The adolescent brain: insights from functional neuroimaging research

With the development of functional neuroimaging tools, the past two decades have witnessed an explosion of work examining functional brain maps, mostly in the adult brain. Against this backdrop of work in adults, developmental research begins to gather a substantial body of knowledge about brain maturation. The purpose of this review is to present some of these findings from the perspective of functional neuroimaging. First, a brief survey of available neuroimaging techniques (i.e., fMRI, MRS, MEG, PET, SPECT, and infrared techniques) is provided. Next, the key cognitive, emotional, and social changes taking place during adolescence are outlined. The third section gives examples of how these behavioral changes can be understood from a neuroscience perspective. The conclusion places this functional neuroimaging research in relation to clinical and molecular work, and shows how answers will ultimately come from the combined efforts of these disciplines.     

Dermal-type macrophages expressing CD209/DC-SIGN show inherent resistance to dengue virus growth

Background

An important question in dengue pathogenesis is the identity of immune cells involved in the control of dengue virus infection at the site of the mosquito bite. There is evidence that infection of immature myeloid dendritic cells plays a crucial role in dengue pathogenesis and that the interaction of the viral envelope E glycoprotein with CD209/DC-SIGN is a key element for their productive infection. Dermal macrophages express CD209, yet little is known about their role in dengue virus infection.

Methods and Findings

Here, we showed that dermal macrophages bound recombinant envelope E glycoprotein fused to green fluorescent protein. Because dermal macrophages stain for IL-10 in situ, we generated dermal-type macrophages from monocytes in the presence of IL-10 to study their infection by dengue virus. The macrophages were able to internalize the virus, but progeny virus production was undetectable in the infected cells. In addition, no IFN-α was produced in response to the virus. The inability of dengue virus to grow in the macrophages was attributable to accumulation of internalized virus particles into poorly-acidified phagosomes.

Conclusions

Aborting infection by viral sequestration in early phagosomes would present a novel means to curb infection of enveloped virus and may constitute a prime defense system to prevent dengue virus spread shortly after the bite of the infected mosquito.     

Indicators of UV Exposure in Corals and Their Relevance to Global Climate Change and Coral Bleaching

A compelling aspect of the deterioration of coral reefs is the phenomenon of coral bleaching. Through interactions with other factors such as sedimentation, pollution, and bacterial infection, bleaching can impact large areas of a reef with limited recovery, and it might be induced by a variety of stressors including temperature and salinity extremes, and ultraviolet light. Under conditions of ocean warming, often associated with calm and stratified waters, photobleaching of UV-absorb-ing chromophoric dissolved organic matter (CDOM) is increased, and penetration of both UV-B and UV-A is greatly enhanced. Indices of UV-specific effects in coral tissue are needed to test whether UV increases, associated with global climate change, are harmful to corals. To address this challenge, we have evaluated UV-specific effects in corals and have characterized factors that alter penetration of UV radiation over coral reefs. An immunoblotting assay was developed to examine UV-specific lesions (thymine dimers) in coral and zooxanthellae DNA. We observed dose-dependent increases of thymine dimers in coral (Porites porites var porites) exposed to artificial solar irradiance in a solar simulator, although effects were not strictly proportional. UV measurements were made in July 1999 at Eastern Sambo reef and nearby sites, including profiling along transects from reef to shore. Results of these analyses indicate that the coral at Eastern Sambo reef (at 3-4 meters) were receiving UV-B radiation that was equivalent to 25 to 30% of surface UV irradiance. However, the water just inside the reef in Hawk Channel (located closer to land) was considerably more opaque to UV. This water photobleached with loss of UV absorbance and fluorescence when it was exposed to simulated solar radiation. These results indicate that photobleaching of the DOM and transport of near-shore water out over the reefs might play a key role in controlling UV penetration to the reef surface.     

