel opening. Some fraction of channels presumably inactivate via another route where prior channel opening is not required.     

Circadian organization in the pigeon,Columba livia: the role of the pineal organ and the eye

Summary The roles of the pineal organ and the eye in the control of circadian locomotor rhythmicity were studied in the pigeon (Columba livia). Neither pinealectomy nor blinding abolished the circadian rhythms in constant dim light conditions (LLdim). All the pinealectomized birds and the blinded birds entrained to light-dark (LD) cycles with no discernible anticipatory activity. However, the birds which had been both pinealectomized and blinded showed no circadian rhythms in prolonged LLdim. These birds entrained to LD cycles with anticipatory activity and showed residual rhythmicity for a while after transfer from LD cycles to LLdim. Continuous administration of melatonin induced suppression of the circadian rhythms and reduced total amount of locomotor activity in LLdim. These results suggest that not only the pineal organ but also the eye (perhaps the retina) is involved in the pigeon's circadian system.Abbreviations NAT N-acetyltransferase - LLdim constant dim light - cadian period - SCN suprachiasmatic nucleus - circadian activity time - LD light-dark     

Die Aktivit?tsperiodik bei V?geln mit und ohne dunklem Schlafkasten

Zusammenfassung In 2 Versuchsserien wurden Kohlmeisen(Parus major) und japanische Möwchen(Lonchura striata var.domestica) einzeln und schallisoliert gehalten. In der ersten Versuchsserie, in der alle Vögel einen dunklen Schlafkasten hatten, wurde der Einfluß der Beleuchtungsstärke auf die Periode () der Hüpfaktivität und auf das Verhältnis von Aktivitätszeit zu Ruhezeit ( : -Verhältnis) untersucht. Sowhol Kohlmeisen als auch japanische Möwchen folgen der Regel, daß mit wachsender Beleuchtungsstärke die Periode kürzer und das : -Verhältnis größer wird.In der 2. Serie wurde der Einfluß Ruhe im dunklen Schlafkasten auf die Periodenlänge und auf das : -Verhältnis untersucht. Es wurden die Messungen aus Bedingung 1 (der Vogel hat einen dunklen Schlafkasten zur Verfügung) mit den Messungen aus Bedingung 2 (der Vogel hat keinen oder einen hellen Schlafkasten zur Verfügung) verglichen. Das Ergebnis bei Kohlmeisen entspricht den Befunden bei konstantem Licht verschiedener Intensität. Unter Bedingung 1 ist länger und das : -Verhältnis kleiner als in Bedingung 2. Das Ausmaß der Änderung von nach Fortnahme des dunklen Kastens ist unabhängig von der Periodenlänge in Bedingung 1. Das Ausmaß der änderung von : ist unabhängig von a : in Bedingung 1, jedoch schwach negativ korreliert mit der Periodenlänge in Bedingung 1.Bei japanischen Möwchen entsprechen die Ergebnisse dieser Versuchsserie nicht der Regel für tagaktive Vögel. Mit Benützen des dunklen Schlafkastens ist kürzer als ohne den Schlafkasten. Ohne den Schlafkasten ist etwa 24 Std. Das : -Verhältnis ist in Bedingung 1 unter bestimmten Voraussetzungen kleiner als in Bedingung 2. Das Ausmaß der Änderung von nach Fortnahme des Kastens ist mit der dazugehörigen Periode in Bedingung 1 hochsignifikant korreliert (Regressionskoeffizient b=-1.01, Korrelationskoeffizient r=0.89). Ebenfalls ist das Ausmaß der Änderung von : nach Fortnahme des Kastens mit : aus Bedingung 1 korreliert; es scheint, als würde ein bevorzugtes : -Verhältnis von etwa 2.0 eingeregelt.Die Ergebnisse werden im Hinblick auf 4 Punkte diskutiert: 1) Das circadiane System arbeitet innerhalb eines engen Bereiches von - und : -Werten optimal. 2) Der Optimalbereich wird bevorzugt unter ungünstigen Bedingungen angestrebt. 3) Der Entzug des dunklen Schlafkastens belastet japanische Möwchen mehr als Kohlmeisen. 4) Bei japanischen Möwchen wird in Bedingung 1 durch fortplfanzungsphysiologischen Einfluß verkürzt.

