Wolfgang Engelmann

Different oscillators control the circadian rhythm of eclosion and activity inDrosophila

SummaryPhase shifting and abolishing the circadian oscillation which controls eclosion inDrosophila pseudoobscura does not shorten the life of the flies and does not impair eclosion out of the puparium. However, the activity rhythm of the flies is controlled by a circadian oscillator which differs in period length, sensitivity to light and other features from the one controlling eclosion. Therefore, perturbing the oscillation controlling eclosion does not necessarily imply a corresponding perturbation of the oscillation controlling activity.

A Slowing Down of Circadian Rhythms by Lithium Ions

Abstract Unter the permanent influence of lithium ions the circadian rhythm of movement of Kalanchoe petals is effectively lengthened but a pulse administered up to 12 hours has no influence. Lithium ions could also be demonstrated to similarly slow down the circadian activity rhythm of a small mammal (Meriones crassus). It is hypothesized that the therapeutic effect of lithium salts in endogenous depressions in human beings may result also from its acting on the human circadian system

Circadian rhythm of the locomotor activity in Drosophila melanogaster and its mutants 'sine oculis' and 'small optic lobes'

ABSTRACT. The locomotor activity patterns of wildtype Drosophila melanogaster and the mutants so (sine oculis) and sol (small optic lobes) were investigated. In all strains the proportions showing circadian rhythmicity, arrhythmicity and more complex patterns which could not be thus classified were similar. The occurrence of abnormal activity patterns is thus not a property of the mutation as previously claimed (Mack & Engelmann, 1981). In flies with a distinct circadian rhythmicity, the period lengths (τ) varied between strains, τ for wildtype Italy and the mutant so was longer than for wildtype Berlin and the mutant sol. As different τs have been reported by others, τ does not seem to be closely determined for Drosophila melanogaster. Many flies exhibited two rhythms simultaneously, one with τ shorter and one with τ longer than 24 h, apparently implying two‐oscillator control of the locomotor activity. The eyeless so mutants were entrained by LD cycles, so the compound eyes are not necessary, and so must possess the relevant photoreceptor(s) elsewhere. This may therefore also be true for the wildtype. Histology of the so adults revealed no correlation between the degree of reduction in the medulla and the occurrence of abnormal activity patterns. Since the only structures common to the medulla of so and sol are known to be large tangential cells, it is concluded that either they are of importance for the rhythmic system, or the oscillator(s) controlling locomotor activity is (are) not located in the medulla.

Membrane Models for Circadian Rhythms

Complex systems tend to oscillate, whether they be technical systems like bridges or machines, chemical processes like the Zhabotinsky reaction, or biological systems like organisms or ecosystems. In organisms, rhythmic events are widespread and vary common. For example, the spectrum of rhythmic phenomena in mammals ranges from periods of some milliseconds (nerves) to periods of a day (body temperature), a month (estrous cycle in humans), a year (reproductive cycles in larger mammals), or even longer (rhythmic changes in population density). The daily change of environmental factors such as light and temperature in its 24-h structure has apparently favored those organisms that adapted physiologically to this temporal order. This is just a corollary in the time domain to the structural and functional adaptation of organisms to the environment, and not surprising. We find 24-h rhythms in the mobility or’ bioluminescence of unicellular algae, in the formation of reproductive structures of fungi, in enzyme activities and cell volume changes of plants, and in the nervous activity and sleep-wakefulness pattern of animals, to name just a few.

Influence of Lithium Ions on Human Circadian Rhythms

Abstract Lithium carbonate lengthens the circadian period in humans under temporal isolation (arctic summer four groups.

Circadian activity rhythm of the house fly continues after optic tract severance and lobectomy

Under constant conditions, locomotor activity in about 50% of 63 adult Musca domestica continued to be rhythmic after bilateral severance of optic tracts or bilateral lobectomy. Apparently, the optic lobes of Musca do not contain the oscillator for rhythmic control of locomotor activity as has been proposed for other insects. In 20% of the individuals, several circadian components of activity rhythms were found after operation indicating a role of the optic lobes in the coupling of oscillators. The remaining 30% of the flies with severed optic tracts appeared to be arrhythmic. Most of these flies had vacuolized tissue in the central brain. However, disruption of rhythmicity did not correlate with a common pattern of degeneration. Therefore no conclusions can be drawn as to the localization of the circadian control of locomotor activity in the brain. Flies showing an arrhythmic activity pattern could still be synchronized by LD cycles. Activity did not occur solely during the light period as is the case in controls; but was phase delayed by about 6 hr towards the dark period. Since all flies with severed optic tracts could be synchronized by LD cycles, Musca domestica must possess extraocular photoreceptors.

Effects of cAMP, theophylline, imidazole, and 4-(3,4-dimethoxybenzyl)-2-imidazolidone on the leaf movement rhythm of Trifolium repens—a test of the cAMP-hypothesis of circadian rhythms

The period length of the leaf movement rhythm of Trifolium repens L. is lengthened by continuously offered cAMP (0.5–1.0 mol m-3) and theophylline (0.5–4 mol m-3). At the higher concentrations this effect is more pronounced and the rhythm damps out faster. Imidazole (0.5 and 1 mol m-3) has no effect on the period length; however, after 5 mol m-3 the rhythm is abolished. Offered as 4 h pulses the resulting phase response curves for cAMP and imidazole are similar and show delays of up to 4 h during the day position of the leaves. Theophylline pulses lead to delays of up to 5 h during closure and advances of up to 3 h during opening. No phase shift is brought about by 4-(3,4-dimethoxybenzyl)-2-imidazolidone. The results do not support the cAMP-model of the circadian clock which has been proposed by Cummings (J. theor. Biol. 55, 455–470; 1975). The effect of the substances tested could, however, be based upon influences on the transport of Ca2+.

Evidences for circadian rhythmicity in the per0 mutant of Drosophila melanogaster

per° Mutants of Drosophila melanogaster which are exposed to light-dark cycles (LD) with different Zeitgeber period (T) have a limited range of entrainment. Entrained flies show a characteristic phase relationship of activity to the LD which depends on the period of the driving cycle as expected by oscillator theory. Both facts are taken as evidence that per° possesses endogenous oscillators and that the per gene product is not concerned with central clock structures but rather might be responsible for the mutual coupling between the individual oscillators in a multioscillatory system controlling locomotor activity.

Further Evidence for Period Lengthening Effect of Li+ on Circadian Rhythms

The period length of the activity rhythm of the cockroach Leucophaea maderae is increased by LiCl solution of 100 mol m-3 offered as drinking water by about 1%.

Leaf Movement Rhythm In Arabidopsis Thaliana

A circadian rhythm of leaf movements of Arabidopsis thaliana and its recording in continuous weak light with a video-computer system is described