Dopamine and Insulin Resistance

In has been reported obese individuals have fewer striatal dopamine type 2 receptors (DRD2) compared to normal weight individuals congruent with diet induced obese rodent models and similar to models of addiction. Lower DRD2 levels are associated with addiction and a decreased sense of pleasure. Excessive weight gain also contributes to the onset of impaired insulin signaling (insulin resistance). In the brain insulin regulates monoamines and has trophic effects. We propose that the previous reports of low DRD2 in individuals with obesity will be associated with the degree of insulin resistance. Using PET imaging, we aim to determine DRD2 binding potential (BP) in the striatum and hypothesize these measurements will be associated with insulin resistance and potentially other neuroendocrine hormone levels. Obese participants will be compared to lean, sex and age similar participants. We also aim to determine the effect of caloric restriction on DRD2 BP in obese subjects. We hypothesize the caloric restriction will improve insulin resistance and that changes in DRD2 binding will be associated with changes in insulin signaling.

Inclusion criteria

• Ages 18-60 yrs
• obese BMI > 30kg/m2 and Weight less than 350 lbs
• lean control BMI 18-25kg/m2

Exclusion criteria

• Structured exercise > equivalent to 30mins 5x week of walking times a week
• History of Substance Abuse, including but exclusive to alcohol, cocaine, marijuana, heroin, nicotine
• Current psychiatric disorder or significant h/o disorder
• Use or any antidepressants or antipsychotics for last 3-6months or depot antipsychotics in the last 12 months
• Any condition felt by PI or co-investigators to interfere with ability to complete the study
• Inability to abstain from alcohol, physical exercise or > 1 cup of coffee or equivalent daily for 3 days prior to imaging studies
• Significant co-morbidities including atherosclerotic disease, metabolic disease, liver or renal insufficiency or abnormality found on MRI
• Any condition which would interfere with MRI or PET studies, e.g. claustrophobia, cochlear implant, metal fragments in eyes, cardiac pacemaker, neural stimulator, tattoos with iron pigment and metallic body inclusions or other metal implanted in the body which may interfere with MRI scanning
• Subjects on medications determined by PI, ex. sibutramine, frequent benzodiazepines or related drugs, which could affect quality of study for last 3 months.