Absence of the Earths magnetic field activates stress-related brain circuits in a mammal

The Earth's magnetic field acts as a constant cue for animals that possess a magnetic sense. This phenomenon is most extensively observed in migratory birds, though some mammals also exhibit magnetic navigation capabilities. African mole-rats, specifically those belonging to the Fukomys genus, have been extensively studied due to their unique subterranean lifestyle and the intricate kilometer-long tunnel systems they navigate.

However, the precise neural pathways associated with magnetoreception in these creatures remain largely unexplored. In an effort to shed light on this subject, researchers conducted an unbiased whole-brain screening for magnetic-induced neuronal activity within the mole-rat brain. They developed a novel experimental pipeline named MoBI-DisC (Mole-rat Brain Imaging with iDISCO and ClearMap), which integrated global c-Fos immunolabelling, tissue clearing, light-sheet microscopy, and mapping onto a 3D brain atlas.

The study involved exposing mole-rats to a fluctuating magnetic field and comparing their brain activity to that of control animals subjected to a near-zero magnetic field. A surprising finding was that the near-zero magnetic field exposure triggered activity in numerous brain regions, with a notable emphasis on those related to stress and anxiety responses.

These areas encompassed the amygdala, the bed nucleus of the stria terminalis, the substantia innominata, and the periaqueductal grey. This discovery suggests that magnetic field deprivation functions as a physiological stressor for mole-rats. To further validate this hypothesis, researchers conducted a place-preference test, which revealed that mole-rats actively avoid entering a zone with a near-zero magnetic field.

This avoidance behavior aligns with the notion that this particular condition is not neutral for these animals. Overall, this research presents a groundbreaking pipeline for unbiased mapping of neural activity in subterranean mole-rats, while simultaneously providing compelling evidence of stress and avoidance responses triggered by the absence of an Earth-strength magnetic field.