A. Male morphine-sired rats (n = 8, from 5 sires) do not show any difference in time spent freezing during the 24-hour memory test compared to male saline-sired rats (n = 11, from 7 sires). B. Female morphine-sired rats (n = 10, from 7 sires) do not show any difference in time spent freezing during the long-term contextual fear conditioning memory test compared to female saline-sired rats (n = 8, from 5 sires). Data are expressed as time spent freezing (s, mean ± SEM) during a test 24-hours following fear conditioning. C. Both saline- and morphine-sired female offspring show a preference for the displaced object during the 24-hour memory test. For morphine-sired female rats (n = 20, from 10 sires) and saline-sired female rats (n = 17, from 10 sires). *p<0.001.