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Although [11C]-(+)-PHNO has enabled quantification of the dopamine-D3 receptor (D3R) in the human brain in vivo, its selectivity for the D3R is not sufficiently high to allow us to disregard its binding to the dopamine-D2 receptor (D2R). We quantified the affinity of [11C]-(+)-PHNO for the D2R and D3R in the living primate brain. Two rhesus monkeys were examined on four occasions each, with [11C]-(+)-PHNO administered in a bolus + infusion paradigm. Varying doses of unlabeled (+)-PHNO were coadministered on each occasion (total doses ranging from 0.09 to 5.61 μg kg−1). The regional binding potential (BPND) and the corresponding doses of injected (+)-PHNO were used as inputs in a model that quantified the affinity of (+)-PHNO for the D2R and D3R, as well as the regional fractions of the [11C]-(+)-PHNO signal attributable to D3R binding. (+)-PHNO in vivo affinity for the D3R ( Kd/ fND ∼ 0.23-0.56 nM) was 25- to 48-fold higher than that for the D2R ( Kd/ fND ∼ 11-14 nM). The tracer limits for (+)-PHNO (dose associated with D3R occupancy ∼ 10%) were estimated at ∼0.02-0.04 μg kg−1 injected mass for anesthetized primate and at 0.01-0.02 μg kg−1 for awake human positron emission tomography (PET) studies. Our data enabled a rational design and interpretation of future PET studies with [11C]-(+)-PHNO. Synapse, 2012. © 2011 Wiley Periodicals, Inc. [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]

Summary: Obesity is a major public health issue worldwide. Understanding how the brain controls appetite offers promising inroads toward new therapies for obesity. Peptide YY (PYY) and glucagon-like peptide 1 (GLP-1) are coreleased postprandially and reduce appetite and inhibit food intake when administered to humans. However, the effects of GLP-1 and the ways in which PYY and GLP-1 act together to modulate brain activity in humans are unknown. Here, we have used functional MRI to determine these effects in healthy, normal-weight human subjects and compared them to those seen physiologically following a meal. We provide a demonstration that the combined administration of PYY3-36 and GLP-17-36 amide to fasted human subjects leads to similar reductions in subsequent energy intake and brain activity, as observed physiologically following feeding. [ABSTRACT FROM AUTHOR]

The "behavioral approach system" (BAS) (Gray, 1990) has been primarily associated with reward processing and positive affect. However, additional research has demonstrated that the BAS plays a role in aggressive behavior, heightened experience of anger, and increased attention to facial signals of aggression. Using functional magnetic resonance imaging, we show that variation in the BAS trait in healthy participants predicts activation in neural regions implicated in aggression when participants view facial signals of aggression in others. Increased BAS drive (appetitive motivation) was associated with increased amygdala activation and decreased ventral anterior cingulate and ventral striatal activation to facial signals of aggression, relative to sad and neutral expressions. In contrast, increased behavioral inhibition was associated with increased activation in the dorsal anterior cingulate, a region involved in the perception of fear and threat. Our results provide the first demonstration that appetitive motivation constitutes a significant factor governing the function of neural regions implicated in aggression, and have implications for understanding clinical disorders of aggression. [ABSTRACT FROM AUTHOR]

A network of interconnected brain regions, including orbitofrontal, ventral striatal, amygdala, and midbrain areas, has been widely implicated in a number of aspects of food reward. However, in humans, sensitivity to reward can vary significantly from one person to the next. Individuals high in this trait experience more frequent and intense food cravings and are more likely to be overweight or develop eating disorders associated with excessive food intake. Using functional magnetic resonance imaging, we report that individual variation in trait reward sensitivity (as measured by the Behavioral Activation Scale) is highly correlated with activation to images of appetizing foods (e.g., chocolate cake, pizza) in a fronto-striatal-amygdala-midbrain network. Our findings demonstrate that there is considerable personality-linked variability in the neural response to food cues in healthy participants and provide important insight into the neurobiological factors underlying vulnerability to certain eating problems (e.g., hyperphagic obesity). [ABSTRACT FROM AUTHOR]