Fig 1.

Morphine pretreatment produced dose-, time- and frequency-dependent changes in ICSS. Horizonal axes: Frequency of electrical brain stimulation in hertz (log scale). Vertical axes: ICSS rate expressed as percent maximum control rate (%MCR). Each panel shows ICSS frequency-rate curves determined before (Baseline) or at various times after (10-300 min) treatment with vehicle or morphine (1.0-10 mg/kg). Filled symbols indicate frequencies at which ICSS rates were significantly lower or higher than baseline as determined by the Holm-Sidak post hoc test following a significant analysis of variance (p<0.05). ANOVA results were as follows: Vehicle: significant main effect of frequency [F(9,45)=44.0; p<0.001], significant main effect of time [F(4,20)=3.5; p=0.025], no significant frequency×time interaction [F(36,180)=1.4; NS]; 1 mg/kg morphine: significant main effect of frequency [F(9,45)=148.0; p<0.001], no significant main effect of time [F(4,20)=1.6; NS], significant frequency×time interaction [F(36,180)=3.0; p<0.001]; 3.2 mg/kg morphine: significant main effect of frequency [F(9,45)=98.7; p<0.001], significant main effect of time [F(4,20)=3.9; p<0.02], significant frequency×time interaction [F(36,180)=2.5; p<0.001]; 5.6 mg/kg morphine: significant main effect of frequency [F(9,45)=88.1; p<0.001], significant main effect of time [F(4,20)=4.2; p<0.02], significant frequency×time interaction [F(36,180)=4.0; p<0.001]; 10 mg/kg : significant main effect of frequency [F(9,45)=45.4; p<0.001], significant main effect of time [F(4,20)=4.0; p<0.02], significant frequency×time interaction [F(36,180)=9.0; p<0.001]. All points show mean data for 6 rats, and error bars are omitted for clarity.