Characterization of algal community composition and structure from the nearshore environment, Lake Tahoe (United States).

Periphyton assemblages from the nearshore environment of the west (California) side of Lake Tahoe, were analyzed to determine their taxonomic composition and community structure across habitats and seasons. Lake Tahoe is the second deepest lake in the US and an iconic oligotrophic subalpine lake with remarkable transparency. It has experienced offshore cultural eutrophication since the 1960s with observations of nuisance nearshore algal growth since the mid 2000s attributed to anthropogenic stressors. Samplings from November 2019-September 2020 provide useful snapshots against which older monitoring may be contextualized. A voucher flora, complete with descriptions, photo-documentation and referencing to species concepts employed, was created as a method of providing reproducible identification and enumeration of algal species, and more seamless reconciliation of detailed taxonomic data with future monitoring projects. The eulittoral zone (0-2 m) is seasonally dominated by elongate araphid (Synedra, Ulnaria) and stalked or entubed diatoms (Gomphonema, Cymbella, Encyonema). The sublittoral zone (>2 m) is dominated by a nitrogen-fixing Epithemia-cyanobacteria assemblage with less seasonal changes in dominance and composition that expanded to impinge on the 2 m depths of the eulittoral zone in the Fall. Sublittoral epipsammic samples, despite their proximity to rocks, had a very distinct diatom composition and high species dominance, similar to what was seen in the Fall eulittoral samples, with high numbers of Staurosirella chains and small biraphid diatoms. The deeper samples at 30 and 50 m contained high numbers of live Epithemia, and indicate a thriving sublittoral assemblage at these greater depths, but with less biomass. The 2019-20 data show many of the same diatom taxa observed in the 1970's and 1980's but with changes in species dominance. Notably, there was less of the green alga Mougeotia, when compared to the 1970's data, and a higher dominance by nitrogen fixing Epithemia in the sublittoral zone, persisting year-round. These new data show roughly double the algal species biodiversity that had been documented previously in the Lake Tahoe nearshore, and is largely attributed to the methods employed. Adopting these new methods in future monitoring efforts should improve harmonization of taxonomic data and help advance our knowledge of the contributions to nearshore cultural eutrophication.

Plastic debris in lakes and reservoirs.

Plastic debris is thought to be widespread in freshwater ecosystems globally1. However, a lack of comprehensive and comparable data makes rigorous assessment of its distribution challenging2,3. Here we present a standardized cross-national survey that assesses the abundance and type of plastic debris (>250 µm) in freshwater ecosystems. We sample surface waters of 38 lakes and reservoirs, distributed across gradients of geographical position and limnological attributes, with the aim to identify factors associated with an increased observation of plastics. We find plastic debris in all studied lakes and reservoirs, suggesting that these ecosystems play a key role in the plastic-pollution cycle. Our results indicate that two types of lakes are particularly vulnerable to plastic contamination: lakes and reservoirs in densely populated and urbanized areas and large lakes and reservoirs with elevated deposition areas, long water-retention times and high levels of anthropogenic influence. Plastic concentrations vary widely among lakes; in the most polluted, concentrations reach or even exceed those reported in the subtropical oceanic gyres, marine areas collecting large amounts of debris4. Our findings highlight the importance of including lakes and reservoirs when addressing plastic pollution, in the context of pollution management and for the continued provision of lake ecosystem services.

Salinity and pH effects on survival, growth, and reproduction of quagga mussels.

