Over the seven sessions of heroin self-administration, heroin infusions significantly increased over the course of the self-administration period in all the rats that self-administered heroin (Fig. 1A), and both the H-RI and L-RI rats displayed similar pattern (Fig. 1B). ANOVA revealed significant main effects of Session [F(6,181) = 6.06, p<0.001] and Group x Session interaction [F(12,181) = 2.05, p<0.05]. Newman-Keuls post hoc tests showed that both the H-RI and L-RI rats took significantly more infusions on Session 7 than Session 1 (p<0.001), with no change in number of infusions in the NR rats. In Session 7, both the H-RI and L-RI rats had significantly more infusions than the NR rats (p<0.05), with no differences between the H-RI and L-RI rats. As shown in Fig. 1C and 1D, both the H-RI and L-RI rats had significantly higher overall heroin intake over 7 days of drug self-administration sessions than the NR rats (p<0.05), with no difference between the two groups (Fig. 1D).
