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Biomedical subjects

W Engelmann

Publications and source records attributed to W Engelmann.

At least 19 recordsLinked to original sources
PubMed1999

Circumnutations without gravity: a two-oscillator model.

Helical growth movements termed circumnutations occur in a number of different plant organs. The underlying mechanism are complicated. They consist of an endogenous as well as an erogenous component. Since circumnutations in sunflower hypocotyls occur also under gravity free conditions in Space, gravity is not necessary for them to arise. However, the changes of period and amplitude of circumnutations with the applied gravitational force indicate that gravity plays a modifying role. Models for circumnutations have to take these features into account. It seems natural to study minimum models with at least two oscillating units. Two-oscillator models for circumnutations have already been discussed. We have studied the interaction between two coupled oscillatory units. With this model we could simulate movements of hypocotyls. The results of simulations were compared with experimentally recorded movements of the Arabidopsis hypocotyl.

Arabidopsis↗
PubMed1998

Ultradian rhythms in Desmodium.

The leaves of Desmodium gyrans (L.F.) DC show circadian movements in the terminal and ultradian movements of the lateral leaflets. The movements are due to swelling and shrinking of motor cells in special organs. The anatomy of these pulvini is described for the lateral leaflets. Data from electrophysiological recordings using microelectrodes inserted into the lateral pulvini, together with treatments that affect the proton pumps and ion channels, have been used to develop a physiological model of the ultradian leaflet movement. It explains the oscillations in the motor cells as being due to a change between a pump state and depolarization. During the pump state, ions are taken up, causing water influx and swelling of the motor cells. Depolarization causes loss of ions and water efflux (the motor cells shrink). The roles of calcium and the phosphatidyl inositol signal chain are discussed on the basis of experiments using chemical agents that affect these processes. Since calcium oscillations are known to occur in organisms in both time and space, an attempt has been made to simulate the situation in Desmodium pulvini by a model of specially coupled oscillators. Effects of different other treatments of the lateral pulvini are discussed. Oscillations in the minute range seem to be more common and some might be related to turgor regulation and ion uptake comparable to the situation in Desmodium. The ultradian control of the lateral pulvini and the circadian control of the terminal pulvini are apparently based on different mechanisms.

Activity Cycles↗
PubMed1996

Circadian locomotor activity of Musca flies: recording method and effects of 10 Hz square-wave electric fields.

Musca domestica flies that were exposed to a uniform vertical 10 Hz electric square-wave field of 1 kVm(-1) changed the period length of their circadian locomotor activity rhythm. Under constant conditions, the clock of short-period flies was slowed down by the field, whereas the clock of long-period flies either was affected only scarcely (experiments at about 19 degrees C) or ran faster (experiments at 25 degrees C). If the field was applied for only 12 h daily, then 30-40 percent of the flies were synchronized. Thus, the field could function as a weak "Zeitgeber" (synchronizer). If the field was increased to 10 kVm(-1), then 50-70 percent of the flies were synchronized. Flies avoided becoming active around the onset of the 12 h period of exposure to a 10 Hz field. The results of these experiments are discussed with respect to similar experiments by Wever on the effects of exposure to a 10 Hz field on the circadian system of man.

Animals↗
PubMed1992

Effects of tetraethylammoniumchloride (TEA), vanadate, and alkali ions on the lateral leaflet movement rhythm of Desmodium motorium (Houtt.) Merr.

The period (approximately 3-5 min) of the ultradian rhythm of the lateral leaflet movement of Desmodium motorium is strongly lengthened (less than or equal to 30-40%) by the K+ channel blocker tetraethylammoniumchloride (20, 30, and 40 mM) and vanadate (0.5 and 1 mM), which is an effective inhibitor of the plasma membrane-bound H+ pump. The alkali ions K+, Na+, Rb+, and Cs+ (10-40 mM) shorten the period only slightly (less than or equal to 10-15%). Li+ (5-30 mM), however, increases the period of the leaflet rhythm drastically (less than or equal to 80%). We concluded that the plasmalemma-H(+)-ATPase-driven K+ transport through K+ channels is an essential component of the ultradian oscillator of Desmodium, as has been proposed for the circadian oscillator.

Activity Cycles↗
PubMed1990

Localization of the circadian pacemakers of Hemideina thoracica (Orthoptera; Stenopelmatidae).

