Circadian rhythm of pain in male mice.

1. Circadian rhythm of pain in response to the thermal stimuli was assessed in male mice. 2. The hot-plate method was used. Response latencies were measured every 2 hours and showed a sinusoidal rhythm. 3. Minimal latencies were observed at 10 and 20 h, the highest were obtained at 12 and 4 hours. 4. The circadian changes in pain sensitivity may play an important role in many experiments on stress and post-stress analgesia as well as on susceptibility to pharmacological agents.