PROJECT SUMMARY
Reward association and motivation are key processes guiding goal-directed behaviors. These functions are
modulated by mesolimbic dopamine circuitry, which encompasses dopamine neurons projecting from the ventral
tegmental area (VTA) to the nucleus accumbens (NAc). VTA-NAc dopamine projections broadly facilitate the
learning of action- and cue-outcome associations and regulate the extinction and reinstatement of goal-directed
behaviors. Further, an emerging body of research suggests that specific subregions of the NAc shell integrate
midbrain dopaminergic signals with sensory and limbic inputs to drive actions involved in the maintenance,
extinction, and reinstatement of reward-seeking behaviors. However, little is known about how isolated VTA
dopamine inputs to the NAc medial shell contribute to these behaviors. The primary goal of this proposal is to
dissect the neural circuitry of isolated VTA projections to the NAc medial shell in motivated behavior. To define
the role of a specific VTA dopamine projection to the NAc medial shell, we identified a genetic marker, cerebellin-
4 (Cbln4), that displays restricted expression within a subpopulation of VTA dopamine neurons. Using viral-
mediated circuit mapping in Cbln4-IRES-CRE (Cbln4iCre) mice, I found that VTACbln4 neurons project to the NAc
medial shell region but not lateral shell or core regions. Additionally, in vivo optical stimulation of this circuit is
sufficient to facilitate the maintenance of reward-seeking behaviors in the absence of primary reward
reinforcement. Further, stimulation of this population is sufficient to reinstate an extinguished reward-seeking
behavioral response. Although highly informative, these studies did not examine the role of endogenous neural
activity or dopamine signaling in the VTACbln4-Nac medial shell circuit for its functions in modulating motivated
behavior. Two specific aims are proposed using the Cbln4iCre mouse line with viral-mediated targeting strategies
to dissect the VTACbln4-Nac medial shell circuit. Aim 1 will anatomically and functionally characterize the VTACbln4-
Nac medial shell dopamine projection using high resolution quantitative image analysis and a genetically
encoded dopamine sensor coupled with circuit-specific slice imaging. Aim 2 uses in vivo fiber photometry
recording to determine the neural activity of VTACbln4 neurons during the acquisition, extinction, and cue-induced
reinstatement of food-motivated operant responding. Further, this aim examines the necessity of endogenous
neural activity and dopamine production in the VTACbln4-Nac medial shell circuit in determining the expression of
these behaviors using chemogenetic inhibition and cell-type specific CRISPR/SaCas9-mediated gene knockout
approaches. This study will define how isolated projections within mesolimbic dopamine circuitry regulate distinct
aspects of motivated behavior and provide insight into how disruptions in these circuits contribute to substance
use and obsessive-compulsive disorders. The proposed studies will facilitate my training in in vivo fiber
photometry, ex vivo slice imaging, and computational data analysis methods, as well as prepare me to pursue a
career as an independent researcher.