Weight loss after bariatric surgery normalizes brain opioid receptors in morbid obesity

Positron emission tomography (PET) studies suggest opioidergic system dysfunction in morbid obesity, while evidence for the role of the dopaminergic system is less consistent. Whether opioid dysfunction represents a state or trait in obesity remains unresolved, but could be assessed in obese subjects undergoing weight loss. Here we measured brain μ-opioid receptor (MOR) and dopamine D 2 receptor (D 2 R) availability in 16 morbidly obese women twice—before and 6 months after bariatric surgery—using PET with [ 11 C]carfentanil and [ 11 C]raclopride. Data were compared with those from 14 lean control subjects. Receptor-binding potentials (BP ND ) were compared between the groups and between the pre- and postoperative scans among the obese subjects. Brain MOR availability was initially lower among obese subjects, but weight loss (mean=26.1 kg, s.d.=7.6 kg) reversed this and resulted in ~23% higher MOR availability in the postoperative versus preoperative scan. Changes were observed in areas implicated in reward processing, including ventral striatum, insula, amygdala and thalamus ( P 's