Figure 2.

Serum sufentanil concentrations. (a) Timeline for non-contingent delivery of sufentanil vapor. A drug-naive cohort of rats received 2, 5, or 10 non-contingent sufentanil vapor (3 mg/ml) deliveries (n=3 rats per condition) in a 2 h period. The onset of vapor deliveries across the 2 h period was evenly spaced and timed so that the final vapor delivery occurred at minute 118 of the session, regardless of the number of deliveries. (b) Symbols represent mean serum sufentanil concentrations (ng/ml; +SEM) following 2, 5, and 10 sufentanil vapor deliveries. There was a significant correlation between serum sufentanil concentration and the number of sufentanil vapor deliveries (p<0.05). The data are expressed as ng/ml of serum.