Fig. 5. Heroin self-administration increased the rate of dopamine reuptake in both sexes and phasic-like dopamine release in the medial NAc shell of female rats.

A Representative traces of electrically-evoked dopamine demonstrating increased uptake in heroin-exposed males and females compared to their respective heroin-naïve counterparts. B Stimulated dopamine release did not differ between any treatment groups. C The maximal rate of dopamine uptake (Vmax) was increased in heroin-exposed males and females. D Heroin-exposed and heroin-naïve males did not differ in dopamine elicited by multi-pulse stimulation trains at increasing frequencies; however, heroin females have greater dopamine release across frequencies than heroin-naïve females (E). F A comparison of both sexes and conditions reveal that the increase in phasic dopamine release is specific to female rats after heroin. G Comparison of average phasic/tonic ratios was increased in heroin females compared to their naïve counterparts, as depicted by the concentration of stimulated dopamine release at ten pulses over one pulse. *p < 0.05; **p < 0.01. n = 5–6 rats per group.