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Circadian activity rhythms of birds with and without a dark nest box

Summary Perch-hopping activity of Great tits(Parus major) and Bengales finches(Lonchura striata domestica), housed individually in soundproof boxes, was studied in two series of experiments. In the first series all birds had access to a dark nest box, in which they retired during their subjective night. In this experiment the effect of light intensity on the freerunning circadian activity rhythm was investigated. Both Great tits and Bengalese finches obey the circadian rule by responding to an increase in light intensity with shortening the circadian period () and with an increase of the ratio of activity time and rest time ( : ).In the second series of experiments the influence of sleeping in the dark nest box on both circadian period and : -ratio was studied. The results of two experimental conditions — without and with access to a dark nest box — were compared. In the Great tits, the results are in agreement with the effect of light intensity: when a dark nestbox is available, is longer and the : -ratio is smaller than in the absence of a nest box. The magnitude of the change in free-running period after removal of the nest box is independent of the original value of ; the amount of change : -ratio is likewise independent of the original : -ratio, but is weakly correlated to the original .InLonchura striata var. domestica, removal of the dark nest box leads to a lenghtening of the free-running period to about 24 hours; the : -ratio is smaller in the presence of a dark nestbox, if certain other conditions are fulfilled. The magnitude of the change in after removal of the nest box is highly correlated to the original free-running period (r=-0.89) in such a way that, without nest box, the period approaches a value of 24 hours. Also, the amount of change in : -ratio due to nest box removal is negatively correlated to the original : -ratio. A probably preferred : -ratio of 2.0 is adopted.These results are discussed in the view of 4 points: 1) The circadian system operates at its optimum within a narrow range of - and : -values. 2) This optimal range is especially adopted when conditions become adverse. 3) Removal of the dark nest box results in a more stressful situation for Bengalese finches than for Great tits. 4) In the Bengalese finches, is shortened in the presence of a nest box due to effects on reproductive physiology.

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Herrn Prof. Dr. JürgenAschoff zum 60. Geburtstag gewidemt.     

Formal properties of the circadian rhythm of locomotor activity in Japanese quail

Summary Japanese quail have a circadian rhythm of locomotor activity whose free-run period () in constant darkness (DD) was 22.5±0.1 h (45). A phase response curve of typical form was obtained by illuminating the free-running rhythm with single 1 h light pulses. Using entrainment theory a derived phase response curve was calculated from the phase relationships between the locomotor rhythm and 1 h light periods in light-dark cycles of various lengths (T). Although the limits of entrainment to theseT cycles differed slightly from those predicted, there was a close correlation between the two phase response curves. The phase relationships between the locomotor rhythm and 1–9 h photoperiods in 24 h cycles were in general accord with a prediction based on the short free-run period and the relative sizes of the delay and advance portions of the phase response curve for 1 h light pulses.     

Seasonal effects on the freerunning rhythm of circadian activity of longnose dace (Rhinichthys cataractae)

Synopsis Freerunning circadian rhythms of locomotor activity in individual longnose dace sampled from a population at 41°N latitude were recorded under constant darkness throughout the year. There was an annual cycle in the length of the circadian period, with maximum and minimum lengths of mean period of 23.6 and 21.6 h recorded during summer (June) and winter (December), respectively. These annual changes in period length may have resulted from seasonal changes in entrainment by natural light-dark cycles and their after-effects on endogenous circadian rhythms. The possibility of an endogenous circannual rhythm was also considered.     

Entrainment and phase shifting of the circadian rhythm of cell division by light in cultures of the achlorophyllous ZC mutant ofEuglena gracilis

The photosynthesis-deficient ZC mutant ofEuglena gracilis Klebs (strain Z) was cultured at 16°C on an aerated, magnetically stirred, mineral medium containing 0.1% ethanol (pH 7.0). Cell division could be entrained by a 12: 12 light: dark cycle (LD: 12, 12) or even by a one-pulse skeleton photoperiod (LD: 1,23) The rhythm free-ran in DD for at least 8 days with a circadian period (=25.5 h) in populations that had been previously entrained by LD. The freerunning rhythm could be phase-shifted by a single 1-h light pulse (3000 lx). The strong (Type 0) phase-response curve derived from the resetting effects of such signals given at different circadian times was similar to that for the photosynthetic wild-type strain. These results demonstrate that the presence of a functional chloroplast compartment is not necessary for the circadian clock to function inEuglena and suggest that phase resetting of the circadian clock by light occurs via a similar pathway in both photosynthetic and non-photosynthetic cell types.     