Background: In recent decades, invasive quagga mussels have expanded to the Western United States from the Great Lakes region of North America. Most studies that evaluate the invasion potential of quagga mussels in western water bodies have utilized physiological and life history information from zebra mussels, a related taxon. Few studies have assessed the potential for invasion using specific information from quagga mussel life history or experiments that test for their survival in the fresh and saline waters of the western United States. Methods: We investigated quagga mussel survival, growth, and reproduction using semi-natural experiments under temperature and light controlled conditions across a gradient of water salinity (fresh to brackish) and pH (8.4-11). Water from Lake Mead was used as a positive control in our experiment, and water from Pyramid Lake and the Truckee River was used as brackish and freshwater treatments, respectively. The mussels used in the experiments were collected from Lake Mead. Results: After 12 h in brackish water (4 ppt, pH 9.3), we observed 100% mortality of adult mussels. The swelling and disintegration of body tissues and high mortality rates indicated that high potassium, sodium, and chloride concentrations were the likely causes of death in brackish water treatments. In contrast, mussels were able to survive, grow, and reach sexual maturity in freshwater (0.1 ppt) with a low calcium concentration (17 mg L-1) after 57 days. Mussels died after 2 days at pH 11 and after 12 days at pH 10; during the 14-day monitoring period, no mortality was detected at pH 9.0, 9.3, or 9.5 and mussels did not exhibit any visual indications of stress. Understanding quagga mussel physiological and environmental tolerances appears to be essential for assessing their invasion potential in aquatic habitats.

Fish biodiversity declines with dam development in the Lower Mekong Basin.

Hydropower dams are a source of renewable energy, but dam development and hydropower generation negatively affect freshwater ecosystems, biodiversity, and food security. We assess the effects of hydropower dam development on spatial-temporal changes in fish biodiversity from 2007 to 2014 in the Sekong, Sesan, and Srepok Basins-major tributaries to the Mekong River. By analyzing a 7-year fish monitoring dataset, and regressing fish abundance and biodiversity trends against cumulative number of upstream dams, we found that hydropower dams reduced fish biodiversity, including migratory, IUCN threatened and indicator species in the Sesan and Srepok Basins where most dams have been constructed. Meanwhile, fish biodiversity increased in the Sekong, the basin with the fewest dams. Fish fauna in the Sesan and Srepok Basins decreased from 60 and 29 species in 2007 to 42 and 25 species in 2014, respectively; while they increased from 33 in 2007 to 56 species in 2014 in the Sekong Basin. This is one of the first empirical studies to show reduced diversity following dam construction and fragmentation, and increased diversity in less regulated rivers in the Mekong River. Our results underscore the importance of the Sekong Basin to fish biodiversity and highlight the likely significance of all remaining free-flowing sections of the Lower Mekong Basin, including the Sekong, Cambodian Mekong, and Tonle Sap Rivers to migratory and threatened fish species. To preserve biodiversity, developing alternative renewable sources of energy or re-operating existing dams to increase power generation are recommended over constructing new hydropower dams.

Phenocam observed flowering anomaly of Rhododendron arboreum Sm. in Himalaya: a climate change impact perspective.

Flowering exhibits a significant relationship with environmental stimuli and changes. Effect of photoperiodism and vernalization have been well studied in flowering phenology; however, the effect of soil temperature on flowering is less explored which is one of the major factors of vegetation growth in alpine ecosystem. This study thus focuses on the effects of soil and air temperature on flowering response of Rhododendron arboreum Sm., a Himalayan tree species, which is also an indicator of spring initiation in high altitude regions. To monitor the flowering pattern, we employed automated phenocam, which was set up at 3356 masl in Tungnath (Indian Alpine region of Uttarakhand) for time-lapse photography of timberline ecotone. Soil and air temperature were recorded continuously at the timberline ecotone. Three years (2017 to 2020) of datasets were used for the present study. The phenocam observations displayed an interesting event in the year 2019-2020 with complete absence of flowering in R. arboreum population at Tungnath timberline ecotone. From the soil temperature data, an increase in winter (Dec-Jan, during which floral buds form) soil temperature, by > 1 °C, and no accumulation of freezing degree-days were found for the year 2019-2020. Air temperature however did not display any relationship with the failure of flowering, ruling out aerial chilling or frost injury of floral buds. From the results, a possible relationship between soil temperature and flowering can be suggested pointing towards necessary root apex vernalization stimulus in shallow rooted Rhododendrons. However, the dependency of flowering in Rhododendrons on winter soil temperature further requires continuous monitoring and more observations to make concrete inferences.

