Three-dimensional mapping of cholinergic molecules by confocal laser scanning microscopy in sea urchin larvae.

Confocal laser scanning microscopy (CLSM) was used to examine molecules related to the cholinergic neurotransmission system and detected at all the larval stages of Paracentrotus lividus, by histochemical and immunohistochemical methods. CLSM, providing spatial resolution of the cells located both at the larval surface and at depth, allows a complete mapping in a three-dimensional volumetric frame. At early larval stages acetylcholinesterase- as well as choline acetyltransferase-like molecules were found mainly in the gut wall cells, and along the ciliary bands of the arms, together with muscarinic acetylcholine receptors. At perimetamorphic stages, cholinergic molecules were present in the ciliate strands along the arms, in the larval body and in the rudiment. At metamorphosis, positivity to cholinergic molecules translocated to the juvenile, where a high frequency of mAChR- and ChAT-like positive cells was found.     

Visual spatial memory is enhanced in female rats (but inhibited in males) by dietary soy phytoestrogens

Background  

In learning and memory tasks, requiring visual spatial memory (VSM), males exhibit superior performance to females (a difference attributed to the hormonal influence of estrogen). This study examined the influence of phytoestrogens (estrogen-like plant compounds) on VSM, utilizing radial arm-maze methods to examine varying aspects of memory. Additionally, brain phytoestrogen, calbindin (CALB), and cyclooxygenase-2 (COX-2) levels were determined.     

Quantum amplified isomerization in polymers based on triplet chain reactions

Photoinitiated triplet quantum amplified isomerizations (QAI) of substituted Dewar benzene derivatives in polymeric media are reported. The quantum efficiencies and the ultimate extents of reactant-to-product conversions increase significantly with the incorporation of appropriate co-sensitizers; compounds whose triplet energies are similar to or lower than that of the sensitizer and close to that of the reactant. These co-sensitizers serve to promote chain-propagating energy transfer processes and thereby increase the action sphere of photosensitization. Isomerization quantum yields increase, as predicted, with increasing concentrations of the reactants and the co-sensitizers. Chain amplifications as large as approximately 16 and extents of conversion that approach 100% have been achieved. Mechanistic schemes are proposed to account for the dynamics of the inherent energy transfer processes and provide a predictively useful model for the design of a new class of photoresponsive polymers based on changes in the refractive index of the materials.     

Highly efficient triplet chain isomerization of Dewar benzenes: adiabatic rate constants from cage kinetics

Quantum yields as high as 120 were achieved for triplet-sensitized photoisomerizations of several Dewar benzene reactants, R, to the corresponding benzene products, P. Considerable chain amplification is maintained even at high conversion. All relevant rate constants of this triplet chain reaction were extracted from laser flash photolysis plus steady-state photolysis experiments. The crucial rate constant ka for adiabatic isomerization of the triplet reactant to triplet product (R* --> P*) cannot be directly measured because it is so large relative to the bimolecular rate of R* formation via sensitization. However, ka was obtained indirectly using a cage/encounter complex model to analyze the competition between the dissociation of encounter pairs with the sensitizer, e.g., S/R* --> S + R*, and the in-cage processes, S/R* --> S/P* --> S*/P, in nonviscous and viscous solvents. These measurements yielded ka values of (approximately 4-9) x 10(9) s(-1), which suggests that only a small (approximately 3 kcal/mol) energy barrier exists along the potential energy surface from R* to P*. Steady-state data indicated that the chain-terminating rate constant R* --> R is negligibly small, an ideal condition for chain amplification. Triplet energy transfer from a series of sensitizers to the Dewar benzene derivatives shows a nonclassical falloff in rate constants with decreasing sensitizer triplet energy, suggesting energy transfer to thermally distorted configurations having lower singlet-triplet energy gaps. As a result of distorted geometries of R* and P*, the chain-propagating energy transfer from P* to R proceeds with a rate constant of only approximately 2 x 10(7) M(-1) s(-1), despite strong exothermicity. The isomerization reaction can release over 100 kcal/kcal of absorbed photons due to the high-energy content of the reactant together with the large chain length.     

Degradation and stabilization of polycyanoacrylates

Polycyanoacrylates were found to be inherently unstable. Even in the absence of a deliberately added strong base, their molecular weights decreased drastically on standing in solution in accord with observations by Ryan and McCann (Makromol Chem Rapid Commun 1996, 17, 217). The initial high molecular weight polymer disappeared over the course of a few hours in solution and was replaced by a much lower molecular weight material. For polymers made by anionic polymerization, the entire sample degraded, but for polymers made by free-radical polymerization, only a portion of the sample was affected. This behavior was consistent with the mechanism proposed by Ryan and McCann, in which the polymer chains are in dynamic equilibrium with their monomers and the polymer degrades from its chain terminus. Surprisingly, the degradation in molecular weight even occurred slowly in the solid state. The degradation was inhibited by acids and could be prevented by free-radical copolymerization with small amounts of more stable monomers. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4570–4581, 1999     

The application of homotopy analysis method to solve nonlinear differential equation governing Jeffery–Hamel flow

In this paper Jeffery–Hamel flow has been studied and its nonlinear ordinary differential equation has been solved through homotopy analysis method (HAM). The obtained solution in comparison with the numerical ones represents a remarkable accuracy. The results also indicate that HAM can provide us with a convenient way to control and adjust the convergence region.     

Neuromodulation by soy diets or equol: Anti-depressive &; anti-obesity-like influences,age- &; hormone-dependent effects

Background  

Soy-derived isoflavones potentially protect against obesity and depression. In five different studies we examined the influence of soy-containing diets or equol injections on depression, serotonin levels, body weight gain (BW) and white adipose tissue (WAT) deposition in female Long-Evans rats at various stages of life [rats were intact, ovariectomized or experienced natural ovarian failure (NOF)].     

Two-photon excitation of fluorescence for three-dimensional optical imaging of biological structures

Techniques based on two-photon excitation (TPE) allow three-dimensional (3D) imaging in highly localized volumes, of the order of magnitude of a fraction of a femtolitre up to single-molecule detection. In TPE microscopy a fundamental advantage over conventional widefield or confocal 3D fluorescence microscopy is given by the use of infrared (IR) instead of ultraviolet (UV) radiation to excite those fluorophores requiring UV excitation, hence causing little damage to the specimen or to fluorescent molecules outside the volume of the TPE event and allowing a deeper penetration within the sample compared with conventional one-photon excitation of fluorescence. In our laboratory, within the framework of a national INFM project, we have realized a TPE fluorescence microscope, part of a multipurpose architecture also including lifetime imaging and fluorescence correlation spectroscopy modules. The core of the architecture is a mode-locked Ti:sapphire infrared pulsed laser pumped by a high-power (5 W, 532 nm) solid-state laser and coupled to an ultracompact scanning head. For the source we have measured a pulse width from 65 to 95 fs as a function of wavelength (690-830 nm). The scanning head allows conventional and two-photon confocal imaging. Point spread function measurements are reported with examples of applications to the study of biological systems.