Unilateral lesions of the hamster suprachiasmatic nuclei: evidence for redundant control of circadian rhythms

Summary Several properties of vertebrate circadian rhythms can be attributed to the behavior of an underlying pacemaker system which is composed of two separate but mutually interacting circadian oscillators. As originally formulated, the model for such a pacemaker system proposed that two oscillators or populations of oscillators have different properties, specifically in their responses to light (Pittendrigh 1974; Pittendrigh and Daan 1976b). We have tested the proposition that the right and left suprachiasmatic nuclei (SCN) of the golden hamster contribute in different ways to the regulation of circadian rhythmicity by measuring the wheel-running activity rhythms of hamsters with lesions to either the right or left SCN. Although effects of unilateral or other partial SCN lesions on pacemaker properties were observed, these effects were not different in hamsters receiving right- or left-side lesions. More specifically: (1) free-running period () in constant light was shorter in lesioned hamsters irrespective of the side lesioned (Fig. 3a), and the total amount of SCN destruction was found to correlate with (Fig. 4). (2) Phase-angle difference () of some lesioned hamsters (both right- and left-side) during entrainment to LD, 1410 was significantly more positive than that of controls (Fig. 3b). (3) The rate of phase-shift following a shift of the light/dark cycle was not different in hamsters with right- or left-side lesions (Fig. 3c). And (4) the simultaneous expression of different circadian periods, similar to splitting, was observed in hamsters with unilateral lesions (Fig. 5). It is concluded that the right and left SCN are similar in their contributions to the control of circadian rhythmicity and that there is as yet no evidence for the permanent loss of multioscillator properties resulting from the destruction of only one of the two SCN.Abbreviations SCN suprachiasmatic nuclei or nucleus - LD light/dark cycle - LL constant light - DD constant dark - circadian period - activity time - rest time - phase angle - phase-angle difference - SD standard deviation - SE standard error - ANOVA analysis of variance     

Entrainment of the circadian system of the house sparrow: A population of oscillators in pinealectomized birds

Summary Removal of the pineal gland modifies the entrainment behavior of house sparrows. Abnormal entrainment occurs in pinealectomized sparrows exposed to skeleton photoperiods (light cycles composed of 2 pulses of light per 24-h cycle). This abnormal entrainment depends upon the state of the locomotor activity (rhythmic or arrhythmic) before exposure to the light cycle, and upon the interval between the 2 pulses of light which constitute the skeleton photoperiod. The conditions that produce abnormal entrainment in pinealectomized birds are strongly correlated with those that produce 2 stable phases of entrainment to skeleton photoperiods in normal birds (bistability phenomenon). These results suggest that after pinealectomy, there remains a population of oscillators whose combined output is reflected in the locomotor activity of individual sparrows.Abbreviations LD 12 12 light-dark cycle with 12 h of light and 12 h of dark per 24-h cycle - CT circadian time     

Circadian rhythms of corneal mitotic rate,retinal melatonin and immunoreactive visual pigments,and the effects of melatonin on the rhythms in the Japanese quail

