Dopamine D2 receptor availability is linked to hippocampal–caudate functional connectivity and episodic memory

D1 and D2 dopamine receptors (D1DRs and D2DRs) may contribute differently to various aspects of memory and cognition. The D1DR system has been linked to functions supported by the prefrontal cortex. By contrast, the role of the D2DR system is less clear, although it has been hypothesized that D2DRs make a specific contribution to hippocampus-based cognitive functions. Here we present results from 181 healthy adults between 64 and 68 y of age who underwent comprehensive assessment of episodic memory, working memory, and processing speed, along with MRI and D2DR assessment with [¹¹C]raclopride and PET. Caudate D2DR availability was positively associated with episodic memory but not with working memory or speed. Whole-brain analyses further revealed a relation between hippocampal D2DR availability and episodic memory. Hippocampal and caudate D2DR availability were interrelated, and functional MRI-based resting-state functional connectivity between the ventral caudate and medial temporal cortex increased as a function of caudate D2DR availability. Collectively, these findings indicate that D2DRs make a specific contribution to hippocampus-based cognition by influencing striatal and hippocampal regions, and their interactions.Dopamine (DA) plays a key role in several cognitive processes (1–4). Reductions of D1 and D2 DA receptors (D1DRs and D2DRs) in aging (5–7) have been linked to age-related cognitive deficits (8, 9). The D1DR system has been related to functions supported by the prefrontal cortex (PFC), such as working memory and executive functions (10–12), which may reflect the relatively high density of D1DRs in the PFC (13). However, the role of D2DRs is far less clear. D2DRs are present in the PFC at very low densities (13), and evidence supporting a role for the D2DR system in working memory and executive functions is elusive (10). Pharmacological (14, 15) and PET studies assessing striatal D2DR availability (or binding potential to nondisplacable tissue uptake; BP_ND) with [¹¹C]raclopride (16, 17) have yielded mixed findings in relation to cognition. It has been hypothesized that D2DRs make a specific contribution to hippocampus-based cognitive functions (10, 18, 19). Supporting these claims, positive links between D2DR BP_ND and episodic memory are commonly observed (20–23). PET imaging of hippocampal D2DR BP_ND also provides support for this hypothesis, although some studies indicate that hippocampal D2DRs may be related to both episodic memory and PFC-based executive functions (22, 23), including verbal working memory (24). Medial temporal lobe regions have been implicated in working memory (25, 26), and D2DR-mediated modulation may be exerted via hippocampal–cortical pathways (27). In addition, a [¹¹C]raclopride task-activation PET study demonstrated contributions of striatal D2DRs to a verbal working-memory task (11).Taken together, the specific role of the D2DR system in cognition remains unclear, likely due to the fact that past studies included small and age-heterogeneous samples and lacked comprehensive test batteries that allowed systematic comparison of the role of D2DRs in different cognitive functions. Here we present results from the Cognition, Brain, and Aging (COBRA) study that include assessment of episodic memory, working memory, and processing speed, in combination with [¹¹C]raclopride PET and MRI of 181 healthy adults between 64 and 68 y of age (28). The main analyses concerned caudate D2DR–cognition associations, as this striatal region has been implicated in cognitive functioning (11, 12, 29, 30). Subsequently, whole-brain analyses were conducted to examine extrastriatal (especially hippocampal) D2DRs in relation to cognition. Finally, resting-state functional connectivity patterns were analyzed in relation to D2DR BP_ND, with special focus on interactions between the ventral caudate (31) and medial temporal cortex regions (32, 33).     

