Magnetic Compass Orientation in C57BL/6J Mice

Here at Virginia Tech I have been actively involved in developing a behavioural assay to study magnetic compass orientation in laboratory mice (Muheim, Edgar, Sloan & Phillips, Learning and Behavior, in press). In this assay we train C57BL/6J mice to place their nests in a learned magnetic direction and then test their nest-building ability in a radially symmetric, circular arena in one of four magnetic field alignments (magnetic North at geographic North, South, East or West).

Four vertical shelves, each holding three mouse cages stacked on top of each other are centered in the middle of the training room (large square) so that each shelf looks into one of the four magnetic directions, i.e. 70°, 160°, 250° and 340°. The cages are placed into the shelves so that the short side with the house is pointed to the dark middle (inside of the shelves) and the part with the food and water bottle to the lighter outside. This provides a light gradient that encourages the mouse to build its nest at the dark end of the cage.

Mice are tested individually, one per night. Tests begin in the late afternoon (approximately 2-3 hours before the beginning of the dark phase of their light cycle) and end the next morning. Each mouse is tested in one of four magnetic field alignments, with magnetic North at either geographic North, South, East, or West. Before placing a mouse into the arena, the arena floor surrounding the Plexiglas disk is covered with a thin layer of pine shavings. Four pieces of food, four nestlets and four small cups with water are placed symmetrically around the center of the arena.

On average, the mice place their nests relative to the trained magnetic direction, thus they use a magnetic compass to position the nest into the learned magnetic direction. These findings indicate that C57BL/6J mice are capable of goal-directed magnetic compass orientation. The mice learn the direction of the nest box in their training cages and position their nests in the testing arena in this learned direction relative to the magnetic field. An auditory compass assay that our lab has developed in parallel (Edgar et al., submitted) allows us to carry out control experiments to test whether any change in the animals’ behaviour (i.e. no nest building, disorientation) is due to an impairment of the magnetic compass receptor per se or whether it is an effect not related to the magnetoreception pathway.

Current and future projects of the Phillips lab:

• Use of cryptochrome knockouts to study involvement of CRY in the primary magnetoreception mechanism
• Use of radio-frequency EMF to study interference with proposed light-dependent magnetic compass receptor
• Use of early gene expression to localize neural activity involved in transduction and neural processing mechanisms

For more information see the homepage of the Phillips lab!

Last updated: 11/11/2007