Multiplicity of cerebrospinal fluid functions: New challenges in health and disease

This review integrates eight aspects of cerebrospinal fluid (CSF) circulatory dynamics: formation rate, pressure, flow, volume, turnover rate, composition, recycling and reabsorption. Novel ways to modulate CSF formation emanate from recent analyses of choroid plexus transcription factors (E2F5), ion transporters (NaHCO3 cotransport), transport enzymes (isoforms of carbonic anhydrase), aquaporin 1 regulation, and plasticity of receptors for fluid-regulating neuropeptides. A greater appreciation of CSF pressure (CSFP) is being generated by fresh insights on peptidergic regulatory servomechanisms, the role of dysfunctional ependyma and circumventricular organs in causing congenital hydrocephalus, and the clinical use of algorithms to delineate CSFP waveforms for diagnostic and prognostic utility. Increasing attention focuses on CSF flow: how it impacts cerebral metabolism and hemodynamics, neural stem cell progression in the subventricular zone, and catabolite/peptide clearance from the CNS. The pathophysiological significance of changes in CSF volume is assessed from the respective viewpoints of hemodynamics (choroid plexus blood flow and pulsatility), hydrodynamics (choroidal hypo- and hypersecretion) and neuroendocrine factors (i.e., coordinated regulation by atrial natriuretic peptide, arginine vasopressin and basic fibroblast growth factor). In aging, normal pressure hydrocephalus and Alzheimer's disease, the expanding CSF space reduces the CSF turnover rate, thus compromising the CSF sink action to clear harmful metabolites (e.g., amyloid) from the CNS. Dwindling CSF dynamics greatly harms the interstitial environment of neurons. Accordingly the altered CSF composition in neurodegenerative diseases and senescence, because of adverse effects on neural processes and cognition, needs more effective clinical management. CSF recycling between subarachnoid space, brain and ventricles promotes interstitial fluid (ISF) convection with both trophic and excretory benefits. Finally, CSF reabsorption via multiple pathways (olfactory and spinal arachnoidal bulk flow) is likely complemented by fluid clearance across capillary walls (aquaporin 4) and arachnoid villi when CSFP and fluid retention are markedly elevated. A model is presented that links CSF and ISF homeostasis to coordinated fluxes of water and solutes at both the blood-CSF and blood-brain transport interfaces

Vertical structure and color of Jovian latitudinal cloud bands during the Juno era

The identity of the coloring agent(s) in Jupiter's atmosphere and the exact structure of Jupiter's uppermost cloud deck are yet to be conclusively understood. The Crème Brulée model of Jupiter's tropospheric clouds, originally proposed by Baines et al. and expanded upon by Sromovsky et al. and Baines et al., presumes that the chromophore measured by Carlson et al. is the singular coloring agent in Jupiter's troposphere. In this work, we test the validity of the Crème Brulée model of Jupiter's uppermost cloud deck using spectra measured during the Juno spacecraft's fifth perijove pass in 2017 March. These data were obtained as part of an international ground-based observing campaign in support of the Juno mission using the New Mexico State University Acousto-optic Imaging Camera at the 3.5 m telescope at Apache Point Observatory in Sunspot, NM, USA. We find that the Crème Brulée model cloud-layering scheme can reproduce Jupiter's visible spectrum both with the Carlson et al. chromophore and with modifications to its imaginary index of refraction spectrum. While the Crème Brulée model provides reasonable results for regions of Jupiter's cloud bands such as the North Equatorial Belt and Equatorial Zone, we find that it is not a safe assumption for unique weather events, such as the 2016–2017 Southern Equatorial Belt outbreak that was captured by our measurements