Presence of Insulin-Like Growth Factor Binding Proteins Correlates With Tumor-Promoting Effects of Matrix Metalloproteinase 9 in Breast Cancer

The stroma of breast cancer can promote the disease’s progression, but whether its composition and functions are shared among different subtypes is poorly explored. We compared stromal components of a luminal [mouse mammary tumor virus (MMTV)–Neu] and a triple-negative/basal-like [C3(1)–Simian virus 40 large T antigen (Tag)] genetically engineered breast cancer mouse model. The types of cytokines and their expression levels were very different in the two models, as was the extent of innate immune cell infiltration; however, both models showed infiltration of innate immune cells that expressed matrix metalloproteinase 9 (MMP9), an extracellular protease linked to the progression of many types of cancer. By intercrossing with Mmp9 null mice, we found that the absence of MMP9 delayed tumor onset in the C3(1)-Tag model but had no effect on tumor onset in the MMTV-Neu model. We discovered that protein levels of insulin-like growth factor binding protein-1 (IGFBP-1), an MMP9 substrate, were increased in C3(1)-Tag;Mmp9^−/− compared to C3(1)-Tag;Mmp9^+/+ tumors. In contrast, IGFBP-1 protein expression was low in MMTV-Neu tumors regardless of Mmp9 status. IGFBP-1 binds and antagonizes IGFs, preventing them from activating their receptors to promote cell proliferation and survival. Tumors from C3(1)-Tag;Mmp9^−/− mice had reduced IGF-1 receptor phosphorylation, consistent with slower tumor onset. Finally, gene expression analysis of human breast tumors showed that high expression of IGFBP mRNA was strongly correlated with good prognosis but not when MMP9 mRNA was also highly expressed. In conclusion, MMP9 has different effects on breast cancer progression depending on whether IGFBPs are expressed.Abbreviations: αSMA, α smooth muscle actin, C3(1)-Tag, transgene mouse expressing Simian virus 40 large T antigen under a C3(1) promoter, HER2, human epidermal growth factor receptor 2, IGF, insulin-like growth factor, IGFBP, insulin-like growth factor binding protein, IL, interleukin, MMP, matrix metalloproteinase, MMTV, mouse mammary tumor virus, NF-κB, nuclear factor κB, PyMT, polyoma middle T antigen     

From the Cover: Bacteriophage adhering to mucus provide a non–host-derived immunity

Mucosal surfaces are a main entry point for pathogens and the principal sites of defense against infection. Both bacteria and phage are associated with this mucus. Here we show that phage-to-bacteria ratios were increased, relative to the adjacent environment, on all mucosal surfaces sampled, ranging from cnidarians to humans. In vitro studies of tissue culture cells with and without surface mucus demonstrated that this increase in phage abundance is mucus dependent and protects the underlying epithelium from bacterial infection. Enrichment of phage in mucus occurs via binding interactions between mucin glycoproteins and Ig-like protein domains exposed on phage capsids. In particular, phage Ig-like domains bind variable glycan residues that coat the mucin glycoprotein component of mucus. Metagenomic analysis found these Ig-like proteins present in the phages sampled from many environments, particularly from locations adjacent to mucosal surfaces. Based on these observations, we present the bacteriophage adherence to mucus model that provides a ubiquitous, but non–host-derived, immunity applicable to mucosal surfaces. The model suggests that metazoan mucosal surfaces and phage coevolve to maintain phage adherence. This benefits the metazoan host by limiting mucosal bacteria, and benefits the phage through more frequent interactions with bacterial hosts. The relationships shown here suggest a symbiotic relationship between phage and metazoan hosts that provides a previously unrecognized antimicrobial defense that actively protects mucosal surfaces.     

Attitudes among parents of persons with autism spectrum disorder towards information about genetic risk and future health

