Mouse Magnet Methods

Template text for describing magnetic-field exposure and behavioral scoring of mice in high strength static magnetic field.

The reference for citation is: Lockwood, D.R.; Kwon, B.S.; Smith, J.C.; Houpt, T.A. (2003) Behavioral effects of static high magnetic fields on unrestrained and restrained mice. Physiol. Behav. 78 : 635-40, PMID 12782218 [PDF file]

Restrained

Apparatus used to contain mice during exposures. Mice were either restrained (left) or allowed to move more freely (unrestrained) (right) during the 30-min magnet or sham exposure. Two mice were exposed at the same time in each treatment condition.

Mice in the restrained magnet-exposed group, were restrained by placing them in a plastic tube made from a 50 ml conical cylinder, with the head of the mouse positioned at the cone end. A hole in the tip of the cone allowed for breathing. A plastic plug with a hole to allow for the tail of the mouse at the caudal end of the tube restrained the mouse from moving. Two restrained mice in these tubes were fitted into a plastic collar that was inserted vertically into the bore of the magnet and exposed to the 14.1-T magnetic field.

Unrestrained (Freely-Moving)

Unrestrained magnet-exposed mice in the second group were individually placed into plastic cups with lids, approximately 11.5 cm in length and 7.0 cm in diameter. Two cups were then stacked on top of one another to be inserted vertically into the magnet. The mice were inserted into the bore so that in the restrained condition the mouse heads were at the center of the magnetic field and in the unrestrained condition the center of the field was placed equidistant from the bottom of each cup where the mouse would sit. Because the magnetic field is homogeneous at 14.1 T within 15 cm of the center, mice in both restrained and unrestrained groups would experience equivalent field exposures.

Sham Controls

As sham controls, mice were either restrained or placed in cups then were placed into an opaque PVC tube with the same diameter as the inside of the magnet bore and in the same room to control for light, sound and temperature. The sham-magnet tube was placed beyond the 5 G line, and pairs of either restrained or unrestrained sham control mice were run at the same time as matched restrained or unrestrained magnet-exposed mice.

Scoring Locomotor Activity

After the 30-min magnet or sham exposure, mice were placed in an open Plexiglas cage (37 x 47 x 20 cm) with cob bedding in the same room as the magnet and sham– magnet. The locomotor behavior of the mice was video-recored for 2 min and the mice were then returned to their home cages in the animal facility room. Two minutes was chosen because in previous experiments almost all circling behavior ends within 2 min. Behavior was scored for number of rears (with at least one paw touching cage side) or tight circling (complete turns with a diameter no longer than the body of the mouse) by an individual blind to treatment condition.