Sex Differences in Behavioral Responding and Dopamine Release during Pavlovian Learning

Abstract

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

Critical periods in which dopamine exerts control over behavioral responding during Pavlovian learning

“…To familiarize rats with the chamber and food retrieval, rats underwent a single magazine training session in which 20 food pellets (45 mg, BioServ) were non-contingently delivered at a 90 ± 15 s variable interval. Rats then underwent 30 sessions (1/day) of Pavlovian training under the Pavlovian Reward Size or Pavlovian Reward Rate tasks as described previously (Fonzi et al, 2017; Stelly et al, 2021; Lefner et al, 2022).…”

“…Training sessions for the Pavlovian Reward Rate task consisted of 50 trials where the termination of a 5 s audio cue (white noise or 4.5 kHz tone, counterbalanced across animals) resulted in the delivery of a single food pellet and illumination of the food port light for 4.5 s. Each session contained 25 High Rate trials in which the CS was presented after a 20 ± 5 s ITI, and 25 Low Rate trials in which the CS was presented after a 70 ± 5 s ITI, delivered in a pseudorandom order. Conditioned responding was quantified as the change in the rate of head entries during the 5 s CS relative to the 5 s preceding the CS delivery (Fonzi et al, 2017; Stelly et al, 2021; Lefner et al, 2022). We also quantified the latency to initiate a head entry during the CS.…”

“…After the subject experiences multiple cue-reward pairings, the reward-evoked dopamine response decays and the cue-evoked dopamine response increases (Schultz et al, 1997; Day et al, 2007; Coddington and Dudman, 2018). In well-trained animals, dopamine neurons respond to cues to encode differences in reward-related information including reward size (Tobler et al, 2005; Roesch et al, 2007; Gan et al, 2010; Lefner et al, 2022), reward probability (Fiorillo et al, 2003; Hart et al, 2015), and reward rate (Fonzi et al, 2017; Stelly et al, 2021). However our recent work demonstrates that cue-evoked dopamine release does not signal differences in reward value during early training sessions, though these value signals emerge after extended training (Fonzi et al, 2017; Stelly et al, 2021; Lefner et al, 2022).…”

“…In well-trained animals, dopamine neurons respond to cues to encode differences in reward-related information including reward size (Tobler et al, 2005; Roesch et al, 2007; Gan et al, 2010; Lefner et al, 2022), reward probability (Fiorillo et al, 2003; Hart et al, 2015), and reward rate (Fonzi et al, 2017; Stelly et al, 2021). However our recent work demonstrates that cue-evoked dopamine release does not signal differences in reward value during early training sessions, though these value signals emerge after extended training (Fonzi et al, 2017; Stelly et al, 2021; Lefner et al, 2022). These findings suggest that the dopamine system may differentially regulate behavioral responding depending on whether the subject is learning the task or is well-trained.…”

“…In this study, we trained separate groups of rats on two different Pavlovian tasks that elicit goal-tracking behavior. In the Pavlovian Reward Size task, two distinct audio cues signaled the delivery of either a small reward or a large reward (Lefner et al, 2022). In the Pavlovian Reward Rate task, two distinct audio cues both signaled the delivery of a small reward but differed in the time elapsed since the previous reward delivery (i.e.…”