FIGURE 7.

Latency between bursts of oxycodone infusions decreases in females and males under LgA, but not ShA, self-administration conditions. Schematics illustrating methods to calculate interval latencies between oxycodone infusions are generated from representative data and shown in (A–C). In panel (A), raster plots show oxycodone infusions (blue ticks) from the escalation days 9 and 22 from a LgA rat. All inter-infusion intervals (s) are quantified example intervals demarcated with red lines (A). Frequency distributions of log-transformed inter-infusion intervals across the 6-h self-administration days reveal bimodal distributions that consist of a population of long (long mode), and a population of short (short mode), intervals (B,C). Mo₁ represents the inter-infusion interval in the short mode with the highest frequency of occurrence, and Mo₂ represents the inter-infusion interval in the long mode with the highest frequency of occurrence. Data in panels (D–G) are dot and line plots representing average inter-infusion intervals for the long mode (D,E) and short mode (F,G) on escalation days 9 (ESC d9) and 22 (ESC d22) for each rat under LgA (D,F) and ShA (E,G) conditions. 2-way ANOVAs (Sex × ESC day) show a main effect of ESC day and a significant decrease in Long Mode inter-infusion intervals in both males and females under LgA conditions on ESC d22 compared to ESC d9 (D). *p < 0.05, **p < 0.01, Bonferroni’s multiple comparisons of ESC d9 to ESC d22 per sex. LgA (22 females, 26 males); ShA (15 females, 13 males).