For the brain to work efficiently, nerve impulses must reach their destination as quickly and precisely as possible. The nerve fibres, also known as axons, pass on the impulses, and an insulating sheath around the axons increases their speed of conduction in vertebrates. This insulating sheath, called myelin, is formed by a major component of the brain – the glial cells. Researchers at the University of Münster, in collaboration with colleagues at the University of Bonn, have now discovered that glial cells not only influence the speed of nerve conduction, but also the precision of signal transduction. In the absence of these insulating sheaths, short-circuit-like processes occur. The study has been published in the journal “Nature Communications”.

Glial cells are not only indispensable for providing energy – they also have a broad range of other tasks in the brain. They are responsible for transport of metabolite and xenobiotics, regulating fluid exchanges, and maintaining ion homeostasis. In order to better understand the importance of glial cells for neuronal signalling, the researchers studied changes in behaviour after the induced activation of individual neurones in fruit flies (Drosophila melanogaster). “For this purpose we either removed individual glial cells from the nervous system or specifically disturbed their development concomitant to a light-induced, optogenetic, neuronal activation,” says lead author Prof. Christian Klämbt from the Institute of Neuro- and Behavioural Biology at Münster University. As a result of these activities, the researchers were first able to ascertain that glial cells control the radial growth of the axons.

Analysis of the movement behavior of fruit flies

In order to determine the performance of the axons, Dr. Andreas Schoofs from the research group of Prof. Michael Pankratz at the LIMES Institute at the University of Bonn carried out electrophysiological measurements. The researchers found, that axons without wrapping glia cells have, as expected, a slower conduction speed. Astonishingly, it became apparent that the changes in movement behavior are caused only to a minor degree by a slower conduction speed. The more important contribution made here by glial cells is the formation of membrane processes between individual axons – which prevents electrical coupling (i.e. short circuits) and thus makes a decisive contribution to the precision of neuronal signalling.

The researchers undertook a detailed analysis of larval locomotion by means of a special custom made device. The development of the so-called FIM (Frustrated total internal reflection-based Imaging Method), together with self-developed software, allows a high-resolution depiction and analysis of movements made by even minute organisms.

The function of glial cells as active modulators of the speed and, in particular, the precision of stimulus conduction, has not previously been described. “What our research makes clear is the role played by glial cells as active components in the nervous system,” says Christian Klämbt. “With these new findings we are creating a basis for a better understanding of some of the symptoms of diseases of the nervous system.” These include Multiple Sclerosis and Morbus Charcot-Marie-Tooth.

The research work was funded by the German Research Foundation (DFG).

Publication: Kottmeier, R., Bittern, J., Schoofs, A., Scheiwe, F., Matzat, T., Pankratz, M., Klämbt, C. (2020): Wrapping glia regulates neuronal signaling speed and precision in the peripheral nervous system of Drosophila. Nature Communications; doi.org/10.1038/s41467-020-18291-1