We investigated circadian ocular rhythms in the Japanese quail, Coturnix coturnix japonica. The birds were placed under light-dark cycles (LD 1212), constant light (LL) and constant darkness (DD), and the retinas were dissected out at four-hour intervals throughout 24 h. Following measurements were performed. (1) Melatonin content in the retina was measured by radioimmunoassay. It was low in light and several folds higher in darkness under LD 1212. The rhythm continued in DD, but disappeared in LL. (2) Mitotic figures in the corneal epithelium were counted. Similar rhythms to the melatonin content were observed in the corneal mitotic rate with a slight phase delay. (3) The retinas were fixed at 4-h intervals and immunostained with anti-bovine rhodopsin serum and anti-chicken iodopsin monoclonal antibodies. The outer segments of photoreceptor cells were stained intensively throughout 24 h in LD 1212, LL and DD. In contrast, the stainability of the locus close to the outer limiting membrane where the Golgi apparatus exists changed diurnally. Scores showing the ratio of cells with positive staining indicated high values from 4 h after the onset of light to the beginning of dark phase under LD 1212. The values were high throughout 24 h in LL and intermediate or low in DD. (4) To investigate the effect of melatonin on the corneal mitotic rate and visual pigments at the Golgi region, melatonin was injected into one eye and saline into the contralateral eye. Melatonin induced a phase advance in the corneal mitotic rate under LD 1212, but did not induce a rhythm under LL. The ratio of photoreceptor cells with positive staining to anti-visual pigment antibodies at the Golgi region was not affected by melatonin injection.Abbreviations ANOVA analysis of variance - BSA bovine serum albumin - DD constant darkness - Io-mAb monoclonal antibodies against chicken iodospin - LD light-dark - LL constant light - mRNA messenger ribonucleic acid - PBS phosphate buffer solution - Rh-As antiserum against bovine rhodopsin - SCN suprachiasmatic nucleus - T transducin - T transducin      

Circadian organization in the lizardAnolis carolinensis: a multioscillator system

Summary The locomotor activity rhythm of normal anoles freerunning in conditions of constant darkness or constant dim light typically shows a bimodal pattern. Pinealectomy of freerunning anoles renders the lizards arrhythmic (continuously active). Pinealectomy of anoles entrained to light-dark (LD) cycles often causes a large phase advance of the lizards' daily activity onsets relative to light onsets. Also, the activity onsets of individual pinealectomized anoles entrained to LD cycles often alternate between two preferred phase relationships relative to the LD cycle. These data support the hypothesis that at least two circadian oscillators (or sets of oscillators) drive the overt rhythm of locomotor activity and the pineal acts either as a circadian pacemaker or as a coupling device for these oscillators.Abbreviation SCN suprachiasmatic nuclei     

Die Aktivitätsperiodik von zwei tagaktiven Nagern,Funambulus palmarum undEutamias sibiricus,unter Dauerlichtbedingungen

Zusammenfassung Bei, in kleinen Käfigen mit Zugang zu einer Lauftrommel, einzeln gehaltenen Tieren der beiden ArtenFunambulus palmarum (Palmenhörnchen) undEutamias sibiricus (asiatisches Streifenhörnchen) wurde der Einfluß verschiedener Beleuchtungsstärke unter Dauerlichtbedingungen auf die circadiane Aktivitätsperiodik untersucht.4 Palmenhörnchen wurden in verschiedenen Beleuchtungsstärken von nicht meßbarer Intensität bis etwa 1000 Lux gemessen. Von etwa 1 Lux bis 1000 Lux war die Periodendauer () positiv mit der Beleuchtungsstärke korreliert. Über den gesamten Bereich der untersuchten Lichtintensitäten war die Aktivitätsmenge positiv mit dem Logarithmus der Beleuchtungsstärke (logI _LL ) korreliert. Es bestand jedoch ebenso wie zwischen und logI _LL keine lineare Beziehung zwischen beiden Größen (Fig. 1). Das Verhältnis Aktivitätszeit zu Ruhezeit (:) war bei allen untersuchten Tieren weder mit noch mit der Aktivitätsmenge korreliert.Von insgesamt 15 unter Dauerlichtbedingungen zwischen 0,01 und 100 Lux gemessenen asiatischen Streifenhörnchen zeigten nur 7 Tiere circadiane Perioden der Aktivität. Infolge der großen Streuung der Aktivitätsanfänge und -enden sowie des Aktivitätsmusters konnten a und : bei den meisten Tieren nicht bestimmt werden. Die -Werte streuten um einen mittleren Wert von 23,6 Std; sie zeigten jedoch keine regelhafte Abhängigkeit von der Beleuchtungsstärke (Fig. 5).Bei einzelnen Tieren beider Arten wurde bei Beleuchtungsstärken von etwa 3–4 Lux eine Aufspaltung (temporäre Dissoziation) einzelner Aktivitätskomponenten mit verschiedenen Frequenzen beobachtet (Figs. 2 und 4).Aufgrund der unterschiedlichen Abhängigkeit der Aktivitätsparameter (Aktivitätszeit und Aktivitätsmenge) von bei verschiedenen Tiergruppen wird vermutet, daß das Licht sowohl verschiedene Parameter der circadianen Aktivitätsperiodik als auch einzelne Komponenten des der Aktivität zugrunde liegenden circadianen Systems unabhängig voneinander beeinflußt. Tag- und nachtaktive Säuger unterscheiden sich im wesentlichen nur in den kritischen Beleuchtungsstärken, d.h. den Beleuchtungsstärken, bei welchen die kürzesten Perioden gemessen werden (Fig. 6).

