Effect of time-of-day on the yawning response to apomorphine in normal subjects

The yawning response to the dopamine (DA) receptor agonist apomorphine HCl (Apo, 7 mu g/kg s.c.) and placebo (physiological saline) were examined in t wo groups of normal men. One group (n = 11)was investigated in the morning and the other group (n = 16) in the afternoon. The frequency of yawning was polygraphically monitored for 60 min following injection. Apo increased ya wning compared with placebo when given in the morning (p < 0.02), but not w hen given in the afternoon. Yawning frequency was increased after both Apo (p < 0.01) and placebo (p < 0.025) when given in the morning compared with responses in the afternoon. These results suggest that yawning frequency wi th bath Apo and placebo is influenced by time of day, possibly as a result of diurnal variation in DA receptor sensitivity. Copyright (C) 2000 S. Karg er AG, Baser.