Orientation within a high magnetic field determines swimming direction and laterality of c-Fos induction in mice

Abstract

High-strength static magnetic fields (>7 tesla) perturb the vestibular system causing dizziness, nystagmus, and nausea in humans; and head motion, locomotor circling, conditioned taste aversion, and c-Fos induction in brain stem vestibular nuclei in rodents. To determine the role of head orientation, mice were exposed for 15 min within a 14.1-tesla magnet at six different angles (mice oriented parallel to the field with the head toward B+ at 0°; or pitched rostrally down at 45°, 90°, 90° sideways, 135°, and 180°), followed by a 2-min swimming test. Additional mice were exposed at 0°, 90°, and 180° and processed for c-Fos immunohistochemistry. Magnetic field exposure induced circular swimming that was maximal at 0° and 180° but attenuated at 45° and 135°. Mice exposed at 0° and 45° swam counterclockwise, whereas mice exposed at 135° and 180° swam clockwise. Mice exposed at 90° (with their rostral-caudal axis perpendicular to the magnetic field) did not swim differently than controls. In parallel, exposure at 0° and 180° induced c-Fos in vestibular nuclei with left-right asymmetries that were reversed at 0° vs. 180°. No significant c-Fos was induced after 90° exposure. Thus, the optimal orientation for magnetic field effects is the rostral-caudal axis parallel to the field, such that the horizontal canal and utricle are also parallel to the field. These results have mechanistic implications for modeling magnetic field interactions with the vestibular apparatus of the inner ear (e.g., the model of Roberts et al. of an induced Lorenz force causing horizontal canal cupula deflection).

Vestibular stimulation by magnetic fields

“…Additional studies suggested an intact labyrinth was critical for these behavioral responses, that responses depended on static magnetic field and not the field gradient, that effects scaled with magnetic field strength, and that after‐effects were present only after prolonged exposures . Most recently, mice exposed to strong magnetic fields at different pitch angles demonstrated null positions, that is, where no circling or c‐Fos activation was observed, consistent with our human data demonstrating null positions where no nystagmus is observed . Interestingly, Houpt et al .…”

Optogenetic fMRI interrogation of brain-wide central vestibular pathways

“…It is worth noting that the bulk of literature on the effects of a static magnetic field on the vestibular system discussed above were studies of humans, but not animals. Although there are studies performed on rodents that showed physiological effects of high-field MRI scanners on the animal behavior (65, 66), there is a limited understanding of the large-scale effects of magnetic fields on the vestibular system. Indeed, these physiological effects can be complex, and more in-depth investigations to localize and identify the effects of a static magnetic field on the central nervous system during fMRI are desired in the future.…”

Effect of head pitch and roll orientations on magnetically induced vertigo

“…; Houpt et al . ), the head is rotated relative to a fixed magnetic field. This involves changes in the direction of gravity relative to the head, and thus altered tonic stimulation of the otoliths by gravity.…”

“…) and locomotor circling in rodents (Houpt et al . ) is modulated by orientation of the head in the magnetic field. In the current study, we examine the influence of head pitch (rotation about head medio‐lateral axis) and head roll (rotation about head antero‐posterior axis) orientations on the vertigo produced when exposed to a strong magnetic field.…”