Fig. 3.  Effects of spinal nerve ligation (SNL) on morphine facilitation of electrical stimulation of the ventral tegmental area for drug-incubation times of 15 (A ) and 60 min (B ). Reduction in EF⁵⁰(frequency at which rats emitted 50% of maximal responding) was calculated by subtracting the EF⁵⁰values for the three components following drug injection (components 5–7) from the EF⁵⁰value for the two components preceding drug injection (components 3–4) for each dose assessed. Data shown are averages across control (n = 7–8) and SNL (n = 6–7) rats. Frequency-response curves before and after 3 mg/kg of morphine (60-min) are shown for control (C ; n = 8) and SNL (D ; n = 7) rats. *Significantly different from saline treatment P ≤ 0.05; #significantly different from SNL rats (P ≤ 0.05).