Slow motion extinction: inbreeding,introgression, and loss in the critically endangered mangrove finch (<Emphasis Type="Italic">Camarhynchus heliobates</Emphasis>)

The critically endangered mangrove finch is now limited to one small population on the west coast of Isabela Island in the Galápagos, but 100 years ago multiple populations were found on the islands of Isabela and Fernandina. By accessing genetic datasets through museum sampling, we are able to put current levels of genetic diversity and hybridization with congenerics into a historical context for enhanced conservation. In this study, we compared neutral genetic diversity of the now extinct Fernandina population to historical and current diversity of the Isabela population using 14 microsatellite markers. We found that current genetic diversity of the last remnant population (~80–100 individuals) is far below levels 100 years ago, with only about half of the allelic diversity retained. Current genetic diversity is close to levels in the Fernandina population that went extinct by the 1970s. Bottleneck analysis did not show a strong signature of recent decline, and instead implies that this species may have consistently had low population sizes with wide fluctuations. Hybridization with congeneric woodpecker finches was found in the modern Isabela population, implying that some individuals within the few remaining breeding pairs are finding mates with woodpecker finches. Within the context of historical low population sizes and wide fluctuations, current conservation efforts may help the mangrove finch face current extinction threats and avoid the fate of the Fernandina population. However, this historically small lineage will likely continue to face challenges associated with small specialist species surrounded by a widely-distributed sister lineage producing viable hybrids.     

Towards the co‐ordination of terrestrial ecosystem protocols across European research infrastructures

The study of ecosystem processes over multiple scales of space and time is often best achieved using comparable data from multiple sites. Yet, long‐term ecological observatories have often developed their own data collection protocols. Here, we address this problem by proposing a set of ecological protocols suitable for widespread adoption by the ecological community. Scientists from the European ecological research community prioritized terrestrial ecosystem parameters that could benefit from a more consistent approach to data collection within the resources available at most long‐term ecological observatories. Parameters for which standard methods are in widespread use, or for which methods are evolving rapidly, were not selected. Protocols were developed by domain experts, building on existing methods where possible, and refined through a process of field testing and training. They address above‐ground plant biomass; decomposition; land use and management; leaf area index; soil mesofaunal diversity; soil C and N stocks, and greenhouse gas emissions from soils. These complement existing methods to provide a complete assessment of ecological integrity. These protocols offer integrated approaches to ecological data collection that are low cost and are starting to be used across the European Long Term Ecological Research community.     

Selection on a behaviour‐related gene during the first stages of the biological invasion pathway

Human‐induced biological invasions are common worldwide and often have negative impacts on wildlife and human societies. Several studies have shown evidence for selection on invaders after introduction to the new range. However, selective processes already acting prior to introduction have been largely neglected. Here, we tested whether such early selection acts on known behaviour‐related gene variants in the yellow‐crowned bishop (Euplectes afer), a pet‐traded African songbird. We tested for nonrandom allele frequency changes after trapping, acclimation and survival in captivity. We also compared the native source population with two independent invasive populations. Allele frequencies of two SNPs in the dopamine receptor D4 (DRD4) gene—known to be linked to behavioural activity in response to novelty in this species—significantly changed over all early invasion stages. They also differed between the African native population and the two invading European populations. The two‐locus genotype associated with reduced activity declined consistently, but strongest at the trapping stage. Overall genetic diversity did not substantially decrease, and there is little evidence for new alleles in the introduced populations, indicating that selection at the DRD4 gene predominantly worked on the standing genetic variation already present in the native population. Our study demonstrates selection on a behaviour‐related gene during the first stages of a biological invasion. Thus, pre‐establishment stages of a biological invasion do not only determine the number of propagules that are introduced (their quantity), but also their phenotypic and genetic characteristics (their quality).     

Biogeography of mutualistic fungi cultivated by leafcutter ants

Leafcutter ants propagate co‐evolving fungi for food. The nearly 50 species of leafcutter ants (Atta, Acromyrmex) range from Argentina to the United States, with the greatest species diversity in southern South America. We elucidate the biogeography of fungi cultivated by leafcutter ants using DNA sequence and microsatellite‐marker analyses of 474 cultivars collected across the leafcutter range. Fungal cultivars belong to two clades (Clade‐A and Clade‐B). The dominant and widespread Clade‐A cultivars form three genotype clusters, with their relative prevalence corresponding to southern South America, northern South America, Central and North America. Admixture between Clade‐A populations supports genetic exchange within a single species, Leucocoprinus gongylophorus. Some leafcutter species that cut grass as fungicultural substrate are specialized to cultivate Clade‐B fungi, whereas leafcutters preferring dicot plants appear specialized on Clade‐A fungi. Cultivar sharing between sympatric leafcutter species occurs frequently such that cultivars of Atta are not distinct from those of Acromyrmex. Leafcutters specialized on Clade‐B fungi occur only in South America. Diversity of Clade‐A fungi is greatest in South America, but minimal in Central and North America. Maximum cultivar diversity in South America is predicted by the Kusnezov–Fowler hypothesis that leafcutter ants originated in subtropical South America and only dicot‐specialized leafcutter ants migrated out of South America, but the cultivar diversity becomes also compatible with a recently proposed hypothesis of a Central American origin by postulating that leafcutter ants acquired novel cultivars many times from other nonleafcutter fungus‐growing ants during their migrations from Central America across South America. We evaluate these biogeographic hypotheses in the light of estimated dates for the origins of leafcutter ants and their cultivars.     