Intercontinental analysis of temperate steppe stream food webs reveals consistent autochthonous support of fishes.

Quantifying the trophic basis of production for freshwater metazoa at broad spatial scales is key to understanding ecosystem function and has been a research priority for decades. However, previous lotic food web studies have been limited by geographic coverage or methodological constraints. We used compound-specific stable carbon isotope analysis of amino acids (AAs) to estimate basal resource contributions to fish consumers in streams spanning grassland, montane and semi-arid ecoregions of the temperate steppe biome on two continents. Across a range of stream sizes and light regimes, we found consistent trophic importance of aquatic resources. Essential AAs of heterotrophic microbial origin generally provided secondary support for fishes, while terrestrial carbon did not seem to provide significant, direct support. These findings provide strong evidence for the dominant contribution of carbon to higher-order consumers by aquatic autochthonous resources (primarily) and heterotrophic microbial communities (secondarily) in temperate steppe streams.

Reimagine fire science for the anthropocene.

Fire is an integral component of ecosystems globally and a tool that humans have harnessed for millennia. Altered fire regimes are a fundamental cause and consequence of global change, impacting people and the biophysical systems on which they depend. As part of the newly emerging Anthropocene, marked by human-caused climate change and radical changes to ecosystems, fire danger is increasing, and fires are having increasingly devastating impacts on human health, infrastructure, and ecosystem services. Increasing fire danger is a vexing problem that requires deep transdisciplinary, trans-sector, and inclusive partnerships to address. Here, we outline barriers and opportunities in the next generation of fire science and provide guidance for investment in future research. We synthesize insights needed to better address the long-standing challenges of innovation across disciplines to (i) promote coordinated research efforts; (ii) embrace different ways of knowing and knowledge generation; (iii) promote exploration of fundamental science; (iv) capitalize on the "firehose" of data for societal benefit; and (v) integrate human and natural systems into models across multiple scales. Fire science is thus at a critical transitional moment. We need to shift from observation and modeled representations of varying components of climate, people, vegetation, and fire to more integrative and predictive approaches that support pathways toward mitigating and adapting to our increasingly flammable world, including the utilization of fire for human safety and benefit. Only through overcoming institutional silos and accessing knowledge across diverse communities can we effectively undertake research that improves outcomes in our more fiery future.

Blue Waters, Green Bottoms: Benthic Filamentous Algal Blooms Are an Emerging Threat to Clear Lakes Worldwide.

Nearshore (littoral) habitats of clear lakes with high water quality are increasingly experiencing unexplained proliferations of filamentous algae that grow on submerged surfaces. These filamentous algal blooms (FABs) are sometimes associated with nutrient pollution in groundwater, but complex changes in climate, nutrient transport, lake hydrodynamics, and food web structure may also facilitate this emerging threat to clear lakes. A coordinated effort among members of the public, managers, and scientists is needed to document the occurrence of FABs, to standardize methods for measuring their severity, to adapt existing data collection networks to include nearshore habitats, and to mitigate and reverse this profound structural change in lake ecosystems. Current models of lake eutrophication do not explain this littoral greening. However, a cohesive response to it is essential for protecting some of the world's most valued lakes and the flora, fauna, and ecosystem services they sustain.

Hierarchical genetic structure and implications for conservation of the world's largest salmonid, Hucho taimen.

