Characterizing Dopamine Receptor Binding in Treatment Resistant Depression

It is estimated that 30% of individuals with Major Depressive Disorder (MDD) fail to respond to conventional antidepressant medication which accounts for over 1 million Canadians in their lifetime. Treatment resistant depression (TRD) patients also have greater psychiatric and medical comorbidity, poorer quality of life and increased suicidal ideation. Yet, there are few treatment strategies available to target TRD and there is a significant lack of evidence about how TRD differs from treatment-responsive depression. This proposal represents the first study to elucidate the neurobiology of TRD with a focus on dopamine receptor function throughout the brain, in order to inform treatment development and clinical characterization of TRD.The ultimate goal of this unique study is to characterize striatal and extrastriatal dopamine D2 and D3 receptor binding potential in patients with TRD, non-resistant MDD and healthy controls. The primary hypothesis is that TRD patients will exhibit greater D2/D3 receptor binding potential compared to non-TRD patients in the following regions of interest: dorsolateral prefrontal cortex, orbitofrontal cortex, and ventral striatum. Secondarily, non-TRD patients will also demonstrate increased binding potential compared to healthy controls in the same brain regions. Whole brain analyses will allow us to take an exploratory approach to other brain regions that may differentiate TRD from non-TRD patients. Participants will be assessed at St. Michael's Hospital (SMH) and the Centre for Addiction and Mental Health (CAMH), which are within a 10 minute driving distance of each other. There will be 3 study visits following written informed consent. Eligibility will be confirmed at a screening visit at SMH where demographic information, including age, sex, education, and medication history will be obtained, as well as the administration of a structured Mini-International Neuropsychiatric Interview (MINI) for Diagnostic and Statistical Manual of Mental Disorders (DSM-5) Axis I diagnoses (Sheehan et al, 2015), and an HRSD-17. Within two weeks of the screening visit, participants will undergo a structural magnetic resonance imaging (MRI) scan at SMH prior to the positron-emission tomography (PET) scan at CAMH. The order of the PHNO scans will be counterbalanced.