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It has been suggested that the BDNF Val66Met polymorphism modulates episodic memory performance via effects on hippocampal neural circuitry. However, fMRI studies have yielded inconsistent results in this respect. Moreover, very few studies have examined the effect of met allele load on activation of memory circuitry. In the present study, we carried out a comprehensive analysis of the effects of the BDNF polymorphism on brain responses during episodic memory encoding and retrieval, including an investigation of the effect of met allele load on memory related activation in the medial temporal lobe. In contrast to previous studies, we found no evidence for an effect of BDNF genotype or met load during episodic memory encoding. Met allele carriers showed increased activation during successful retrieval in right hippocampus but this was contrast-specific and unaffected by met allele load. These results suggest that the BDNF Val66Met polymorphism does not, as previously claimed, exert an observable effect on neural systems underlying encoding of new information into episodic memory but may exert a subtle effect on the efficiency with which such information can be retrieved. [ABSTRACT FROM AUTHOR]

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT • Analysis of allelic variation in large populations has identified numerous single nucleotide polymorphisms (SNPs) in the P2RX7 gene. In vitro transfection has demonstrated SNP-dependent alterations (gain or loss) of P2X7 receptor function, as measured by ATP-induced ethidium uptake and interleukin-1β production. WHAT THIS STUDY ADDS • We provide definitive evidence of SNP-dependent alteration in P2X7 receptor pharmacodynamics to a specific antagonist (GSK1370319A) in a small sample of prospectively genotyped subjects. These effects on drug response underline the importance of genetic stratification in drug development of P2X7 receptor antagonists. AIMS To investigate the effects of two single nucleotide polymorphisms (SNPs) in the human P2X7 receptor gene ( P2RX7) - 1068G>A (A348T) and 1513A>C (E496A) - on P2X7 receptor function, using a specific receptor antagonist (GSK1370319A) and prospective genetic stratification. METHODS Lipopolysaccharide- and ATP-stimulated interleukin-1β production was determined in the presence or absence of GSK1370319A in blood culture from 32 prospectively genotyped subjects. RESULTS There was approximately 6.7-fold difference ( P < 0.0001) in IC50 for inhibition of ATP-stimulated interleukin-1β release by GSK1370319A between individuals with the homozygous gain- (1068A) and loss-of-function (1513C) genotypes (expressing the 348T, 496E and 348A, 496A alleles, respectively). CONCLUSIONS Leukocyte P2X7 receptors had significantly altered pharmacodynamic responses to a specific antagonist (GSK1370319A), directly related to SNP genotype. [ABSTRACT FROM AUTHOR]

[11C]PHNO is a D2/D3 agonist positron emission tomography radiotracer, with higher in vivo affinity for D3 than for D2 receptors. As [11C]-(+)-PHNO is an agonist, its in vivo binding is expected to be more affected by acute fluctuations in synaptic dopamine than that of antagonist radiotracers such as [11C]raclopride. In this study, the authors compared the effects of an oral dose of the dopamine releaser amphetamine (0.3 mg/kg) on in vivo binding of [11C]-(+)-PHNO and [11C]raclopride in healthy subjects, using a within-subjects, counterbalanced, open-label design. In the dorsal striatum, where the density of D3 receptors is negligible and both tracers predominantly bind to D2 receptors, the reduction of [11C]-(+)-PHNO binding potential (BPND) was 1.5 times larger than that of [11C]raclopride. The gain in sensitivity associated with the agonist [11C]-(+)-PHNO implies that ∼65% of D2 receptors are in the high-affinity state in vivo. In extrastriatal regions, where [11C]-(+)-PHNO predominantly binds to D3 receptors, the amphetamine effect on [11C]-(+)-PHNO BPND was even larger, consistent with the higher affinity of dopamine for D3. This study indicates that [11C]-(+)-PHNO is superior to [11C]raclopride for studying acute fluctuations in synaptic dopamine in the human striatum. [11C]-(+)-PHNO also enables measurement of synaptic dopamine in D3 regions. [ABSTRACT FROM AUTHOR]

We used functional magnetic resonance imaging to explore brain responses to food images in overweight humans, examining independently the impact of a prescan meal ("satiety") and the anti-obesity drug sibutramine, a serotonin and noradrenaline reuptake inhibitor. We identified significantly different responses to these manipulations in amygdala, hypothalamus, and ventral striatum. Each region was specifically responsive to high-calorie compared to low-calorie food images. However, the ventral striatal response was attenuated by satiety (but unaffected by sibutramine), while the hypothalamic and amygdala responses were attenuated by drug but unaffected by satiety. Direct assessment of regional interactions confirmed the significance of this double dissociation. We explored the regional responses in greater detail by determining whether they were predictive of eating behavior and weight change. We observed that across the different regions, the individual-specific magnitude of drugand satiety-induced modulation was associated with both variables: the sibutramine-induced modulation of the hypothalamic response was correlated with the drug's impact on both weight and subsequently measured ad libitum eating. The satiety-induced modulation of striatal response also correlated with subsequent ad libitum eating. These results suggest that hypothalamus and amygdala have roles in the control of food intake that are distinct from those of ventral striatum. Furthermore, they support a regionally specific effect on brain function through which sibutramine exerts its clinical effect. [ABSTRACT FROM AUTHOR]

We have recently reported a validation study of a prototype low-field strength quantitative magnetic resonance (QMR) instrument for measurement of human body composition (EchoMRI-AH). QMR was very precise, but underreported fat mass (FM) by 2-4 kg when compared to a 4-compartment (4C) model in this cross-sectional study. Here, we report the performance of an updated instrument in two longitudinal studies where FM was decreasing. Healthy obese volunteers were given a modest energy deficit diet for 8 weeks (study A) and obese patients with heart failure and/or at high cardiovascular risk were prescribed a low energy liquid diet for 6 weeks (study B). FM was measured at the start and end of these periods by QMR, dual-energy X-ray absorptiometry (DXA) and 4C. A higher proportion of the weight lost came from fat in study A compared with study B, where loss of total body water (TBW) played a greater part. The intraclass correlation between QMR and 4C estimates of FM loss (DeltaFat) was 0.95, but 20 of 22 estimates of DeltaFat by QMR were lower than the corresponding estimate by the 4C model. Bland-Altman analysis demonstrated that estimates of FM loss by QMR were ~1.0 and 0.7 kg lower than those obtained with 4C (P = 0.0008) and DXA (P = 0.049), respectively. Measurement precision remained high. QMR measurement should prove valuable for quantifying modest changes of FM in small trials.