Role of Dopamine D2 Receptors in Human Reinforcement Learning

Influential neurocomputational models emphasize dopamine (DA) as an electrophysiological and neurochemical correlate of reinforcement learning. However, evidence of a specific causal role of DA receptors in learning has been less forthcoming, especially in humans. Here we combine, in a between-subjects design, administration of a high dose of the selective DA D2/3-receptor antagonist sulpiride with genetic analysis of the DA D2 receptor in a behavioral study of reinforcement learning in a sample of 78 healthy male volunteers. In contrast to predictions of prevailing models emphasizing DA's pivotal role in learning via prediction errors, we found that sulpiride did not disrupt learning, but rather induced profound impairments in choice performance. The disruption was selective for stimuli indicating reward, while loss avoidance performance was unaffected. Effects were driven by volunteers with higher serum levels of the drug, and in those with genetically-determined lower density of striatal DA D2 receptors. This is the clearest demonstration to date for a causal modulatory role of the DA D2 receptor in choice performance that might be distinct from learning. Our findings challenge current reward prediction error models of reinforcement learning, and suggest that classical animal models emphasizing a role of postsynaptic DA D2 receptors in motivational aspects of reinforcement learning may apply to humans as well.Neuropsychopharmacology accepted article peview online, 09 April 2014; doi:10.1038/npp.2014.84

Fatal prostate cancer incidence trends in the United States and England by race, stage, and treatment

Background: Differential uptake of prostate-specific antigen testing in the US and UK has been linked to between-country differences for prostate cancer incidence. We examined stage-specific fatal prostate cancer incidence trends in the US and England, by treatment and race/ethnicity. Methods: Using data from the National Cancer Institute’s Surveillance, Epidemiology, and End Results program and Public Health England’s National Cancer Registration and Analysis Service, we identified prostate cancer patients diagnosed between 1995 and 2005, aged 45–84 years. Fatal prostate cancer was defined as death attributed to the disease within 10 years of diagnosis. We used age–period–cohort models to assess trends in fatal prostate cancer incidence. Results: Fatal prostate cancer incidence declined in the US by −7.5% each year and increased in England by 7.7% annually. These trends were primarily driven by locoregional disease in the US and distant disease in England. Black men in both countries had twofold to threefold higher fatal prostate cancer incidence rates, when compared with their white counterparts; however, receipt of radical prostatectomy lessened this disparity. Conclusions: We report a significant increasing rate of fatal prostate cancer incidence among English men. The black–white racial disparity appears pervasive but is attenuated among those who received radical prostatectomy in the US

Dysregulation at multiple points of the kynurenine pathway is a ubiquitous feature of renal cancer: implications for tumour immune evasion

Funder: EC | EC Seventh Framework Programm | FP7 Ideas: European Research Council (FP7-IDEAS-ERC - Specific Programme: "Ideas" Implementing the Seventh Framework Programme of the European Community for Research, Technological Development and Demonstration Activities (2007 to 2013)); doi: https://doi.org/10.13039/100011199Funder: DH | National Institute for Health Research (NIHR); doi: https://doi.org/10.13039/501100000272Abstract: Background: Indoleamine 2,3-dioxygenase (IDO), the first step in the kynurenine pathway (KP), is upregulated in some cancers and represents an attractive therapeutic target given its role in tumour immune evasion. However, the recent failure of an IDO inhibitor in a late phase trial raises questions about this strategy. Methods: Matched renal cell carcinoma (RCC) and normal kidney tissues were subject to proteomic profiling. Tissue immunohistochemistry and gene expression data were used to validate findings. Phenotypic effects of loss/gain of expression were examined in vitro. Results: Quinolate phosphoribosyltransferase (QPRT), the final and rate-limiting enzyme in the KP, was identified as being downregulated in RCC. Loss of QPRT expression led to increased potential for anchorage-independent growth. Gene expression, mass spectrometry (clear cell and chromophobe RCC) and tissue immunohistochemistry (clear cell, papillary and chromophobe), confirmed loss or decreased expression of QPRT and showed downregulation of other KP enzymes, including kynurenine 3-monoxygenase (KMO) and 3-hydroxyanthranilate-3,4-dioxygenase (HAAO), with a concomitant maintenance or upregulation of nicotinamide phosphoribosyltransferase (NAMPT), the key enzyme in the NAD+ salvage pathway. Conclusions: Widespread dysregulation of the KP is common in RCC and is likely to contribute to tumour immune evasion, carrying implications for effective therapeutic targeting of this critical pathwa