Population genetic analyses can evaluate how evolutionary processes shape diversity and inform conservation and management of imperiled species. Taimen (Hucho taimen), the world's largest freshwater salmonid, is threatened, endangered, or extirpated across much of its range due to anthropogenic activity including overfishing and habitat degradation. We generated genetic data using high throughput sequencing of reduced representation libraries for taimen from multiple drainages in Mongolia and Russia. Nucleotide diversity estimates were within the range documented in other salmonids, suggesting moderate diversity despite widespread population declines. Similar to other recent studies, our analyses revealed pronounced differentiation among the Arctic (Selenge) and Pacific (Amur and Tugur) drainages, suggesting historical isolation among these systems. However, we found evidence for finer-scale structure within the Pacific drainages, including unexpected differentiation between tributaries and the mainstem of the Tugur River. Differentiation across the Amur and Tugur basins together with coalescent-based demographic modeling suggests the ancestors of Tugur tributary taimen likely diverged in the eastern Amur basin, prior to eventual colonization of the Tugur basin. Our results suggest the potential for differentiation of taimen at different geographic scales, and suggest more thorough geographic and genomic sampling may be needed to inform conservation and management of this iconic salmonid.

Global data set of long-term summertime vertical temperature profiles in 153 lakes.

Climate change and other anthropogenic stressors have led to long-term changes in the thermal structure, including surface temperatures, deepwater temperatures, and vertical thermal gradients, in many lakes around the world. Though many studies highlight warming of surface water temperatures in lakes worldwide, less is known about long-term trends in full vertical thermal structure and deepwater temperatures, which have been changing less consistently in both direction and magnitude. Here, we present a globally-expansive data set of summertime in-situ vertical temperature profiles from 153 lakes, with one time series beginning as early as 1894. We also compiled lake geographic, morphometric, and water quality variables that can influence vertical thermal structure through a variety of potential mechanisms in these lakes. These long-term time series of vertical temperature profiles and corresponding lake characteristics serve as valuable data to help understand changes and drivers of lake thermal structure in a time of rapid global and ecological change.

Valley-scale hydrogeomorphology drives river fish assemblage variation in Mongolia.

River hydrogeomorphology is a major driver shaping biodiversity and community composition. Here, we examine how hydrogeomorphic heterogeneity expressed by Functional Process Zones (FPZs) in river networks is associated with fish assemblage variation. We examined this association in two distinct ecoregions in Mongolia expected to display different gradients of river network hydrogeomorphic heterogeneity. We delineated FPZs by extracting valley-scale hydrogeomorphic variables at 10 km sample intervals in forest steppe (FS) and in grassland (G) river networks. We sampled fish assemblages and examined variation associated with changes in gradients of hydrogeomorphology as expressed by the FPZs. Thus, we examined assemblage variation as patterns of occurrence- and abundance-based beta diversities for the taxonomic composition of assemblages and as functional beta diversity. Overall, we delineated 5 and 6 FPZs in river networks of the FS and G, respectively. Eight fish species were found in the FS river network and seventeen in the G, four of them common to both ecoregions. Functional richness was correspondingly higher in the G river network. Variation in the taxonomic composition of assemblages was driven by species turnover and was only significant in the G river network. Abundance-based taxonomic variation was significant in river networks of both ecoregions, while the functional beta diversity results were inconclusive. We show that valley-scale hydrogeomorphology is a significant driver of variation in fish assemblages at a macrosystem scale. Both changes in the composition of fish assemblages and the carrying capacity of the river network were driven by valley-scale hydrogeomorphic variables. River network hydrogeomorphology as accounted for in the study has, therefore, the potential to inform macrosystem scale community ecology research and conservation efforts.

Widespread deoxygenation of temperate lakes.

