Depressive effect of intravenous morphine (3 mg/kg) on the effect of PBil neurons. A, Effect in one individual case. Noxious stimuli (48°C) was applied for 24 secbetween the arrows. 5′,10′, Nalo 5′, Responses 5 and 10 min after morphine and 5 min after naloxone administration.B, Mean effect of morphine in percent of the control response. CTRL, Mean control response of PBil neurons (n = 5). 5′, 10′,Nalo 5′, Mean response of the same neurons 5 and 10 min after morphine and 5 min after naloxone administration.