The location of the circadian pacemakers of the orthopteran Hemideina thoracica (White) has been investigated through observation of the effects of surgical removal of brain tissues (principally optic lobes and tracts) on free-running and entrained locomotor rhythms. Bilobectomy and severance of optic tracts invariably resulted in arrhythmicity, whereas rhythmicity was sustained following unilateral lobectomy, generally with increases in the free-running period (FRP) and decreases in both the active-phase lengths and activity-to-rest ratios of the rhythm. Bilobectomized subjects could be entrained by temperature cycles, but exhibited no transients or residual rhythmicity, indicating that temperature brought about a direct response or masking effect. These results support the hypothesis that the circadian locomotor pacemakers of Hemideina are located within each optic lobe, and that there are no extraoptic centers for the control of the timing of locomotor activity. Although confirmation of the pacemaker role of the optic lobes requires transplantation of the tissues, the conclusion may be drawn by inference from other studies (e.g., Leucophaea maderae--Page, 1983; Gryllus bimaculatus--Tomioka and Chiba, 1986). Light entrainment continued after surgical binding and blackening of the compound eyes and ocelli, supporting the view that direct illumination of neural tissue through the cuticle may be one possible pathway for light entrainment.

Animals↗
PubMed1987

Chronobiology of lithium--studies on healthy, middle-aged women.

3 women aged 37, 44 and 53 years were examined in a long term study (4-5 months) with and without lithium carbonate medication. The subjective condition and complaints of the subjects were recorded. The body temperature was measured each night with a rectal probe and the data analysed using TIMESDIA-program. During the lithium medication, deterioration in the subjects well-being, and somatic disturbances can occur. At the same time variations in the circadian course of the body temperature were demonstrated. In addition to the 24-hour period, longer and shorter periods appear. Based on a chronobiological model a possible dissociation of the oscillator controlling body temperature is suggested.

Adult↗
PubMed1985

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.

Animals↗
PubMed1983

Effect of a putative antidepressant, Rolipram, on the circadian running wheel activity of a day-active chipmunk, Eutamias sibiricus.

Siberian chipmunks (Eutamias sibiricus) were kept individually in small cages attached to a running wheel. Under continuous illumination of two different light intensities (0.4-0.9 lux and 400-1200 lux) the influence of Rolipram, a putative new antidepressant, on the period length tau was tested. Under both conditions Rolipram caused a lengthening of tau, a decrease of activity time alpha and an increase of rest time delta, resulting in a decrease of the alpha/delta ratio. These effects of Rolipram could be due to a slowing down of the circadian oscillatory system or an influence on the sensitivity towards light.

Animals↗
PubMed1983

Period lengthening of human circadian rhythms by lithium carbonate, a prophylactic for depressive disorders.

The effect of lithium carbonate on the circadian system of man was studied. Four out of eight volunteers living without time cues in isolated huts in the arctic showed a lengthening of the periods of the body temperature rhythm, activity rhythm, and sleep/wakefulness rhythm by c. 1 h. Four of the participants did not show a change in the periods between the placebo and lithium ingestion phases. Two subjects who did not receive lithium salt showed internal desynchronization between the temperature rhythm and the sleep/wakefulness rhythm. Extreme isolation in bunkers is not necessary to allow free running of the circadian system in man. The sleep/wakefulness rhythm, which is very easy to record, was a reliable indicator of the circadian system in the internally-synchronized state.

Antidepressive Agents↗
PubMed1982

Circadian course of body temperature and the excretion of MHPG and VMA in a patient with bipolar depression.

A 38-year old woman with a bipolar affective disorder was examined for 10 days during a serious retarded depression phase and for 10 days during the subsequent symptom -free interval. During depression the MHPG-excretion showed a significantly shorter circadian periodicity of 20.5 hours, whereas the periodicity of body temperature and VMA amounted to 24 hours. During the symptom-free interval the circadian periodicity of all parameters was 24 hours. These results indicated that the depression phase of a bipolar affective disorder in this patient is related to a desynchronization of central NA function with peripheral NA activity and body temperature.

Adult↗
PubMed1979

Effect of lithium carbonate on circadian periodicity in humans.

Five groups of two volunteers lived during four weeks under arctic summer conditions (Spitsbergen) isolated in huts, without time information. They received lithium carbonate or placebo. All showed free-run of their circadian temperature and activity/rest rhythms with periods longer than 24 hours. Under lithium carbonate, a period-lengthening effect can be shown. This could help to understand theprophylactic effect of lithium salts in manic-depressive episodes.

Body Temperature↗
PubMed1976

[The effects of lithium ions on circadian rhythms (author's transl)].

Lithium ions lengthen the critical dark period in short-day plants, increase the period length of circadian rhythms in Kalanchoe plants, in the rodent Meriones and influence the activity rhythm of birds. In the case of the Kalanchoe rhythm, mainly the process of the petal opening is affected.

Animals↗