Fig. 2.

Fentanyl antinociception potency shifts, midpoint titer levels and antibody affinity over the entire 20-week experimental period. A timeline of experimental procedures is depicted in a. b shows fentanyl vaccine effects on fentanyl antinociceptive potency as a function of experimental week. Abscissa: timeline with arrows indicating dates of vaccination. Ordinate: fold shift in fentanyl antinociceptive potency relative to pre-vaccination ED₅₀ values. c shows anti-fentanyl midpoint titers as a function of experimental week. Abscissa: timeline with arrows indicating dates of vaccination. Ordinate: Midpoint titer levels. d shows anti-fentanyl antibody affinity as a function of experimental week. Abscissa: timeline with arrows indicating dates of vaccination. Ordinate: Fentanyl IC₅₀ values (nM) determined from antiserum. e shows the correlation between midpoint tier levels and fold shifts in fentanyl antinociceptive potency (R = 0.53, p = 0.003). Up to Week 6 of vaccination schedule: n = 3 males, 3 females; Weeks 7–8: n = 3 males, 2 females; Weeks 9–20: n = 2 males, 2 females. With the exception of e, points represent mean ± SEM