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06/02/2021 | Portraits and stories

How long does the present last? Research on biological clocks

Is biological time continuous? And the present measurable? Biologist Monika Stengl explores the inner clock of life. With philosophical added value.

Image: University of Kassel.
Prof. Dr. Monika Stengl.

Satt clicks a dozen metronomes. In this popular physics experiment, the devices are connected by a gently vibrating floor, their tick-tock does not have the same frequency, moreover they are started at different moments - an acoustic mess. But after a short time, the metronomes synchronize, as amazing as it is pleasing to the eye and ear. "A case of self-organization," explains Kassel biology professor Dr. Monika Stengl. "It happens without external intervention, without conscious, deliberate control. It happens by itself." She encounters this principle of self-synchronization of oscillations again and again, in the world of sound, in nature and especially in her work.

Stengl has been researching biological clocks or oscillators of organisms for years. Every living being has a multitude of them - they generate short-term cycles, medium-term and long-term cycles - these oscillations structure life, from the cell division of plants to the evening fatigue of humans to the hibernation of bears. They have not been deciphered. However, the Kassel biologist is certain that self-organization, the oscillation to a common, harmonious frequency in harmony with the rhythms of the environment, plays a decisive role.

Stengl, a native of Upper Bavaria, has been a professor at the University of Kassel since 2007. Since her early days as a scientist, she has been fascinated by how organisms process and transmit stimuli and thereby control themselves and their behavior. More than 20 years ago, she was the first in the world to develop a method of cultivating odor cells of an insect, a moth, in vitro and activating them with pheromones (scents with hormonal effects): The cells of the male hawkmoth, while in the Petri dish, can "smell" the females. To date, her research group is the best internationally that can cultivate insect neurons, and she is also using this method in current research on biological clocks.

It is well known that so-called circadian clocks in our bodies control various daily rhythms in the biological diurnal cycle: The eyes perceive the 24-hour cycle of day and night and report it to the circadian master clock in the brain. This then orchestrates the other clocks in the body and synchronizes our body time with the time of our environment. In our cellular clocks, clock genes are rhythmically read and clock proteins are produced, which decay again within a day. Specialized body clocks produce neuropeptides and hormones to synchronize other body clocks, such as the hormone melatonin, which makes us tired. At night, melatonin levels rise and we fall asleep. Fatigue, hunger, performance, pain sensitivity, cell repair - everything runs synchronized at defined times of day in the daily 24-hour cycle.

But there are other clocks as well. The movement of celestial bodies has been deeply inscribed in nature over the course of evolution and has shaped monthly and annual cycles - every autumn leaf bears witness to this. "An organism that wants to survive has tremendous advantages if it can adjust to, anticipate, the rhythmic changes of nature, changes in temperature, light, ebb and flow, and so on," Stengl explains. In other words, "Our environment is a timer, an oscillator on many time scales. An organism is also a multi-layered oscillator with fast and slow time scales, and it synchronizes its multiple cycles with the environment." Like metronomes. But how does an organism coordinate 24-hour cycles with short-term cycles and long-term loops? To find out, Stengl not only studies olfactory cells, but also eavesdrops on the Madeira cockroach's brain impulses.

Secrets of the cockroach

The laboratory of Stengl's "Animal Physiology" department in Oberzwehren: Bright light and numerous measuring instruments. Not only do the tobacco hawkmoth's olfactory cells work here in their Petri dishes, but the thumb-sized Madeira cockroaches also have an attachment placed on their heads that can measure the impulses of their brains. The Kassel research group has been working with insects for years and has identified a group of neuropeptide-containing neurons in the cockroach brain that form a central internal clock. The basic logic of their clockwork is transferable to our human clock: For example, the brain clock releases numerous neuropeptides as coupling factors at specific times of the day, orchestrating numerous cyclical processes in the body. If certain neuropeptides are missing, then the organism, whether human or cockroach, can neither build up a sense of time nor sleep and eat regularly. Numerous diseases and mental disorders are based on a disturbance or desynchronization of our body clocks.

What the Kassel biologist is currently particularly interested in: How exactly do these clock neuropeptides synchronize other neuronal clocks, how are these chemical signals in the cell translated into electrical impulses for the brain, which ultimately works on this electrical basis? What is clear is that the cell membrane transcribes chemical information into electrical impulses. But is there perhaps an additional code in this translation? "There is some evidence to suggest that the membrane itself is also an oscillator, that it oscillates in certain fast and slow beats and thus simultaneously represents the link between the circadian clock and various fast clocks in the body," Stengl suspects. Together with numerous colleagues from other disciplines in Kassel, she has submitted an application for a DFG Research Training Group that aims to clarify these and other questions. In doing so, the researchers can build on the results of a project that the university launched five years ago using its own funds to promote promising research clusters.
The results should help to understand how not only living organisms but also entire ecological systems synchronize, and ultimately also say something about us as humans and social beings: How can we come into harmony with our biology, with our environment? (Stengl: "Mobile phone in bed, eating at inopportune times - we actually do everything to upset our inner clock") What is the significance of music, rhythms, rituals for the synchronization of groups?
Even philosophical questions are touched upon. Ultimately, even our individual body time can be measured and its coupling to the time structure of our environment, the biologist is convinced - not with the second hand of our mechanical watches, but with the electrical oscillations of our brain, with the chemical rhythms in the cells of our body. "Biological time can individually stretch or contract," says Stengl. Present, past, future are created in our brain: "The past, for example, is the physically stored experiences, information in our heads." And the present? The fleeting moment that the senses and brain need to notice and process momentary stimuli. Until they are just stored.

This text appears in the 2021/2 issue of the university magazine publik (June 2021). Author: Sebastian Mense