Neuromodulation is crucial for information processing throughout the brain. Neuromodulators influence neuronal function by acting through G protein-coupled receptors (GPCRs) to alter neuronal excitability and synaptic transmission, which can then affect circuit functions. GPCRs are major drug targets used to treat a variety of diseases, including neurological disorders. The causal link between in vivo subcellular signaling mechanisms and behaviors is poorly understood due to the limited tools available to monitor signaling in freely behaving animals. Activation of GPCRs stimulates G-protein signaling to increase or decrease cyclic monophosphate (cAMP) accumulation and bidirectionally control Protein Kinase A (PKA) and Exchange Protein directly Activated by cAMP (EPAC) signaling. Although GPCRs are diverse, the downstream second messenger systems are limited. Therefore, the overarching hypothesis of this proposal is that GPCRs decode incoming modulatory inputs by generating distinct spatiotemporal patterns of cAMP-mediated signaling to control basal ganglia circuit functions. To test this hypothesis, I propose two innovative specific aims: Specific Aim 1 – I will determine the spatiotemporal dynamics in real- time of A-kinase phosphorylation using virally expressed A-kinase activity reporter (AKAR) and cAMP using the EPAC Föster resonance energy transfer (FRET) - based sensors before and after the induction of striatal long- term depression (LTD) in specific cell types. To execute this Aim, I will use transgenic mice to target specific neuronal cell types and two-photon fluorescence lifetime imaging microscopy (FLIM) to quantify FRET activity. These results will build on my previous published findings and will be of broad interest to the basal ganglia field. Specific Aim 2 – I will monitor cAMP and PKA temporal signaling profiles in specific striatal cell types in freely-moving mice during spontaneous locomotion and motor-skill learning on the accelerated rotarod using virally expressed AKAR and EPAC sensors and deep brain in vivo fiber photometry. This proposal will be the first to determine the cAMP mediated signaling dynamics in striatum during synaptic plasticity and learned behaviors. Throughout my career, I have been interested in determining the causal link between synaptic plasticity and behaviors. At every stage of my career, I have advanced in my technical abilities and refined my scientific experimental design. As I train with my mentors, Drs. Lovinger and Vogel, I will further expand my technical abilities and increase my scientific sophistication to ask impactful questions and design appropriate experiments to address these questions. Additionally, my mentors will train me to communicate my scientific findings effectively, run a successful lab, and mentor to students. I have recruited two extramural investigators, Drs. Cheer and Gremel to serve as advisory committee members and aid in my successful transition to an independent faculty...