Clinical relevance of genetic testing is increasing in autism spectrum disorder (ASD). Information about genetic risk may contribute to improved diagnostics, treatment and family planning, but may also be perceived as a burden. Knowledge about the families’ preferences with regard to genetic risk information is important for both health care professionals and policy makers. We investigated attitudes towards sharing information about genetic risk of ASD and knowledge about future health among parent members of the Norwegian Autism Association (N = 1455) using a questionnaire, and the relationships with parent and child characteristics, such as age, gender and ASD severity. Most preferred autonomy in deciding whom to inform about genetic risk of ASD (74.4%) and a minority supported extensive intra-familial disclosure of the genetic risk (41.1%). The majority agreed that it is an obligation to know as much as possible relevant for future health (58.0%) and only 51.7% agreed to a principle of a ‘right not to know’. In regression models, the attitudes were associated with opinions about benefits and harms of genetic testing (e.g., treatment, family planning, understanding of ASD pathology, insurance discrimination and family conflict). In sum, the findings show that most parents want to know as much as possible relevant for their children’s future health and keep their autonomy and intra-familial confidentiality about genetic risk information. Nearly half of the parents were not concerned with a “right not to know”. These attitudes can inform development of guidelines and bioethics in the age of genomic precision medicine.Subject terms: Genetic counselling, Ethics, Medical ethics     

Breast cancer among Danish women occupationally exposed to diesel exhaust and polycyclic aromatic hydrocarbons, 1964–2016

Objective:The aim of this study was to explore the association between occupational exposure to diesel exhaust and polycyclic aromatic hydrocarbons (PAH), respectively, and breast cancer subtypes.Methods:The study included 38 375 women <70 years with incident breast cancer, identified in the Danish Cancer Registry, and 5 breast cancer-free controls per case who were randomly selected from the Danish Civil Registration System and matched on year of birth. Full employment history was obtained for all study subjects from a nationwide pension fund, and exposure to diesel exhaust and PAH was assessed using a job exposure matrix. Conditional logistic regression was used for estimation of odds ratios (OR) with adjustment for reproductive factors and socioeconomic status.Results:No noteworthy associations were observed for overall breast cancer in women exposed to diesel exhaust. However, diesel exhaust modestly elevated the risk of estrogen receptor negative breast tumors before age 50 [OR 1.26, 95% confidence interval (CI) 1.09–1.46]. Duration– and dose–response relationships were further observed for this subtype in this age group. No notable risk patterns were generally observed for PAH exposure.Conclusion:Occupational exposure to diesel exhaust may increase the risk of early-onset estrogen receptor negative breast tumors in women. Future studies exploring this association are warranted.     

Prediction of outcome at 5 years from assessments at 2 years among extremely preterm children: a Norwegian national cohort study

Aim: To examine the predictive value of early assessments on developmental outcome at 5 years in children born extremely preterm. Methods: This is a prospective observational study of all infants born in Norway in 1999–2000 with gestational age (GA) <28 weeks or birth weight (BW) <1000 g. At 2 years of age, paediatricians assessed mental and motor development from milestones. At 5 years, parents completed questionnaires on development and professional support before cognitive function was assessed with Wechsler Preschool and Primary Scale of Intelligence‐Revised (WPPSI‐R) and motor function with the Movement Assessment Battery for children (ABC test). Results: Twenty‐six of 373 (7%) children had cerebral palsy at 2 and 29 of 306 (9%) children at 5 years. Of children without major impairments, 51% (95% CI 35–67) of those with and 22% (95% CI 16–28) without mental delay at 2 years had IQ <85 at 5 years, and 36% (95% CI 20–53 with and 16% (95% CI 11–21) without motor delay at 2 years had an ABC score >95th percentile (poor function). Approximately half of those without major impairments but IQ <85 or ABC score >95th percentile had received support or follow‐up beyond routine primary care. Conclusion: Previous assessments had limited value in predicting cognitive and motor function at 5 years in these extremely preterm children without major impairments.     

Similar frontal and distinct posterior cortical regions mediate visual and auditory perceptual awareness

Activity in ventral visual cortex is a consistent neural correlate of visual consciousness. However, activity in this area seems insufficient to produce awareness without additional involvement of frontoparietal regions. To test the generality of the frontoparietal response, neural correlates of auditory awareness were investigated in a paradigm that previously has revealed frontoparietal activity during conscious visual perception. A within-experiment comparison showed that frontal regions were related to both visual and auditory awareness, whereas parietal activity was correlated with visual awareness and superior temporal activity with auditory awareness. These results indicate that frontal regions interact with specific posterior regions to produce awareness in different sensory modalities.