Figure 6.

WAY-100635 enhanced the effect of systemic fentanyl. (a) Arrows indicate injection of WAY-100635 (0.3 mg kg⁻¹, s.c.) at t=−0.5 h and fentanyl (0.2 mg kg⁻¹, s.c.) 30 min later (t=0). The effect of WAY-100635 followed by fentanyl was compared to control groups injected with WAY-100635 followed by vehicle (1 ml kg⁻¹; 0.9% NaCl) or vehicle followed by fentanyl. The dashed line indicates the sum of the increases for the two control groups (WAY-100635+vehicle and vehicle+fentanyl). The increase in 5-HT was significantly greater in rats treated with WAY-100635 followed by fentanyl compared to WAY-100635+vehicle (F_(1,12)=9.016, ^aP=0.01, p<0.05 ) and compared to vehicle+fentanyl (F_(1,10)=11.982, P=0.0061, ^bp<0.05). (b) Calculated AUC values during the first, second and third hour after fentanyl injection. In the first hour, the AUC value for the effect of fentanyl following WAY-100635 pretreatment (open bar; WAY+fentanyl) is greater than the AUC value shown by the height of the stacked bar, which represents the sum of the effects of WAY-100635 alone and fentanyl alone (horizontal striped bar; WAY+vehicle; obliquely striped bar; vehicle+fentanyl). For the second and third hours, AUC values for the WAY+fentanyl group were equivalent to the sum of the effects of the two control groups.