Carbonate ooids of the Mesoarchaean Pongola Supergroup,South Africa

Ooids from the Mesoarchaean Chobeni Formation, Pongola Supergroup, KwaZulu‐Natal, South Africa are older than any ooids reported to date. They are made of dolomite and ankerite and show concentric, radial‐concentric, micritic, and radial fabrics. Radial ooids are interpreted to have originated from high‐Mg‐calcite and probably formed by microbial activity in a low‐energy regime, while concentric ooids had an aragonite precursor and formed biotically under agitated/high‐energy environmental conditions. Micritic ooids formed via the recrystallization of concentric ooids. Ooids and other allochems, such as intraclasts and peloids, contain carbonaceous matter. The close association of carbonaceous matter within ooid cortices with metabolically important elements, such as N, S and P, as identified by nano‐scale secondary ion mass spectrometry analysis, allows us to propose a biologically induced origin for some ooids. By analogy with modern examples, a variety of microbial communities probably played a role in carbonate precipitation and ooid formation. Shale‐normalized rare earth element (REE) distribution patterns of ooids and other allochems show positive La_SN, Gd_SN and Y_SN anomalies, superchondritic Y/Ho ratios and depleted light rare earth elements (LREEs) relative to the heavy rare earth elements (HREEs), which resemble those of seawater. These anomalies are less pronounced than expected for an open marine setting, which is interpreted as evidence for deposition in restricted shallow marine environments. Non‐seawater REE patterns in recrystallized matrix and pore‐ and vein‐filling carbonate likely reflect redistribution of rare earth elements during post‐depositional alteration and/or reflect differences in the elemental and REE compositions of diagenetic fluids.     

Heterogeneity of CD4 and CD8+ memory T cells in localized and generalized Wegener's granulomatosis

Memory T cells display phenotypic heterogeneity. Surface antigens previously regarded as exclusive markers of naive T cells, such as L-selectin (CD62L), can also be detected on some memory T cells. Moreover, a fraction of CD45RO⁺ (positive for the short human isoform of CD45) memory T cells reverts to the CD45RA⁺ (positive for the long human isoform of CD45) phenotype. We analyzed patients with biopsy-proven localized Wegener's granulomatosis (WG) (n = 5), generalized WG (n = 16) and age- and sex-matched healthy controls (n = 13) to further characterize memory T cells in WG. The cell-surface expression of CD45RO, CD45RA, CD62L, CCR3, CCR5 and CXCR3 was determined on blood-derived T cells by four-color flow cytometric analysis. The fractions of CCR5⁺ and CCR3⁺ cells within the CD4⁺CD45RO⁺ and CD8⁺CD45RO⁺ memory T cell populations were significantly expanded in localized and generalized WG. The mean percentage of Th1-type CCR5 expression was higher in localized WG. Upregulated CCR5 and CCR3 expression could also be detected on a fraction of CD45RA⁺ T cells. CD62L expression was seen on approximately half of the memory T cell populations expressing chemokine receptors. This study demonstrates for the first time that expression of the inducible inflammatory chemokine receptors CCR5 and CCR3 on CD45RO⁺ memory T cells, as well as on CD45RA⁺ T cells ('revertants'), contributes to phenotypic heterogeneity in an autoimmune disease, namely WG. Upregulated CCR5 and CCR3 expression suggests that the cells belong to the effector memory T cell population. CCR5 and CCR3 expression on CD4⁺ and CD8⁺ memory T cells indicates a potential to respond to chemotactic gradients and might be important in T cell migration contributing to granuloma formation and vasculitis in WG.