Decreased dopamine type 2 receptor availability after bariatric surgery: Preliminary findings

Background: Diminished dopaminergic neurotransmission contributes to decreased reward and negative eating behaviors in obesity. Bariatric surgery is the most effective therapy for obesity and rapidly reduces hunger and improves satiety through unknown mechanisms. We hypothesized that dopaminergic neurotransmission would be enhanced after Roux-en-Y-Gastric Bypass (RYGB) and Vertical Sleeve Gastrectomy (VSG) surgery and that these changes would influence eating behaviors and contribute to the positive outcomes from bariatric surgery. Methods: Five females with obesity were studied preoperatively and at ∼ 7 weeks after RYGB or VSG surgery. Subjects underwent positron emission tomography (PET) imaging with a dopamine type 2 (DA D2) receptor radioligand whose binding is sensitive to competition with endogenous dopamine. Regions of interest (ROI) relevant to eating behaviors were delineated. Fasting enteroendocrine hormones were quantified at each time point. Results: Body weight decreased as expected after surgery. DA D2 receptor availability decreased after surgery. Regional decreases (mean ± SEM) were caudate 10 ± 3%, putamen 9 ± 4%, ventral striatum 8 ± 4%, hypothalamus 9 ± 3%, substantia nigra 10±2%, medial thalamus 8±2%, and amygdala 9 ± 3%. These were accompanied by significant decreases in plasma insulin (62%) and leptin (41%). Conclusion: The decreases in DA D2 receptor availability after RYGB and VSG most likely reflect increases in extracellular dopamine levels. Enhanced dopaminergic neurotransmission may contribute to improved eating behavior (e.g. reduced hunger and improved satiety) following these bariatric procedures.