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The activity rhythm of two day-active rodents,Funambulus palmarum andEutamias sibiricus, in continuous illumination

Summary Palm squirrels (Funambulus palmarum) and Sibirian chipmunks (Eutamias sibiricus) were kept individually in small cages attached to a running wheel. Under continuous illumination the influence of different light intensities on the circadian rhythm of activity was measured.Four palm squirrels were exposed to light intensities between unmeasurable intensity (total darkness) and about 1000 lux. Between 1 and 1000 lux the period length () of the circadian rhythm of activity was positively correlated with light intensity. The amount of activity per period showed a positive relationship with light intensity over the range of intensities tested (Fig. 1). In all 4 animals the ratio activity-time to rest-time (: ) was neither correlated with the amount of activity per period nor with .From a total of 15 Sibirian chipmunks tested under continuous illumination between 0.01 and 100 lux only 7 animals showed circadian rhythms of activity. As a consequence of the great variability of the beginning and the end of activity as well as in the temporal activity pattern, a (activity time) and : could not be determined in most animals of this species. The values of varied around a mean of 23.6 hr, but did not change as a function of light intensity (Fig. 5).In some individuals of both species a splitting or temporary dissociation of single components of activity with different frequencies was observed at light intensities of about 3 to 4 lux (Figs. 2 and 4).On the basis of the different relationships between the activity functions (amount of activity and activity-time) and in various groups of animals (cf. day-active mammals and birds), it is assumed that light acts separately on the parameters of the circadian activity rhythm as well as on single components of the circadian system underlying activity. Day- and night-active mammals differ essentially only in respect to their critical light intensities, i.e. the light intensities at which the shortest circadian periods are measured (Fig. 6).

     

Photocurrent kinetics of purple-membrane sheets bound to planar bilayer membranes

Summary The kinetics of light-driven proton transport by bacteriorhodopsin has been studied in a model system consisting of a planar lipid bilayer membrane to which purple membrane fragments have been attached. After excitation with a 10-nsec laser flash a fast negative current-transient occurs, followed by a positive transient which decays to zero. The time course of the photocurrent may be represented by a sum of four exponentials with time constants ₁= 1.2sec, ₂= 17sec, ₄= 57sec, ₁= 950sec (at 25°C). In a D₂O medium ₂ and ₃ are increased by a factor of 2.6 and 2.9, respectively, whereas ₁ remains unaffected. The observed components of the photocurrent can be correlated to photochemical reaction steps inferred from flash-photometric experiments on the basis of the observed time constants, the activation energies, and the effects of pH and D₂O. From the photocurrent signals information may be obtained on the magnitude of the charge displacement associated with the elementary transitions of the bacteriorhodopsin molecule.     

Pineal melatonin rhythms in the lizardAnolis carolinensis: effects of light and temperature cycles

