Fig. 2.

Raw data for behavioral testing, and heroin reinforced and non-reinforced behaviors in female and male rats. The black bar within each violin plot indicates the median value of the data. Prior to starting heroin self-administration training, (a) female rats travelled a greater distance during the open field test and (b) spent more time in the open arm of the elevated plus maze relative to male rats. (c) Sexes did not differ in analgesic threshold under baseline conditions (p=0.78), however, (d) males exhibited a greater heroin-induced analgesic threshold compared to females. Though male and female rats had similar levels of escalation of heroin intake across training, female rats showed potentiated (f) consumption of heroin across training, (g) motivation to work for an infusion of heroin (break point), refraining behavior at both the (h) start (extinction burst) and (j) end of extinction training (extinction day 6). Furthermore, female rats exhibited greater levels of both (i) heroin primed and (k) cue-induced reinstatement of heroin-seeking behavior relative to males. *p<0.05 (Males, n= 264; Females, n=243)