JUNE 30, 2015

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Green spaces and cognitive growth in children Patches of greenery in cities packed with buildings are thought to have a positive effect on cognitive development in children, but few studies have uncovered population-level evidence for such a link. To test the association between cognitive maturation and exposure to green spaces at home, school, and during commutes, Payam Dadvand et al. (pp. 7937–7942) monitored changes in cognitive measures every 3 months between January 2012 and March 2013 among 2,593 primary schoolchildren 7–10 years of age in Barcelo-na, Spain. Over a 12-month period, exposure to greenness within and around schools, as determined by satellite data, was linked with enhanced mental ability to continuously manipulate and update information—faculties called working memory and superior work-

ing memory, respectively—and with reduced inattentiveness, re-gardless of ethnicity, maternal education, and parental employment. Each interquartile range increment in total surrounding greenness was linked with 5% increase in working memory, 6% increase in superior working memory, and 1% reduction in inattentiveness. Modeling analysis suggested that elemental carbon, a common air pollutant, might account for 20–65% of the estimated links between school greenness and cognitive development. However, no link was observed between exposure to greenness at home and cognitive measures. Given the soaring rates of global urbanization, expanding green spaces at schools might be a step toward improving academic attainment among children, according to the authors. — P.N.

Transmission of Rickettsia felis by mosquitoesThe bacterium Rickettsia felis has been implicated as a causal agent in patients diagnosed with “fever of unknown origin” in sub- Saharan Africa. The bacterium can be transmitted by fleas, but whether other possible modes of transmission exist is unclear. Constentin Dieme et al. (pp. 8088–8093) explored the possibility

that the mosquito Anopheles gambiae, which transmits malaria, can also transmit R. felis, given that human R. felis infections are prev-alent in malaria-endemic regions. The authors fed mosquitoes on either blood or cellular media, both infected with R. felis, and R. felis DNA was found in the mosquitoes’ tissues for up to 2 weeks after feeding. R. felis DNA was also found on the cotton used to feed the mosquitoes after infection, suggesting that mosquito bites might transmit bacteria through saliva. Accordingly, the authors directly observed bacteria in the salivary glands of infected mos-quitoes, as well as in mosquito ovaries, although the mosquitoes did not transmit the infection to their offspring. Notably, when infected mosquitoes fed on healthy mice, the mice developed transient in-fections. The authors’ findings suggest that A. gambiae mosquitoes might transmit R. felis infection in the wild. — B.D.

Dynamics of tropical forest succession In recovering tropical forests, species vie for survival and domi-nance in a dynamic period of readjustment called forest succession. Researchers seeking to explain forest succession often approach

www.pnas.org/cgi/doi/10.1073/iti2615112 PNAS | June 30, 2015 | vol. 112 | no. 26 | 7873–7874

Urban greenery and cognitive development.

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Rickettsia felis (red) in cell culture and its potential mosquito vector.

Shifting cultivation landscape in Chiapas, Mexico.

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the problem as a predictable process, but a number of studies have shown that succession can follow widely varying trajectories, even among nearby stands with similar environments and land use histories. Noting that both deterministic and stochastic processes drive community assembly in mature forests, Natalia Norden et al. (pp. 8013–8018) examined predictability and uncertainty during tropical forest succession. The authors used mathematical models to describe the interactions between three well-established attri-butes of forest dynamics. Based on seven study sites, the authors found that all three attributes follow trajectories that vary signifi-cantly both within and among the sites. Furthermore, whereas the models were able to reproduce general successional trends, the authors found that adding high levels of noise increases predict-ability. This uncertainty suggests that external factors strongly in-fluence tropical forest succession in a context-dependent manner, thus undermining a common premise that successional processes can be treated as consistent in space and time. The findings chal-lenge the traditional approach by which many ecologists investi-gate forest regeneration, according to the authors. — T.J.

Hypoxia in estuariesEstuarine nurseries are among the coastal ecosystems sensitive to anthropogenic stressors, such as increasing nutrient inputs that can lead to algal blooms and hypoxic conditions. Brent Hughes et al. (pp. 8025–8030) examined 40 years of observations at the Elkhorn Slough estuary in California, a nursery ground for English sole and other fish found in offshore fisheries. The authors found that pres-ence of English sole and other flatfish in the estuary was positively

correlated with dissolved O2 concentration, suggesting that hypoxia can create unfavorable conditions in fish habitats. Further, hypoxic conditions in the estuarine nursery were negatively correlated with the numbers of English sole entering offshore commercial fisheries from Elkhorn Slough, suggesting that hypoxia in the estuary may lead to cascading effects in the offshore population. Climate also played a role in estuary hypoxia, with El Niño-related increases in precipitation boosting dissolved O2 and decreasing salinity in the estuary. The results suggest that coastal land use, along with climate fluctuations, can affect the diversity and life cycle of offshore fish that use estuaries as nurseries, and that both anthropogenic stress-ors and climate factors should be incorporated into predictions of climate change impacts on sensitive estuarine ecosystems, according to the authors. — P.G.

Faulty lipid metabolism and ALSGenetic studies suggest that some neuromuscular diseases may be linked to abnormal metabolism of cell membrane lipids known as glycosphingolipids. Most research has focused on three neuromus-cular diseases: hereditary spastic paraplegia, hereditary sensory neu-ropathy type 1, and non-5q spinal muscular atrophy. James Dodge et al. (pp. 8100–8105) explored whether faulty glycosphingolipid me-tabolism contributes to neurodegeneration in patients with a fourth condition: amyotrophic lateral sclerosis (ALS). Previous studies have suggested a possible link between ALS and disruption of glycosphin-golipid homeostasis. Consistent with this idea, the authors found that humans with ALS and a mouse model of familial ALS exhibit al-tered levels of spinal cord glycosphingolipids as well as enzymes that regulate metabolism of these lipids during the disease process. Fur-ther experiments in mice revealed that inhibiting glycosphingolipid production exacerbated the progression of ALS. By contrast, disease progression was slowed in mice infused with a subtype of glyco-sphingolipid known as GM3. According to the authors, the findings implicate glycosphingolipids as potentially important factors in ALS pathogenesis and as possible targets for drug development. — A.G.

Neural mechanism of ketamineKetamine can produce rapid and long-lasting antidepressant ef-fects, but the drug’s potential for side effects and abuse limits its widespread use, and the cellular mechanisms of ketamine’s effects are not yet known. To determine the role of the brain region called the infralimbic prefrontal cortex (IL-PFC) in ketamine’s antide-pressant action, Manabu Fuchikami et al. (pp. 8106–8111) mod-ulated the activity of IL-PFC neurons in rats and monitored the rats’ behavioral responses, as well as changes in neuronal structure. The authors found that inactivation of the IL-PFC region blocked the effects of systemic ketamine and that localized ketamine injec-tion into the IL-PFC reproduced the behavioral effects of systemic ketamine. The authors further found that optogenetic stimulation of IL-PFC neurons produced rapid and long-lasting antidepressant effects similar to ketamine, and that some IL-PFC neurons devel-oped additional synapses in response to stimulation. Ketamine may stimulate a burst of the neurotransmitter glutamate in the prefrontal cortex, an area previously recognized as playing a role in depressive behavior. Further study of the IL-PFC region may lead to the development of other rapid and long-lasting antidepres-sant treatments, according to the authors. — P.G.

Optogenetic stimulation increases number and function of spine synapses in IL-PFC neurons (Left, control; Right, stimulated).

Outlet of the Elkhorn Slough estuary into Monterey Bay, California.

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