Neurochemical pathways involved in pathological overeating and obesity are poorly understood. Although previous studies have shown increased -opioid receptor (MOR) and decreased dopamine D 2 receptor (D 2 R) availability in addictive disorders, the role that these systems play in human obesity still remains unclear. We studied 13 morbidly obese women [mean body mass index (BMI), 42 kg/m 2 ] and 14 nonobese age-matched women, and measured brain MOR and D 2 R availability using PET with selective radioligands [11 C]carfentanil and [11 C]raclopride, respectively. We also used quantitative meta-analytic techniques to pool previous evidence on the effects of obesity on altered D 2 R availability. Morbidly obese subjects had significantly lower MOR availability than control subjects in brain regions relevant for reward processing, including ventral striatum, insula, and thalamus. Moreover, in these areas, BMI correlated negatively with MOR availability. Striatal MOR availability was also negatively associated with self-reported food addiction and restrained eating patterns. There were no significant differences in D 2 R availability between obese and nonobese subjects in any brain region. Meta-analysis confirmed that current evidence for altered D 2 R availability in obesity is only modest. Obesity appears to have unique neurobiological underpinnings in the reward circuit, whereby it is more similar to opioid addiction than to other addictive disorders. The opioid system modulates motivation and reward processing, and low -opioid availability may promote overeating to compensate decreased hedonic responses in this system. Behavioral and pharmacological strategies for recovering opioidergic function might thus be critical to curb the obesity epidemic.

At group level the elevated N-methyl-[(11)C]2-(4'-methylaminophenyl)-6-hydroxybenzothiazole ([(11)C]PIB) uptake in patients with mild cognitive impairment (MCI) resembled that seen in Alzheimer disease (AD). At the individual level, about half of the MCI patients had [(11)C]PIB uptake in the AD range, suggestive of early AD process.

Voxel-based analysis revealed widespread distribution of increased [(11)C]PIB uptake in Alzheimer disease (AD). These findings are in accordance with the distribution and phases of amyloid pathology in AD, previously documented in postmortem studies.

Impaired mitochondrial function, oxidative stress and formation of excessive levels of reactive oxygen species play a key role in neurodegeneration in Parkinson's disease. Myeloperoxidase is a reactive oxygen generating enzyme and is expressed by microglia. The novel compound AZD3241 is a selective and irreversible inhibitor of myeloperoxidase. The hypothesized mechanism of action of AZD3241 involves reduction of oxidative stress leading to reduction of sustained neuroinflammation. The purpose of this phase 2a randomized placebo controlled multicentre positron emission tomography study was to examine the effect of 8 weeks treatment with AZD3241 on microglia in patients with Parkinson's disease. Parkinson patients received either AZD3241 600 mg orally twice a day or placebo (in 3:1 ratio) for 8 weeks. The binding of (11)C-PBR28 to the microglia marker 18 kDa translocator protein, was examined using positron emission tomography at baseline, 4 weeks and 8 weeks. The outcome measure was the total distribution volume, estimated with the invasive Logan graphical analysis. The primary statistical analysis examined changes in total distribution volume after treatment with AZD3241 compared to baseline. Assessments of safety and tolerability of AZD3241 included records of adverse events, vital signs, electrocardiogram, and laboratory tests. The patients had a mean age of 62 (standard deviation = 6) years; 21 were male, three female and mean Unified Parkinson's Disease Rating Scale III score (motor examination) ranged between 6 and 29. In the AD3241 treatment group (n = 18) the total distribution volume of (11)C-PBR28 binding to translocator protein was significantly reduced compared to baseline both at 4 and 8 weeks (P < 0.05). The distribution volume reduction across nigrostriatal regions at 8 weeks ranged from 13-16%, with an effect size equal to 0.5-0.6. There was no overall change in total distribution volume in the placebo group (n = 6). AZD3241 was safe and well tolerated. The reduction of (11)C-PBR28 binding to translocator protein in the brain of patients with Parkinson's disease after treatment with AZD3241 supports the hypothesis that inhibition of myeloperoxidase has an effect on microglia. The results of the present study provide support for proof of mechanism of AZD3241 and warrant extended studies on the efficacy of AZD3241 in neurodegenerative disorders.