Fish assemblage recovery along a riverine disturbance gradient

Artificial fluctuations in streamflow have been documented to alter the composition andstructure of stream communities. This study tests the hypothesis that a spatial recovery gradientin fish assemblage structure exists downstream of a hydroelectric dam, and that recovery can be identified by the presence and abundance of species largely restricted to flowing-water habitats(fluvial specialists). A longitudinal gradient of change in a shoreline fish assemblage wasquantified in a 66-km reach of a mid-sized, species-rich river (Tallapoosa River, Alabama) withdaily flow fluctuations from hydropower generation. The shoreline fish assemblage in a nearbyand similar river (Cahaba River, Alabama) was quantified as a regional reference for theoccurrence of fish assemblage gradients. Fish were collected with prepositioned areaelectrofishers in 240 randomly located sampling sites, and physical habitat was quantified. Usingdistributional and habitat use information, fish species were categorized as fluvial specialists ormacrohabitat generalists (species that occur in a wide variety of aquatic systems). Sampledhabitats were similar between rivers and along each study reach. The longitudinal pattern ofspecies occurrence and fish abundance was consistent in the free-flowing river. A longitudinalgradient of increasing abundance and richness of only fluvial specialist species existeddownstream of the hydroelectric dam. No similar spatial gradient existed for macrohabitatgeneralists in either river. Although a fish community recovery gradient was identified, a recoveryendpoint was not evident because assemblage change was gradual and possibly incomplete.The preservation and management of riverine fish faunas will partly depend on incorporatingspatial recovery into decisions about permitting and siting of anthropogenic changes like hydroelectric dams. http://dx.doi.org/10.2307/194192

The influence of a toxic cyanobacterial bloom and water hydrology on algal populations and macroinvertebrate abundance in the upper littoral zone of Lake Krugersdrift, South Africa

The biological interactions and the physical and chemical properties of the littoral zone of Lake Krugersdrift were studied for a 4-month period when a dense, toxic cyanobacterial bloom dominated by Microcystis aeruginosa was present in the main lake basin. The presence of a toxic strain of M. aeruginosa was confirmed through the use of ELISA and molecular markers that detect the presence of the mcyB and mcyD genes of the mcy gene cluster that synthesizes microcystin. An increase in Microcystis toxicity at sites dominated by the cyanobacterial scum was accompanied by an increase in total abundance of the macroinvertebrate families Hirudinae, Chironomidae, and Tubificidae. Sites located away from the cyanobacterial scum had a lower abundance but a higher diversity of macroinvertebrates. The water quality under the Microcystis scum was characterized by low pH values, low concentrations of dissolved oxygen, and lower total alkalinity values. The periphytic alga Ulothrix zonata was absent in areas dominated by the cyanobacterial scum, possibly as a result of overshadowing by the scum or direct toxic allelopathic effects on growth and photosynthesis. The diatom Diatoma vulgare dominated the benthic algal flora beneath the cyanobacterial scum

Hydroclimatic and hydrochemical controls on Plecoptera diversity and distribution in northern freshwater ecosystems

Freshwater ecosystems in the mid- to upper-latitudes of the northern hemisphere are particularly vulnerable to the impact of climate change as slight changes in air temperature can alter the form, timing, and magnitude of precipitation and consequent influence of snowmelt on streamflow dynamics. Here, we examine the effects of hydro-climate, flow regime, and hydrochemistry on Plecoptera (stonefly) alpha (α) diversity and distribution in northern freshwater ecosystems. We characterized the hydroclimatic regime of seven catchments spanning a climatic gradient across the northern temperate region and compared them with estimates of Plecoptera genera richness. By a space-for-time substitution, we assessed how warmer temperatures and altered flow regimes may influence Plecoptera alpha diversity and composition at the genus level. Our results show wide hydroclimatic variability among sites, including differences in temporal streamflow dynamics and temperature response. Principal component analysis showed that Plecoptera genera richness was positively correlated with catchment relief (m), mean and median annual air temperature (°C), and streamflow. These results provide a preliminary insight into how hydroclimatic change, particularly in terms of increased air temperature and altered streamflow regimes, may create future conditions more favorable to some Plecopteras in northern catchments

Division of labour in microorganisms: an evolutionary perspective

The division of labour, whereby individuals within a group specialize in certain tasks, has long been appreciated as central to the evolution of complex biological societies. In recent years, several examples of division of labour in microorganisms have arisen, which suggests that this strategy may also be important in microbial species. In this Opinion article, we explore the set of conditions that define division of labour and propose that cooperation between different phenotypes is a defining feature of division of labour. Furthermore, we discuss how clarifying what constitutes division of labour highlights key evolutionary questions, including what form division of labour takes and why it is favoured by natural selection