The concentration of dissolved oxygen in aquatic systems helps to regulate biodiversity1,2, nutrient biogeochemistry3, greenhouse gas emissions4, and the quality of drinking water5. The long-term declines in dissolved oxygen concentrations in coastal and ocean waters have been linked to climate warming and human activity6,7, but little is known about the changes in dissolved oxygen concentrations in lakes. Although the solubility of dissolved oxygen decreases with increasing water temperatures, long-term lake trajectories are difficult to predict. Oxygen losses in warming lakes may be amplified by enhanced decomposition and stronger thermal stratification8,9 or oxygen may increase as a result of enhanced primary production10. Here we analyse a combined total of 45,148 dissolved oxygen and temperature profiles and calculate trends for 393 temperate lakes that span 1941 to 2017. We find that a decline in dissolved oxygen is widespread in surface and deep-water habitats. The decline in surface waters is primarily associated with reduced solubility under warmer water temperatures, although dissolved oxygen in surface waters increased in a subset of highly productive warming lakes, probably owing to increasing production of phytoplankton. By contrast, the decline in deep waters is associated with stronger thermal stratification and loss of water clarity, but not with changes in gas solubility. Our results suggest that climate change and declining water clarity have altered the physical and chemical environment of lakes. Declines in dissolved oxygen in freshwater are 2.75 to 9.3 times greater than observed in the world's oceans6,7 and could threaten essential lake ecosystem services2,3,5,11.

Smoke from regional wildfires alters lake ecology.

Wildfire smoke often covers areas larger than the burned area, yet the impacts of smoke on nearby aquatic ecosystems are understudied. In the summer of 2018, wildfire smoke covered Castle Lake (California, USA) for 55 days. We quantified the influence of smoke on the lake by comparing the physics, chemistry, productivity, and animal ecology in the prior four years (2014-2017) to the smoke year (2018). Smoke reduced incident ultraviolet-B (UV-B) radiation by 31% and photosynthetically active radiation (PAR) by 11%. Similarly, underwater UV-B and PAR decreased by 65 and 44%, respectively, and lake heat content decreased by 7%. While the nutrient limitation of primary production did not change, shallow production in the offshore habitat increased by 109%, likely due to a release from photoinhibition. In contrast, deep-water, primary production decreased and the deep-water peak in chlorophyll a did not develop, likely due to reduced PAR. Despite the structural changes in primary production, light, and temperature, we observed little significant change in zooplankton biomass, community composition, or migration pattern. Trout were absent from the littoral-benthic habitat during the smoke period. The duration and intensity of smoke influences light regimes, heat content, and productivity, with differing responses to consumers.

Deeper waters are changing less consistently than surface waters in a global analysis of 102 lakes.

Globally, lake surface water temperatures have warmed rapidly relative to air temperatures, but changes in deepwater temperatures and vertical thermal structure are still largely unknown. We have compiled the most comprehensive data set to date of long-term (1970-2009) summertime vertical temperature profiles in lakes across the world to examine trends and drivers of whole-lake vertical thermal structure. We found significant increases in surface water temperatures across lakes at an average rate of + 0.37 °C decade-1, comparable to changes reported previously for other lakes, and similarly consistent trends of increasing water column stability (+ 0.08 kg m-3 decade-1). In contrast, however, deepwater temperature trends showed little change on average (+ 0.06 °C decade-1), but had high variability across lakes, with trends in individual lakes ranging from - 0.68 °C decade-1 to + 0.65 °C decade-1. The variability in deepwater temperature trends was not explained by trends in either surface water temperatures or thermal stability within lakes, and only 8.4% was explained by lake thermal region or local lake characteristics in a random forest analysis. These findings suggest that external drivers beyond our tested lake characteristics are important in explaining long-term trends in thermal structure, such as local to regional climate patterns or additional external anthropogenic influences.

Ecosystem response to earlier ice break-up date: Climate-driven changes to water temperature, lake-habitat-specific production, and trout habitat and resource use.

