Behavioral effects on rats of motion within a high static magnetic field

Abstract

Some human subjects report vestibular disturbances such as vertigo, apparent motion, and nausea around or within high strength MRI systems operating at 4 T to 9.4 T. These vestibular effects have been ascribed to the consequences of movement through the high magnetic field. We have previously found that exposure to magnetic fields above 7 T suppresses rearing, causes locomotor circling, and induces conditioned taste aversion (CTA) in rodents. The present experiments were designed to test the effects on rats of motion through the magnetic field of the 14.1 T superconducting magnet. In experiment 1, we compared the effects of multiple rapid insertions and removals from the center of the magnet to the effects of continuous exposure. Repeated traversal of the magnetic field gradient with only momentary exposure to 14.1 T was sufficient to suppress rearing and induce a significant CTA. Repeated insertion and removal from the magnet, however, did not have a greater effect than a single 30-min exposure on either acute locomotor behavior or CTA acquisition. Prolonged exposure was required to induce locomotor circling. In the second series of experiments, we controlled the rate of insertion and removal by means of an electric motor. Locomotor circling appeared to be dependent on the speed of insertion and removal, but the suppression of rearing and the acquisition of CTA were independent of speed of insertion and removal. In experiment 3, we inserted rats into the center of the magnet and then rotated them about their rostral-caudal axis during a 30-min 14.1 T exposure. Rotation within the magnet did not modulate the behavioral effects of exposure. We conclude that, in rats, movement through the steep gradient of a high magnetic field has some behavioral effects, but sustained exposure to the homogenous center of the field is required for the full behavioral consequences.

Head tilt in rats during exposure to a high magnetic field

“…Rather, rats must be exposed to the static field at the center of the magnet for several minutes to observe maximal locomotor circling or CTA [14, 40]. The present results are consistent with these parameters.…”

“…In rats, we have found that movement into and out of the 14.1 magnet cannot account for the entire response of the animal [40]. Rather, rats must be exposed to the static field at the center of the magnet for several minutes to observe maximal locomotor circling or CTA [14, 40].…”

Exposure to MRI-related magnetic fields and vertigo in MRI workers

“…This finding might therefore imply that, in addition to the exposure intensity, the total time a worker is exposed to motion-induced TVMF during a full workday also plays a role in the underlying physiological mechanism of MRI-induced vertigo. Studies on rats exposed to a 14.1 T superconducting magnet revealed that magnetic-field-induced circling behaviour was only displayed after at least 5 min of exposure and not at shorter durations 21 22. This suggests a potential effect of duration of magnetic field exposure on vestibular effects among rats.…”

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

“…It is a logical possibility that the vestibular system is more activated by the release from stimulation when removed from the magnet than it is by the exposure itself (or indeed the vestibular system might be more activated by the transition from the high magnetic field back to ambient conditions). However, the behavioral effects are largely correlated with duration of exposure, not with movement in and out of the magnet (12,16). However, the release from stimulation upon removal from the magnet would seem to be concomitant with any discrete period of stimulation within the magnet, and so may not be separable.…”