Neuroimaging Studies of Reward Processing in Depression

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Major Depressive Disorder (MDD) remains a major public health problem with poorly understood etiology and pathophysiology. Impairment in reward processing and anhedonia are core features of MDD. Findings during the prior award period have shown that MDD and anhedonic phenotypes are characterized by functional, structural and molecular abnormalities within a CorticoStriatal Valuation Circuit critically implicated in value encoding and reinforcement learning. The main goal of the this R37 renewal is to expand this line of work in several fundamental new directions to (1) attain a better mechanistic understanding of MDD and anhedonia by focusing on a novel target - Nociceptin/Orphanin FQ Receptors - expected to yield molecular abnormalities associated with CorticoStriatal Valuation Circuit and stress- induced inflammatory abnormalities (Aims 1 and 2); and (2) identify abnormalities that map disease course (Aim 3). This will be achieved through an innovative integration of (1) molecular imaging techniques with a novel positron emission tomography (PET) NOP tracer ([11C]NOP1A) in unmedicated individuals with current or past MDD, (2) state-of-the-art analyses of stress-related pro-inflammatory transcription control pathways, (3) behavioral and functional neuroimaging markers of key depressive phenotypes, and (4) a naturalistic follow-up design. To differentiate between state- and trait-like markers of vulnerability, currently depressed individuals (MDD), remitted individuals with a history of MDD (rMDD), and never-depressed healthy controls will be included. Based on findings from the prior project period, we hypothesize that, relative to healthy controls, MDD and rMDD participants will show significantly higher [11C]NOP1A binding potential in brain regions critically implicated in stress regulation and reward processing (Hypotheses 1). Moreover, among individuals with current or past MDD, N/OFQ abnormalities in brain regions implicated in stress regulation and reward processing will be associated with (1) behavioral and neural markers of anhedonic phenotypes; (2) lower ability to regulate stress responses; and (3) higher stress-related proinflammatory cytokines and transcription control pathways (Hypotheses 2). Finally, we expect that N/OFQ abnormalities (and associated behavioral, fMRI, hormonal, and inflammatory markers) will predict anhedonic symptoms and poorer general functioning at follow-up (Hypothesis 3). Collectively, the proposed research promises to improve our mechanistic understanding of stress-induced anhedonia and the pathophysiology of MDD, as well as our ability to identify mechanisms that prospectively predict reward deficit-related symptoms, thus opening novel avenues for improved treatment and prevention.