Climate warming has yielded earlier ice break-up dates in recent decades for lakes leading to water temperature increases, altered habitat, and both increases and decreases to ecosystem productivity. Within lakes, the effect of climate warming on secondary production in littoral and pelagic habitats remains unclear. The intersection of changing habitat productivity and warming water temperatures on salmonids is important for understanding how climate warming will impact mountain ecosystems. We develop and test a conceptual model that expresses how earlier ice break-up dates influence within lake habitat production, water temperatures and the habitat utilized by, resources obtained and behavior of salmonids in a mountain lake. We measured zoobenthic and zooplankton production from the littoral and pelagic habitats, thermal conditions, and the habitat use, resource use, and fitness of Brook Trout (Salvelinus fontinalis). We show that earlier ice break-up conditions created a "resource-rich" littoral-benthic habitat with increases in zoobenthic production compared to the pelagic habitat which decreased in zooplankton production. Despite the increases in littoral-benthic food resources, trout did not utilize littoral habitat or zoobenthic resources due to longer durations of warm water temperatures in the littoral zone. In addition, 87% of their resources were supported by the pelagic habitat during periods with earlier ice break-up when pelagic resources were least abundant. The decreased reliance on littoral-benthic resources during earlier ice break-up caused reduced fitness (mean reduction of 12 g) to trout. Our data show that changes to ice break-up drive multi-directional results for resource production within lake habitats and increase the duration of warmer water temperatures in food-rich littoral habitats. The increased duration of warmer littoral water temperatures reduces the use of energetically efficient habitats culminating in decreased trout fitness.

Population dynamics of threatened Lahontan cutthroat trout in Summit Lake, Nevada.

Summit Lake, Nevada (USA) is the last high-desert terminal lake to have a native self-sustaining population of threatened Lahontan cutthroat trout (Oncorhynchus clarkii henshawi). From spring 2015 to fall 2017, we quantified adult abundance and survival and the total annual spawning run. Abundance and survival were estimated with mark-recapture using PIT tags, and the annual spawning run was estimated with PIT tag detections and counts of spawners. Adult abundance fluctuated from 830 (95% CI 559-1248) to 1085 (95% CI 747-1614), with no overall temporal trend, as a decrease in male abundance was generally offset by an equal increase in female abundance. Estimated mean adult survival was 0.51 (95% CI 0.44-0.58). The spawning run increased from 645 (2015) to 868 (2016), but then decreased slightly to 824 (2017, mean = 789 ± 118). Female spawners increased in 2016 but decreased slightly in 2017, whereas male spawners decreased each year. In addition, the proportion of adults that spawned each year increased overall. Our study suggests that the adult population remained stable although most of the study period included the recent, severe regional drought in the western United States (2012-2016).

Non-invasive molecular tracking method that measures ocular drug distribution in non-human primates.

Intravitreal (IVT) injection has become the standard route for drug administration in retinal diseases. However, the ability to measure biodistribution of ocular therapeutics in large species remains limited, due to the invasive nature of some techniques or their lack of spatial information. The aim of this study was to develop in cynomolgus monkeys a non-invasive fluorescence imaging technology that enables tracking of IVT-dosed drugs and could be easily translated into humans. Here, we show a proof-of-concept for labeled ranibizumab with observed half-lives of 3.34 and 4.52 days at the retina and in the vitreous, respectively. We further investigate a long acting anti-VEGF antibody, which remains as an agglomerate with some material leaking out until the end of the study at Day 35. Overall, we were able to visualize and measure differences in the in vivo behavior between short and long-acting antibodies, demonstrating the power of the technology for ocular pharmacokinetics.

Traditional Herbal Knowledge among the Inhabitants: A Case Study in Urgam Valley of Chamoli Garhwal, Uttarakhand, India.

The Indian Himalaya is rich in plant species, including many medicinal plants, greatly valued by local inhabitants for health care needs. The study in Urgam Valley of Uttarakhand, India, is to identity and document traditional knowledge of medicinal plants. The study revealed high consensus on medicinal plant usage, with 51 species belonging to 31 families used for local health care. Number of species and uses known increases with age, and elders and specialist healers retain higher levels of traditional medicinal plant knowledge, having unique knowledge of medicinal plants and their uses as well as preparation.

Communities associated with the Functional Process Zone scale: A case study of stream macroinvertebrates in endorheic drainages.

