Spatial and temporal woodland patterns along the lower Turkwel River, Kenya

Spatial and temporal patterns of riverine woodlands in arid regions of Africa are poorly documented despite their considerable conservation value. We studied 1540 ha of riverine woodland in the lower Turkwel River floodplain, Kenya, between 1990 and 1998. Forty‐one woodland patches were mapped and their soil physical and chemical characteristics, tree species diversity, woody cover, tree density, wood volume and woodland regeneration were determined. The riverine woodland comprised nine vegetation types and a total of 14 woody species. Woodland patch mosaics were associated with microtopographical features and selected soil attributes. The most important woody species were Hyphaene compressa H. Wendl., Acacia tortilis (Forssk.) Hayne and Cadaba rotundifolia Forssk. The exotic Prosopis chilensis (Mol.) St. was invading parts of the riverine woodland. Overall, woody species diversity was low compared to similar riverine woodlands in East Africa. Tree density, wood volume and woody plant regeneration declined over the 8‐year study period, while woody cover was unchanged. Reduced tree density, wood volume and regeneration of woody species might be linked to changes in river flood patterns following the impoundment of the Turkwel Gorge Dam. It is suggested that spatially heterogeneous and temporally stochastic regeneration events, together with occasional tree mortality caused by channel abandonment, create the complex pattern of woodland patches in the lower Turkwel River floodplain. The mapped woodland patches may serve as monitoring units, which in future could reveal the interplay between changes in flooding patterns as a result of dam impoundment, anthropogenic disturbance and the well‐being of the riverine woodlands.     

Neurobiological mechanisms of the meridian and the propagation of needle feeling along the meridian pathway

The present experiments attempt to find the meridian phenomenon and how the needle feeling propagates along the given meridian channels. The neurobiological mechanisms of the meridian were studied with neuroelectrical recording from the motor neurons and CB-HRP retrograde histochemistry technique in both rats and cats. The results demonstrated that most, but not all, of alpha motor neurons supplying a muscle group of a given meridian were selectively activated by afferent inputs originating not only from homonymous or heterogeneous, but synergistic muscle, but also from the skin nerve overlying the muscle group of the homonymous meridian. However, the afferent inputs from the heterogeneous meridian have very weak or no effect. On the other hand, the labeled motor neurons supplying a given meridian muscles form a discrete longitudinal column with a definite bound in the lateral ventral horn. There are oriented dendro-dendristes projections between the labeled motor neurons.The characteristics of both sel     

Spatial propagation of interictal discharges along the cortex

Interictal discharges (IIDs) accompany epileptic seizures and highlight the mechanisms of pathological activity. The propagation of IIDs along the neural tissue is not well understood. To simulate IID propagation, this study proposes a new mathematical model that uses the conductance-based refractory density approach for glutamatergic and GABAergic neuronal populations. The mathematical model is found to be consistent with experimental double-patch registrations in the 4-aminopyridine in vitro model of epilepsy. In slices, the spontaneous activity of interneurons leads to their synchronization by means of the depolarizing GABAmediated response, thus initiating IIDs. Modeling reveals a clustering of interneuronal synchronization followed by IIDs with activity fronts that propagate along the cortex. The GABA-mediated depolarization either remains to be subthreshold for the principal neurons and thus results in pure GABAergic IIDs (IID1s) or leads to glutamatergic excitation, thus resulting in another type of IIDs (IID2s). In both the model and experiment, IIDs propagate as waves, with constant activity profiles and velocity. The speed of IIDs is of the order of tens of mm/s and is larger for IID2s than for IID1s (40 and 20?mm/s, respectively). The simulations, consistent with experimental observations, show that the wavelike propagation of IIDs initiated by interneurons is determined by local synaptic connectivity under the conditions of depolarizing GABA.     

Protein trafficking along the exocytotic pathway

Proteins of the exocytotic (secretory) pathway are initially targeted to the endoplasmic reticulum (ER) and then translocated across and/or inserted into the membrane of the ER. During their anterograde transport with the bulk of the membrane flow along the exocytotic pathway, some proteins are selectively retained in various intracellular compartments, while others are sorted to different branches of the pathway. The signals or structural motifs that are involved in these selective targeting processes are being revealed and investigations into the mechanistic nature of these processes are actively underway.     

