Diversity cascades and malaria vectors.

The interactions between predator diversity and primary consumer abundance can include direct effects and indirect, cascading effects. Understanding these effects on immature Anopheles mosquitoes is important in sub-Saharan Africa, where most cases of malaria occur. Aquatic predators and immature mosquitoes were collected from shallow pools of varying age previously excavated by brickmakers in the western highlands of Kenya.

Laboratory evaluation of the aqueous extract of Azadirachta indica (neem) wood chippings on Anopheles gambiae s.s. (Diptera: Culicidae) mosquitoes.

Azadirachta indica A. Juss (the neem tree), a source of limonoid insect growth regulatory (IGRs), grows well in many places in sub-Saharan Africa. We explored the potential of neem wood and bark chippings in malaria vector control by evaluating their aqueous extracts as a larvicide and growth disruptor of Anopheles gambiae s.

Anopheles gambiae exploits the treehole ecosystem in western Kenya: a new urban malaria risk?

At six sites in western Kenya, we explored the presence of Anopheles immature stages in treeholes. An. gambiae larvae were found in 19 species, 13 of which are exotic.

Abandoning small-scale fish farming in western Kenya leads to higher malaria vector abundance.

Fishponds become abandoned due to lack of access to both young fish and technical support and faster economic returns from other activities. Certain conditions found in abandoned fishponds, such as absence of fish and presence of aquatic vegetation, are conducive to the presence of malaria vectors. We conducted a district-wide fishpond census to determine the maintenance status and mosquito populations of fishponds in Kisii Central District in western Kenya.

Malaria mosquito control using edible fish in western Kenya: preliminary findings of a controlled study.

Background: Biological control methods are once again being given much research focus for malaria vector control. This is largely due to the emerging threat of strong resistance to pesticides. Larvivorous fish have been used for over 100 years in mosquito control and many species have proved effective.

The antiplasmodial activity of spermine alkaloids isolated from Albizia gummifera.

In the present study the methanolic extract of Albizia gummifera was fractionated into various fractions. These fractions were tested against choroquine sensitive (NF54) and resistant (ENT30) strains of Plasmodium falciparum. All other fractions apart from the alkaloidal fraction showed low activity with IC 50 above 3 microg/ml.

Field assessments in western Kenya link malaria vectors to environmentally disturbed habitats during the dry season.

Background: Numerous malaria epidemics have occurred in western Kenya, with increasing frequency over the past 20 years. A variety of hypotheses on the etiology of these epidemics have been put forth, with different implications for surveillance and control. We investigated the ecological and socioeconomic factors promoting highland malaria vectors in the dry season after the 2002 epidemic.

Optic disc and optic nerve of the blind cape mole-rat (Georychus capensis): a proposed model for naturally occurring reactive gliosis.

Recent studies of the visual system of animal species that live in a subterranean environment show not only regressive but also progressive morphological features. In this regard the aim of the present investigation is to describe the structural organisation of the eye and optic nerve of the adult Cape mole-rat, with special emphasis on both glial cell population and myelination. The main results are: (a) astrocytes show identical features to those occurring in reactive gliosis; (b) optic fibers vary greatly in diameter; (c) very small axons are myelinated and are often surrounded by a thicker sheath than larger optic fibers; (d) a large onion bulb-like structure composed of optic fibers, glia, and ganglion cells is found within the choriocapillary layer.

Cells with neuronal characteristics differentiate and persist for one year in rat optic nerve explants cultures.

Evidence concerning the presence or absence of common neuronglia lineages in the postnatal mammalian central nervous system is still a matter of speculation. We address this problem using optic nerve explants, which show an extremely long survival in culture. Morphological, immunocytochemical and immunochemical methods were applied.

Differentiation of neuron-like cells in cultured rat optic nerves: a neuron or common neuron-glia progenitor?

The optic nerve consists of axons, glia, and undifferentiated cells; neuronal cell bodies are absent. To study the developmental potential of glia and precursor cells in vitro, we devised an original, long-term culture system of optic nerve explants, called minisegments, of newborn rats; at this stage the nerves are composed of naked axons, astrocytes, and undifferentiated cells. After about 4-5 weeks in culture, neuron-like cells appeared, which showed morphological, fine structural, and immunocytochemical properties ascribed to neurons.

Substrate-dependent migration of myelin-associated glycoprotein immunoreactive cells in cultured explants of dorsal root ganglia from chick embryos.

The aim of this study was to investigate the influence of collagen or polyornithine substrates on cell migration in explant cultures of dorsal root ganglia (DRG) by means of light microscopy and immunocytochemistry. Myelin-associated glycoprotein (MAG) immunoreactivity was used to characterize the subpopulation of small B ganglion cells, whereas neuron-specific enolase (NSE) immunoreactivity acted as a general neuronal cell marker. After a few days in culture, DRG explants grown on collagen substrate showed a flattened shape consisting of a core surrounded by a crown of neurites, which were mixed up with migrating cells of different types.

Myelin instability and oligodendrocyte metabolism in myelin-deficient mutant mice.