Rivers are being increasingly analyzed from a holistic scale focus, imposing the challenge to establish a clear sampling framework that integrates complex valley-to-reach hydrogeomorphic features. Here, we address this challenge by examining macroinvertebrate communities of different hydrogeomorphic patches, or Functional Process Zones (FPZs), established by the GIS-based model RESonate. We delineated FPZs across three endorheic drainages in the Great Basin, USA, using a self-emerging clustering method that classifies segments of rivers with similar hydrogeomorphic characteristics. We sampled macroinvertebrate communities across different FPZs. We examined the taxonomic and functional organizations of these communities, and we assessed the relative contributions of in-stream and watershed-scale environmental filters in structuring these communities. We found discreet macroinvertebrate communities associated with FPZs across drainages, where elevation prevailed on valley confinement in structuring these communities. Communities of upland FPZs exhibited a higher heterogeneity suggested by higher ß-diversity and nested structure of communities, while lowland FPZs showed a higher pairwise abundance agreement across communities. Eltonian trait composition, primarily describing bionomic traits, showed a higher degree of niche differentiation in upland FPZs, thereby increasing the overall ecosystem function. Differences in variance partitioning among environmental filters acting at different spatial scales show a strong spatial structure in the response of communities in different FPZs. Overall, environmental filters had a stronger control of the communities' functional organization than the taxonomic composition. Our results support the paradigm of different FPZs having distinct communities that express different ecosystem properties. Findings of this study constitute a fruitful avenue for expanding community-based research using the FPZ template as a tool for riverine ecology. However, the unique nature of rivers in endorheic basins needs to be considered when applying our conclusions to other systems, as some findings (e.g., the higher community homogenization in lowland FPZs) might be specific to this rarely examined type of river systems.

Imaging B Cells in a Mouse Model of Multiple Sclerosis Using 64Cu-Rituximab PET.

B lymphocytes are a key pathologic feature of multiple sclerosis (MS) and are becoming an important therapeutic target for this condition. Currently, there is no approved technique to noninvasively visualize B cells in the central nervous system (CNS) to monitor MS disease progression and response to therapies. Here, we evaluated 64Cu-rituximab, a radiolabeled antibody specifically targeting the human B cell marker CD20, for its ability to image B cells in a mouse model of MS using PET. Methods: To model CNS infiltration by B cells, experimental autoimmune encephalomyelitis (EAE) was induced in transgenic mice that express human CD20 on B cells. EAE mice were given subcutaneous injections of myelin oligodendrocyte glycoprotein fragment1-125 emulsified in complete Freund adjuvant. Control mice received complete Freund adjuvant alone. PET imaging of EAE and control mice was performed 1, 4, and 19 h after 64Cu-rituximab administration. Mice were perfused and sacrificed after the final PET scan, and radioactivity in dissected tissues was measured with a γ-counter. CNS tissues from these mice were immunostained to quantify B cells or were further analyzed via digital autoradiography. Results: Lumbar spinal cord PET signal was significantly higher in EAE mice than in controls at all evaluated time points (e.g., 1 h after injection: 5.44 ± 0.37 vs. 3.33 ± 0.20 percentage injected dose [%ID]/g, P < 0.05). 64Cu-rituximab PET signal in brain regions ranged between 1.74 ± 0.11 and 2.93 ± 0.15 %ID/g for EAE mice, compared with 1.25 ± 0.08 and 2.24 ± 0.11 %ID/g for controls (P < 0.05 for all regions except striatum and thalamus at 1 h after injection). Similarly, ex vivo biodistribution results revealed notably higher 64Cu-rituximab uptake in the brain and spinal cord of huCD20tg EAE, and B220 immunostaining verified that increased 64Cu-rituximab uptake in CNS tissues corresponded with elevated B cells. Conclusion: B cells can be detected in the CNS of EAE mice using 64Cu-rituximab PET. Results from these studies warrant further investigation of 64Cu-rituximab in EAE models and consideration of use in MS patients to evaluate its potential for detecting and monitoring B cells in the progression and treatment of this disease. These results represent an initial step toward generating a platform to evaluate B cell-targeted therapeutics en route to the clinic.