Polyol pathway along the bovine epididymis

During the epididymal transit, male gametes acquire new surface proteins necessary for their fertilizing ability. We have previously shown that membranous vesicles, called epididymosomes, interact with sperm surface within the epididymal fluid allowing transfer of some proteins to different subcellular compartments of spermatozoa. We previously showed that one of the major proteins associated with epididymosomes was an aldose reductase (gene: AKR1B5) and confirmed that aldose reductase is located in the epithelial cells bordering the intraluminal compartment of the epididymis. The present study shows that cytosolic aldose reductase activity was maximal in the proximal and middle segments of the epididymis and decreased in the distal epididymis. Western and Northern blot analysis confirmed the distribution pattern of aldose reductase and of the encoding mRNA. The optimal pH of epididymal aldose reductase was 6.0-6.5 when glucose was used as a substrate; this corresponds to the pH of the intraluminal epididymal fluid. In order to evaluate the possible involvement of sorbitol in sperm physiology, Western blot of tissue homogenates were probed with an anti-sorbitol dehydrogenase antibody. The amount of enzyme immunodetected was higher in the proximal and distal segments of the epididymis when compared to the amount detectable in the middle segment of the epididymis. Sorbitol dehydrogenase activity as well as the level of the encoding mRNA showed the same pattern of distribution. Furthermore, immunohistological studies using the anti-sorbitol dehydrogenase revealed that this enzyme was synthesized by the epididymal epithelial cells bordering the intraluminal compartment. Knowing the importance of sorbitol and fructose in sperm metabolism, we hypothesized that the polyol pathway is involved in the modulation of sperm motility within the epididymis.     

Membrane trafficking along the phagocytic pathway

Phagosome maturation involves extensive remodelling of the phagosomal membrane as a result of intracellular transport events. Newly formed phagosomes exchange membrane-associated and soluble proteins with early endosomes by fusion. Budding of vesicles from the phagosome and fusion with Golgi-derived vesicles may also contribute to the remodelling of the phagosomal compartment. As a consequence of changes in membrane composition, phagosomes acquire the ability to fuse with late endocytic compartments. In vitro reconstitution and other studies suggest that the trafficking events underlying phagosome maturation require several GTP-binding proteins, including Rab5 and Galphas', NSF-SNAP-SNARE complexes and coatomers.     

TANGOing along the protein secretion pathway

Although the organization and functions of the constitutive secretory pathway have been intensively studied for decades, a recent genome-wide RNAi screen in Drosophila cells has identified about 100 genes encoding novel so-called TANGO proteins (for transport and Golgi organization) that may be direct regulators of various aspects of protein exocytosis or secretion.     

Nymphal Ixodes dammini: models of the temporal abundance patterns.

A difference equation model was developed to explore the sensitivity of the temporal pattern of relative abundance of active, host-seeking nymphal Ixodes dammini. Inputs to the model were the temporal patterns of recruitment of nymphs into the active class, mortality and successful acquisition of hosts by the ticks. Input parameters were varied both in the temporal pattern (shape) and in the cumulative level (summed over the period of activity). The output of the models, the temporal abundance pattern, was examined for (1) overall shape and (2) the timing of the peak abundance of host-seeking nymphs. The shape of the temporal pattern of nymphal abundance was not sensitive to changes in the shape of the functions used as input for host-finding. The time of peak abundance of nymphs is slightly sensitive to changes in the overall level of host-finding and mortality. When more ticks are removed from the active class (host-finding or mortality increasing), the time of the peak abundance of the nymphs shifts earlier. However, this shift is small compared to variation in field data. The general shape of the activity pattern was sensitive to changes in the temporal pattern of recruitment. A left-skewed distribution produced output which most resembles field data. The temporal pattern of nymphs entering the active class is important, and is an area which needs further empirical work.     

