Head tilt in rats during exposure to a high magnetic field.

During exposure to high strength static magnetic fields, humans report vestibular symptoms such as vertigo, apparent motion, and nausea. Rodents also show signs of vestibular perturbation after magnetic field exposure at 7 tesla (T) and above, such as locomotor circling, activation of vestibular nuclei, and acquisition of conditioned taste aversions. We hypothesized that the acute effects of the magnetic field might be seen as changes in head position during exposure within the magnet. Using a yoked restraint tube that allowed movement of the head and neck, we found that rats showed an immediate and persistent deviation of the head during exposure to a static 14.1 T magnetic field. The direction of the head tilt was dependent on the orientation of the rat in the magnetic field (B), such that rats oriented head-up (snout towards B+) showed a rightward tilt of the head, while rats oriented head-down (snout towards B-) showed a leftward tilt of the head. The tilt of the head during magnet exposure was opposite to the direction of locomotor circling immediately after exposure observed previously. Rats exposed in the yoked restraint tube showed significantly more locomotor circling compared to rats exposed with the head restrained. There was little difference in CTA magnitude or extinction rate, however. The deviation of the head was seen when the rats were motionless within the homogenous static field; movement through the field or exposure to the steep gradients of the field was not necessary to elicit the apparent vestibulo-collic reflex.