The Neurobiology of Magnetic Orientation in Mammals

ongoing

Many animals use the Earth’s magnetic field for orientation, but the sensory cells and molecular mechanisms of the magnetic sense remain a mystery. I propose to tackle this fundamental problem in sensory biology with a top-down approach that exploits state-of-the-art methodology to unravel the neural circuits underlying magnetic orientation. To take advantage of the knowledge and toolkits available for rodent brains I chose a rodent model organism: Mole-rats, which navigate through a maze of underground tunnels for their entire life in total darkness. Their magnetic sense is well established and they can be bred in the laboratory. My project has three ambitious aims: (1) the identification of brain regions that process magnetic stimuli, (2) the discovery of the primary receptor cells, and (3) the characterization of magnetic inputs into head direction cells. Aim 1: Modern tissue clearing techniques allow rendering brains transparent to analyse them in toto. We couple iDISCO brain clearing with the detection of immediate early genes to create a global map of the mole-rat brain regions that process magnetic fields. Aim 2: We make use of the circuitry discovered in Aim 1 to deduce the locus of the magnetoreceptors. Combining neuronal tracing with high-sensitivity imaging methods to detect of magnetite, we will meticulously search for the magnetoreceptors in peripheral tissues. Aim 3: We will establish the first single-unit recordings in freely moving mole-rats. How do head direction (HD) cells function in an animal without access to visual landmarks? My hypothesis is that the HD signal in the mole-rat brain encodes magnetic directions. We will test this by recording from brain areas identified in Aim 1 under different magnetic conditions. Can we discover the first mammal magnetic compass neurons? This project employs a systematic neurobiological approach that will fundamentally advance our understanding of the neuronal substrates of the magnetic sense.