Potentiation of cortical inhibition by visual deprivation

The fine-tuning of circuits in sensory cortex requires sensory experience during an early critical period. Visual deprivation during the critical period has catastrophic effects on visual function, including loss of visual responsiveness to the deprived eye, reduced visual acuity, and loss of tuning to many stimulus characteristics. These changes occur faster than the remodelling of thalamocortical axons, but the intracortical plasticity mechanisms that underlie them are incompletely understood. Long-term depression of excitatory intracortical synapses has been proposed as a general candidate mechanism for the loss of cortical responsiveness after visual deprivation. Alternatively (or in addition), the decreased ability of the deprived eye to activate cortical neurons could be due to enhanced intracortical inhibition. Here we show that visual deprivation leaves excitatory connections in layer 4 (the primary input layer to cortex) unaffected, but markedly potentiates inhibitory feedback between fast-spiking basket cells (FS cells) and star pyramidal neurons (star pyramids). Further, a previously undescribed form of long-term potentiation of inhibition (LTPi) could be induced at synapses from FS cells to star pyramids, and was occluded by previous visual deprivation. These data suggest that potentiation of inhibition is a major cellular mechanism underlying the deprivation-induced degradation of visual function, and that this form of LTPi is important in fine-tuning cortical circuitry in response to visual experience.     

The Phaeodactylum genome reveals the evolutionary history of diatom genomes

Diatoms are photosynthetic secondary endosymbionts found throughout marine and freshwater environments, and are believed to be responsible for around one-fifth of the primary productivity on Earth. The genome sequence of the marine centric diatom Thalassiosira pseudonana was recently reported, revealing a wealth of information about diatom biology. Here we report the complete genome sequence of the pennate diatom Phaeodactylum tricornutum and compare it with that of T. pseudonana to clarify evolutionary origins, functional significance and ubiquity of these features throughout diatoms. In spite of the fact that the pennate and centric lineages have only been diverging for 90 million years, their genome structures are dramatically different and a substantial fraction of genes ( approximately 40%) are not shared by these representatives of the two lineages. Analysis of molecular divergence compared with yeasts and metazoans reveals rapid rates of gene diversification in diatoms. Contributing factors include selective gene family expansions, differential losses and gains of genes and introns, and differential mobilization of transposable elements. Most significantly, we document the presence of hundreds of genes from bacteria. More than 300 of these gene transfers are found in both diatoms, attesting to their ancient origins, and many are likely to provide novel possibilities for metabolite management and for perception of environmental signals. These findings go a long way towards explaining the incredible diversity and success of the diatoms in contemporary oceans.     

The Metric Bridge Partition Problem: Partitioning of a Metric Space into Two Subspaces Linked by an Edge in Any Optimal Realization

Let G = (V,E,w) be a graph with vertex and edge sets V and E, respectively, and w:E → R ⁺ a function which assigns a positive weight or length to each edge of G. G is called a realization of a finite metric space (M,d), with M = { 1,...,n} if and only if { 1,...,n} ⫅ V and d(i,j) is equal to the length of the shortest chain linking i and j in G ∀ i,j = 1,...,n. A realization G of (M,d), is said optimal if the sum of its weights is minimal among all the realizations of (M,d). Consider a partition of M into two nonempty subsets K and L, and let e be an edge in a realization G of (M,d); we say that e is a bridge linking K with L if e belongs to all chains in G linking a vertex of K with a vertex of L. The Metric Bridge Partition Problem is to determine if the elements of a finite metric space (M,d) can be partitioned into two nonempty subsets K and L such that all optimal realizations of (M,d) contain a bridge linking K with L. We prove in this paper that this problem is polynomially solvable. We also describe an algorithm that constructs an optimal realization of (M,d) from optimal realizations of (K,d|_K) and (L,d|_L).     

The Metric Cutpoint Partition Problem

Let G = (V, E,w) be a graph with vertex and edge sets V and E, respectively, and w: E → a function which assigns a positive weight or length to each edge of G. G is called a realization of a finite metric space (M, d), with M = {1, ..., n} if and only if {1, ..., n} ⊆ V and d(i, j) is equal to the length of the shortest chain linking i and j in G ∀i, j = 1, ..., n. A realization G of (M, d), is called optimal if the sum of its weights is minimal among all the realizations of (M, d). A cutpoint in a graph G is a vertex whose removal strictly increases the number of connected components of G. The Metric Cutpoint Partition Problem is to determine if a finite metric space (M, d) has an optimal realization containing a cutpoint. We prove in this paper that this problem is polynomially solvable. We also describe an algorithm that constructs an optimal realization of (M, d) from optimal realizations of subspaces that do not contain any cutpoint. Supported by grant PA002-104974/2 from the Swiss National Science Foundation. Published online xx, xx, xxxx.     

