Magnetic field effects on stress-induced analgesia in mice: modulation by light

Exposure of adult male CD-1 mice to restraint stress for 60 min increased their hindpaw-licking latency in a hot-plate test (50 degrees C); this analgesia was significantly reduced after exposure to a stable magnetic field (MF) (30-40 G) under white light. In contrast, MF exposure under either red light or total darkness did not alter stress-induced analgesia. Results suggest that in rodents perception of magnetism might involve a light-dependent mechanism as recently found for migratory birds and amphibians.