Dopamine has long been implicated in impulsivity, but the precise mechanisms linking human variability in dopamine signaling to differences in impulsive traits remain largely unknown. Using a dual PET scan approach in healthy human volunteers with amphetamine and the D2/D3 ligand 18F-fallypride, we found that higher levels of trait impulsivity were predicted by diminished midbrain D2/D3 autoreceptor binding and greater amphetamine-induced DA release in the striatum, which was in turn associated with stimulant craving. Path analysis confirmed that the impact of decreased midbrain D2/D3 autoreceptor availability on trait impulsivity is mediated in part through its effect on stimulated striatal dopamine release.

Psychopathy is a personality disorder that is strongly linked to criminal behavior. Using [18F]fallypride PET and BOLD fMRI, we show that impulsive-antisocial psychopathic traits selectively predict nucleus accumbens dopamine release and reward anticipation-related neural activity in response to pharmacological and monetary reinforcers, respectively. These findings suggest that neurochemical and neurophysiological hyperreactivity of the dopaminergic reward system may comprise a neural substrate for impulsivity, antisocial behavior and substance abuse in psychopathy.

Preferences for different combinations of costs and benefits are a key source of variability in economic decision-making. However, the neurochemical basis of individual differences in these preferences is poorly understood. Studies in both animals and humans have demonstrated that direct manipulation of the neurotransmitter dopamine (DA) significantly impacts cost/benefit decision-making, but less is known about how naturally occurring variation in DA systems may relate to individual differences in economic behavior. In the present study, 25 healthy volunteers completed a dual-scan PET imaging protocol with [18F]fallypride and d-amphetamine to measure DA responsivity, and separately completed the Effort Expenditure for Rewards Task, a behavioral measure of cost/benefit decision-making in humans. We found that individual differences in DA function in the left striatum and ventromedial prefrontal cortex were correlated with a willingness to expend greater effort for larger rewards, particularly when probability of reward receipt was low. Additionally, variability in DA responses in the bilateral insula was negatively correlated with willingness to expend effort for rewards, consistent with evidence implicating this region in the processing of response costs. These findings highlight the role of DA signaling in striatal, prefrontal and insular regions as key neurochemical mechanisms underlying individual differences in cost/benefit decision-making.

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Novelty-seeking personality traits are a major risk factor for the development of drug abuse and other unsafe behaviors. Rodent models of temperament indicate that high novelty responding is associated with decreased inhibitory autoreceptor control of midbrain dopamine neurons. It has been speculated that individual differences in dopamine functioning also underlie the personality trait of novelty seeking in humans. However, differences in the dopamine system of rodents and humans, as well as the methods for assessing novelty responding/seeking across species leave unclear to what extent the animal models inform our understanding of human personality. In the present study we examined the correlation between novelty-seeking traits in humans and

OBJECTIVEMidbrain dopamine (DA) neurons, which are involved with reward and motivation, are modulated by hormones that regulate food intake (insulin, leptin, and acyl ghrelin [AG]). We hypothesized that these hormones are associated with deficits in DA signaling in obesity.RESEARCH DESIGN AND METHODSWe assessed the relationships between fasting levels of insulin and leptin, and AG, BMI, and insulin sensitivity index (SI) with the availability of central DA type 2 receptor (D2R). We measured D2R availability using positron emission tomography and [18F]fallypride (radioligand that competes with endogenous DA) in lean (n = 8) and obese (n = 14) females. Fasting hormones were collected prior to scanning and SI was determined by modified oral glucose tolerance test.RESULTSParametric image analyses revealed associations between each metabolic measure and D2R. The most extensive findings were negative associations of AG with clusters involving the striatum and inferior temporal cortices. Regional regression analyses also found extensive negative relationships between AG and D2R in the caudate, putamen, ventral striatum (VS), amygdala, and temporal lobes. SI was negatively associated with D2R in the VS, while insulin was not. In the caudate, BMI and leptin were positively associated with D2R availability. The direction of associations of leptin and AG with D2R availability are consistent with their opposite effects on DA levels (decreasing and increasing, respectively). After adjusting for BMI, AG maintained a significant relationship in the VS. We hypothesize that the increased D2R availability in obese subjects reflects relatively reduced DA levels competing with the radioligand.CONCLUSIONSOur findings provide evidence for an association between the neuroendocrine hormones and DA brain signaling in obese females.

Study Type – Therapy (case series)
Level of Evidence 4OBJECTIVETo analyse the factors predicting the mortality and need for nephrectomy in patients with emphysematous pyelonephritis (EPN).PATIENTS AND METHODSClinical features, laboratory variables, imaging studies, management strategy and the final outcomes were analysed in 39 consecutive patients with EPN. The mean (sd) age was 57 (7.2) years and the male to female ratio was 2:11. The baseline risk factors (clinical, laboratory and radiological) were compared among three groups; group 1, survived with renal salvage (26); group 2, survived after nephrectomy (eight); and group 3, died (five).RESULTSThe overall survival rate was 87% (34/39) and the kidney was salvaged in 67% (26) patients at a median follow‐up of 18 months. Altered mental status, thrombocytopenia, renal failure and severe hyponatremia at presentation were significantly associated with mortality rate. There was no significant difference in final outcome based on radiological classification. Extensive renal parenchymal destruction of >50% (based on computed tomography) significantly predicted the need for nephrectomy (P < 0.001) and death (P = 0.02). Early (<1 week) nephrectomy resulted in a higher mortality rate (three of seven patients) than initial conservative management. There were no deaths in selected patients who received antibiotics alone or had delayed nephrectomy (four patients each). Of 24 patients who had minimally invasive treatment alone, two (8%) died. Minimally invasive treatment resulted in high renal salvage (22/24, 92%).CONCLUSIONAltered mental status, thrombocytopenia, renal failure and severe hyponatremia at presentation are associated with higher mortality rates, whereas extensive renal parenchymal destruction is associated with a need for nephrectomy. Early nephrectomy is associated with higher mortality rates than is initial conservative management.

This study examined D-amphetamine (D-AMPH)-induced displacements of [18 F] fallypride in striatal and extrastriatal regions and the correlations of these displacements with cognition, affect, and sensation-seeking behavior. In all, 14 normal subjects, six females and eight males (ages 21-32, mean age 25.9 years), underwent positron emission tomography (PET) with [18 F]fallypride before and 3 h after a 0.43 mg/kg oral dose of D-AMPH. Levels of dopamine (DA) D 2 receptor density were calculated with the reference region method of Lammerstma. Percent displacements in striatal and extrastriatal regions were calculated for the caudate, putamen, ventral striatum, medial thalamus, amygdala, substantia nigra, and temporal cortex. Correlations of changes in cognition, affect, and sensation seeking with parametric images of D-AMPH-induced DA release were computed. Significant displacements were seen in the caudate, putamen, ventral striatum substantia nigra, and temporal cortex with a trend level change in the amygdala. Greatest displacements were seen in striatal subdivisionsF5.6% in caudate, 11.2% in putamen, 7.2% in ventral striatum, and 6.6% in substantia nigra. Lesser decrements were seen in amygdalaF4.4%, temporal cortexF3.7%, and thalamusF2.8%. Significant clusters of correlations of regional DA release with cognition and sensation-seeking behavior were observed. The current study demonstrates that [ 18 F]fallypride PET studies using oral D-AMPH (0.43 mg/kg) can be used to study D-AMPH-induced DA release in the striatal and extrastriatal regions in humans, and their relationship with cognition and sensation-seeking behavior.