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
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
For Most Mice
After the 30-min magnet or sham exposure, mice were placed in an open Plexiglas cage (37 x 47 x 20 cm) with pine-chip bedding in the same room as the magnet and sham– magnet. The locomotor behavior of the mice was video-recorded 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 i) number of rears (with at least one paw touching cage side), ii) latency to rear, iii) tight circling (complete and continuous turns with a diameter no longer than the body of the mouse; clockwise (CW) and counterclockwise (CC) circling were scored separately), or iv) immobility (in Experiment 1; duration of inactivity longer than 10 seconds during which there was no grooming, foraging, or exploratory behavior) by an individual blind to treatment condition. [EDIT FOR SPECIFIC BEHAVIORS]
For EL Mice
(scored by Alison Hood)
Immediately after the 30-min magnet or sham exposure, mice were placed individually in an open Plexiglas cage (37 x 47 x 20 cm) with pince-chip bedding in the same room as the magnet and sham-magnet. Each mouse was videotaped for 10 minutes and then returned to their home cage. Ten minutes was selected because EL mice displayed 5-10 of immobility after a seizure.
The presence and frequency of several behaviors were scored:
- Rearing: latency to rear and number of rears with at least one front paw touching side of cage.
- Circling : number of complete and continuous turns with a diameter no longer than the body of the mouse. Clockwise (CW) and counterclockwise (CC) circling were scored separately.
- Trembling: the occurrence of full or slightly, full body high or low amplitude tremor, most often accompanied by head bobbing and difficulty walking. [DEFINE FULL, SLIGHTLY, & LOW]
- Head bobbing: uncontrolled head movement and weaving [MORE DEFINITION]
- Seizure: occurrence of an epileptic episode involving the entire body characterized by a series of high pitched vocal sounds, muscle rigidity, and the tail extending straight out and flexing rostrally over the body. and then points over the body and muscle rigidy. A seizure is usually followed by reptitive turning of the head from left to right.
- Immobility: duration of inactivity longer than 10 seconds during which there is no grooming, foraging, or exploratory behavior;
- Jumping: number of times the mouse jumps with all paws off the floor while in the “rearing” position.