Chronic stress induces the release of hormones and neuropeptides including dynorphin, which activates Kappa Opioid Receptors (KOR) to encode the anxiogenic components of the stress response. Previous studies have identified the specific dynorphin-KOR neurochemical signaling responses in the regions of the brain known for regulation of reward systems, and thus may be potential therapeutic targets for stress-related conditions such as depression, anxiety, and substance use disorders. Formally, cells containing dynorphin-KOR have been difficult to study due to technical limitations of the available reagents. However, the generation of new tools including mice expressing promotor-driven cre-recombinase (e.g. KOR-Cre and prodynorphin-Cre) have allowed cell-specific gene expression using Cre-dependent viral expression of fluorophores combined with in-situ staining. In this study, the reliability of a phospho-KOR antibody was tested. The specificity of the immunostaining was verified by administering a KOR agonist, U50,488, in wild-type animals or transgenic animals lacking the G protein-coupled receptor kinase 3 (GRK3), which phosphorylates the KOR. Additionally, wild-type mice with a pre-treatment of norBNI, a KOR antagonist, followed by U50 were also tested. Immunohistochemistry of animal brain tissue showed that the norBNI pre-treated, wild-type animals and GRK3 knock-out animals had lower KORp-IR fluorescence compared to their wild-type counterparts treated with U50,488, verifying that the KORp antibody was reliable. After verification, this KORp antibody was utilized to characterize the dynorphin-KOR circuitry in the mouse brain. To do so, an excitatory opsin was injected into the DR of pDyn-Cre mice with an optic fiber implant. The DR region was then optically stimulated with blue light and dynorphin-releasing projections into the ventral tegmental area were verified by measuring KORp fluorescence. This experiment details one specific dynorphin-KOR pathway in the mouse brain that was not previously studied, and future experiments will utilize this approach to map the extent of dynorphin/KOR localization within the reward circuitry.