Author Contributions: MJL and MID performed the experiments and analyzed the data. MJL and MJW designed the experiments and wrote the manuscript.

Learning associations between cues and rewards requires the mesolimbic dopamine system. The dopamine response to cues signals differences in reward value in well-trained animals. These value-related dopamine responses are absent during early learning when cues signal differences in the reward rate, which suggests cue-evoked dopamine release conveys differences between outcomes only after extensive training. However, it is unclear if this lack of value coding by cue-evoked dopamine release during early learning is unique to when cues signal differences in reward rate, or if this is also evident when cues signal differences in other value-related parameters such as reward size. To address this, we utilized a Pavlovian conditioning task in which one audio cue was associated with a small reward (one pellet) and another audio cue was associated with a large reward (three pellets). We performed fast-scan cyclic voltammetry to record changes in dopamine release in the nucleus accumbens of male and female rats throughout early learning. Cue-evoked dopamine release did not encode differences in reward value, and there were no differences in this response between males and females. However, female rats exhibited higher levels of conditioned responding and a faster latency to respond. Reward-evoked dopamine release scaled with reward size in both sexes, though there were transient sex differences in the dynamics of this response. We additionally identified sex differences in the number of post-reward head entries. Collectively these data illustrate sustained sex differences in behavioral responding as well as transient sex differences in reward-evoked dopamine release.