Summary Pineal and ocular melatonin was assessed, over 24 h periods, in male lizards (Anolis carolinensis) entrained to 24 h light-dark (LD) cycles and a constant 32 C, and in lizards entrained to both 24 h LD cycles and 24 h temperature cycles (32 C/20 C). At a constant temperature, the duration of the photoperiod has a profound effect on the duration, amplitude, and phase of the pineal melatonin rhythm (Fig. 1). The pineal melatonin rhythm under cyclic temperature peaks during the cool (20 C) phase of the cycle regardless of whether or not the cool phase occurs during the light or dark phase of a LD 1212 cycle (Fig. 3). Under a temperature cycle and constant dim illumination, a pineal melatonin rhythm is observed which peaks during the cool phase of the temperature cycle, but the amplitude of the rhythm is depressed relative to that observed under LD (Fig. 2). Illumination up to 2 h in duration does not suppress the nocturnal melatonin peak in theAnolis pineal (Fig. 4). No melatonin rhythm was observed in the eyes ofAnolis under either 24 h LD cycles and a constant temperature (Fig. 1), or under simultaneous light and temperature cycles (Fig. 3). Ocular melatonin content was, in all cases, either very low or non-detectable.Abbreviations HIOMT hydroxyindole-O-methyltransferase - NAT N-acetyltransferase     

Circadian oscillators,cell cycles,and singularities: light perturbations of the free-running rhythm of cell division inEuglena

Summary The free-running circadian rhythm of cell division in the algal flagellate,Euglena gracilis (Z) was perturbed by 3-h light signals of varying intensities imposed at different circadian times (CT). Light pulses within the range of 700 to 7,500 lux were found to yield the same strong (Type 0) phase response curve (PRC) comprising both advance and delaye phase shifts as great as 15 h. Dark signals generated a PRC of reduced amplitude with very little, if any, phase advance being observed. Light perturbations of lower intensity, however, elicited quite different responses if applied at a quite specific circadian time: A 40- to 400-lux pulse given at approximately CT 0 (late subjective night) induced total arrhythmicity, and the culture reverted to asynchronous, exponential growth. Different degrees of arryhtmicity were induced by the same low-intensity perturbations (I ^*) given slightly before or after this sensitive phase point (T ^*), but if imposed at other circadian times, they generated normal type 0 phase resetting. The demonstration of the existence of this critical pulse (T ^*,I ^*) provides further evidence that the cell division cycle ofEuglena (and presumably other microorganisms) is regulated by a circadian oscillator and, in particular, by one having limit cycle dynamics.Abbreviations LL continuous illumination - DD continuous darkness - LD light-dark cycle - LD x, y, light-dark cycle comprisingx h of light andy h of dark - t period of a LD cycle - CO circadian oscillator - CR circadian rhythm - period of a freerunning circadian rhythm in constant conditions (taken here to be the time between onsets of cell division in a population of cells - _R phase marker, or phase reference point (here, the onset of the division burst) - phase of the rhythm - change in phase (phase shift) - new phase attained after phase shift - CT circadian time (CT 0 indicates the phase point of a free-running rhythm that has been normalized to 24 h which corresponds to that occurring at the onset of light in aLD:12, 12 reference cycle) - PRC phase response curve (plot of phase shift engendered by a perturbation as a function of the circadian time of its application) - T ^*,I ^*) coordinates of an annihilating (light) stimulus given at a critical circadian time (T ^*, corresponding to the singularity point) and having a critical strength (I ^*) - CDC cell division cycle - average generation (doubling) time of a cell population - average step-size, or factorial increase in cell titer (plateau to plateau) after a phased division burst Dedicated to Prof. Colin S. Pittendrigh on only his 65th birthday     

Photoperiodic control of reproduction in the male lizardAnolis carolinensis

Summary In contrast to the higher vertebrates the photoperiodic time measuring system in the male lizardAnolis carolinensis seems to rely on an hourglass timer which lacks endogenous rhythmicity. This timer appears to measure the absolute length of the light portion of light-dark (LD) cycles. The present study further characterized the nature of theAnolis photoperiodic timer and demonstrated: (1) The gonadal response is quite sensitive to photostimulation. Exposure to as few as three 16 h photoperiods (over a 3 week period) can maintain testicular function in summer anoles whereas exposure to as few as six 16 h photoperiods (over a 3 week period) can elicit maximal testicular development in the fall. (2) The photoperiodic timer does not have to be reset daily by a dark interruption. (3) The dark portion of LD cycles may be involved in a complex fashion in reversing a light-initiated reaction and (4) Comparisons of entrained circadian activity rhythms with testicular responses to various light cycles argue against the participation of a circadian clock in photoperiodic time measurement.Abbreviation CRPP circadian rhythm of photoperiodic photo-sensitivity