The Max Planck Research Group Neurobiology of Magnetoreception studies the neuronal pathways involved in magnetic orientation in mammals. Which brain regions process magnetic information? How are the different parameters of the Earth's magnetic field encoded? Where and to which degree is magnetic information integrated with other senses? Ultimately, we hope that knowledge on the central neuronal networks of the magnetic sense will reveal the location and nature of the primary receptors cells, the magnetoreceptors. So far, these have not been identified in any species.
We hope that our work will gain insights into the neuronal machinery that enables mammals to detect magnetic fields. An understanding of how mammals detect weak magnetic fields promises advances in the auspicious field of magnetogenetics and provides the missing mechanistical basis to assess and predict effects of man-made electromagnetic fields on vertebrates. For example, electromagnetic fields from power lines have been suggested as a potential cause of human circadian rhythm disorders and even cancer, but such claims lack any mechanistical basis. Our work also aims to get us into a better position to judge the detrimental effects of man-made magnetic fields on mammals.
We use African mole-rats of the genus Fukomys as a model system. These animals are strictly subterranean, spending their entire lives in underground tunnel systems. Evolutionary adaptations to the underground environment have equipped them with the ability to build and navigate kilometre long and highly complex tunnel systems in absolute darkness. It is therefore not surprising that they have magnetic compass sense. In fact, they were the first mammals for which a magnetic sense was demonstrated and independently confirmed (Burda et al. 1990, Němec et al. 2001).
Mapping of magnetically induced brain activity in rodents
Here, we aim to map the neural circuits involved in magnetic orientation by means of whole brain activity mapping after magnetic stimulation. We make use of immediate early genes as a surrogate marker of neuronal activity, which we can automatically quantify in the whole brain with the iDISCO+ clearing technique (Renier et al. 2016) coupled with lightsheet-microscopy (see video of a cleared mole-rat brain in a lightsheet-microscope). We intend to reveal the primary sensory tissue by retrograde tracing starting from brain regions that process magnetic stimuli. As the magnetoreceptors of mole-rats are likely to contain the iron-oxide magnetite, we screen the target tissue with a variety of modern histological techniques (Electron microscopy, Synchrotron-XRF, etc.).
Neuronal processing of magnetic cues
In this project, our goal is to characterize how the brain processes magnetic stimuli. To this end we perform single-unit electrophysiological recordings in freely moving mole-rats. Recording from brain regions that have been identified in project 1 we are adressing how magnetic information is represented in the mole-rat navigation circuit. Do magnetic head direction cells exist? How are different cues integrated in the mole-rat navigation circuit?
The magnetic sense of planarians
In this project, co-funded by the DFG and ANR, we explore the magnetic sense of flatworms in collaboration with Hervè Cadiou. Hervé found that planarians use the Earth's magnetic field for orientation and that they have a light-independent, diurnal periodic inclination compass. Since these invertebrates do not express cryptochromes and they are also very easy to reproduce (clone), the animals are very well suited as a model organism to study the mechanisms of magnetic sense. In order to shed light on the molecular mechanisms of the magnetic sense of these animals, we carry out a series of behavioural, physiological and histological experiments. We pay particular attention to the magnetite and induction hypotheses of magnetoreception with the main objectives of identifying and characterising magnetite-containing cells (if present) and the behavioural and molecular characterisation of the electrical sense of the planarians.
Burda, H.S., Marhold, T., Westenberger, R., Wiltschko, W. 1990. Magnetic compass orientation in the subterranean rodent Cryptomys hottentotus. Experientia 46, 528–530.
Němec, P., Altmann, J., Marhold, S., Burda, H., Oelschläger, H.H.A. 2001. Neuroanatomy of magnetoreception: The superior colliculus involved in magnetic orientation in a mammal. Science 294, 366-368.
Renier, N., Adams, E.L., Kirst, C., Wu, Z., Azevedo, R., Kohl, J., Autry, A.E., Kadiri, L., Venkataraju, K.U., Zhou, Y., Wang, V.X., Tang, C.Y., Olsen, O., Dulac, C., Osten, P., Tessier-Lavigne, M. 2016. Mapping of brain activity by automated volume analysis of immediate early genes. Cell 165, 1789-1802.