Effect of pathogenic mutations on the structure and dynamics of Alzheimer’s Aβ42-amyloid oligomers

Converging lines of evidence suggest that soluble Aβ-amyloid oligomers play a pivotal role in the pathogenesis of Alzheimer’s disease, and present direct effectors of synaptic and cognitive dysfunction. Three pathological E22-Aβ-amyloid point mutants (E22G, E22K, E22Q) and the deletion mutant E22Δ exhibit an enhanced tendency to form prefibrillar aggregates. The present study assessed the effect of these four mutations using molecular dynamics simulations and subsequent structural and energetic analyses. Our data shows that E22 plays a unique role in wild type Aβ, since it has a destabilising effect on the oligomer structure due to electrostatic repulsion between adjacent E22 side chains. Mutations in which E22 is replaced by an uncharged residue result in higher oligomer stability. This effect is also observed to a lesser extent for the E22K mutation and is consistent with its lower pathogenicity compared to other mutants. Interestingly, deletion of E22 does not destroy the amyloid fold but is compensated by local changes in the backbone geometry that allow the preservation of a structurally important salt bridge. The finding that all mutant oligomers investigated exhibit higher internal stability than the wild type offers an explanation for the experimentally observed enhanced oligomer formation and stability.     

Measurement of Acetylcholine Release in Freely Moving Rats by Means of Automated Intracerebral Dialysis

The present study demonstrates the feasibility of measuring acetylcholine in perfusion samples collected by means of in vivo brain dialysis in the striata of freely moving rats. The output of the dialysis device was directly connected to an automated sample valve of a HPLC-assay system that comprises a cation exchanger, a post-column enzyme reactor, and an electrochemical detector. The presence of an acetylcholinesterase inhibitor (neostigmine) in the perfusion fluid was required for the detection of acetylcholine in the perfusate. Increasing concentrations of neostigmine induced increasing amounts of acetylcholine. Continuous perfusion with a fixed concentration (2 microM) of neostigmine resulted in gradually increasing amounts of collected acetylcholine over time although a considerable variation between successive samples exists. The brain dialysis technique was further validated by studying the effect of various drugs. Systemically administered atropine increased the output of acetylcholine, whereas the addition of tetrodotoxin to the perfusion fluid resulted in a complete disappearance of the neurotransmitter.     

Aspergillus nomius,a new aflatoxin-producing species related to Aspergillus flavus and Aspergillus tamarii

Aspergillus nomius is described and represents a new aflatoxigenic species phenotypically similar to A. flavus. Strains examined were isolated from insects and agricultural commodities. Separation from A. flavus is based on the presence of indeterminate sclerotia and a lower growth temperature. Comparisons of DNA relatedness show A. nomius to have only relatively recently evolved from A. flavus and A. tamarii.     

TGF-beta 1-induced inhibition of mouse mammary ductal growth: developmental specificity and characterization

TGF-beta 1, implanted into growing mouse mammary glands, was previously shown to inhibit ductal growth in an apparently normal and fully reversible manner. In this report we extend these findings to show that TGF-beta 1 inhibition is highly specific. In pregnant or hormone-treated mice, doses of TGF-beta 1 that were capable of fully inhibiting ductal elongation had little effect on the proliferation of lobuloalveolar structures. Additionally, the inhibitory action of TGF-beta 1 on ducts is epithelium-specific, resulting in cessation of DNA synthesis in the rapidly proliferating epithelium of mammary end buds, but does not inhibit DNA synthesis in the stroma surrounding the end buds. At the cellular level, transplant studies showed that TGF-beta 1 inhibited the regeneration of mammary ductal cells when implanted into mammary gland-free fat pads by suppressing the formation of new end buds, without inhibiting maintenance DNA synthesis in ductal lumenal epithelium; this observation indicates the potential of TGF-beta 1 to maintain patterning by suppressing adventitious lateral branching. The time-course of TGF-beta 1 inhibition of end buds was rapid, with cessation of DNA synthesis by 12 hr, followed by loss of the stem cell (cap cell) layer. The question of glandular exposure to TGF-beta 1 administered in EVAc implants was also investigated. Incorporation of TGF-beta 1 into EVAc was found not to degrade the hormone, while the release kinetics of the ligand from implants, its retention in the gland, and the demonstrable zone of exposure were consistent with observed inhibitory effects. These results support the hypothesis that TGF-beta 1 is a natural regulator of mammary ductal growth.     

Reduction of a Hodgkin-Huxley-type model for a mammalian neuron at body temperature

Hodgkin-Huxley-type models mimick the electrical behavior of excitable membranes quite realistically. However, inclusion of many different ionic channels into such a model yields a highly complex set of differential equations. In this paper a reduction of a full Hodgkin-Huxley-type model based on voltage-clamp data from small rat neurons in the supraoptic nucleus area is introduced. It was found that two of the ionic channel gating variables of the full model preserved a rather close relationship during simulations. This allowed to express one of these gating variables in terms of the other one thus reducing the number of differential equations the model is based on. The behavior of the reduced model was very similar to that of the full model. In particular, important physiological features as spike shape and constant-input-to-interspike-interval relationship were (almost) identical in the full and the reduced model.     

Granulocyte-mediated airway edema in guinea pigs

To determine the role of polymorphonuclear leukocytes (PMNs) in the airway edema that accompanies airway inflammation, we studied the effects of a 1-h exposure to 2 ppm toluene diisocyanate (TDI) on tracheal extravasation of Evans blue dye and on the concentration of PMNs in the tracheal wall. Tracheal Evans blue content was significantly increased by TDI exposure (53.6 +/- 8.0 micrograms/g tracheal tissue (mean +/- SE) for animals exposed to TDI and 16.3 +/- 2.0 for animals exposed to air, P less than 0.0025) as were both the intravascular and extravascular concentration of PMNs in tracheal sections (intravascular PMNs were 28.0 +/- 8.4 X 10(3) cells/mm3 for TDI and 1.5 +/- 1.5 X 10(3) for air, P less than 0.025, extravascular PMNs were 10.9 +/- 4.5 X 10(3) for TDI and 0 for air, P less than 0.05). PMN depletion with vinblastine or with hydroxyurea abolished both the increase in tracheal Evans blue extravasation and the increase in the concentration of intravascular and extravascular PMNs in animals exposed to TDI. PMN depletion with hydroxyurea did not significantly inhibit the increase in tracheal Evans blue extravasation caused by intravenous histamine. Administration of donor PMNs to animals depleted of PMNs with hydroxyurea reconstituted the TDI-induced increase in tracheal Evans blue extravasation (80.4 +/- 17.3 micrograms/g tissue (mean +/- SE) in animals exposed to TDI vs. 21.3 +/- 2.9 in animals exposed to air, P less than 0.025) and in the intravascular concentration of PMNs in tracheal sections [18.5 +/- 3.4 X 10(3) cells/mm3 (mean +/- SE) in animals exposed to TDI vs. 1.3 +/- 1.3 X 10(3) in animals exposed to air, P less than 0.0025].(ABSTRACT TRUNCATED AT 250 WORDS)