Figure 4.

Time course of the effects of 1 μg kg⁻¹ sufentanil on the C-fibre responses (A) and on the tonic inter-stimulus discharges (B) in sham-operated and obex-transected animals. Presentation as in Figure 2. In sham-operated animals the depressive (Aa) and facilitatory effects (Ba) of 1 μg kg⁻¹ sufentanil were similar to that seen in intact rats (Figure 2). In obex-transected animals the sufentanil-induced depression increased (Ab) and the tonic inter-stimulus discharges (Bb) seen in sham-operated rats were never observed. In obex-transected animals the prior administration of 10 mg kg⁻¹ (+)-HA966 (Ac) potentiated and prolonged the depressive effect of 1 μg kg⁻¹ sufentanil.