Ophiuroid biodiversity patterns along the Antarctic Peninsula

Benthic ecological surveys using standardized methods are crucial for assessing changes associated with several threats in the Southern Ocean. The acquisition of data on assemblage structure over a variety of spatial scales is important to understand the variation of biodiversity patterns. During the ANT XXIX/3 (PS81) expedition of RV Polarstern, three different regions at the tip of the Antarctic Peninsula were sampled: the northwestern Weddell Sea, the Bransfield Strait, and the northern boundary of the South Shetland Archipelago in the Drake Passage. The aim of this study was to characterize the distribution and biodiversity patterns of ophiuroid assemblages in these regions and depths. We quantified different community parameters in terms of the number of species, abundance, and biomass. Additionally, we calculated various components of species diversity (alpha, beta, and gamma diversity) over the three regions. Based on the benthic surveys, we collected 3331 individuals that were identified to species level (17 species). Overall, species diversity, as measured based on rarefaction, species richness and evenness estimators, was higher in the Bransfield Strait compared to the Weddell Sea and Drake Passage. Two deep stations in the Weddell Sea showed high dominance only of Ophionotus victoriae. Significant differences in the patterns of alpha diversity were found among the regions but not between depth zones, whereas beta diversity showed no differences. Regarding the resemblance among the ophiuroid assemblages of each region, there was a significant gradient from east to west with a maximum distance between the stations in the Drake Passage and the Weddell Sea. This study provides a baseline for detecting potential effects related to climate change, and it furnishes a basis for the implementation of monitoring schemes of Antarctic assemblages.     

Epsilon-aminocaproic acid inhibits the propagation of damage along the nerve fiber

An inhibitor of proteinases--epsilon-aminocaproic acid--inhibits the propagation of destruction along the muscle fiber isolated from frog m. iliofibularis. It is assumed that generalization of the injury is hampered by a protein precipitate formed at the site of the injury, which is preserved due to inhibition of proteinase activity.     

Tree-line changes along the Andes: implications of spatial patterns and dynamics

The Andes provide an extensive latitudinal and topographical framework for studying the factors that control the spatial patterns of forests (timberlines) and their species components expressed through the presence of tree growth forms (tree lines). Despite consistent overall similarities in landscape patterns, many processes must be unique, given the dramatic differences in species richness and biophysical constraints along the Andes. In all cases evaluated to date, morphological plasticity is a common trait of plant species that dominate at tree lines. In fact, many changes observed can be related to species-specific traits. Physiological limitations on tree growth form only explain species limits, while disturbances and cyclical climate fluctuations interact to affect many landscape patterns. Over long periods of time, tree lines provide unique habitats and perhaps opportunities for speciation. Understanding the spatial organization of tree-line dynamics is one viable research approach for evaluating the likely past fluxes and possible future changes.     

Spatial and temporal patterns of aboveground net primary productivity (ANPP) along two freshwater-estuarine transects in the Florida Coastal Everglades

We present here a 4-year dataset (2001–2004) on the spatial and temporal patterns of aboveground net primary production (ANPP) by dominant primary producers (sawgrass, periphyton, mangroves, and seagrasses) along two transects in the oligotrophic Florida Everglades coastal landscape. The 17 sites of the Florida Coastal Everglades Long Term Ecological Research (FCE LTER) program are located along fresh-estuarine gradients in Shark River Slough (SRS) and Taylor River/C-111/Florida Bay (TS/Ph) basins that drain the western and southern Everglades, respectively. Within the SRS basin, sawgrass and periphyton ANPP did not differ significantly among sites but mangrove ANPP was highest at the site nearest the Gulf of Mexico. In the southern Everglades transect, there was a productivity peak in sawgrass and periphyton at the upper estuarine ecotone within Taylor River but no trends were observed in the C-111 Basin for either primary producer. Over the 4 years, average sawgrass ANPP in both basins ranged from 255 to 606 g m⁻² year⁻¹. Average periphyton productivity at SRS and TS/Ph was 17–68 g C m⁻² year⁻¹ and 342–10371 g C m⁻² year⁻¹, respectively. Mangrove productivity ranged from 340 g m⁻² year⁻¹ at Taylor River to 2208 g m⁻² year⁻¹ at the lower estuarine Shark River site. Average Thalassia testudinum productivity ranged from 91 to 396 g m⁻² year⁻¹ and was 4-fold greater at the site nearest the Gulf of Mexico than in eastern Florida Bay. There were no differences in periphyton productivity at Florida Bay. Interannual comparisons revealed no significant differences within each primary producer at either SRS or TS/Ph with the exception of sawgrass at SRS and the C−111 Basin. Future research will address difficulties in assessing and comparing ANPP of different primary producers along gradients as well as the significance of belowground production to the total productivity of this ecosystem.