During the active phase of myelination in myelin-deficient mutant mice (mld), myelin basic protein (MBP) synthesis is defective and the myelin lamellae are uncompacted. In these mutants, we found a fast metabolism of the myelin-associated glycoprotein (MAG) and of sulfatides, and the presence of cholesterol esters and a degradation product of MAG, dMAG, indicating that mld myelin was unstable. The increased synthesis of MAG and Wolfgram protein, two proteins present in uncompacted myelin sheath and paranodal loops, was demonstrated by high levels of messengers.

Myelin-associated glycoprotein immunoreactive material: an early neuronal marker of dorsal root ganglion cells during chick development.

Immunostaining of myelin-associated glycoprotein (MAG) was performed in chick dorsal root ganglia (DRG) during development. The MAG-immunoreactive material appeared first around 7 days of incubation in immature neurons of DRG. Immunoprecipitates first confined to one pole of nucleus were gradually redistributed in the perinuclear Golgi apparatus of small DRG cells.

Minisegments of newborn rat optic nerves in vitro: gliogenesis and myelination.

The question of whether the development of CNS glial cells requires the presence of axons or not can be studied with in vitro systems. In order to compare the differentiation of glial cells during development in vitro with that in situ, we have selected the optic nerve, which is anatomically as well as histotypically a well defined structure. For the in vitro investigations, small explants, called minisegments, of newborn rat optic nerves were cultivated taking four major conditions into account: the regular size of the minisegments should guarantee a permanent exchange of the culture medium in order to avoid cell death, neither mechanical nor enzymatic dissociation of the tissue were applied, the minisegments were explanted into flasks without substrate for cell adhesion and the minisegments were under constant gyratory agitation.

Expression of myelin-associated glycoprotein by small neurons of the dorsal root ganglion in chickens.

Biochemical and immunocytochemical investigations have shown that myelin-associated glycoprotein (MAG) is exclusively related to myelin and myelin-forming cells in mammals. In the present study it was found that dorsal root ganglia in young chickens display MAG-immunoreactive material in most small sensory neurons. The presence of MAG at the surface of small sensory neurons raises the question of whether this glycoprotein acts as a cell adhesion molecule in lower vertebrates.

Serum-free aggregate cultures of rat CNS glial cells: biochemical, immunocytochemical and morphological characterization.

Aggregate cultures of mixed glial cells, as well as of enriched astrocytes and oligodendrocytes were prepared, and maintained in serum-free medium for up to 25 days. Biochemical measurements of both neuron-specific and glia-specific enzyme activities showed that these three types of aggregate cultures were virtually devoid of neurons. Astrocyte-enriched cultures were greater than 95% pure, with oligodendrocytes as the only apparent contaminant, whereas oligodendrocyte-enriched cultures still contained a considerable proportion of astrocytes.

Murine leukodystrophies as tools to study myelinogenesis in normal and pathological conditions.

Myelinogenesis is controlled by several genes. Therefore, the study of mutations affecting myelination should provide better understanding of the assembly and maintenance of myelin, and in the case of similitude with human diseases, a direct insight into the pathogenesis of these diseases. Murine mutants can be bred readily and sequential analyses allow an examination of the dynamic processes of myelination.

Myelination in the CNS of mld mutant mice: comparison between composition and structure.

Myelination was studied between 15 and 135 days postnatally in the brain and optic nerves of myelin deficient (mld) mutant mice. Between 15 and 30 days almost no myelin basic protein (MBP) could be detected in mld myelin. The axons were loosely wrapped by membranes which only fused at the extracellular sites forming the intraperiod line.

Abnormal cell relationships in Jimpy mice: electron microscopic and immunocytochemical findings.

The mutant mouse strain Jimpy is characterized by a deficiency of myelin formation throughout the C.N.S.

Myelin basic protein deficit in the PNS of mld mutant mice recovers during development.

Myelination was studied between 15 and 135 days postnatally in peripheral nerves of myelin deficient (mld) mice and in unaffected littermates. The nerve weights were not affected by the mutation and showed a 4-fold increase during the developmental period studied. The amounts of myelin present in peripheral nerves, as shown by biochemical and morphological techniques, were slightly reduced in mld in comparison to control mice.

Immunocytochemical localization of basic protein in major dense line regions of central and peripheral myelin.

To localize basic protein (BP) in the lamellar structure of central and peripheral myelin, we perfused newborn and 7-11-day rat pups with a phosphate-buffered fixative that contained 4% paraformaldehyde and 0.05 or 0.2% glutaraldehyde.

Myelin and glial membrane structures in the optic nerve of normal and jimpy mouse. A freeze-etching study.

In order to investigate the myelin and the glial cell membranes in the optic nerve of the mutant mouse "Jimpy," the method of freeze-etching was applied. The compact myelin lamellae and the first two glial membranes of the mutant, as compared to the normal mouse, show several abnormalities: absence of intramembraneous particles on the P-face, myelin lamellae separated by cytoplasmic layers, vesicular protrusions forming irregular invaginations, and elevations and tight junctions with a discontinuous, zigzag course. Some of these characteristics were found in the membrane of the oligodendroglia cell of the pathological animal, as well.