Fig. 2.
Naloxone effects on ICSS and antagonism of oxycodone (1 mg/kg). (A) Naloxone (1–10 mg/kg) did not produce any effects on ICSS frequency-rate curves; there was no effect of dose (F3, 18 = 2.90, P = 0.06) and no interaction between dose and frequency (F27, 162 = 1.16, P = 0.31). (B) Naloxone did not produce any effects on percent baseline stimulations either (F3, 18 = 1.75, P = 0.19). (C) Administration of naloxone (3 mg/kg) blocks effects on ICSS produced by 1 mg/kg oxycodone. Vehicle plus oxycodone was the only treatment that was significantly different from vehicle plus vehicle; there was no main effect of treatment (F3, 18 = 2.10, P = 0.14), but there was a significant interaction between treatment and frequency (F27, 162 = 2.51, P < 0.001). Significant differences for frequency-rate curves (A and C) are denoted by filled symbols (gray: P < 0.05; black: P < 0.01). All values represent means ± S.E.M., and error bars on frequency-rate curves are omitted for clarity (n = 7). oxy, oxycodone.