The glycerophosphoinositols: cellular metabolism and biological functions

The glycerophosphoinositols are cellular products of phospholipase A₂ and lysolipase activities on the membrane phosphoinositides. Their intracellular concentrations can vary upon oncogenic transformation, cell differentiation and hormonal stimulation. Specific glycerophosphodiester phosphodiesterases are involved in their catabolism, which, as with their formation, is under hormonal regulation. With their mechanisms of action including modulation of adenylyl cyclase, intracellular calcium levels, and Rho-GTPases, the glycerophosphoinositols have diverse effects in multiple cell types: induction of cell proliferation in thyroid cells; modulation of actin cytoskeleton organisation in fibroblasts; and reduction of the invasive potential of tumour cell lines. More recent investigations include their effects in inflammatory and immune responses. Indeed, the glycerophosphoinositols enhance cytokine-dependent chemotaxis in T-lymphocytes induced by SDF-1α-receptor activation, indicating roles for these compounds as modulators of T-cell signalling and T-cell responses.     

Brood parasitism and nest survival of Brown-headed Cowbird hosts at high-elevation riparian sites in the eastern Sierra Nevada, California

Deciduous riparian ecosystems in the western United States provide habitat for a higher density of breeding birds than reported for any other avian habitat type and provide habitat for more breeding bird species than adjacent uplands. On the east slope of the Sierra Nevada, riparian ecosystems make up Molothrus ater )—an obligate brood parasite that forages on bare ground and feedlots but typically commutes to distinct shrubland or woodland habitats for breeding. We examined nest survival, brood parasitism, breeding phenology, and causes of nest failure for birds at North Lake and Rock Creek: 2 high-elevation (>2500 m) riparian breeding habitats adjacent to recreational development and within cowbird commuting distance to additional potential foraging sites. Nest survival tended to be higher for host species at Rock Creek than for those at North Lake, but parasitism rates were not significantly different between plots. Of 21 open-cup nesting species, 12 were parasitized. We found the highest rate of parasitism (92%) for Warbling Vireos ( Vireo gilvus ) at North Lake, and parasitism contributed to lower total nest survival there (14%). For nearly all species, parasitized nests were less successful and produced fewer young than nonparasitized nests. However, predation was the leading cause of complete nest failure across all species and contributed to the lowest total nest survival estimates for Western Wood-Pewees ( Contopus sordidulus, 11%) and Dusky Flycatchers ( Empidonax oberholseri, 15%) at North Lake and for Dark-eyed Juncos ( Junco hyemalis, 15%) at Rock Creek. Nest survival was relatively high for Western Wood-Pewees (41%) at Rock Creek and for Yellow Warblers ( Dendroica petechia, 47%) at North Lake. We noted whether the arrival of pack animals at pack-station corrals contributed to variation in cowbird numbers at corrals or in parasitism rates at the 2 sites. Cowbirds occupied corrals before and after pack-stock arrival, and most host clutches were completed prior to pack-stock arrival at nearby corrals, suggesting that the presence of pack animals did not directly affect cowbird host species.     

L'Analyse chimique des végétaux: Le cas du quinquina

In 1820, J. Pelletier and J.-B. Caventou, two French pharmacist-chemists working at the Ecole de Pharmacie of Paris, extracted quinine, a new substance, from cinchona bark. We use this example to illustrate the processes which lead from a crude natural product through the isolation of an active principle to the production of a pure manufactured drug. This allows us to discuss the development of chemical analysis in relation to pharmacy, natural history, medicine and the early pharmaceutical industry. The dynamics of the disciplines involved here show how organic chemistry, which was developing rapidly during these crucial years, expanded and became autonomous. Theoretical aspects (and in particular atomic theory) and practical innovations are relevant to the scientific methods developed by the first generation of those who integrated the new chemistry into their daily work. Beyond these historical issues, this paper aims to show how a holistic approach can contribute to the debate on discovery and invention in a science that is often considered empirical.